examples/advanced_faults/ipc_failure_during_stream.py

@@ -21,75 +21,12 @@ import trio
 import pytest
 
 
-async def break_ipc(
-    stream: MsgStream,
-    method: str|None = None,
-    pre_close: bool = False,
-
-    def_method: str = 'eof',
-
-) -> None:
-    '''
-    XXX: close the channel right after an error is raised
-    purposely breaking the IPC transport to make sure the parent
-    doesn't get stuck in debug or hang on the connection join.
-    this more or less simulates an infinite msg-receive hang on
-    the other end.
-
-    '''
-    # close channel via IPC prot msging before
-    # any transport breakage
-    if pre_close:
-        await stream.aclose()
-
-    method: str = method or def_method
-    print(
-        '#################################\n'
-        'Simulating CHILD-side IPC BREAK!\n'
-        f'method: {method}\n'
-        f'pre `.aclose()`: {pre_close}\n'
-        '#################################\n'
-    )
-
-    match method:
-        case 'trans_aclose':
-            await stream._ctx.chan.transport.stream.aclose()
-
-        case 'eof':
-            await stream._ctx.chan.transport.stream.send_eof()
-
-        case 'msg':
-            await stream._ctx.chan.send(None)
-
-        # TODO: the actual real-world simulated cases like
-        # transport layer hangs and/or lower layer 2-gens type
-        # scenarios..
-        #
-        # -[ ] already have some issues for this general testing
-        # area:
-        #  - https://github.com/goodboy/tractor/issues/97
-        #  - https://github.com/goodboy/tractor/issues/124
-        #   - PR from @guille:
-        #     https://github.com/goodboy/tractor/pull/149
-        # case 'hang':
-        # TODO: framework research:
-        #
-        # - https://github.com/GuoTengda1993/pynetem
-        # - https://github.com/shopify/toxiproxy
-        # - https://manpages.ubuntu.com/manpages/trusty/man1/wirefilter.1.html
-
-        case _:
-            raise RuntimeError(
-                f'IPC break method unsupported: {method}'
-            )
-
-
 async def break_ipc_then_error(
     stream: MsgStream,
     break_ipc_with: str|None = None,
     pre_close: bool = False,
 ):
-    await break_ipc(
+    await _testing.break_ipc(
         stream=stream,
         method=break_ipc_with,
         pre_close=pre_close,
@@ -121,6 +58,7 @@ async def recv_and_spawn_net_killers(
     Receive stream msgs and spawn some IPC killers mid-stream.
 
     '''
+    broke_ipc: bool = False
     await ctx.started()
     async with (
         ctx.open_stream() as stream,
@@ -128,13 +66,17 @@ async def recv_and_spawn_net_killers(
     ):
         async for i in stream:
             print(f'child echoing {i}')
-            await stream.send(i)
+            if not broke_ipc:
+                await stream.send(i)
+            else:
+                await trio.sleep(0.01)
 
             if (
                 break_ipc_after
                 and
                 i >= break_ipc_after
             ):
+                broke_ipc = True
                 n.start_soon(
                     iter_ipc_stream,
                     stream,
@@ -242,14 +184,13 @@ async def main(
                         # await stream._ctx.chan.send(None)
                         # await stream._ctx.chan.transport.stream.send_eof()
                         await stream._ctx.chan.transport.stream.aclose()
-
                         ipc_break_sent = True
 
                     # it actually breaks right here in the
-                    # mp_spawn/forkserver backends and thus the zombie
-                    # reaper never even kicks in?
-                    print(f'parent sending {i}')
+                    # mp_spawn/forkserver backends and thus the
+                    # zombie reaper never even kicks in?
                     try:
+                        print(f'parent sending {i}')
                         await stream.send(i)
                     except ContextCancelled as ctxc:
                         print(
@@ -262,6 +203,13 @@ async def main(
                         # TODO: is this needed or no?
                         raise
 
+                    except trio.ClosedResourceError:
+                        # NOTE: don't send if we already broke the
+                        # connection to avoid raising a closed-error
+                        # such that we drop through to the ctl-c
+                        # mashing by user.
+                        await trio.sleep(0.01)
+
                     # timeout: int = 1
                     # with trio.move_on_after(timeout) as cs:
                     async with stuff_hangin_ctlc() as timeout:

examples/debugging/pm_in_subactor.py

@@ -0,0 +1,56 @@
+import trio
+import tractor
+
+
+@tractor.context
+async def name_error(
+    ctx: tractor.Context,
+):
+    '''
+    Raise a `NameError`, catch it and enter `.post_mortem()`, then
+    expect the `._rpc._invoke()` crash handler to also engage.
+
+    '''
+    try:
+        getattr(doggypants)  # noqa (on purpose)
+    except NameError:
+        await tractor.post_mortem()
+        raise
+
+
+async def main():
+    '''
+    Test 3 `PdbREPL` entries:
+      - one in the child due to manual `.post_mortem()`,
+      - another in the child due to runtime RPC crash handling.
+      - final one here in parent from the RAE.
+
+    '''
+    # XXX NOTE: ideally the REPL arrives at this frame in the parent
+    # ONE UP FROM the inner ctx block below!
+    async with tractor.open_nursery(
+        debug_mode=True,
+        # loglevel='cancel',
+    ) as an:
+        p: tractor.Portal = await an.start_actor(
+            'child',
+            enable_modules=[__name__],
+        )
+
+        # XXX should raise `RemoteActorError[NameError]`
+        # AND be the active frame when REPL enters!
+        try:
+            async with p.open_context(name_error) as (ctx, first):
+                assert first
+        except tractor.RemoteActorError as rae:
+            assert rae.boxed_type is NameError
+
+            # manually handle in root's parent task
+            await tractor.post_mortem()
+            raise
+        else:
+            raise RuntimeError('IPC ctx should have remote errored!?')
+
+
+if __name__ == '__main__':
+    trio.run(main)

examples/debugging/shielded_pause.py

@@ -0,0 +1,88 @@
+import trio
+import tractor
+
+
+async def cancellable_pause_loop(
+    task_status: trio.TaskStatus[trio.CancelScope] = trio.TASK_STATUS_IGNORED
+):
+    with trio.CancelScope() as cs:
+        task_status.started(cs)
+        for _ in range(3):
+            try:
+                # ON first entry, there is no level triggered
+                # cancellation yet, so this cp does a parent task
+                # ctx-switch so that this scope raises for the NEXT
+                # checkpoint we hit.
+                await trio.lowlevel.checkpoint()
+                await tractor.pause()
+
+                cs.cancel()
+
+                # parent should have called `cs.cancel()` by now
+                await trio.lowlevel.checkpoint()
+
+            except trio.Cancelled:
+                print('INSIDE SHIELDED PAUSE')
+                await tractor.pause(shield=True)
+        else:
+            # should raise it again, bubbling up to parent
+            print('BUBBLING trio.Cancelled to parent task-nursery')
+            await trio.lowlevel.checkpoint()
+
+
+async def pm_on_cancelled():
+    async with trio.open_nursery() as tn:
+        tn.cancel_scope.cancel()
+        try:
+            await trio.sleep_forever()
+        except trio.Cancelled:
+            # should also raise `Cancelled` since
+            # we didn't pass `shield=True`.
+            try:
+                await tractor.post_mortem(hide_tb=False)
+            except trio.Cancelled as taskc:
+
+                # should enter just fine, in fact it should
+                # be debugging the internals of the previous
+                # sin-shield call above Bo
+                await tractor.post_mortem(
+                    hide_tb=False,
+                    shield=True,
+                )
+                raise taskc
+
+        else:
+            raise RuntimeError('Dint cancel as expected!?')
+
+
+async def cancelled_before_pause(
+):
+    '''
+    Verify that using a shielded pause works despite surrounding
+    cancellation called state in the calling task.
+
+    '''
+    async with trio.open_nursery() as tn:
+        cs: trio.CancelScope = await tn.start(cancellable_pause_loop)
+        await trio.sleep(0.1)
+
+    assert cs.cancelled_caught
+
+    await pm_on_cancelled()
+
+
+async def main():
+    async with tractor.open_nursery(
+        debug_mode=True,
+    ) as n:
+        portal: tractor.Portal = await n.run_in_actor(
+            cancelled_before_pause,
+        )
+        await portal.result()
+
+        # ensure the same works in the root actor!
+        await pm_on_cancelled()
+
+
+if __name__ == '__main__':
+    trio.run(main)

examples/debugging/sync_bp.py

@@ -1,13 +1,21 @@
+from functools import partial
+import time
+
 import trio
 import tractor
 
 
 def sync_pause(
-    use_builtin: bool = True,
+    use_builtin: bool = False,
     error: bool = False,
+    hide_tb: bool = True,
+    pre_sleep: float|None = None,
 ):
+    if pre_sleep:
+        time.sleep(pre_sleep)
+
     if use_builtin:
-        breakpoint(hide_tb=False)
+        breakpoint(hide_tb=hide_tb)
 
     else:
         tractor.pause_from_sync()
@@ -25,44 +33,114 @@ async def start_n_sync_pause(
     # sync to parent-side task
     await ctx.started()
 
-    print(f'entering SYNC PAUSE in {actor.uid}')
+    print(f'Entering `sync_pause()` in subactor: {actor.uid}\n')
     sync_pause()
-    print(f'back from SYNC PAUSE in {actor.uid}')
+    print(f'Exited `sync_pause()` in subactor: {actor.uid}\n')
 
 
 async def main() -> None:
-    async with tractor.open_nursery(
-        # NOTE: required for pausing from sync funcs
-        maybe_enable_greenback=True,
-        debug_mode=True,
-    ) as an:
+    async with (
+        tractor.open_nursery(
+            # NOTE: required for pausing from sync funcs
+            maybe_enable_greenback=True,
+            debug_mode=True,
+            # loglevel='cancel',
+        ) as an,
+        trio.open_nursery() as tn,
+    ):
+        # just from root task
+        sync_pause()
 
         p: tractor.Portal  = await an.start_actor(
             'subactor',
             enable_modules=[__name__],
             # infect_asyncio=True,
             debug_mode=True,
-            loglevel='cancel',
         )
 
         # TODO: 3 sub-actor usage cases:
+        # -[x] via a `.open_context()`
         # -[ ] via a `.run_in_actor()` call
         # -[ ] via a `.run()`
-        # -[ ] via a `.open_context()`
-        #
+        # -[ ] via a `.to_thread.run_sync()` in subactor
         async with p.open_context(
             start_n_sync_pause,
         ) as (ctx, first):
             assert first is None
 
-            await tractor.pause()
-            sync_pause()
+            # TODO: handle bg-thread-in-root-actor special cases!
+            #
+            # there are a couple very subtle situations possible here
+            # and they are likely to become more important as cpython
+            # moves to support no-GIL.
+            #
+            # Cases:
+            # 1. root-actor bg-threads that call `.pause_from_sync()`
+            #   whilst an in-tree subactor also is using ` .pause()`.
+            # |_ since the root-actor bg thread can not
+            #   `Lock._debug_lock.acquire_nowait()` without running
+            #   a `trio.Task`, AND because the
+            #   `PdbREPL.set_continue()` is called from that
+            #   bg-thread, we can not `._debug_lock.release()`
+            #   either!
+            #  |_ this results in no actor-tree `Lock` being used
+            #    on behalf of the bg-thread and thus the subactor's
+            #    task and the thread trying to to use stdio
+            #    simultaneously which results in the classic TTY
+            #    clobbering!
+            #
+            # 2. mutiple sync-bg-threads that call
+            #   `.pause_from_sync()` where one is scheduled via
+            #   `Nursery.start_soon(to_thread.run_sync)` in a bg
+            #   task.
+            #
+            #   Due to the GIL, the threads never truly try to step
+            #   through the REPL simultaneously, BUT their `logging`
+            #   and traceback outputs are interleaved since the GIL
+            #   (seemingly) on every REPL-input from the user
+            #   switches threads..
+            #
+            #   Soo, the context switching semantics of the GIL
+            #   result in a very confusing and messy interaction UX
+            #   since eval and (tb) print output is NOT synced to
+            #   each REPL-cycle (like we normally make it via
+            #   a `.set_continue()` callback triggering the
+            #   `Lock.release()`). Ideally we can solve this
+            #   usability issue NOW because this will of course be
+            #   that much more important when eventually there is no
+            #   GIL!
 
-        # TODO: make this work!!
-        await trio.to_thread.run_sync(
-            sync_pause,
-            abandon_on_cancel=False,
-        )
+            # XXX should cause double REPL entry and thus TTY
+            # clobbering due to case 1. above!
+            tn.start_soon(
+                partial(
+                    trio.to_thread.run_sync,
+                    partial(
+                        sync_pause,
+                        use_builtin=False,
+                        # pre_sleep=0.5,
+                    ),
+                    abandon_on_cancel=True,
+                    thread_name='start_soon_root_bg_thread',
+                )
+            )
+
+            await tractor.pause()
+
+            # XXX should cause double REPL entry and thus TTY
+            # clobbering due to case 2. above!
+            await trio.to_thread.run_sync(
+                partial(
+                    sync_pause,
+                    # NOTE this already works fine since in the new
+                    # thread the `breakpoint()` built-in is never
+                    # overloaded, thus NO locking is used, HOWEVER
+                    # the case 2. from above still exists!
+                    use_builtin=True,
+                ),
+                abandon_on_cancel=False,
+                thread_name='inline_root_bg_thread',
+            )
 
         await ctx.cancel()
 

examples/full_fledged_streaming_service.py

@@ -1,6 +1,11 @@
 import time
 import trio
 import tractor
+from tractor import (
+    ActorNursery,
+    MsgStream,
+    Portal,
+)
 
 
 # this is the first 2 actors, streamer_1 and streamer_2
@@ -12,14 +17,18 @@ async def stream_data(seed):
 
 # this is the third actor; the aggregator
 async def aggregate(seed):
-    """Ensure that the two streams we receive match but only stream
+    '''
+    Ensure that the two streams we receive match but only stream
     a single set of values to the parent.
-    """
-    async with tractor.open_nursery() as nursery:
-        portals = []
+
+    '''
+    an: ActorNursery
+    async with tractor.open_nursery() as an:
+        portals: list[Portal] = []
         for i in range(1, 3):
-            # fork point
-            portal = await nursery.start_actor(
+
+            # fork/spawn call
+            portal = await an.start_actor(
                 name=f'streamer_{i}',
                 enable_modules=[__name__],
             )
@@ -43,7 +52,11 @@ async def aggregate(seed):
         async with trio.open_nursery() as n:
 
             for portal in portals:
-                n.start_soon(push_to_chan, portal, send_chan.clone())
+                n.start_soon(
+                    push_to_chan,
+                    portal,
+                    send_chan.clone(),
+                )
 
             # close this local task's reference to send side
             await send_chan.aclose()
@@ -60,7 +73,7 @@ async def aggregate(seed):
 
             print("FINISHED ITERATING in aggregator")
 
-        await nursery.cancel()
+        await an.cancel()
         print("WAITING on `ActorNursery` to finish")
     print("AGGREGATOR COMPLETE!")
 
@@ -75,18 +88,21 @@ async def main() -> list[int]:
 
     '''
     # yes, a nursery which spawns `trio`-"actors" B)
-    nursery: tractor.ActorNursery
-    async with tractor.open_nursery() as nursery:
+    an: ActorNursery
+    async with tractor.open_nursery(
+        loglevel='cancel',
+        debug_mode=True,
+    ) as an:
 
         seed = int(1e3)
         pre_start = time.time()
 
-        portal: tractor.Portal = await nursery.start_actor(
+        portal: Portal = await an.start_actor(
             name='aggregator',
             enable_modules=[__name__],
         )
 
-        stream: tractor.MsgStream
+        stream: MsgStream
         async with portal.open_stream_from(
             aggregate,
             seed=seed,
@@ -95,11 +111,12 @@ async def main() -> list[int]:
             start = time.time()
             # the portal call returns exactly what you'd expect
             # as if the remote "aggregate" function was called locally
-            result_stream = []
+            result_stream: list[int] = []
             async for value in stream:
                 result_stream.append(value)
 
-        await portal.cancel_actor()
+        cancelled: bool = await portal.cancel_actor()
+        assert cancelled
 
         print(f"STREAM TIME = {time.time() - start}")
         print(f"STREAM + SPAWN TIME = {time.time() - pre_start}")

examples/service_discovery.py

@@ -9,7 +9,7 @@ async def main(service_name):
     async with tractor.open_nursery() as an:
         await an.start_actor(service_name)
 
-        async with tractor.get_arbiter('127.0.0.1', 1616) as portal:
+        async with tractor.get_registry('127.0.0.1', 1616) as portal:
             print(f"Arbiter is listening on {portal.channel}")
 
         async with tractor.wait_for_actor(service_name) as sockaddr:

tests/test_advanced_faults.py

@@ -13,6 +13,7 @@ import trio
 import tractor
 from tractor._testing import (
     examples_dir,
+    break_ipc,
 )
 
 
@@ -90,10 +91,12 @@ def test_ipc_channel_break_during_stream(
 
         # non-`trio` spawners should never hit the hang condition that
         # requires the user to do ctl-c to cancel the actor tree.
-        expect_final_exc = trio.ClosedResourceError
+        # expect_final_exc = trio.ClosedResourceError
+        expect_final_exc = tractor.TransportClosed
 
     mod: ModuleType = import_path(
-        examples_dir() / 'advanced_faults' / 'ipc_failure_during_stream.py',
+        examples_dir() / 'advanced_faults'
+        / 'ipc_failure_during_stream.py',
         root=examples_dir(),
         consider_namespace_packages=False,
     )
@@ -155,7 +158,7 @@ def test_ipc_channel_break_during_stream(
         if pre_aclose_msgstream:
             expect_final_exc = KeyboardInterrupt
 
-    # NOTE when the parent IPC side dies (even if the child's does as well
+    # NOTE when the parent IPC side dies (even if the child does as well
     # but the child fails BEFORE the parent) we always expect the
     # IPC layer to raise a closed-resource, NEVER do we expect
     # a stop msg since the parent-side ctx apis will error out
@@ -167,7 +170,8 @@ def test_ipc_channel_break_during_stream(
         and
         ipc_break['break_child_ipc_after'] is False
     ):
-        expect_final_exc = trio.ClosedResourceError
+        # expect_final_exc = trio.ClosedResourceError
+        expect_final_exc = tractor.TransportClosed
 
     # BOTH but, PARENT breaks FIRST
     elif (
@@ -178,7 +182,8 @@ def test_ipc_channel_break_during_stream(
             ipc_break['break_parent_ipc_after']
         )
     ):
-        expect_final_exc = trio.ClosedResourceError
+        # expect_final_exc = trio.ClosedResourceError
+        expect_final_exc = tractor.TransportClosed
 
     with pytest.raises(
         expected_exception=(
@@ -197,8 +202,8 @@ def test_ipc_channel_break_during_stream(
                     **ipc_break,
                 )
             )
-        except KeyboardInterrupt as kbi:
-            _err = kbi
+        except KeyboardInterrupt as _kbi:
+            kbi = _kbi
             if expect_final_exc is not KeyboardInterrupt:
                 pytest.fail(
                     'Rxed unexpected KBI !?\n'
@@ -207,6 +212,21 @@ def test_ipc_channel_break_during_stream(
 
             raise
 
+        except tractor.TransportClosed as _tc:
+            tc = _tc
+            if expect_final_exc is KeyboardInterrupt:
+                pytest.fail(
+                    'Unexpected transport failure !?\n'
+                    f'{repr(tc)}'
+                )
+            cause: Exception = tc.__cause__
+            assert (
+                type(cause) is trio.ClosedResourceError
+                and
+                cause.args[0] == 'another task closed this fd'
+            )
+            raise
+
     # get raw instance from pytest wrapper
     value = excinfo.value
     if isinstance(value, ExceptionGroup):
@@ -225,9 +245,15 @@ async def break_ipc_after_started(
 ) -> None:
     await ctx.started()
     async with ctx.open_stream() as stream:
-        await stream.aclose()
-        await trio.sleep(0.2)
-        await ctx.chan.send(None)
+
+        # TODO: make a test which verifies the error
+        # for this, i.e. raises a `MsgTypeError`
+        # await ctx.chan.send(None)
+
+        await break_ipc(
+            stream=stream,
+            pre_close=True,
+        )
         print('child broke IPC and terminating')
 
 

tests/test_cancellation.py

@@ -89,17 +89,30 @@ def test_remote_error(reg_addr, args_err):
         assert excinfo.value.boxed_type == errtype
 
     else:
-        # the root task will also error on the `.result()` call
-        # so we expect an error from there AND the child.
-        with pytest.raises(BaseExceptionGroup) as excinfo:
+        # the root task will also error on the `Portal.result()`
+        # call so we expect an error from there AND the child.
+        # |_ tho seems like on new `trio` this doesn't always
+        #    happen?
+        with pytest.raises((
+            BaseExceptionGroup,
+            tractor.RemoteActorError,
+        )) as excinfo:
             trio.run(main)
 
-        # ensure boxed errors
-        for exc in excinfo.value.exceptions:
+        # ensure boxed errors are `errtype`
+        err: BaseException = excinfo.value
+        if isinstance(err, BaseExceptionGroup):
+            suberrs: list[BaseException] = err.exceptions
+        else:
+            suberrs: list[BaseException] = [err]
+
+        for exc in suberrs:
             assert exc.boxed_type == errtype
 
 
-def test_multierror(reg_addr):
+def test_multierror(
+    reg_addr: tuple[str, int],
+):
     '''
     Verify we raise a ``BaseExceptionGroup`` out of a nursery where
     more then one actor errors.

tests/test_caps_based_msging.py

@@ -0,0 +1,917 @@
+'''
+Low-level functional audits for our
+"capability based messaging"-spec feats.
+
+B~)
+
+'''
+import typing
+from typing import (
+    Any,
+    Type,
+    Union,
+)
+
+from msgspec import (
+    structs,
+    msgpack,
+    Struct,
+    ValidationError,
+)
+import pytest
+
+import tractor
+from tractor import (
+    _state,
+    MsgTypeError,
+    Context,
+)
+from tractor.msg import (
+    _codec,
+    _ctxvar_MsgCodec,
+
+    NamespacePath,
+    MsgCodec,
+    mk_codec,
+    apply_codec,
+    current_codec,
+)
+from tractor.msg.types import (
+    _payload_msgs,
+    log,
+    PayloadMsg,
+    Started,
+    mk_msg_spec,
+)
+import trio
+
+
+def mk_custom_codec(
+    pld_spec: Union[Type]|Any,
+    add_hooks: bool,
+
+) -> MsgCodec:
+    '''
+    Create custom `msgpack` enc/dec-hooks and set a `Decoder`
+    which only loads `pld_spec` (like `NamespacePath`) types.
+
+    '''
+    uid: tuple[str, str] = tractor.current_actor().uid
+
+    # XXX NOTE XXX: despite defining `NamespacePath` as a type
+    # field on our `PayloadMsg.pld`, we still need a enc/dec_hook() pair
+    # to cast to/from that type on the wire. See the docs:
+    # https://jcristharif.com/msgspec/extending.html#mapping-to-from-native-types
+
+    def enc_nsp(obj: Any) -> Any:
+        print(f'{uid} ENC HOOK')
+        match obj:
+            case NamespacePath():
+                print(
+                    f'{uid}: `NamespacePath`-Only ENCODE?\n'
+                    f'obj-> `{obj}`: {type(obj)}\n'
+                )
+                # if type(obj) != NamespacePath:
+                #     breakpoint()
+                return str(obj)
+
+        print(
+            f'{uid}\n'
+            'CUSTOM ENCODE\n'
+            f'obj-arg-> `{obj}`: {type(obj)}\n'
+        )
+        logmsg: str = (
+            f'{uid}\n'
+            'FAILED ENCODE\n'
+            f'obj-> `{obj}: {type(obj)}`\n'
+        )
+        raise NotImplementedError(logmsg)
+
+    def dec_nsp(
+        obj_type: Type,
+        obj: Any,
+
+    ) -> Any:
+        print(
+            f'{uid}\n'
+            'CUSTOM DECODE\n'
+            f'type-arg-> {obj_type}\n'
+            f'obj-arg-> `{obj}`: {type(obj)}\n'
+        )
+        nsp = None
+
+        if (
+            obj_type is NamespacePath
+            and isinstance(obj, str)
+            and ':' in obj
+        ):
+            nsp = NamespacePath(obj)
+            # TODO: we could built a generic handler using
+            # JUST matching the obj_type part?
+            # nsp = obj_type(obj)
+
+        if nsp:
+            print(f'Returning NSP instance: {nsp}')
+            return nsp
+
+        logmsg: str = (
+            f'{uid}\n'
+            'FAILED DECODE\n'
+            f'type-> {obj_type}\n'
+            f'obj-arg-> `{obj}`: {type(obj)}\n\n'
+            f'current codec:\n'
+            f'{current_codec()}\n'
+        )
+        # TODO: figure out the ignore subsys for this!
+        # -[ ] option whether to defense-relay backc the msg
+        #   inside an `Invalid`/`Ignore`
+        # -[ ] how to make this handling pluggable such that a
+        #   `Channel`/`MsgTransport` can intercept and process
+        #   back msgs either via exception handling or some other
+        #   signal?
+        log.warning(logmsg)
+        # NOTE: this delivers the invalid
+        # value up to `msgspec`'s decoding
+        # machinery for error raising.
+        return obj
+        # raise NotImplementedError(logmsg)
+
+    nsp_codec: MsgCodec = mk_codec(
+        ipc_pld_spec=pld_spec,
+
+        # NOTE XXX: the encode hook MUST be used no matter what since
+        # our `NamespacePath` is not any of a `Any` native type nor
+        # a `msgspec.Struct` subtype - so `msgspec` has no way to know
+        # how to encode it unless we provide the custom hook.
+        #
+        # AGAIN that is, regardless of whether we spec an
+        # `Any`-decoded-pld the enc has no knowledge (by default)
+        # how to enc `NamespacePath` (nsp), so we add a custom
+        # hook to do that ALWAYS.
+        enc_hook=enc_nsp if add_hooks else None,
+
+        # XXX NOTE: pretty sure this is mutex with the `type=` to
+        # `Decoder`? so it won't work in tandem with the
+        # `ipc_pld_spec` passed above?
+        dec_hook=dec_nsp if add_hooks else None,
+    )
+    return nsp_codec
+
+
+def chk_codec_applied(
+    expect_codec: MsgCodec,
+    enter_value: MsgCodec|None = None,
+
+) -> MsgCodec:
+    '''
+    buncha sanity checks ensuring that the IPC channel's
+    context-vars are set to the expected codec and that are
+    ctx-var wrapper APIs match the same.
+
+    '''
+    # TODO: play with tricyle again, bc this is supposed to work
+    # the way we want?
+    #
+    # TreeVar
+    # task: trio.Task = trio.lowlevel.current_task()
+    # curr_codec = _ctxvar_MsgCodec.get_in(task)
+
+    # ContextVar
+    # task_ctx: Context = task.context
+    # assert _ctxvar_MsgCodec in task_ctx
+    # curr_codec: MsgCodec = task.context[_ctxvar_MsgCodec]
+
+    # NOTE: currently we use this!
+    # RunVar
+    curr_codec: MsgCodec = current_codec()
+    last_read_codec = _ctxvar_MsgCodec.get()
+    # assert curr_codec is last_read_codec
+
+    assert (
+        (same_codec := expect_codec) is
+        # returned from `mk_codec()`
+
+        # yielded value from `apply_codec()`
+
+        # read from current task's `contextvars.Context`
+        curr_codec is
+        last_read_codec
+
+        # the default `msgspec` settings
+        is not _codec._def_msgspec_codec
+        is not _codec._def_tractor_codec
+    )
+
+    if enter_value:
+        enter_value is same_codec
+
+
+def iter_maybe_sends(
+    send_items: dict[Union[Type], Any] | list[tuple],
+    ipc_pld_spec: Union[Type] | Any,
+    add_codec_hooks: bool,
+
+    codec: MsgCodec|None = None,
+
+) -> tuple[Any, bool]:
+
+    if isinstance(send_items, dict):
+        send_items = send_items.items()
+
+    for (
+        send_type_spec,
+        send_value,
+    ) in send_items:
+
+        expect_roundtrip: bool = False
+
+        # values-to-typespec santiy
+        send_type = type(send_value)
+        assert send_type == send_type_spec or (
+            (subtypes := getattr(send_type_spec, '__args__', None))
+            and send_type in subtypes
+        )
+
+        spec_subtypes: set[Union[Type]] = (
+             getattr(
+                 ipc_pld_spec,
+                 '__args__',
+                 {ipc_pld_spec,},
+             )
+        )
+        send_in_spec: bool = (
+            send_type == ipc_pld_spec
+            or (
+                ipc_pld_spec != Any
+                and  # presume `Union` of types
+                send_type in spec_subtypes
+            )
+            or (
+                ipc_pld_spec == Any
+                and
+                send_type != NamespacePath
+            )
+        )
+        expect_roundtrip = (
+            send_in_spec
+            # any spec should support all other
+            # builtin py values that we send
+            # except our custom nsp type which
+            # we should be able to send as long
+            # as we provide the custom codec hooks.
+            or (
+                ipc_pld_spec == Any
+                and
+                send_type == NamespacePath
+                and
+                add_codec_hooks
+            )
+        )
+
+        if codec is not None:
+            # XXX FIRST XXX ensure roundtripping works
+            # before touching any IPC primitives/APIs.
+            wire_bytes: bytes = codec.encode(
+                Started(
+                    cid='blahblah',
+                    pld=send_value,
+                )
+            )
+            # NOTE: demonstrates the decoder loading
+            # to via our native SCIPP msg-spec
+            # (structurred-conc-inter-proc-protocol)
+            # implemented as per,
+            try:
+                msg: Started = codec.decode(wire_bytes)
+                if not expect_roundtrip:
+                    pytest.fail(
+                        f'NOT-EXPECTED able to roundtrip value given spec:\n'
+                        f'ipc_pld_spec -> {ipc_pld_spec}\n'
+                        f'value -> {send_value}: {send_type}\n'
+                    )
+
+                pld = msg.pld
+                assert pld == send_value
+
+            except ValidationError:
+                if expect_roundtrip:
+                    pytest.fail(
+                        f'EXPECTED to roundtrip value given spec:\n'
+                        f'ipc_pld_spec -> {ipc_pld_spec}\n'
+                        f'value -> {send_value}: {send_type}\n'
+                    )
+
+        yield (
+            str(send_type),
+            send_value,
+            expect_roundtrip,
+        )
+
+
+def dec_type_union(
+    type_names: list[str],
+) -> Type:
+    '''
+    Look up types by name, compile into a list and then create and
+    return a `typing.Union` from the full set.
+
+    '''
+    import importlib
+    types: list[Type] = []
+    for type_name in type_names:
+        for mod in [
+            typing,
+            importlib.import_module(__name__),
+        ]:
+            if type_ref := getattr(
+                mod,
+                type_name,
+                False,
+            ):
+                types.append(type_ref)
+
+    # special case handling only..
+    # ipc_pld_spec: Union[Type] = eval(
+    #     pld_spec_str,
+    #     {},  # globals
+    #     {'typing': typing},  # locals
+    # )
+
+    return Union[*types]
+
+
+def enc_type_union(
+    union_or_type: Union[Type]|Type,
+) -> list[str]:
+    '''
+    Encode a type-union or single type to a list of type-name-strings
+    ready for IPC interchange.
+
+    '''
+    type_strs: list[str] = []
+    for typ in getattr(
+        union_or_type,
+        '__args__',
+        {union_or_type,},
+    ):
+        type_strs.append(typ.__qualname__)
+
+    return type_strs
+
+
+@tractor.context
+async def send_back_values(
+    ctx: Context,
+    expect_debug: bool,
+    pld_spec_type_strs: list[str],
+    add_hooks: bool,
+    started_msg_bytes: bytes,
+    expect_ipc_send: dict[str, tuple[Any, bool]],
+
+) -> None:
+    '''
+    Setup up a custom codec to load instances of `NamespacePath`
+    and ensure we can round trip a func ref with our parent.
+
+    '''
+    uid: tuple = tractor.current_actor().uid
+
+    # debug mode sanity check (prolly superfluous but, meh)
+    assert expect_debug == _state.debug_mode()
+
+    # init state in sub-actor should be default
+    chk_codec_applied(
+        expect_codec=_codec._def_tractor_codec,
+    )
+
+    # load pld spec from input str
+    ipc_pld_spec = dec_type_union(
+        pld_spec_type_strs,
+    )
+    pld_spec_str = str(ipc_pld_spec)
+
+    # same as on parent side config.
+    nsp_codec: MsgCodec = mk_custom_codec(
+        pld_spec=ipc_pld_spec,
+        add_hooks=add_hooks,
+    )
+    with (
+        apply_codec(nsp_codec) as codec,
+    ):
+        chk_codec_applied(
+            expect_codec=nsp_codec,
+            enter_value=codec,
+        )
+
+        print(
+            f'{uid}: attempting `Started`-bytes DECODE..\n'
+        )
+        try:
+            msg: Started = nsp_codec.decode(started_msg_bytes)
+            expected_pld_spec_str: str = msg.pld
+            assert pld_spec_str == expected_pld_spec_str
+
+        # TODO: maybe we should add our own wrapper error so as to
+        # be interchange-lib agnostic?
+        # -[ ] the error type is wtv is raised from the hook so we
+        #   could also require a type-class of errors for
+        #   indicating whether the hook-failure can be handled by
+        #   a nasty-dialog-unprot sub-sys?
+        except ValidationError:
+
+            # NOTE: only in the `Any` spec case do we expect this to
+            # work since otherwise no spec covers a plain-ol'
+            # `.pld: str`
+            if pld_spec_str == 'Any':
+                raise
+            else:
+                print(
+                    f'{uid}: (correctly) unable to DECODE `Started`-bytes\n'
+                    f'{started_msg_bytes}\n'
+                )
+
+        iter_send_val_items = iter(expect_ipc_send.values())
+        sent: list[Any] = []
+        for send_value, expect_send in iter_send_val_items:
+            try:
+                print(
+                    f'{uid}: attempting to `.started({send_value})`\n'
+                    f'=> expect_send: {expect_send}\n'
+                    f'SINCE, ipc_pld_spec: {ipc_pld_spec}\n'
+                    f'AND, codec: {codec}\n'
+                )
+                await ctx.started(send_value)
+                sent.append(send_value)
+                if not expect_send:
+
+                    # XXX NOTE XXX THIS WON'T WORK WITHOUT SPECIAL
+                    # `str` handling! or special debug mode IPC
+                    # msgs!
+                    await tractor.pause()
+
+                    raise RuntimeError(
+                        f'NOT-EXPECTED able to roundtrip value given spec:\n'
+                        f'ipc_pld_spec -> {ipc_pld_spec}\n'
+                        f'value -> {send_value}: {type(send_value)}\n'
+                    )
+
+                break  # move on to streaming block..
+
+            except tractor.MsgTypeError:
+                await tractor.pause()
+
+                if expect_send:
+                    raise RuntimeError(
+                        f'EXPECTED to `.started()` value given spec:\n'
+                        f'ipc_pld_spec -> {ipc_pld_spec}\n'
+                        f'value -> {send_value}: {type(send_value)}\n'
+                    )
+
+        async with ctx.open_stream() as ipc:
+            print(
+                f'{uid}: Entering streaming block to send remaining values..'
+            )
+
+            for send_value, expect_send in iter_send_val_items:
+                send_type: Type = type(send_value)
+                print(
+                    '------ - ------\n'
+                    f'{uid}: SENDING NEXT VALUE\n'
+                    f'ipc_pld_spec: {ipc_pld_spec}\n'
+                    f'expect_send: {expect_send}\n'
+                    f'val: {send_value}\n'
+                    '------ - ------\n'
+                )
+                try:
+                    await ipc.send(send_value)
+                    print(f'***\n{uid}-CHILD sent {send_value!r}\n***\n')
+                    sent.append(send_value)
+
+                    # NOTE: should only raise above on
+                    # `.started()` or a `Return`
+                    # if not expect_send:
+                    #     raise RuntimeError(
+                    #         f'NOT-EXPECTED able to roundtrip value given spec:\n'
+                    #         f'ipc_pld_spec -> {ipc_pld_spec}\n'
+                    #         f'value -> {send_value}: {send_type}\n'
+                    #     )
+
+                except ValidationError:
+                    print(f'{uid} FAILED TO SEND {send_value}!')
+
+                    # await tractor.pause()
+                    if expect_send:
+                        raise RuntimeError(
+                            f'EXPECTED to roundtrip value given spec:\n'
+                            f'ipc_pld_spec -> {ipc_pld_spec}\n'
+                            f'value -> {send_value}: {send_type}\n'
+                        )
+                    # continue
+
+            else:
+                print(
+                    f'{uid}: finished sending all values\n'
+                    'Should be exiting stream block!\n'
+                )
+
+        print(f'{uid}: exited streaming block!')
+
+        # TODO: this won't be true bc in streaming phase we DO NOT
+        # msgspec check outbound msgs!
+        # -[ ] once we implement the receiver side `InvalidMsg`
+        #   then we can expect it here?
+        # assert (
+        #     len(sent)
+        #     ==
+        #     len([val
+        #          for val, expect in
+        #          expect_ipc_send.values()
+        #          if expect is True])
+        # )
+
+
+def ex_func(*args):
+    print(f'ex_func({args})')
+
+
+@pytest.mark.parametrize(
+    'ipc_pld_spec',
+    [
+        Any,
+        NamespacePath,
+        NamespacePath|None,  # the "maybe" spec Bo
+    ],
+    ids=[
+        'any_type',
+        'nsp_type',
+        'maybe_nsp_type',
+    ]
+)
+@pytest.mark.parametrize(
+    'add_codec_hooks',
+    [
+        True,
+        False,
+    ],
+    ids=['use_codec_hooks', 'no_codec_hooks'],
+)
+def test_codec_hooks_mod(
+    debug_mode: bool,
+    ipc_pld_spec: Union[Type]|Any,
+    # send_value: None|str|NamespacePath,
+    add_codec_hooks: bool,
+):
+    '''
+    Audit the `.msg.MsgCodec` override apis details given our impl
+    uses `contextvars` to accomplish per `trio` task codec
+    application around an inter-proc-task-comms context.
+
+    '''
+    async def main():
+        nsp = NamespacePath.from_ref(ex_func)
+        send_items: dict[Union, Any] = {
+            Union[None]: None,
+            Union[NamespacePath]: nsp,
+            Union[str]: str(nsp),
+        }
+
+        # init default state for actor
+        chk_codec_applied(
+            expect_codec=_codec._def_tractor_codec,
+        )
+
+        async with tractor.open_nursery(
+            debug_mode=debug_mode,
+        ) as an:
+            p: tractor.Portal = await an.start_actor(
+                'sub',
+                enable_modules=[__name__],
+            )
+
+            # TODO: 2 cases:
+            # - codec not modified -> decode nsp as `str`
+            # - codec modified with hooks -> decode nsp as
+            #   `NamespacePath`
+            nsp_codec: MsgCodec = mk_custom_codec(
+                pld_spec=ipc_pld_spec,
+                add_hooks=add_codec_hooks,
+            )
+            with apply_codec(nsp_codec) as codec:
+                chk_codec_applied(
+                    expect_codec=nsp_codec,
+                    enter_value=codec,
+                )
+
+                expect_ipc_send: dict[str, tuple[Any, bool]] = {}
+
+                report: str = (
+                    'Parent report on send values with\n'
+                    f'ipc_pld_spec: {ipc_pld_spec}\n'
+                    '       ------ - ------\n'
+                )
+                for val_type_str, val, expect_send in iter_maybe_sends(
+                    send_items,
+                    ipc_pld_spec,
+                    add_codec_hooks=add_codec_hooks,
+                ):
+                    report += (
+                        f'send_value: {val}: {type(val)} '
+                        f'=> expect_send: {expect_send}\n'
+                    )
+                    expect_ipc_send[val_type_str] = (val, expect_send)
+
+                print(
+                    report +
+                    '       ------ - ------\n'
+                )
+                assert len(expect_ipc_send) == len(send_items)
+                # now try over real IPC with a the subactor
+                # expect_ipc_rountrip: bool = True
+                expected_started = Started(
+                    cid='cid',
+                    pld=str(ipc_pld_spec),
+                )
+                # build list of values we expect to receive from
+                # the subactor.
+                expect_to_send: list[Any] = [
+                    val
+                    for val, expect_send in expect_ipc_send.values()
+                    if expect_send
+                ]
+
+                pld_spec_type_strs: list[str] = enc_type_union(ipc_pld_spec)
+
+                # XXX should raise an mte (`MsgTypeError`)
+                # when `add_codec_hooks == False` bc the input
+                # `expect_ipc_send` kwarg has a nsp which can't be
+                # serialized!
+                #
+                # TODO:can we ensure this happens from the
+                # `Return`-side (aka the sub) as well?
+                if not add_codec_hooks:
+                    try:
+                        async with p.open_context(
+                            send_back_values,
+                            expect_debug=debug_mode,
+                            pld_spec_type_strs=pld_spec_type_strs,
+                            add_hooks=add_codec_hooks,
+                            started_msg_bytes=nsp_codec.encode(expected_started),
+
+                            # XXX NOTE bc we send a `NamespacePath` in this kwarg
+                            expect_ipc_send=expect_ipc_send,
+
+                        ) as (ctx, first):
+                            pytest.fail('ctx should fail to open without custom enc_hook!?')
+
+                    # this test passes bc we can go no further!
+                    except MsgTypeError:
+                        # teardown nursery
+                        await p.cancel_actor()
+                        return
+
+                # TODO: send the original nsp here and
+                # test with `limit_msg_spec()` above?
+                # await tractor.pause()
+                print('PARENT opening IPC ctx!\n')
+                async with (
+
+                    # XXX should raise an mte (`MsgTypeError`)
+                    # when `add_codec_hooks == False`..
+                    p.open_context(
+                        send_back_values,
+                        expect_debug=debug_mode,
+                        pld_spec_type_strs=pld_spec_type_strs,
+                        add_hooks=add_codec_hooks,
+                        started_msg_bytes=nsp_codec.encode(expected_started),
+                        expect_ipc_send=expect_ipc_send,
+                    ) as (ctx, first),
+
+                    ctx.open_stream() as ipc,
+                ):
+                    # ensure codec is still applied across
+                    # `tractor.Context` + its embedded nursery.
+                    chk_codec_applied(
+                        expect_codec=nsp_codec,
+                        enter_value=codec,
+                    )
+                    print(
+                        'root: ENTERING CONTEXT BLOCK\n'
+                        f'type(first): {type(first)}\n'
+                        f'first: {first}\n'
+                    )
+                    expect_to_send.remove(first)
+
+                    # TODO: explicit values we expect depending on
+                    # codec config!
+                    # assert first == first_val
+                    # assert first == f'{__name__}:ex_func'
+
+                    async for next_sent in ipc:
+                        print(
+                            'Parent: child sent next value\n'
+                            f'{next_sent}: {type(next_sent)}\n'
+                        )
+                        if expect_to_send:
+                            expect_to_send.remove(next_sent)
+                        else:
+                            print('PARENT should terminate stream loop + block!')
+
+                    # all sent values should have arrived!
+                    assert not expect_to_send
+
+            await p.cancel_actor()
+
+    trio.run(main)
+
+
+def chk_pld_type(
+    payload_spec: Type[Struct]|Any,
+    pld: Any,
+
+    expect_roundtrip: bool|None = None,
+
+) -> bool:
+
+    pld_val_type: Type = type(pld)
+
+    # TODO: verify that the overridden subtypes
+    # DO NOT have modified type-annots from original!
+    # 'Start',  .pld: FuncSpec
+    # 'StartAck',  .pld: IpcCtxSpec
+    # 'Stop',  .pld: UNSEt
+    # 'Error',  .pld: ErrorData
+
+    codec: MsgCodec = mk_codec(
+        # NOTE: this ONLY accepts `PayloadMsg.pld` fields of a specified
+        # type union.
+        ipc_pld_spec=payload_spec,
+    )
+
+    # make a one-off dec to compare with our `MsgCodec` instance
+    # which does the below `mk_msg_spec()` call internally
+    ipc_msg_spec: Union[Type[Struct]]
+    msg_types: list[PayloadMsg[payload_spec]]
+    (
+        ipc_msg_spec,
+        msg_types,
+    ) = mk_msg_spec(
+        payload_type_union=payload_spec,
+    )
+    _enc = msgpack.Encoder()
+    _dec = msgpack.Decoder(
+        type=ipc_msg_spec or Any,  # like `PayloadMsg[Any]`
+    )
+
+    assert (
+        payload_spec
+        ==
+        codec.pld_spec
+    )
+
+    # assert codec.dec == dec
+    #
+    # ^-XXX-^ not sure why these aren't "equal" but when cast
+    # to `str` they seem to match ?? .. kk
+
+    assert (
+        str(ipc_msg_spec)
+        ==
+        str(codec.msg_spec)
+        ==
+        str(_dec.type)
+        ==
+        str(codec.dec.type)
+    )
+
+    # verify the boxed-type for all variable payload-type msgs.
+    if not msg_types:
+        breakpoint()
+
+    roundtrip: bool|None = None
+    pld_spec_msg_names: list[str] = [
+        td.__name__ for td in _payload_msgs
+    ]
+    for typedef in msg_types:
+
+        skip_runtime_msg: bool = typedef.__name__ not in pld_spec_msg_names
+        if skip_runtime_msg:
+            continue
+
+        pld_field = structs.fields(typedef)[1]
+        assert pld_field.type is payload_spec # TODO-^ does this need to work to get all subtypes to adhere?
+
+        kwargs: dict[str, Any] = {
+            'cid': '666',
+            'pld': pld,
+        }
+        enc_msg: PayloadMsg = typedef(**kwargs)
+
+        _wire_bytes: bytes = _enc.encode(enc_msg)
+        wire_bytes: bytes = codec.enc.encode(enc_msg)
+        assert _wire_bytes == wire_bytes
+
+        ve: ValidationError|None = None
+        try:
+            dec_msg = codec.dec.decode(wire_bytes)
+            _dec_msg = _dec.decode(wire_bytes)
+
+            # decoded msg and thus payload should be exactly same!
+            assert (roundtrip := (
+                _dec_msg
+                ==
+                dec_msg
+                ==
+                enc_msg
+            ))
+
+            if (
+                expect_roundtrip is not None
+                and expect_roundtrip != roundtrip
+            ):
+                breakpoint()
+
+            assert (
+                pld
+                ==
+                dec_msg.pld
+                ==
+                enc_msg.pld
+            )
+            # assert (roundtrip := (_dec_msg == enc_msg))
+
+        except ValidationError as _ve:
+            ve = _ve
+            roundtrip: bool = False
+            if pld_val_type is payload_spec:
+                raise ValueError(
+                   'Got `ValidationError` despite type-var match!?\n'
+                    f'pld_val_type: {pld_val_type}\n'
+                    f'payload_type: {payload_spec}\n'
+                ) from ve
+
+            else:
+                # ow we good cuz the pld spec mismatched.
+                print(
+                    'Got expected `ValidationError` since,\n'
+                    f'{pld_val_type} is not {payload_spec}\n'
+                )
+        else:
+            if (
+                payload_spec is not Any
+                and
+                pld_val_type is not payload_spec
+            ):
+                raise ValueError(
+                   'DID NOT `ValidationError` despite expected type match!?\n'
+                    f'pld_val_type: {pld_val_type}\n'
+                    f'payload_type: {payload_spec}\n'
+                )
+
+    # full code decode should always be attempted!
+    if roundtrip is None:
+        breakpoint()
+
+    return roundtrip
+
+
+def test_limit_msgspec():
+
+    async def main():
+        async with tractor.open_root_actor(
+            debug_mode=True
+        ):
+
+            # ensure we can round-trip a boxing `PayloadMsg`
+            assert chk_pld_type(
+                payload_spec=Any,
+                pld=None,
+                expect_roundtrip=True,
+            )
+
+            # verify that a mis-typed payload value won't decode
+            assert not chk_pld_type(
+                payload_spec=int,
+                pld='doggy',
+            )
+
+            # parametrize the boxed `.pld` type as a custom-struct
+            # and ensure that parametrization propagates
+            # to all payload-msg-spec-able subtypes!
+            class CustomPayload(Struct):
+                name: str
+                value: Any
+
+            assert not chk_pld_type(
+                payload_spec=CustomPayload,
+                pld='doggy',
+            )
+
+            assert chk_pld_type(
+                payload_spec=CustomPayload,
+                pld=CustomPayload(name='doggy', value='urmom')
+            )
+
+            # yah, we can `.pause_from_sync()` now!
+            # breakpoint()
+
+    trio.run(main)

tests/test_context_stream_semantics.py

@@ -6,6 +6,7 @@ sync-opening a ``tractor.Context`` beforehand.
 
 '''
 from itertools import count
+import math
 import platform
 from pprint import pformat
 from typing import (
@@ -24,6 +25,7 @@ from tractor._exceptions import (
     StreamOverrun,
     ContextCancelled,
 )
+from tractor._state import current_ipc_ctx
 
 from tractor._testing import (
     tractor_test,
@@ -143,6 +145,8 @@ async def simple_setup_teardown(
     global _state
     _state = True
 
+    assert current_ipc_ctx() is ctx
+
     # signal to parent that we're up
     await ctx.started(data + 1)
 
@@ -203,6 +207,7 @@ def test_simple_context(
                             block_forever=callee_blocks_forever,
                         ) as (ctx, sent),
                     ):
+                        assert current_ipc_ctx() is ctx
                         assert sent == 11
 
                         if callee_blocks_forever:
@@ -795,10 +800,12 @@ async def test_callee_cancels_before_started(
 
         # raises a special cancel signal
         except tractor.ContextCancelled as ce:
+            _ce = ce  # for debug on crash
             ce.boxed_type == trio.Cancelled
 
             # the traceback should be informative
-            assert 'itself' in ce.msgdata['tb_str']
+            assert 'itself' in ce.tb_str
+            assert ce.tb_str == ce.msgdata['tb_str']
 
         # teardown the actor
         await portal.cancel_actor()
@@ -845,7 +852,10 @@ async def keep_sending_from_callee(
         ('caller', 1, never_open_stream),
         ('callee', 0, keep_sending_from_callee),
     ],
-    ids='overrun_condition={}'.format,
+    ids=[
+         ('caller_1buf_never_open_stream'),
+         ('callee_0buf_keep_sending_from_callee'),
+    ]
 )
 def test_one_end_stream_not_opened(
     overrun_by: tuple[str, int, Callable],
@@ -869,29 +879,30 @@ def test_one_end_stream_not_opened(
                 enable_modules=[__name__],
             )
 
-            async with portal.open_context(
-                entrypoint,
-            ) as (ctx, sent):
-                assert sent is None
+            with trio.fail_after(1):
+                async with portal.open_context(
+                    entrypoint,
+                ) as (ctx, sent):
+                    assert sent is None
 
-                if 'caller' in overrunner:
+                    if 'caller' in overrunner:
 
-                    async with ctx.open_stream() as stream:
+                        async with ctx.open_stream() as stream:
 
-                        # itersend +1 msg more then the buffer size
-                        # to cause the most basic overrun.
-                        for i in range(buf_size):
-                            print(f'sending {i}')
-                            await stream.send(i)
+                            # itersend +1 msg more then the buffer size
+                            # to cause the most basic overrun.
+                            for i in range(buf_size):
+                                print(f'sending {i}')
+                                await stream.send(i)
 
-                        else:
-                            # expect overrun error to be relayed back
-                            # and this sleep interrupted
-                            await trio.sleep_forever()
+                            else:
+                                # expect overrun error to be relayed back
+                                # and this sleep interrupted
+                                await trio.sleep_forever()
 
-                else:
-                    # callee overruns caller case so we do nothing here
-                    await trio.sleep_forever()
+                    else:
+                        # callee overruns caller case so we do nothing here
+                        await trio.sleep_forever()
 
             await portal.cancel_actor()
 
@@ -1055,54 +1066,63 @@ def test_maybe_allow_overruns_stream(
                 loglevel=loglevel,
                 debug_mode=debug_mode,
             )
-            seq = list(range(10))
-            async with portal.open_context(
-                echo_back_sequence,
-                seq=seq,
-                wait_for_cancel=cancel_ctx,
-                be_slow=(slow_side == 'child'),
-                allow_overruns_side=allow_overruns_side,
 
-            ) as (ctx, sent):
-                assert sent is None
+            # stream-sequence batch info with send delay to determine
+            # approx timeout determining whether test has hung.
+            total_batches: int = 2
+            num_items: int = 10
+            seq = list(range(num_items))
+            parent_send_delay: float = 0.16
+            timeout: float = math.ceil(
+                total_batches * num_items * parent_send_delay
+            )
+            with trio.fail_after(timeout):
+                async with portal.open_context(
+                    echo_back_sequence,
+                    seq=seq,
+                    wait_for_cancel=cancel_ctx,
+                    be_slow=(slow_side == 'child'),
+                    allow_overruns_side=allow_overruns_side,
 
-                async with ctx.open_stream(
-                    msg_buffer_size=1 if slow_side == 'parent' else None,
-                    allow_overruns=(allow_overruns_side in {'parent', 'both'}),
-                ) as stream:
+                ) as (ctx, sent):
+                    assert sent is None
 
-                    total_batches: int = 2
-                    for _ in range(total_batches):
-                        for msg in seq:
-                            # print(f'root tx {msg}')
-                            await stream.send(msg)
-                            if slow_side == 'parent':
-                                # NOTE: we make the parent slightly
-                                # slower, when it is slow, to make sure
-                                # that in the overruns everywhere case
-                                await trio.sleep(0.16)
+                    async with ctx.open_stream(
+                        msg_buffer_size=1 if slow_side == 'parent' else None,
+                        allow_overruns=(allow_overruns_side in {'parent', 'both'}),
+                    ) as stream:
 
-                        batch = []
-                        async for msg in stream:
-                            print(f'root rx {msg}')
-                            batch.append(msg)
-                            if batch == seq:
-                                break
+                        for _ in range(total_batches):
+                            for msg in seq:
+                                # print(f'root tx {msg}')
+                                await stream.send(msg)
+                                if slow_side == 'parent':
+                                    # NOTE: we make the parent slightly
+                                    # slower, when it is slow, to make sure
+                                    # that in the overruns everywhere case
+                                    await trio.sleep(parent_send_delay)
+
+                            batch = []
+                            async for msg in stream:
+                                print(f'root rx {msg}')
+                                batch.append(msg)
+                                if batch == seq:
+                                    break
+
+                    if cancel_ctx:
+                        # cancel the remote task
+                        print('Requesting `ctx.cancel()` in parent!')
+                        await ctx.cancel()
+
+                res: str|ContextCancelled = await ctx.result()
 
                 if cancel_ctx:
-                    # cancel the remote task
-                    print('Requesting `ctx.cancel()` in parent!')
-                    await ctx.cancel()
+                    assert isinstance(res, ContextCancelled)
+                    assert tuple(res.canceller) == current_actor().uid
 
-            res: str|ContextCancelled = await ctx.result()
-
-            if cancel_ctx:
-                assert isinstance(res, ContextCancelled)
-                assert tuple(res.canceller) == current_actor().uid
-
-            else:
-                print(f'RX ROOT SIDE RESULT {res}')
-                assert res == 'yo'
+                else:
+                    print(f'RX ROOT SIDE RESULT {res}')
+                    assert res == 'yo'
 
             # cancel the daemon
             await portal.cancel_actor()
@@ -1143,7 +1163,8 @@ def test_maybe_allow_overruns_stream(
 
         elif slow_side == 'parent':
             assert err.boxed_type == tractor.RemoteActorError
-            assert 'StreamOverrun' in err.msgdata['tb_str']
+            assert 'StreamOverrun' in err.tb_str
+            assert err.tb_str == err.msgdata['tb_str']
 
     else:
         # if this hits the logic blocks from above are not

tests/test_debugger.py

@@ -12,7 +12,6 @@ TODO:
 """
 from functools import partial
 import itertools
-from typing import Optional
 import platform
 import pathlib
 import time
@@ -30,6 +29,7 @@ from tractor._testing import (
 from tractor.devx._debug import (
     _pause_msg,
     _crash_msg,
+    _repl_fail_msg,
 )
 from .conftest import (
     _ci_env,
@@ -144,9 +144,10 @@ def in_prompt_msg(
     log/REPL output for a given `pdb` interact point.
 
     '''
+    __tracebackhide__: bool = False
+
     for part in parts:
         if part not in prompt:
-
             if pause_on_false:
                 import pdbp
                 pdbp.set_trace()
@@ -158,6 +159,10 @@ def in_prompt_msg(
 
     return True
 
+
+# TODO: todo support terminal color-chars stripping so we can match
+# against call stack frame output from the the 'll' command the like!
+# -[ ] SO answer for stipping ANSI codes: https://stackoverflow.com/a/14693789
 def assert_before(
     child,
     patts: list[str],
@@ -165,6 +170,7 @@ def assert_before(
     **kwargs,
 
 ) -> None:
+    __tracebackhide__: bool = False
 
     # as in before the prompt end
     before: str = str(child.before.decode())
@@ -217,7 +223,10 @@ def ctlc(
     ],
     ids=lambda item: f'{item[0]} -> {item[1]}',
 )
-def test_root_actor_error(spawn, user_in_out):
+def test_root_actor_error(
+    spawn,
+    user_in_out,
+):
     '''
     Demonstrate crash handler entering pdb from basic error in root actor.
 
@@ -282,7 +291,7 @@ def do_ctlc(
     child,
     count: int = 3,
     delay: float = 0.1,
-    patt: Optional[str] = None,
+    patt: str|None = None,
 
     # expect repl UX to reprint the prompt after every
     # ctrl-c send.
@@ -463,8 +472,12 @@ def test_subactor_breakpoint(
     child.expect(PROMPT)
 
     before = str(child.before.decode())
-    assert "RemoteActorError: ('breakpoint_forever'" in before
-    assert 'bdb.BdbQuit' in before
+    assert in_prompt_msg(
+        before,
+        ['RemoteActorError:',
+         "('breakpoint_forever'",
+         'bdb.BdbQuit',]
+    )
 
     if ctlc:
         do_ctlc(child)
@@ -476,8 +489,12 @@ def test_subactor_breakpoint(
     child.expect(pexpect.EOF)
 
     before = str(child.before.decode())
-    assert "RemoteActorError: ('breakpoint_forever'" in before
-    assert 'bdb.BdbQuit' in before
+    assert in_prompt_msg(
+        before,
+        ['RemoteActorError:',
+         "('breakpoint_forever'",
+         'bdb.BdbQuit',]
+    )
 
 
 @has_nested_actors
@@ -745,8 +762,9 @@ def test_multi_daemon_subactors(
             # boxed error raised in root task
             # "Attaching to pdb in crashed actor: ('root'",
             _crash_msg,
-            "('root'",
-            "_exceptions.RemoteActorError: ('name_error'",
+            "('root'",  # should attach in root
+            "_exceptions.RemoteActorError:",  # with an embedded RAE for..
+            "('name_error'",  # the src subactor which raised
         ]
     )
 
@@ -847,10 +865,11 @@ def test_multi_nested_subactors_error_through_nurseries(
     # https://github.com/goodboy/tractor/issues/320
     # ctlc: bool,
 ):
-    """Verify deeply nested actors that error trigger debugger entries
+    '''
+    Verify deeply nested actors that error trigger debugger entries
     at each actor nurserly (level) all the way up the tree.
 
-    """
+    '''
     # NOTE: previously, inside this script was a bug where if the
     # parent errors before a 2-levels-lower actor has released the lock,
     # the parent tries to cancel it but it's stuck in the debugger?
@@ -870,22 +889,31 @@ def test_multi_nested_subactors_error_through_nurseries(
         except EOF:
             break
 
-    assert_before(child, [
+    assert_before(
+        child,
+        [ # boxed source errors
+            "NameError: name 'doggypants' is not defined",
+            "tractor._exceptions.RemoteActorError:",
+            "('name_error'",
+            "bdb.BdbQuit",
 
-        # boxed source errors
-        "NameError: name 'doggypants' is not defined",
-        "tractor._exceptions.RemoteActorError: ('name_error'",
-        "bdb.BdbQuit",
+            # first level subtrees
+            # "tractor._exceptions.RemoteActorError: ('spawner0'",
+            "src_uid=('spawner0'",
 
-        # first level subtrees
-        "tractor._exceptions.RemoteActorError: ('spawner0'",
-        # "tractor._exceptions.RemoteActorError: ('spawner1'",
+            # "tractor._exceptions.RemoteActorError: ('spawner1'",
 
-        # propagation of errors up through nested subtrees
-        "tractor._exceptions.RemoteActorError: ('spawn_until_0'",
-        "tractor._exceptions.RemoteActorError: ('spawn_until_1'",
-        "tractor._exceptions.RemoteActorError: ('spawn_until_2'",
-    ])
+            # propagation of errors up through nested subtrees
+            # "tractor._exceptions.RemoteActorError: ('spawn_until_0'",
+            # "tractor._exceptions.RemoteActorError: ('spawn_until_1'",
+            # "tractor._exceptions.RemoteActorError: ('spawn_until_2'",
+            # ^-NOTE-^ old RAE repr, new one is below with a field
+            # showing the src actor's uid.
+            "src_uid=('spawn_until_0'",
+            "relay_uid=('spawn_until_1'",
+            "src_uid=('spawn_until_2'",
+        ]
+    )
 
 
 @pytest.mark.timeout(15)
@@ -1019,13 +1047,16 @@ def test_different_debug_mode_per_actor(
     # msg reported back from the debug mode actor is processed.
     # assert "tractor._exceptions.RemoteActorError: ('debugged_boi'" in before
 
-    assert "tractor._exceptions.RemoteActorError: ('crash_boi'" in before
-
     # the crash boi should not have made a debugger request but
     # instead crashed completely
-    assert "tractor._exceptions.RemoteActorError: ('crash_boi'" in before
-    assert "RuntimeError" in before
-
+    assert_before(
+        child,
+        [
+            "tractor._exceptions.RemoteActorError:",
+            "src_uid=('crash_boi'",
+            "RuntimeError",
+        ]
+    )
 
 
 def test_pause_from_sync(
@@ -1040,52 +1071,289 @@ def test_pause_from_sync(
 
     '''
     child = spawn('sync_bp')
+
+    # first `sync_pause()` after nurseries open
     child.expect(PROMPT)
     assert_before(
         child,
         [
-            '`greenback` portal opened!',
             # pre-prompt line
-            _pause_msg, "('root'",
+            _pause_msg,
+            "<Task '__main__.main'",
+            "('root'",
         ]
     )
     if ctlc:
         do_ctlc(child)
+
     child.sendline('c')
+
+
+    # first `await tractor.pause()` inside `p.open_context()` body
     child.expect(PROMPT)
 
-    # XXX shouldn't see gb loaded again
+    # XXX shouldn't see gb loaded message with PDB loglevel!
     before = str(child.before.decode())
     assert not in_prompt_msg(
         before,
         ['`greenback` portal opened!'],
     )
+    # should be same root task
     assert_before(
         child,
-        [_pause_msg, "('root'",],
+        [
+            _pause_msg,
+            "<Task '__main__.main'",
+            "('root'",
+        ]
     )
 
     if ctlc:
         do_ctlc(child)
-    child.sendline('c')
-    child.expect(PROMPT)
-    assert_before(
-        child,
-        [_pause_msg, "('subactor'",],
-    )
 
-    if ctlc:
-        do_ctlc(child)
-    child.sendline('c')
-    child.expect(PROMPT)
-    # non-main thread case
-    # TODO: should we agument the pre-prompt msg in this case?
-    assert_before(
-        child,
-        [_pause_msg, "('root'",],
-    )
+    # one of the bg thread or subactor should have
+    # `Lock.acquire()`-ed
+    # (NOT both, which will result in REPL clobbering!)
+    attach_patts: dict[str, list[str]] = {
+        'subactor': [
+            "'start_n_sync_pause'",
+            "('subactor'",
+        ],
+        'inline_root_bg_thread': [
+            "<Thread(inline_root_bg_thread",
+            "('root'",
+        ],
+        'start_soon_root_bg_thread': [
+            "<Thread(start_soon_root_bg_thread",
+            "('root'",
+        ],
+    }
+    while attach_patts:
+        child.sendline('c')
+        child.expect(PROMPT)
+        before = str(child.before.decode())
+        for key in attach_patts.copy():
+            if key in before:
+                expected_patts: str = attach_patts.pop(key)
+                assert_before(
+                    child,
+                    [_pause_msg] + expected_patts
+                )
+                break
+
+        # ensure no other task/threads engaged a REPL
+        # at the same time as the one that was detected above.
+        for key, other_patts in attach_patts.items():
+            assert not in_prompt_msg(
+                before,
+                other_patts,
+            )
+
+        if ctlc:
+            do_ctlc(child)
 
-    if ctlc:
-        do_ctlc(child)
     child.sendline('c')
     child.expect(pexpect.EOF)
+
+
+def test_post_mortem_api(
+    spawn,
+    ctlc: bool,
+):
+    '''
+    Verify the `tractor.post_mortem()` API works in an exception
+    handler block.
+
+    '''
+    child = spawn('pm_in_subactor')
+
+    # First entry is via manual `.post_mortem()`
+    child.expect(PROMPT)
+    assert_before(
+        child,
+        [
+            _crash_msg,
+            "<Task 'name_error'",
+            "NameError",
+            "('child'",
+            "tractor.post_mortem()",
+        ]
+    )
+    if ctlc:
+        do_ctlc(child)
+    child.sendline('c')
+
+    # 2nd is RPC crash handler
+    child.expect(PROMPT)
+    assert_before(
+        child,
+        [
+            _crash_msg,
+            "<Task 'name_error'",
+            "NameError",
+            "('child'",
+        ]
+    )
+    if ctlc:
+        do_ctlc(child)
+    child.sendline('c')
+
+    # 3rd is via RAE bubbled to root's parent ctx task and
+    # crash-handled via another manual pm call.
+    child.expect(PROMPT)
+    assert_before(
+        child,
+        [
+            _crash_msg,
+            "<Task '__main__.main'",
+            "('root'",
+            "NameError",
+            "tractor.post_mortem()",
+            "src_uid=('child'",
+        ]
+    )
+    if ctlc:
+        do_ctlc(child)
+    child.sendline('c')
+
+    # 4th and FINAL is via RAE bubbled to root's parent ctx task and
+    # crash-handled via another manual pm call.
+    child.expect(PROMPT)
+    assert_before(
+        child,
+        [
+            _crash_msg,
+            "<Task '__main__.main'",
+            "('root'",
+            "NameError",
+            "src_uid=('child'",
+        ]
+    )
+    if ctlc:
+        do_ctlc(child)
+
+
+    # TODO: ensure we're stopped and showing the right call stack frame
+    # -[ ] need a way to strip the terminal color chars in order to
+    #    pattern match... see TODO around `assert_before()` above!
+    # child.sendline('w')
+    # child.expect(PROMPT)
+    # assert_before(
+    #     child,
+    #     [
+    #         # error src block annot at ctx open
+    #         '-> async with p.open_context(name_error) as (ctx, first):',
+    #     ]
+    # )
+
+    # # step up a frame to ensure the it's the root's nursery
+    # child.sendline('u')
+    # child.expect(PROMPT)
+    # assert_before(
+    #     child,
+    #     [
+    #         # handler block annotation
+    #         '-> async with tractor.open_nursery(',
+    #     ]
+    # )
+
+    child.sendline('c')
+    child.expect(pexpect.EOF)
+
+
+def test_shield_pause(
+    spawn,
+):
+    '''
+    Verify the `tractor.pause()/.post_mortem()` API works inside an
+    already cancelled `trio.CancelScope` and that you can step to the
+    next checkpoint wherein the cancelled will get raised.
+
+    '''
+    child = spawn('shielded_pause')
+
+    # First entry is via manual `.post_mortem()`
+    child.expect(PROMPT)
+    assert_before(
+        child,
+        [
+            _pause_msg,
+            "cancellable_pause_loop'",
+            "('cancelled_before_pause'",  # actor name
+        ]
+    )
+
+    # since 3 tries in ex. shield pause loop
+    for i in range(3):
+        child.sendline('c')
+        child.expect(PROMPT)
+        assert_before(
+            child,
+            [
+                _pause_msg,
+                "INSIDE SHIELDED PAUSE",
+                "('cancelled_before_pause'",  # actor name
+            ]
+        )
+
+    # back inside parent task that opened nursery
+    child.sendline('c')
+    child.expect(PROMPT)
+    assert_before(
+        child,
+        [
+            _crash_msg,
+            "('cancelled_before_pause'",  # actor name
+            _repl_fail_msg,
+            "trio.Cancelled",
+            "raise Cancelled._create()",
+
+            # we should be handling a taskc inside
+            # the first `.port_mortem()` sin-shield!
+            'await DebugStatus.req_finished.wait()',
+        ]
+    )
+
+    # same as above but in the root actor's task
+    child.sendline('c')
+    child.expect(PROMPT)
+    assert_before(
+        child,
+        [
+            _crash_msg,
+            "('root'",  # actor name
+            _repl_fail_msg,
+            "trio.Cancelled",
+            "raise Cancelled._create()",
+
+            # handling a taskc inside the first unshielded
+            # `.port_mortem()`.
+            # BUT in this case in the root-proc path ;)
+            'wait Lock._debug_lock.acquire()',
+        ]
+    )
+    child.sendline('c')
+    child.expect(pexpect.EOF)
+
+
+# TODO: needs ANSI code stripping tho, see `assert_before()` # above!
+def test_correct_frames_below_hidden():
+    '''
+    Ensure that once a `tractor.pause()` enages, when the user
+    inputs a "next"/"n" command the actual next line steps
+    and that using a "step"/"s" into the next LOC, particuarly
+    `tractor` APIs, you can step down into that code.
+
+    '''
+    ...
+
+
+def test_cant_pause_from_paused_task():
+    '''
+    Pausing from with an already paused task should raise an error.
+
+    Normally this should only happen in practise while debugging the call stack of `tractor.pause()` itself, likely
+    by a `.pause()` line somewhere inside our runtime.
+
+    '''
+    ...

tests/test_discovery.py

@@ -26,7 +26,7 @@ async def test_reg_then_unreg(reg_addr):
         portal = await n.start_actor('actor', enable_modules=[__name__])
         uid = portal.channel.uid
 
-        async with tractor.get_arbiter(*reg_addr) as aportal:
+        async with tractor.get_registry(*reg_addr) as aportal:
             # this local actor should be the arbiter
             assert actor is aportal.actor
 
@@ -160,7 +160,7 @@ async def spawn_and_check_registry(
     async with tractor.open_root_actor(
         registry_addrs=[reg_addr],
     ):
-        async with tractor.get_arbiter(*reg_addr) as portal:
+        async with tractor.get_registry(*reg_addr) as portal:
             # runtime needs to be up to call this
             actor = tractor.current_actor()
 
@@ -298,7 +298,7 @@ async def close_chans_before_nursery(
     async with tractor.open_root_actor(
         registry_addrs=[reg_addr],
     ):
-        async with tractor.get_arbiter(*reg_addr) as aportal:
+        async with tractor.get_registry(*reg_addr) as aportal:
             try:
                 get_reg = partial(unpack_reg, aportal)
 

tests/test_docs_examples.py

@@ -19,7 +19,7 @@ from tractor._testing import (
 @pytest.fixture
 def run_example_in_subproc(
     loglevel: str,
-    testdir,
+    testdir: pytest.Testdir,
     reg_addr: tuple[str, int],
 ):
 

tests/test_infected_asyncio.py

@@ -444,6 +444,7 @@ def test_basic_interloop_channel_stream(reg_addr, fan_out):
                 infect_asyncio=True,
                 fan_out=fan_out,
             )
+            # should raise RAE diectly
             await portal.result()
 
     trio.run(main)
@@ -461,12 +462,11 @@ def test_trio_error_cancels_intertask_chan(reg_addr):
             # should trigger remote actor error
             await portal.result()
 
-    with pytest.raises(BaseExceptionGroup) as excinfo:
+    with pytest.raises(RemoteActorError) as excinfo:
         trio.run(main)
 
-    # ensure boxed errors
-    for exc in excinfo.value.exceptions:
-        assert exc.boxed_type == Exception
+    # ensure boxed error type
+    excinfo.value.boxed_type == Exception
 
 
 def test_trio_closes_early_and_channel_exits(reg_addr):
@@ -477,7 +477,7 @@ def test_trio_closes_early_and_channel_exits(reg_addr):
                 exit_early=True,
                 infect_asyncio=True,
             )
-            # should trigger remote actor error
+            # should raise RAE diectly
             await portal.result()
 
     # should be a quiet exit on a simple channel exit
@@ -492,15 +492,17 @@ def test_aio_errors_and_channel_propagates_and_closes(reg_addr):
                 aio_raise_err=True,
                 infect_asyncio=True,
             )
-            # should trigger remote actor error
+            # should trigger RAE directly, not an eg.
             await portal.result()
 
-    with pytest.raises(BaseExceptionGroup) as excinfo:
+    with pytest.raises(
+        # NOTE: bc we directly wait on `Portal.result()` instead
+        # of capturing it inside the `ActorNursery` machinery.
+        expected_exception=RemoteActorError,
+    ) as excinfo:
         trio.run(main)
 
-    # ensure boxed errors
-    for exc in excinfo.value.exceptions:
-        assert exc.boxed_type == Exception
+    excinfo.value.boxed_type == Exception
 
 
 @tractor.context

tests/test_inter_peer_cancellation.py

@@ -55,9 +55,10 @@ from tractor._testing import (
 
 
 @tractor.context
-async def sleep_forever(
+async def open_stream_then_sleep_forever(
     ctx: Context,
     expect_ctxc: bool = False,
+
 ) -> None:
     '''
     Sync the context, open a stream then just sleep.
@@ -67,6 +68,10 @@ async def sleep_forever(
     '''
     try:
         await ctx.started()
+
+        # NOTE: the below means this child will send a `Stop`
+        # to it's parent-side task despite that side never
+        # opening a stream itself.
         async with ctx.open_stream():
             await trio.sleep_forever()
 
@@ -100,7 +105,7 @@ async def error_before_started(
     '''
     async with tractor.wait_for_actor('sleeper') as p2:
         async with (
-            p2.open_context(sleep_forever) as (peer_ctx, first),
+            p2.open_context(open_stream_then_sleep_forever) as (peer_ctx, first),
             peer_ctx.open_stream(),
         ):
             # NOTE: this WAS inside an @acm body but i factored it
@@ -185,6 +190,10 @@ async def sleep_a_bit_then_cancel_peer(
         await trio.sleep(cancel_after)
         await peer.cancel_actor()
 
+        # such that we're cancelled by our rent ctx-task
+        await trio.sleep(3)
+        print('CANCELLER RETURNING!')
+
 
 @tractor.context
 async def stream_ints(
@@ -200,9 +209,13 @@ async def stream_ints(
 @tractor.context
 async def stream_from_peer(
     ctx: Context,
+    debug_mode: bool,
     peer_name: str = 'sleeper',
 ) -> None:
 
+    # sanity
+    assert tractor._state.debug_mode() == debug_mode
+
     peer: Portal
     try:
         async with (
@@ -236,20 +249,54 @@ async def stream_from_peer(
                 assert msg is not None
                 print(msg)
 
-    # NOTE: cancellation of the (sleeper) peer should always
-    # cause a `ContextCancelled` raise in this streaming
-    # actor.
-    except ContextCancelled as ctxc:
-        ctxerr = ctxc
+    # NOTE: cancellation of the (sleeper) peer should always cause
+    # a `ContextCancelled` raise in this streaming actor.
+    except ContextCancelled as _ctxc:
+        ctxc = _ctxc
 
-        assert peer_ctx._remote_error is ctxerr
-        assert peer_ctx._remote_error.msgdata == ctxerr.msgdata
+        # print("TRYING TO ENTER PAUSSE!!!")
+        # await tractor.pause(shield=True)
+        re: ContextCancelled = peer_ctx._remote_error
+
+        # XXX YES XXX, remote error should be unpacked only once!
+        assert (
+            re
+            is
+            peer_ctx.maybe_error
+            is
+            ctxc
+            is
+            peer_ctx._local_error
+        )
+        # NOTE: these errors should all match!
+        #   ------ - ------
+        # XXX [2024-05-03] XXX
+        #   ------ - ------
+        # broke this due to a re-raise inside `.msg._ops.drain_to_final_msg()`
+        # where the `Error()` msg was directly raising the ctxc
+        # instead of just returning up to the caller inside
+        # `Context.return()` which would results in a diff instance of
+        # the same remote error bubbling out above vs what was
+        # already unpacked and set inside `Context.
+        assert (
+            peer_ctx._remote_error.msgdata
+            ==
+            ctxc.msgdata
+        )
+        # ^-XXX-^ notice the data is of course the exact same.. so
+        # the above larger assert makes sense to also always be true!
+
+        # XXX YES XXX, bc should be exact same msg instances
+        assert peer_ctx._remote_error._ipc_msg is ctxc._ipc_msg
+
+        # XXX NO XXX, bc new one always created for property accesss
+        assert peer_ctx._remote_error.ipc_msg != ctxc.ipc_msg
 
         # the peer ctx is the canceller even though it's canceller
         # is the "canceller" XD
         assert peer_name in peer_ctx.canceller
 
-        assert "canceller" in ctxerr.canceller
+        assert "canceller" in ctxc.canceller
 
         # caller peer should not be the cancel requester
         assert not ctx.cancel_called
@@ -273,12 +320,13 @@ async def stream_from_peer(
 
         # TODO / NOTE `.canceller` won't have been set yet
         # here because that machinery is inside
-        # `.open_context().__aexit__()` BUT, if we had
+        # `Portal.open_context().__aexit__()` BUT, if we had
         # a way to know immediately (from the last
         # checkpoint) that cancellation was due to
         # a remote, we COULD assert this here..see,
         # https://github.com/goodboy/tractor/issues/368
         #
+        # await tractor.pause()
         # assert 'canceller' in ctx.canceller
 
         # root/parent actor task should NEVER HAVE cancelled us!
@@ -382,12 +430,13 @@ def test_peer_canceller(
             try:
                 async with (
                     sleeper.open_context(
-                        sleep_forever,
+                        open_stream_then_sleep_forever,
                         expect_ctxc=True,
                     ) as (sleeper_ctx, sent),
 
                     just_caller.open_context(
                         stream_from_peer,
+                        debug_mode=debug_mode,
                     ) as (caller_ctx, sent),
 
                     canceller.open_context(
@@ -413,10 +462,11 @@ def test_peer_canceller(
 
                     # should always raise since this root task does
                     # not request the sleeper cancellation ;)
-                    except ContextCancelled as ctxerr:
+                    except ContextCancelled as _ctxc:
+                        ctxc = _ctxc
                         print(
                             'CAUGHT REMOTE CONTEXT CANCEL\n\n'
-                            f'{ctxerr}\n'
+                            f'{ctxc}\n'
                         )
 
                         # canceller and caller peers should not
@@ -427,7 +477,7 @@ def test_peer_canceller(
                         # we were not the actor, our peer was
                         assert not sleeper_ctx.cancel_acked
 
-                        assert ctxerr.canceller[0] == 'canceller'
+                        assert ctxc.canceller[0] == 'canceller'
 
                         # XXX NOTE XXX: since THIS `ContextCancelled`
                         # HAS NOT YET bubbled up to the
@@ -438,7 +488,7 @@ def test_peer_canceller(
 
                         # CASE_1: error-during-ctxc-handling,
                         if error_during_ctxerr_handling:
-                            raise RuntimeError('Simulated error during teardown')
+                            raise RuntimeError('Simulated RTE re-raise during ctxc handling')
 
                         # CASE_2: standard teardown inside in `.open_context()` block
                         raise
@@ -503,6 +553,9 @@ def test_peer_canceller(
                 #   should be cancelled by US.
                 #
                 if error_during_ctxerr_handling:
+                    print(f'loc_err: {_loc_err}\n')
+                    assert isinstance(loc_err, RuntimeError)
+
                     # since we do a rte reraise above, the
                     # `.open_context()` error handling should have
                     # raised a local rte, thus the internal
@@ -511,9 +564,6 @@ def test_peer_canceller(
                     # a `trio.Cancelled` due to a local
                     # `._scope.cancel()` call.
                     assert not sleeper_ctx._scope.cancelled_caught
-
-                    assert isinstance(loc_err, RuntimeError)
-                    print(f'_loc_err: {_loc_err}\n')
                     # assert sleeper_ctx._local_error is _loc_err
                     # assert sleeper_ctx._local_error is _loc_err
                     assert not (
@@ -550,9 +600,12 @@ def test_peer_canceller(
 
                         else:  # the other 2 ctxs
                             assert (
-                                re.canceller
-                                ==
-                                canceller.channel.uid
+                                isinstance(re, ContextCancelled)
+                                and (
+                                    re.canceller
+                                    ==
+                                    canceller.channel.uid
+                                )
                             )
 
                     # since the sleeper errors while handling a
@@ -801,8 +854,7 @@ async def serve_subactors(
     async with open_nursery() as an:
 
         # sanity
-        if debug_mode:
-            assert tractor._state.debug_mode()
+        assert tractor._state.debug_mode() == debug_mode
 
         await ctx.started(peer_name)
         async with ctx.open_stream() as ipc:
@@ -1081,7 +1133,6 @@ def test_peer_spawns_and_cancels_service_subactor(
                             '-> root checking `client_ctx.result()`,\n'
                             f'-> checking that sub-spawn {peer_name} is down\n'
                         )
-                    # else:
 
                     try:
                         res = await client_ctx.result(hide_tb=False)

tests/test_local.py

@@ -38,7 +38,7 @@ async def test_self_is_registered_localportal(reg_addr):
     "Verify waiting on the arbiter to register itself using a local portal."
     actor = tractor.current_actor()
     assert actor.is_arbiter
-    async with tractor.get_arbiter(*reg_addr) as portal:
+    async with tractor.get_registry(*reg_addr) as portal:
         assert isinstance(portal, tractor._portal.LocalPortal)
 
         with trio.fail_after(0.2):

tests/test_multi_program.py

@@ -32,7 +32,7 @@ def test_abort_on_sigint(daemon):
 @tractor_test
 async def test_cancel_remote_arbiter(daemon, reg_addr):
     assert not tractor.current_actor().is_arbiter
-    async with tractor.get_arbiter(*reg_addr) as portal:
+    async with tractor.get_registry(*reg_addr) as portal:
         await portal.cancel_actor()
 
     time.sleep(0.1)
@@ -41,7 +41,7 @@ async def test_cancel_remote_arbiter(daemon, reg_addr):
 
     # no arbiter socket should exist
     with pytest.raises(OSError):
-        async with tractor.get_arbiter(*reg_addr) as portal:
+        async with tractor.get_registry(*reg_addr) as portal:
             pass
 
 

tests/test_pldrx_limiting.py

@@ -0,0 +1,364 @@
+'''
+Audit sub-sys APIs from `.msg._ops`
+mostly for ensuring correct `contextvars`
+related settings around IPC contexts.
+
+'''
+from contextlib import (
+    asynccontextmanager as acm,
+)
+
+from msgspec import (
+    Struct,
+)
+import pytest
+import trio
+
+import tractor
+from tractor import (
+    Context,
+    MsgTypeError,
+    current_ipc_ctx,
+    Portal,
+)
+from tractor.msg import (
+    _ops as msgops,
+    Return,
+)
+from tractor.msg import (
+    _codec,
+)
+from tractor.msg.types import (
+    log,
+)
+
+
+class PldMsg(
+    Struct,
+
+    # TODO: with multiple structs in-spec we need to tag them!
+    # -[ ] offer a built-in `PldMsg` type to inherit from which takes
+    #      case of these details?
+    #
+    # https://jcristharif.com/msgspec/structs.html#tagged-unions
+    # tag=True,
+    # tag_field='msg_type',
+):
+    field: str
+
+
+maybe_msg_spec = PldMsg|None
+
+
+@acm
+async def maybe_expect_raises(
+    raises: BaseException|None = None,
+    ensure_in_message: list[str]|None = None,
+    post_mortem: bool = False,
+    timeout: int = 3,
+) -> None:
+    '''
+    Async wrapper for ensuring errors propagate from the inner scope.
+
+    '''
+    if tractor._state.debug_mode():
+        timeout += 999
+
+    with trio.fail_after(timeout):
+        try:
+            yield
+        except BaseException as _inner_err:
+            inner_err = _inner_err
+            # wasn't-expected to error..
+            if raises is None:
+                raise
+
+            else:
+                assert type(inner_err) is raises
+
+                # maybe check for error txt content
+                if ensure_in_message:
+                    part: str
+                    err_repr: str = repr(inner_err)
+                    for part in ensure_in_message:
+                        for i, arg in enumerate(inner_err.args):
+                            if part in err_repr:
+                                break
+                        # if part never matches an arg, then we're
+                        # missing a match.
+                        else:
+                            raise ValueError(
+                                'Failed to find error message content?\n\n'
+                                f'expected: {ensure_in_message!r}\n'
+                                f'part: {part!r}\n\n'
+                                f'{inner_err.args}'
+                        )
+
+                if post_mortem:
+                    await tractor.post_mortem()
+
+        else:
+            if raises:
+                raise RuntimeError(
+                    f'Expected a {raises.__name__!r} to be raised?'
+                )
+
+
+@tractor.context(
+    pld_spec=maybe_msg_spec,
+)
+async def child(
+    ctx: Context,
+    started_value: int|PldMsg|None,
+    return_value: str|None,
+    validate_pld_spec: bool,
+    raise_on_started_mte: bool = True,
+
+) -> None:
+    '''
+    Call ``Context.started()`` more then once (an error).
+
+    '''
+    expect_started_mte: bool = started_value == 10
+
+    # sanaity check that child RPC context is the current one
+    curr_ctx: Context = current_ipc_ctx()
+    assert ctx is curr_ctx
+
+    rx: msgops.PldRx = ctx._pld_rx
+    curr_pldec: _codec.MsgDec = rx.pld_dec
+
+    ctx_meta: dict = getattr(
+        child,
+        '_tractor_context_meta',
+        None,
+    )
+    if ctx_meta:
+        assert (
+            ctx_meta['pld_spec']
+            is curr_pldec.spec
+            is curr_pldec.pld_spec
+        )
+
+    # 2 cases: hdndle send-side and recv-only validation
+    # - when `raise_on_started_mte == True`, send validate
+    # - else, parent-recv-side only validation
+    mte: MsgTypeError|None = None
+    try:
+        await ctx.started(
+            value=started_value,
+            validate_pld_spec=validate_pld_spec,
+        )
+
+    except MsgTypeError as _mte:
+        mte = _mte
+        log.exception('started()` raised an MTE!\n')
+        if not expect_started_mte:
+            raise RuntimeError(
+                'Child-ctx-task SHOULD NOT HAVE raised an MTE for\n\n'
+                f'{started_value!r}\n'
+            )
+
+        boxed_div: str = '------ - ------'
+        assert boxed_div not in mte._message
+        assert boxed_div not in mte.tb_str
+        assert boxed_div not in repr(mte)
+        assert boxed_div not in str(mte)
+        mte_repr: str = repr(mte)
+        for line in mte.message.splitlines():
+            assert line in mte_repr
+
+        # since this is a *local error* there should be no
+        # boxed traceback content!
+        assert not mte.tb_str
+
+        # propagate to parent?
+        if raise_on_started_mte:
+            raise
+
+    # no-send-side-error fallthrough
+    if (
+        validate_pld_spec
+        and
+        expect_started_mte
+    ):
+        raise RuntimeError(
+            'Child-ctx-task SHOULD HAVE raised an MTE for\n\n'
+            f'{started_value!r}\n'
+        )
+
+    assert (
+        not expect_started_mte
+        or
+        not validate_pld_spec
+    )
+
+    # if wait_for_parent_to_cancel:
+    #     ...
+    #
+    # ^-TODO-^ logic for diff validation policies on each side:
+    #
+    # -[ ] ensure that if we don't validate on the send
+    #   side, that we are eventually error-cancelled by our
+    #   parent due to the bad `Started` payload!
+    # -[ ] the boxed error should be srced from the parent's
+    #   runtime NOT ours!
+    # -[ ] we should still error on bad `return_value`s
+    #   despite the parent not yet error-cancelling us?
+    #   |_ how do we want the parent side to look in that
+    #     case?
+    #     -[ ] maybe the equiv of "during handling of the
+    #       above error another occurred" for the case where
+    #       the parent sends a MTE to this child and while
+    #       waiting for the child to terminate it gets back
+    #       the MTE for this case?
+    #
+
+    # XXX should always fail on recv side since we can't
+    # really do much else beside terminate and relay the
+    # msg-type-error from this RPC task ;)
+    return return_value
+
+
+@pytest.mark.parametrize(
+    'return_value',
+    [
+        'yo',
+        None,
+    ],
+    ids=[
+        'return[invalid-"yo"]',
+        'return[valid-None]',
+    ],
+)
+@pytest.mark.parametrize(
+    'started_value',
+    [
+        10,
+        PldMsg(field='yo'),
+    ],
+    ids=[
+        'Started[invalid-10]',
+        'Started[valid-PldMsg]',
+    ],
+)
+@pytest.mark.parametrize(
+    'pld_check_started_value',
+    [
+        True,
+        False,
+    ],
+    ids=[
+        'check-started-pld',
+        'no-started-pld-validate',
+    ],
+)
+def test_basic_payload_spec(
+    debug_mode: bool,
+    loglevel: str,
+    return_value: str|None,
+    started_value: int|PldMsg,
+    pld_check_started_value: bool,
+):
+    '''
+    Validate the most basic `PldRx` msg-type-spec semantics around
+    a IPC `Context` endpoint start, started-sync, and final return
+    value depending on set payload types and the currently applied
+    pld-spec.
+
+    '''
+    invalid_return: bool = return_value == 'yo'
+    invalid_started: bool = started_value == 10
+
+    async def main():
+        async with tractor.open_nursery(
+            debug_mode=debug_mode,
+            loglevel=loglevel,
+        ) as an:
+            p: Portal = await an.start_actor(
+                'child',
+                enable_modules=[__name__],
+            )
+
+            # since not opened yet.
+            assert current_ipc_ctx() is None
+
+            if invalid_started:
+                msg_type_str: str = 'Started'
+                bad_value: int = 10
+            elif invalid_return:
+                msg_type_str: str = 'Return'
+                bad_value: str = 'yo'
+            else:
+                # XXX but should never be used below then..
+                msg_type_str: str = ''
+                bad_value: str = ''
+
+            maybe_mte: MsgTypeError|None = None
+            should_raise: Exception|None = (
+                MsgTypeError if (
+                    invalid_return
+                    or
+                    invalid_started
+                ) else None
+            )
+            async with (
+                maybe_expect_raises(
+                    raises=should_raise,
+                    ensure_in_message=[
+                        f"invalid `{msg_type_str}` msg payload",
+                        f'{bad_value}',
+                        f'has type {type(bad_value)!r}',
+                        'not match type-spec',
+                        f'`{msg_type_str}.pld: PldMsg|NoneType`',
+                    ],
+                    # only for debug
+                    # post_mortem=True,
+                ),
+                p.open_context(
+                    child,
+                    return_value=return_value,
+                    started_value=started_value,
+                    validate_pld_spec=pld_check_started_value,
+                ) as (ctx, first),
+            ):
+                # now opened with 'child' sub
+                assert current_ipc_ctx() is ctx
+
+                assert type(first) is PldMsg
+                assert first.field == 'yo'
+
+                try:
+                    res: None|PldMsg = await ctx.result(hide_tb=False)
+                    assert res is None
+                except MsgTypeError as mte:
+                    maybe_mte = mte
+                    if not invalid_return:
+                        raise
+
+                    # expected this invalid `Return.pld` so audit
+                    # the error state + meta-data
+                    assert mte.expected_msg_type is Return
+                    assert mte.cid == ctx.cid
+                    mte_repr: str = repr(mte)
+                    for line in mte.message.splitlines():
+                        assert line in mte_repr
+
+                    assert mte.tb_str
+                    # await tractor.pause(shield=True)
+
+                    # verify expected remote mte deats
+                    assert ctx._local_error is None
+                    assert (
+                        mte is
+                        ctx._remote_error is
+                        ctx.maybe_error is
+                        ctx.outcome
+                    )
+
+            if should_raise is None:
+                assert maybe_mte is None
+
+            await p.cancel_actor()
+
+    trio.run(main)

tests/test_spawning.py

@@ -2,7 +2,9 @@
 Spawning basics
 
 """
-from typing import Optional
+from typing import (
+    Any,
+)
 
 import pytest
 import trio
@@ -25,13 +27,11 @@ async def spawn(
     async with tractor.open_root_actor(
         arbiter_addr=reg_addr,
     ):
-
         actor = tractor.current_actor()
         assert actor.is_arbiter == is_arbiter
         data = data_to_pass_down
 
         if actor.is_arbiter:
-
             async with tractor.open_nursery() as nursery:
 
                 # forks here
@@ -95,7 +95,9 @@ async def test_movie_theatre_convo(start_method):
         await portal.cancel_actor()
 
 
-async def cellar_door(return_value: Optional[str]):
+async def cellar_door(
+    return_value: str|None,
+):
     return return_value
 
 
@@ -105,16 +107,18 @@ async def cellar_door(return_value: Optional[str]):
 )
 @tractor_test
 async def test_most_beautiful_word(
-    start_method,
-    return_value
+    start_method: str,
+    return_value: Any,
+    debug_mode: bool,
 ):
     '''
     The main ``tractor`` routine.
 
     '''
     with trio.fail_after(1):
-        async with tractor.open_nursery() as n:
-
+        async with tractor.open_nursery(
+            debug_mode=debug_mode,
+        ) as n:
             portal = await n.run_in_actor(
                 cellar_door,
                 return_value=return_value,

tractor/__init__.py

@@ -31,7 +31,7 @@ from ._streaming import (
     stream as stream,
 )
 from ._discovery import (
-    get_arbiter as get_arbiter,
+    get_registry as get_registry,
     find_actor as find_actor,
     wait_for_actor as wait_for_actor,
     query_actor as query_actor,
@@ -43,11 +43,14 @@ from ._supervise import (
 from ._state import (
     current_actor as current_actor,
     is_root_process as is_root_process,
+    current_ipc_ctx as current_ipc_ctx,
 )
 from ._exceptions import (
-    RemoteActorError as RemoteActorError,
-    ModuleNotExposed as ModuleNotExposed,
     ContextCancelled as ContextCancelled,
+    ModuleNotExposed as ModuleNotExposed,
+    MsgTypeError as MsgTypeError,
+    RemoteActorError as RemoteActorError,
+    TransportClosed as TransportClosed,
 )
 from .devx import (
     breakpoint as breakpoint,

tractor/_discovery.py

@@ -26,8 +26,8 @@ from typing import (
     TYPE_CHECKING,
 )
 from contextlib import asynccontextmanager as acm
-import warnings
 
+from tractor.log import get_logger
 from .trionics import gather_contexts
 from ._ipc import _connect_chan, Channel
 from ._portal import (
@@ -40,11 +40,13 @@ from ._state import (
     _runtime_vars,
 )
 
-
 if TYPE_CHECKING:
     from ._runtime import Actor
 
 
+log = get_logger(__name__)
+
+
 @acm
 async def get_registry(
     host: str,
@@ -56,14 +58,12 @@ async def get_registry(
 ]:
     '''
     Return a portal instance connected to a local or remote
-    arbiter.
+    registry-service actor; if a connection already exists re-use it
+    (presumably to call a `.register_actor()` registry runtime RPC
+    ep).
 
     '''
-    actor = current_actor()
-
-    if not actor:
-        raise RuntimeError("No actor instance has been defined yet?")
-
+    actor: Actor = current_actor()
     if actor.is_registrar:
         # we're already the arbiter
         # (likely a re-entrant call from the arbiter actor)
@@ -72,6 +72,8 @@ async def get_registry(
             Channel((host, port))
         )
     else:
+        # TODO: try to look pre-existing connection from
+        # `Actor._peers` and use it instead?
         async with (
             _connect_chan(host, port) as chan,
             open_portal(chan) as regstr_ptl,
@@ -80,19 +82,6 @@ async def get_registry(
 
 
 
-# TODO: deprecate and this remove _arbiter form!
-@acm
-async def get_arbiter(*args, **kwargs):
-    warnings.warn(
-        '`tractor.get_arbiter()` is now deprecated!\n'
-        'Use `.get_registry()` instead!',
-        DeprecationWarning,
-        stacklevel=2,
-    )
-    async with get_registry(*args, **kwargs) as to_yield:
-        yield to_yield
-
-
 @acm
 async def get_root(
     **kwargs,
@@ -110,22 +99,53 @@ async def get_root(
         yield portal
 
 
+def get_peer_by_name(
+    name: str,
+    # uuid: str|None = None,
+
+) -> list[Channel]|None:  # at least 1
+    '''
+    Scan for an existing connection (set) to a named actor
+    and return any channels from `Actor._peers`.
+
+    This is an optimization method over querying the registrar for
+    the same info.
+
+    '''
+    actor: Actor = current_actor()
+    to_scan: dict[tuple, list[Channel]] = actor._peers.copy()
+    pchan: Channel|None = actor._parent_chan
+    if pchan:
+        to_scan[pchan.uid].append(pchan)
+
+    for aid, chans in to_scan.items():
+        _, peer_name = aid
+        if name == peer_name:
+            if not chans:
+                log.warning(
+                    'No IPC chans for matching peer {peer_name}\n'
+                )
+                continue
+            return chans
+
+    return None
+
+
 @acm
 async def query_actor(
     name: str,
-    arbiter_sockaddr: tuple[str, int] | None = None,
-    regaddr: tuple[str, int] | None = None,
+    regaddr: tuple[str, int]|None = None,
 
 ) -> AsyncGenerator[
-    tuple[str, int] | None,
+    tuple[str, int]|None,
     None,
 ]:
     '''
-    Make a transport address lookup for an actor name to a specific
-    registrar.
+    Lookup a transport address (by actor name) via querying a registrar
+    listening @ `regaddr`.
 
-    Returns the (socket) address or ``None`` if no entry under that
-    name exists for the given registrar listening @ `regaddr`.
+    Returns the transport protocol (socket) address or `None` if no
+    entry under that name exists.
 
     '''
     actor: Actor = current_actor()
@@ -137,14 +157,10 @@ async def query_actor(
             'The current actor IS the registry!?'
         )
 
-    if arbiter_sockaddr is not None:
-        warnings.warn(
-            '`tractor.query_actor(regaddr=<blah>)` is deprecated.\n'
-            'Use `registry_addrs: list[tuple]` instead!',
-            DeprecationWarning,
-            stacklevel=2,
-        )
-        regaddr: list[tuple[str, int]] = arbiter_sockaddr
+    maybe_peers: list[Channel]|None = get_peer_by_name(name)
+    if maybe_peers:
+        yield maybe_peers[0].raddr
+        return
 
     reg_portal: Portal
     regaddr: tuple[str, int] = regaddr or actor.reg_addrs[0]
@@ -159,10 +175,28 @@ async def query_actor(
         yield sockaddr
 
 
+@acm
+async def maybe_open_portal(
+    addr: tuple[str, int],
+    name: str,
+):
+    async with query_actor(
+        name=name,
+        regaddr=addr,
+    ) as sockaddr:
+        pass
+
+    if sockaddr:
+        async with _connect_chan(*sockaddr) as chan:
+            async with open_portal(chan) as portal:
+                yield portal
+    else:
+        yield None
+
+
 @acm
 async def find_actor(
     name: str,
-    arbiter_sockaddr: tuple[str, int]|None = None,
     registry_addrs: list[tuple[str, int]]|None = None,
 
     only_first: bool = True,
@@ -179,29 +213,12 @@ async def find_actor(
     known to the arbiter.
 
     '''
-    if arbiter_sockaddr is not None:
-        warnings.warn(
-            '`tractor.find_actor(arbiter_sockaddr=<blah>)` is deprecated.\n'
-            'Use `registry_addrs: list[tuple]` instead!',
-            DeprecationWarning,
-            stacklevel=2,
-        )
-        registry_addrs: list[tuple[str, int]] = [arbiter_sockaddr]
-
-    @acm
-    async def maybe_open_portal_from_reg_addr(
-        addr: tuple[str, int],
-    ):
-        async with query_actor(
-            name=name,
-            regaddr=addr,
-        ) as sockaddr:
-            if sockaddr:
-                async with _connect_chan(*sockaddr) as chan:
-                    async with open_portal(chan) as portal:
-                        yield portal
-            else:
-                yield None
+    # optimization path, use any pre-existing peer channel
+    maybe_peers: list[Channel]|None = get_peer_by_name(name)
+    if maybe_peers and only_first:
+        async with open_portal(maybe_peers[0]) as peer_portal:
+            yield peer_portal
+            return
 
     if not registry_addrs:
         # XXX NOTE: make sure to dynamically read the value on
@@ -217,10 +234,13 @@ async def find_actor(
     maybe_portals: list[
         AsyncContextManager[tuple[str, int]]
     ] = list(
-        maybe_open_portal_from_reg_addr(addr)
+        maybe_open_portal(
+            addr=addr,
+            name=name,
+        )
         for addr in registry_addrs
     )
-
+    portals: list[Portal]
     async with gather_contexts(
         mngrs=maybe_portals,
     ) as portals:
@@ -254,31 +274,31 @@ async def find_actor(
 @acm
 async def wait_for_actor(
     name: str,
-    arbiter_sockaddr: tuple[str, int] | None = None,
     registry_addr: tuple[str, int] | None = None,
 
 ) -> AsyncGenerator[Portal, None]:
     '''
-    Wait on an actor to register with the arbiter.
-
-    A portal to the first registered actor is returned.
+    Wait on at least one peer actor to register `name` with the
+    registrar, yield a `Portal to the first registree.
 
     '''
     actor: Actor = current_actor()
 
-    if arbiter_sockaddr is not None:
-        warnings.warn(
-            '`tractor.wait_for_actor(arbiter_sockaddr=<foo>)` is deprecated.\n'
-            'Use `registry_addr: tuple` instead!',
-            DeprecationWarning,
-            stacklevel=2,
-        )
-        registry_addr: tuple[str, int] = arbiter_sockaddr
+    # optimization path, use any pre-existing peer channel
+    maybe_peers: list[Channel]|None = get_peer_by_name(name)
+    if maybe_peers:
+        async with open_portal(maybe_peers[0]) as peer_portal:
+            yield peer_portal
+            return
 
+    regaddr: tuple[str, int] = (
+        registry_addr
+        or
+        actor.reg_addrs[0]
+    )
     # TODO: use `.trionics.gather_contexts()` like
     # above in `find_actor()` as well?
     reg_portal: Portal
-    regaddr: tuple[str, int] = registry_addr or actor.reg_addrs[0]
     async with get_registry(*regaddr) as reg_portal:
         sockaddrs = await reg_portal.run_from_ns(
             'self',

tractor/_entry.py

@@ -20,6 +20,8 @@ Sub-process entry points.
 """
 from __future__ import annotations
 from functools import partial
+import os
+import textwrap
 from typing import (
     Any,
     TYPE_CHECKING,
@@ -32,6 +34,7 @@ from .log import (
     get_logger,
 )
 from . import _state
+from .devx import _debug
 from .to_asyncio import run_as_asyncio_guest
 from ._runtime import (
     async_main,
@@ -56,7 +59,7 @@ def _mp_main(
 
 ) -> None:
     '''
-    The routine called *after fork* which invokes a fresh ``trio.run``
+    The routine called *after fork* which invokes a fresh `trio.run()`
 
     '''
     actor._forkserver_info = forkserver_info
@@ -91,11 +94,111 @@ def _mp_main(
         pass  # handle it the same way trio does?
 
     finally:
-        log.info(f"Actor {actor.uid} terminated")
+        log.info(f"Subactor {actor.uid} terminated")
+
+
+# TODO: move this func to some kinda `.devx._conc_lang.py` eventually
+# as we work out our multi-domain state-flow-syntax!
+def nest_from_op(
+    input_op: str,
+    #
+    # ?TODO? an idea for a syntax to the state of concurrent systems
+    # as a "3-domain" (execution, scope, storage) model and using
+    # a minimal ascii/utf-8 operator-set.
+    #
+    # try not to take any of this seriously yet XD
+    #
+    # > is a "play operator" indicating (CPU bound)
+    #   exec/work/ops required at the "lowest level computing"
+    #
+    # execution primititves (tasks, threads, actors..) denote their
+    # lifetime with '(' and ')' since parentheses normally are used
+    # in many langs to denote function calls.
+    #
+    # starting = (
+    # >(  opening/starting; beginning of the thread-of-exec (toe?)
+    # (>  opened/started,  (finished spawning toe)
+    # |_<Task: blah blah..>  repr of toe, in py these look like <objs>
+    #
+    # >) closing/exiting/stopping,
+    # )> closed/exited/stopped,
+    # |_<Task: blah blah..>
+    #   [OR <), )< ?? ]
+    #
+    # ending = )
+    # >c) cancelling to close/exit
+    # c)> cancelled (caused close), OR?
+    #  |_<Actor: ..>
+    #   OR maybe "<c)" which better indicates the cancel being
+    #   "delivered/returned" / returned" to LHS?
+    #
+    # >x)  erroring to eventuall exit
+    # x)>  errored and terminated
+    #  |_<Actor: ...>
+    #
+    # scopes: supers/nurseries, IPC-ctxs, sessions, perms, etc.
+    # >{  opening
+    # {>  opened
+    # }>  closed
+    # >}  closing
+    #
+    # storage: like queues, shm-buffers, files, etc..
+    # >[  opening
+    # [>  opened
+    #  |_<FileObj: ..>
+    #
+    # >]  closing
+    # ]>  closed
+
+    # IPC ops: channels, transports, msging
+    # =>  req msg
+    # <=  resp msg
+    # <=> 2-way streaming (of msgs)
+    # <-  recv 1 msg
+    # ->  send 1 msg
+    #
+    # TODO: still not sure on R/L-HS approach..?
+    # =>(  send-req to exec start (task, actor, thread..)
+    # (<=  recv-req to ^
+    #
+    # (<=  recv-req ^
+    # <=(  recv-resp opened remote exec primitive
+    # <=)  recv-resp closed
+    #
+    # )<=c req to stop due to cancel
+    # c=>) req to stop due to cancel
+    #
+    # =>{  recv-req to open
+    # <={  send-status that it closed
+
+    tree_str: str,
+
+    # NOTE: so move back-from-the-left of the `input_op` by
+    # this amount.
+    back_from_op: int = 0,
+) -> str:
+    '''
+    Depth-increment the input (presumably hierarchy/supervision)
+    input "tree string" below the provided `input_op` execution
+    operator, so injecting a `"\n|_{input_op}\n"`and indenting the
+    `tree_str` to nest content aligned with the ops last char.
+
+    '''
+    return (
+        f'{input_op}\n'
+        +
+        textwrap.indent(
+            tree_str,
+            prefix=(
+                len(input_op)
+                -
+                (back_from_op + 1)
+            ) * ' ',
+        )
+    )
 
 
 def _trio_main(
-
     actor: Actor,
     *,
     parent_addr: tuple[str, int] | None = None,
@@ -106,7 +209,8 @@ def _trio_main(
     Entry point for a `trio_run_in_process` subactor.
 
     '''
-    __tracebackhide__: bool = True
+    _debug.hide_runtime_frames()
+
     _state._current_actor = actor
     trio_main = partial(
         async_main,
@@ -116,7 +220,6 @@ def _trio_main(
 
     if actor.loglevel is not None:
         get_console_log(actor.loglevel)
-        import os
         actor_info: str = (
             f'|_{actor}\n'
             f'  uid: {actor.uid}\n'
@@ -125,27 +228,54 @@ def _trio_main(
             f'  loglevel: {actor.loglevel}\n'
         )
         log.info(
-            'Started new trio process:\n'
+            'Starting new `trio` subactor:\n'
             +
-            actor_info
+            nest_from_op(
+                input_op='>(',  # see syntax ideas above
+                tree_str=actor_info,
+                back_from_op=1,
+            )
         )
-
+    logmeth = log.info
+    exit_status: str = (
+        'Subactor exited\n'
+        +
+        nest_from_op(
+            input_op=')>',  # like a "closed-to-play"-icon from super perspective
+            tree_str=actor_info,
+            back_from_op=1,
+        )
+    )
     try:
         if infect_asyncio:
             actor._infected_aio = True
             run_as_asyncio_guest(trio_main)
         else:
             trio.run(trio_main)
+
     except KeyboardInterrupt:
-        log.cancel(
-            'Actor received KBI\n'
+        logmeth = log.cancel
+        exit_status: str = (
+            'Actor received KBI (aka an OS-cancel)\n'
             +
-            actor_info
+            nest_from_op(
+                input_op='c)>',  # closed due to cancel (see above)
+                tree_str=actor_info,
+            )
         )
+    except BaseException as err:
+        logmeth = log.error
+        exit_status: str = (
+            'Main actor task exited due to crash?\n'
+            +
+            nest_from_op(
+                input_op='x)>',  # closed by error
+                tree_str=actor_info,
+            )
+        )
+        # NOTE since we raise a tb will already be shown on the
+        # console, thus we do NOT use `.exception()` above.
+        raise err
 
     finally:
-        log.info(
-            'Actor terminated\n'
-            +
-            actor_info
-        )
+        logmeth(exit_status)

tractor/_ipc.py

@@ -23,13 +23,17 @@ from collections.abc import (
     AsyncGenerator,
     AsyncIterator,
 )
-from contextlib import asynccontextmanager as acm
+from contextlib import (
+    asynccontextmanager as acm,
+    contextmanager as cm,
+)
 import platform
 from pprint import pformat
 import struct
 import typing
 from typing import (
     Any,
+    Callable,
     runtime_checkable,
     Protocol,
     Type,
@@ -41,15 +45,38 @@ from tricycle import BufferedReceiveStream
 import trio
 
 from tractor.log import get_logger
-from tractor._exceptions import TransportClosed
+from tractor._exceptions import (
+    MsgTypeError,
+    pack_from_raise,
+    TransportClosed,
+    _mk_send_mte,
+    _mk_recv_mte,
+)
+from tractor.msg import (
+    _ctxvar_MsgCodec,
+    # _codec,  XXX see `self._codec` sanity/debug checks
+    MsgCodec,
+    types as msgtypes,
+    pretty_struct,
+)
 
 log = get_logger(__name__)
 
 _is_windows = platform.system() == 'Windows'
 
 
-def get_stream_addrs(stream: trio.SocketStream) -> tuple:
-    # should both be IP sockets
+def get_stream_addrs(
+    stream: trio.SocketStream
+) -> tuple[
+    tuple[str, int],  # local
+    tuple[str, int],  # remote
+]:
+    '''
+    Return the `trio` streaming transport prot's socket-addrs for
+    both the local and remote sides as a pair.
+
+    '''
+    # rn, should both be IP sockets
     lsockname = stream.socket.getsockname()
     rsockname = stream.socket.getpeername()
     return (
@@ -58,16 +85,22 @@ def get_stream_addrs(stream: trio.SocketStream) -> tuple:
     )
 
 
-MsgType = TypeVar("MsgType")
-
-# TODO: consider using a generic def and indexing with our eventual
-# msg definition/types?
-# - https://docs.python.org/3/library/typing.html#typing.Protocol
-# - https://jcristharif.com/msgspec/usage.html#structs
+# from tractor.msg.types import MsgType
+# ?TODO? this should be our `Union[*msgtypes.__spec__]` alias now right..?
+# => BLEH, except can't bc prots must inherit typevar or param-spec
+#   vars..
+MsgType = TypeVar('MsgType')
 
 
+# TODO: break up this mod into a subpkg so we can start adding new
+# backends and move this type stuff into a dedicated file.. Bo
+#
 @runtime_checkable
 class MsgTransport(Protocol[MsgType]):
+#
+# ^-TODO-^ consider using a generic def and indexing with our
+# eventual msg definition/types?
+# - https://docs.python.org/3/library/typing.html#typing.Protocol
 
     stream: trio.SocketStream
     drained: list[MsgType]
@@ -102,9 +135,9 @@ class MsgTransport(Protocol[MsgType]):
         ...
 
 
-# TODO: not sure why we have to inherit here, but it seems to be an
-# issue with ``get_msg_transport()`` returning a ``Type[Protocol]``;
-# probably should make a `mypy` issue?
+# TODO: typing oddity.. not sure why we have to inherit here, but it
+# seems to be an issue with `get_msg_transport()` returning
+# a `Type[Protocol]`; probably should make a `mypy` issue?
 class MsgpackTCPStream(MsgTransport):
     '''
     A ``trio.SocketStream`` delivering ``msgpack`` formatted data
@@ -123,6 +156,16 @@ class MsgpackTCPStream(MsgTransport):
         stream: trio.SocketStream,
         prefix_size: int = 4,
 
+        # XXX optionally provided codec pair for `msgspec`:
+        # https://jcristharif.com/msgspec/extending.html#mapping-to-from-native-types
+        #
+        # TODO: define this as a `Codec` struct which can be
+        # overriden dynamically by the application/runtime?
+        codec: tuple[
+            Callable[[Any], Any]|None,  # coder
+            Callable[[type, Any], Any]|None,  # decoder
+        ]|None = None,
+
     ) -> None:
 
         self.stream = stream
@@ -132,30 +175,44 @@ class MsgpackTCPStream(MsgTransport):
         self._laddr, self._raddr = get_stream_addrs(stream)
 
         # create read loop instance
-        self._agen = self._iter_packets()
+        self._aiter_pkts = self._iter_packets()
         self._send_lock = trio.StrictFIFOLock()
 
         # public i guess?
         self.drained: list[dict] = []
 
-        self.recv_stream = BufferedReceiveStream(transport_stream=stream)
+        self.recv_stream = BufferedReceiveStream(
+            transport_stream=stream
+        )
         self.prefix_size = prefix_size
 
-        # TODO: struct aware messaging coders
-        self.encode = msgspec.msgpack.Encoder().encode
-        self.decode = msgspec.msgpack.Decoder().decode  # dict[str, Any])
+        # allow for custom IPC msg interchange format
+        # dynamic override Bo
+        self._task = trio.lowlevel.current_task()
+
+        # XXX for ctxvar debug only!
+        # self._codec: MsgCodec = (
+        #     codec
+        #     or
+        #     _codec._ctxvar_MsgCodec.get()
+        # )
 
     async def _iter_packets(self) -> AsyncGenerator[dict, None]:
-        '''Yield packets from the underlying stream.
+        '''
+        Yield `bytes`-blob decoded packets from the underlying TCP
+        stream using the current task's `MsgCodec`.
+
+        This is a streaming routine implemented as an async generator
+        func (which was the original design, but could be changed?)
+        and is allocated by a `.__call__()` inside `.__init__()` where
+        it is assigned to the `._aiter_pkts` attr.
 
         '''
-        import msgspec  # noqa
         decodes_failed: int = 0
 
         while True:
             try:
-                header = await self.recv_stream.receive_exactly(4)
-
+                header: bytes = await self.recv_stream.receive_exactly(4)
             except (
                 ValueError,
                 ConnectionResetError,
@@ -164,25 +221,122 @@ class MsgpackTCPStream(MsgTransport):
                 # seem to be getting racy failures here on
                 # arbiter/registry name subs..
                 trio.BrokenResourceError,
-            ):
-                raise TransportClosed(
-                    f'transport {self} was already closed prior ro read'
-                )
 
+            ) as trans_err:
+
+                loglevel = 'transport'
+                match trans_err:
+                    # case (
+                    #     ConnectionResetError()
+                    # ):
+                    #     loglevel = 'transport'
+
+                    # peer actor (graceful??) TCP EOF but `tricycle`
+                    # seems to raise a 0-bytes-read?
+                    case ValueError() if (
+                        'unclean EOF' in trans_err.args[0]
+                    ):
+                        pass
+
+                    # peer actor (task) prolly shutdown quickly due
+                    # to cancellation
+                    case trio.BrokenResourceError() if (
+                        'Connection reset by peer' in trans_err.args[0]
+                    ):
+                        pass
+
+                    # unless the disconnect condition falls under "a
+                    # normal operation breakage" we usualy console warn
+                    # about it.
+                    case _:
+                        loglevel: str = 'warning'
+
+
+                raise TransportClosed(
+                    message=(
+                        f'IPC transport already closed by peer\n'
+                        f'x)> {type(trans_err)}\n'
+                        f' |_{self}\n'
+                    ),
+                    loglevel=loglevel,
+                ) from trans_err
+
+            # XXX definitely can happen if transport is closed
+            # manually by another `trio.lowlevel.Task` in the
+            # same actor; we use this in some simulated fault
+            # testing for ex, but generally should never happen
+            # under normal operation!
+            #
+            # NOTE: as such we always re-raise this error from the
+            #       RPC msg loop!
+            except trio.ClosedResourceError as closure_err:
+                raise TransportClosed(
+                    message=(
+                        f'IPC transport already manually closed locally?\n'
+                        f'x)> {type(closure_err)} \n'
+                        f' |_{self}\n'
+                    ),
+                    loglevel='error',
+                    raise_on_report=(
+                        closure_err.args[0] == 'another task closed this fd'
+                        or
+                        closure_err.args[0] in ['another task closed this fd']
+                    ),
+                ) from closure_err
+
+            # graceful TCP EOF disconnect
             if header == b'':
                 raise TransportClosed(
-                    f'transport {self} was already closed prior ro read'
+                    message=(
+                        f'IPC transport already gracefully closed\n'
+                        f')>\n'
+                        f'|_{self}\n'
+                    ),
+                    loglevel='transport',
+                    # cause=???  # handy or no?
                 )
 
+            size: int
             size, = struct.unpack("<I", header)
 
             log.transport(f'received header {size}')  # type: ignore
-
-            msg_bytes = await self.recv_stream.receive_exactly(size)
+            msg_bytes: bytes = await self.recv_stream.receive_exactly(size)
 
             log.transport(f"received {msg_bytes}")  # type: ignore
             try:
-                yield self.decode(msg_bytes)
+                # NOTE: lookup the `trio.Task.context`'s var for
+                # the current `MsgCodec`.
+                codec: MsgCodec = _ctxvar_MsgCodec.get()
+
+                # XXX for ctxvar debug only!
+                # if self._codec.pld_spec != codec.pld_spec:
+                #     assert (
+                #         task := trio.lowlevel.current_task()
+                #     ) is not self._task
+                #     self._task = task
+                #     self._codec = codec
+                #     log.runtime(
+                #         f'Using new codec in {self}.recv()\n'
+                #         f'codec: {self._codec}\n\n'
+                #         f'msg_bytes: {msg_bytes}\n'
+                #     )
+                yield codec.decode(msg_bytes)
+
+            # XXX NOTE: since the below error derives from
+            # `DecodeError` we need to catch is specially
+            # and always raise such that spec violations
+            # are never allowed to be caught silently!
+            except msgspec.ValidationError as verr:
+                msgtyperr: MsgTypeError = _mk_recv_mte(
+                    msg=msg_bytes,
+                    codec=codec,
+                    src_validation_error=verr,
+                )
+                # XXX deliver up to `Channel.recv()` where
+                # a re-raise and `Error`-pack can inject the far
+                # end actor `.uid`.
+                yield msgtyperr
+
             except (
                 msgspec.DecodeError,
                 UnicodeDecodeError,
@@ -192,14 +346,15 @@ class MsgpackTCPStream(MsgTransport):
                     # do with a channel drop - hope that receiving from the
                     # channel will raise an expected error and bubble up.
                     try:
-                        msg_str: str | bytes = msg_bytes.decode()
+                        msg_str: str|bytes = msg_bytes.decode()
                     except UnicodeDecodeError:
                         msg_str = msg_bytes
 
-                    log.error(
-                        '`msgspec` failed to decode!?\n'
-                        'dumping bytes:\n'
-                        f'{msg_str!r}'
+                    log.exception(
+                        'Failed to decode msg?\n'
+                        f'{codec}\n\n'
+                        'Rxed bytes from wire:\n\n'
+                        f'{msg_str!r}\n'
                     )
                     decodes_failed += 1
                 else:
@@ -207,25 +362,80 @@ class MsgpackTCPStream(MsgTransport):
 
     async def send(
         self,
-        msg: Any,
+        msg: msgtypes.MsgType,
+
+        strict_types: bool = True,
+        hide_tb: bool = False,
 
-        # hide_tb: bool = False,
     ) -> None:
         '''
-        Send a msgpack coded blob-as-msg over TCP.
+        Send a msgpack encoded py-object-blob-as-msg over TCP.
+
+        If `strict_types == True` then a `MsgTypeError` will be raised on any
+        invalid msg type
 
         '''
-        # __tracebackhide__: bool = hide_tb
+        __tracebackhide__: bool = hide_tb
+
+        # XXX see `trio._sync.AsyncContextManagerMixin` for details
+        # on the `.acquire()`/`.release()` sequencing..
         async with self._send_lock:
 
-            bytes_data: bytes = self.encode(msg)
+            # NOTE: lookup the `trio.Task.context`'s var for
+            # the current `MsgCodec`.
+            codec: MsgCodec = _ctxvar_MsgCodec.get()
+
+            # XXX for ctxvar debug only!
+            # if self._codec.pld_spec != codec.pld_spec:
+            #     self._codec = codec
+            #     log.runtime(
+            #         f'Using new codec in {self}.send()\n'
+            #         f'codec: {self._codec}\n\n'
+            #         f'msg: {msg}\n'
+            #     )
+
+            if type(msg) not in msgtypes.__msg_types__:
+                if strict_types:
+                    raise _mk_send_mte(
+                        msg,
+                        codec=codec,
+                    )
+                else:
+                    log.warning(
+                        'Sending non-`Msg`-spec msg?\n\n'
+                        f'{msg}\n'
+                    )
+
+            try:
+                bytes_data: bytes = codec.encode(msg)
+            except TypeError as _err:
+                typerr = _err
+                msgtyperr: MsgTypeError = _mk_send_mte(
+                    msg,
+                    codec=codec,
+                    message=(
+                        f'IPC-msg-spec violation in\n\n'
+                        f'{pretty_struct.Struct.pformat(msg)}'
+                    ),
+                    src_type_error=typerr,
+                )
+                raise msgtyperr from typerr
 
             # supposedly the fastest says,
             # https://stackoverflow.com/a/54027962
             size: bytes = struct.pack("<I", len(bytes_data))
-
             return await self.stream.send_all(size + bytes_data)
 
+        # ?TODO? does it help ever to dynamically show this
+        # frame?
+        # try:
+        #     <the-above_code>
+        # except BaseException as _err:
+        #     err = _err
+        #     if not isinstance(err, MsgTypeError):
+        #         __tracebackhide__: bool = False
+        #     raise
+
     @property
     def laddr(self) -> tuple[str, int]:
         return self._laddr
@@ -235,7 +445,7 @@ class MsgpackTCPStream(MsgTransport):
         return self._raddr
 
     async def recv(self) -> Any:
-        return await self._agen.asend(None)
+        return await self._aiter_pkts.asend(None)
 
     async def drain(self) -> AsyncIterator[dict]:
         '''
@@ -252,7 +462,7 @@ class MsgpackTCPStream(MsgTransport):
                 yield msg
 
     def __aiter__(self):
-        return self._agen
+        return self._aiter_pkts
 
     def connected(self) -> bool:
         return self.stream.socket.fileno() != -1
@@ -307,7 +517,7 @@ class Channel:
         # set after handshake - always uid of far end
         self.uid: tuple[str, str]|None = None
 
-        self._agen = self._aiter_recv()
+        self._aiter_msgs = self._iter_msgs()
         self._exc: Exception|None = None  # set if far end actor errors
         self._closed: bool = False
 
@@ -318,7 +528,9 @@ class Channel:
 
     @property
     def msgstream(self) -> MsgTransport:
-        log.info('`Channel.msgstream` is an old name, use `._transport`')
+        log.info(
+            '`Channel.msgstream` is an old name, use `._transport`'
+        )
         return self._transport
 
     @property
@@ -349,11 +561,45 @@ class Channel:
         stream: trio.SocketStream,
         type_key: tuple[str, str]|None = None,
 
+        # XXX optionally provided codec pair for `msgspec`:
+        # https://jcristharif.com/msgspec/extending.html#mapping-to-from-native-types
+        codec: MsgCodec|None = None,
+
     ) -> MsgTransport:
-        type_key = type_key or self._transport_key
-        self._transport = get_msg_transport(type_key)(stream)
+        type_key = (
+            type_key
+            or
+            self._transport_key
+        )
+        # get transport type, then
+        self._transport = get_msg_transport(
+            type_key
+        # instantiate an instance of the msg-transport
+        )(
+            stream,
+            codec=codec,
+        )
         return self._transport
 
+    @cm
+    def apply_codec(
+        self,
+        codec: MsgCodec,
+
+    ) -> None:
+        '''
+        Temporarily override the underlying IPC msg codec for
+        dynamic enforcement of messaging schema.
+
+        '''
+        orig: MsgCodec = self._transport.codec
+        try:
+            self._transport.codec = codec
+            yield
+        finally:
+            self._transport.codec = orig
+
+    # TODO: do a .src/.dst: str for maddrs?
     def __repr__(self) -> str:
         if not self._transport:
             return '<Channel with inactive transport?>'
@@ -397,33 +643,53 @@ class Channel:
         )
         return transport
 
+    # TODO: something like,
+    # `pdbp.hideframe_on(errors=[MsgTypeError])`
+    # instead of the `try/except` hack we have rn..
+    # seems like a pretty useful thing to have in general
+    # along with being able to filter certain stack frame(s / sets)
+    # possibly based on the current log-level?
     async def send(
         self,
         payload: Any,
 
-        # hide_tb: bool = False,
+        hide_tb: bool = False,
 
     ) -> None:
         '''
         Send a coded msg-blob over the transport.
 
         '''
-        # __tracebackhide__: bool = hide_tb
-        log.transport(
-            '=> send IPC msg:\n\n'
-            f'{pformat(payload)}\n'
-        )  # type: ignore
-        assert self._transport
+        __tracebackhide__: bool = hide_tb
+        try:
+            log.transport(
+                '=> send IPC msg:\n\n'
+                f'{pformat(payload)}\n'
+            )
+            # assert self._transport  # but why typing?
+            await self._transport.send(
+                payload,
+                hide_tb=hide_tb,
+            )
+        except BaseException as _err:
+            err = _err  # bind for introspection
+            if not isinstance(_err, MsgTypeError):
+                # assert err
+                __tracebackhide__: bool = False
+            else:
+                assert err.cid
 
-        await self._transport.send(
-            payload,
-            # hide_tb=hide_tb,
-        )
+            raise
 
     async def recv(self) -> Any:
         assert self._transport
         return await self._transport.recv()
 
+        # TODO: auto-reconnect features like 0mq/nanomsg?
+        # -[ ] implement it manually with nods to SC prot
+        #      possibly on multiple transport backends?
+        #  -> seems like that might be re-inventing scalability
+        #     prots tho no?
         # try:
         #     return await self._transport.recv()
         # except trio.BrokenResourceError:
@@ -450,8 +716,11 @@ class Channel:
         await self.aclose(*args)
 
     def __aiter__(self):
-        return self._agen
+        return self._aiter_msgs
 
+    # ?TODO? run any reconnection sequence?
+    # -[ ] prolly should be impl-ed as deco-API?
+    #
     # async def _reconnect(self) -> None:
     #     """Handle connection failures by polling until a reconnect can be
     #     established.
@@ -469,7 +738,6 @@ class Channel:
     #             else:
     #                 log.transport("Stream connection re-established!")
 
-    #                 # TODO: run any reconnection sequence
     #                 # on_recon = self._recon_seq
     #                 # if on_recon:
     #                 #     await on_recon(self)
@@ -483,23 +751,42 @@ class Channel:
     #                     " for re-establishment")
     #             await trio.sleep(1)
 
-    async def _aiter_recv(
+    async def _iter_msgs(
         self
     ) -> AsyncGenerator[Any, None]:
         '''
-        Async iterate items from underlying stream.
+        Yield `MsgType` IPC msgs decoded and deliverd from
+        an underlying `MsgTransport` protocol.
+
+        This is a streaming routine alo implemented as an async-gen
+        func (same a `MsgTransport._iter_pkts()`) gets allocated by
+        a `.__call__()` inside `.__init__()` where it is assigned to
+        the `._aiter_msgs` attr.
 
         '''
         assert self._transport
         while True:
             try:
-                async for item in self._transport:
-                    yield item
-                    # sent = yield item
-                    # if sent is not None:
-                    #     # optimization, passing None through all the
-                    #     # time is pointless
-                    #     await self._transport.send(sent)
+                async for msg in self._transport:
+                    match msg:
+                        # NOTE: if transport/interchange delivers
+                        # a type error, we pack it with the far
+                        # end peer `Actor.uid` and relay the
+                        # `Error`-msg upward to the `._rpc` stack
+                        # for normal RAE handling.
+                        case MsgTypeError():
+                            yield pack_from_raise(
+                                local_err=msg,
+                                cid=msg.cid,
+
+                                # XXX we pack it here bc lower
+                                # layers have no notion of an
+                                # actor-id ;)
+                                src_uid=self.uid,
+                            )
+                        case _:
+                            yield msg
+
             except trio.BrokenResourceError:
 
                 # if not self._autorecon:
@@ -529,4 +816,5 @@ async def _connect_chan(
     chan = Channel((host, port))
     await chan.connect()
     yield chan
-    await chan.aclose()
+    with trio.CancelScope(shield=True):
+        await chan.aclose()

tractor/_portal.py

@@ -31,7 +31,7 @@ from typing import (
     Any,
     Callable,
     AsyncGenerator,
-    # Type,
+    TYPE_CHECKING,
 )
 from functools import partial
 from dataclasses import dataclass
@@ -45,9 +45,14 @@ from ._state import (
 )
 from ._ipc import Channel
 from .log import get_logger
-from .msg import NamespacePath
+from .msg import (
+    # Error,
+    PayloadMsg,
+    NamespacePath,
+    Return,
+)
 from ._exceptions import (
-    unpack_error,
+    # unpack_error,
     NoResult,
 )
 from ._context import (
@@ -58,41 +63,12 @@ from ._streaming import (
     MsgStream,
 )
 
+if TYPE_CHECKING:
+    from ._runtime import Actor
 
 log = get_logger(__name__)
 
 
-# TODO: rename to `unwrap_result()` and use
-# `._raise_from_no_key_in_msg()` (after tweak to
-# accept a `chan: Channel` arg) in key block!
-def _unwrap_msg(
-    msg: dict[str, Any],
-    channel: Channel,
-
-    hide_tb: bool = True,
-
-) -> Any:
-    '''
-    Unwrap a final result from a `{return: <Any>}` IPC msg.
-
-    '''
-    __tracebackhide__: bool = hide_tb
-
-    try:
-        return msg['return']
-    except KeyError as ke:
-
-        # internal error should never get here
-        assert msg.get('cid'), (
-            "Received internal error at portal?"
-        )
-
-        raise unpack_error(
-            msg,
-            channel
-        ) from ke
-
-
 class Portal:
     '''
     A 'portal' to a memory-domain-separated `Actor`.
@@ -116,17 +92,26 @@ class Portal:
     # connected (peer) actors.
     cancel_timeout: float = 0.5
 
-    def __init__(self, channel: Channel) -> None:
-        self.chan = channel
+    def __init__(
+        self,
+        channel: Channel,
+    ) -> None:
+
+        self._chan: Channel = channel
         # during the portal's lifetime
-        self._result_msg: dict|None = None
+        self._final_result_pld: Any|None = None
+        self._final_result_msg: PayloadMsg|None = None
 
         # When set to a ``Context`` (when _submit_for_result is called)
         # it is expected that ``result()`` will be awaited at some
         # point.
-        self._expect_result: Context | None = None
+        self._expect_result_ctx: Context|None = None
         self._streams: set[MsgStream] = set()
-        self.actor = current_actor()
+        self.actor: Actor = current_actor()
+
+    @property
+    def chan(self) -> Channel:
+        return self._chan
 
     @property
     def channel(self) -> Channel:
@@ -140,6 +125,8 @@ class Portal:
         )
         return self.chan
 
+    # TODO: factor this out into a `.highlevel` API-wrapper that uses
+    # a single `.open_context()` call underneath.
     async def _submit_for_result(
         self,
         ns: str,
@@ -147,32 +134,34 @@ class Portal:
         **kwargs
     ) -> None:
 
-        assert self._expect_result is None, (
-            "A pending main result has already been submitted"
-        )
+        if self._expect_result_ctx is not None:
+            raise RuntimeError(
+                'A pending main result has already been submitted'
+            )
 
-        self._expect_result = await self.actor.start_remote_task(
+        self._expect_result_ctx: Context = await self.actor.start_remote_task(
             self.channel,
             nsf=NamespacePath(f'{ns}:{func}'),
-            kwargs=kwargs
+            kwargs=kwargs,
+            portal=self,
         )
 
-    async def _return_once(
+    # TODO: we should deprecate this API right? since if we remove
+    # `.run_in_actor()` (and instead move it to a `.highlevel`
+    # wrapper api (around a single `.open_context()` call) we don't
+    # really have any notion of a "main" remote task any more?
+    #
+    # @api_frame
+    async def wait_for_result(
         self,
-        ctx: Context,
-
-    ) -> dict[str, Any]:
-
-        assert ctx._remote_func_type == 'asyncfunc'  # single response
-        msg: dict = await ctx._recv_chan.receive()
-        return msg
-
-    async def result(self) -> Any:
+        hide_tb: bool = True,
+    ) -> Any:
         '''
-        Return the result(s) from the remote actor's "main" task.
+        Return the final result delivered by a `Return`-msg from the
+        remote peer actor's "main" task's `return` statement.
 
         '''
-        # __tracebackhide__ = True
+        __tracebackhide__: bool = hide_tb
         # Check for non-rpc errors slapped on the
         # channel for which we always raise
         exc = self.channel._exc
@@ -180,7 +169,7 @@ class Portal:
             raise exc
 
         # not expecting a "main" result
-        if self._expect_result is None:
+        if self._expect_result_ctx is None:
             log.warning(
                 f"Portal for {self.channel.uid} not expecting a final"
                 " result?\nresult() should only be called if subactor"
@@ -188,16 +177,40 @@ class Portal:
             return NoResult
 
         # expecting a "main" result
-        assert self._expect_result
+        assert self._expect_result_ctx
 
-        if self._result_msg is None:
-            self._result_msg = await self._return_once(
-                self._expect_result
-            )
+        if self._final_result_msg is None:
+            try:
+                (
+                    self._final_result_msg,
+                    self._final_result_pld,
+                ) = await self._expect_result_ctx._pld_rx.recv_msg_w_pld(
+                    ipc=self._expect_result_ctx,
+                    expect_msg=Return,
+                )
+            except BaseException as err:
+                # TODO: wrap this into `@api_frame` optionally with
+                # some kinda filtering mechanism like log levels?
+                __tracebackhide__: bool = False
+                raise err
 
-        return _unwrap_msg(
-            self._result_msg,
-            self.channel,
+        return self._final_result_pld
+
+    # TODO: factor this out into a `.highlevel` API-wrapper that uses
+    # a single `.open_context()` call underneath.
+    async def result(
+        self,
+        *args,
+        **kwargs,
+    ) -> Any|Exception:
+        typname: str = type(self).__name__
+        log.warning(
+            f'`{typname}.result()` is DEPRECATED!\n'
+            f'Use `{typname}.wait_for_result()` instead!\n'
+        )
+        return await self.wait_for_result(
+            *args,
+            **kwargs,
         )
 
     async def _cancel_streams(self):
@@ -240,6 +253,8 @@ class Portal:
         purpose.
 
         '''
+        __runtimeframe__: int = 1  # noqa
+
         chan: Channel = self.channel
         if not chan.connected():
             log.runtime(
@@ -248,14 +263,15 @@ class Portal:
             return False
 
         reminfo: str = (
-            f'`Portal.cancel_actor()` => {self.channel.uid}\n'
-            f' |_{chan}\n'
+            f'c)=> {self.channel.uid}\n'
+            f'  |_{chan}\n'
         )
         log.cancel(
-            f'Sending runtime `.cancel()` request to peer\n\n'
+            f'Requesting actor-runtime cancel for peer\n\n'
             f'{reminfo}'
         )
 
+        # XXX the one spot we set it?
         self.channel._cancel_called: bool = True
         try:
             # send cancel cmd - might not get response
@@ -295,6 +311,8 @@ class Portal:
             )
             return False
 
+    # TODO: do we still need this for low level `Actor`-runtime
+    # method calls or can we also remove it?
     async def run_from_ns(
         self,
         namespace_path: str,
@@ -317,21 +335,23 @@ class Portal:
           internals!
 
         '''
+        __runtimeframe__: int = 1  # noqa
         nsf = NamespacePath(
             f'{namespace_path}:{function_name}'
         )
-        ctx = await self.actor.start_remote_task(
+        ctx: Context = await self.actor.start_remote_task(
             chan=self.channel,
             nsf=nsf,
             kwargs=kwargs,
+            portal=self,
         )
-        ctx._portal = self
-        msg = await self._return_once(ctx)
-        return _unwrap_msg(
-            msg,
-            self.channel,
+        return await ctx._pld_rx.recv_pld(
+            ipc=ctx,
+            expect_msg=Return,
         )
 
+    # TODO: factor this out into a `.highlevel` API-wrapper that uses
+    # a single `.open_context()` call underneath.
     async def run(
         self,
         func: str,
@@ -347,6 +367,8 @@ class Portal:
         remote rpc task or a local async generator instance.
 
         '''
+        __runtimeframe__: int = 1  # noqa
+
         if isinstance(func, str):
             warnings.warn(
                 "`Portal.run(namespace: str, funcname: str)` is now"
@@ -377,13 +399,15 @@ class Portal:
             self.channel,
             nsf=nsf,
             kwargs=kwargs,
+            portal=self,
         )
-        ctx._portal = self
-        return _unwrap_msg(
-            await self._return_once(ctx),
-            self.channel,
+        return await ctx._pld_rx.recv_pld(
+            ipc=ctx,
+            expect_msg=Return,
         )
 
+    # TODO: factor this out into a `.highlevel` API-wrapper that uses
+    # a single `.open_context()` call underneath.
     @acm
     async def open_stream_from(
         self,
@@ -391,6 +415,14 @@ class Portal:
         **kwargs,
 
     ) -> AsyncGenerator[MsgStream, None]:
+        '''
+        Legacy one-way streaming API.
+
+        TODO: re-impl on top `Portal.open_context()` + an async gen
+        around `Context.open_stream()`.
+
+        '''
+        __runtimeframe__: int = 1  # noqa
 
         if not inspect.isasyncgenfunction(async_gen_func):
             if not (
@@ -404,8 +436,8 @@ class Portal:
             self.channel,
             nsf=NamespacePath.from_ref(async_gen_func),
             kwargs=kwargs,
+            portal=self,
         )
-        ctx._portal = self
 
         # ensure receive-only stream entrypoint
         assert ctx._remote_func_type == 'asyncgen'
@@ -414,13 +446,13 @@ class Portal:
             # deliver receive only stream
             async with MsgStream(
                 ctx=ctx,
-                rx_chan=ctx._recv_chan,
-            ) as rchan:
-                self._streams.add(rchan)
-                yield rchan
+                rx_chan=ctx._rx_chan,
+            ) as stream:
+                self._streams.add(stream)
+                ctx._stream = stream
+                yield stream
 
         finally:
-
             # cancel the far end task on consumer close
             # NOTE: this is a special case since we assume that if using
             # this ``.open_fream_from()`` api, the stream is one a one
@@ -439,7 +471,7 @@ class Portal:
 
             # XXX: should this always be done?
             # await recv_chan.aclose()
-            self._streams.remove(rchan)
+            self._streams.remove(stream)
 
     # NOTE: impl is found in `._context`` mod to make
     # reading/groking the details simpler code-org-wise. This
@@ -481,7 +513,7 @@ class LocalPortal:
 async def open_portal(
 
     channel: Channel,
-    nursery: trio.Nursery|None = None,
+    tn: trio.Nursery|None = None,
     start_msg_loop: bool = True,
     shield: bool = False,
 
@@ -489,15 +521,19 @@ async def open_portal(
     '''
     Open a ``Portal`` through the provided ``channel``.
 
-    Spawns a background task to handle message processing (normally
-    done by the actor-runtime implicitly).
+    Spawns a background task to handle RPC processing, normally
+    done by the actor-runtime implicitly via a call to
+    `._rpc.process_messages()`. just after connection establishment.
 
     '''
     actor = current_actor()
     assert actor
-    was_connected = False
+    was_connected: bool = False
 
-    async with maybe_open_nursery(nursery, shield=shield) as nursery:
+    async with maybe_open_nursery(
+        tn,
+        shield=shield,
+    ) as tn:
 
         if not channel.connected():
             await channel.connect()
@@ -509,7 +545,7 @@ async def open_portal(
         msg_loop_cs: trio.CancelScope|None = None
         if start_msg_loop:
             from ._runtime import process_messages
-            msg_loop_cs = await nursery.start(
+            msg_loop_cs = await tn.start(
                 partial(
                     process_messages,
                     actor,
@@ -526,12 +562,10 @@ async def open_portal(
             await portal.aclose()
 
             if was_connected:
-                # gracefully signal remote channel-msg loop
-                await channel.send(None)
-                # await channel.aclose()
+                await channel.aclose()
 
             # cancel background msg loop task
-            if msg_loop_cs:
+            if msg_loop_cs is not None:
                 msg_loop_cs.cancel()
 
-            nursery.cancel_scope.cancel()
+            tn.cancel_scope.cancel()

tractor/_root.py

@@ -18,9 +18,10 @@
 Root actor runtime ignition(s).
 
 '''
-from contextlib import asynccontextmanager
+from contextlib import asynccontextmanager as acm
 from functools import partial
 import importlib
+import inspect
 import logging
 import os
 import signal
@@ -60,7 +61,7 @@ _default_lo_addrs: list[tuple[str, int]] = [(
 logger = log.get_logger('tractor')
 
 
-@asynccontextmanager
+@acm
 async def open_root_actor(
 
     *,
@@ -92,11 +93,16 @@ async def open_root_actor(
     # and that this call creates it.
     ensure_registry: bool = False,
 
+    hide_tb: bool = True,
+
 ) -> Actor:
     '''
     Runtime init entry point for ``tractor``.
 
     '''
+    __tracebackhide__: bool = hide_tb
+    _debug.hide_runtime_frames()
+
     # TODO: stick this in a `@cm` defined in `devx._debug`?
     #
     # Override the global debugger hook to make it play nice with
@@ -110,20 +116,28 @@ async def open_root_actor(
     if (
         debug_mode
         and maybe_enable_greenback
-        and await _debug.maybe_init_greenback(
-            raise_not_found=False,
+        and (
+            maybe_mod := await _debug.maybe_init_greenback(
+                raise_not_found=False,
+            )
         )
     ):
-        os.environ['PYTHONBREAKPOINT'] = (
-            'tractor.devx._debug.pause_from_sync'
+        logger.info(
+            f'Found `greenback` installed @ {maybe_mod}\n'
+            'Enabling `tractor.pause_from_sync()` support!\n'
         )
+        os.environ['PYTHONBREAKPOINT'] = (
+            'tractor.devx._debug._sync_pause_from_builtin'
+        )
+        _state._runtime_vars['use_greenback'] = True
+
     else:
         # TODO: disable `breakpoint()` by default (without
         # `greenback`) since it will break any multi-actor
         # usage by a clobbered TTY's stdstreams!
         def block_bps(*args, **kwargs):
             raise RuntimeError(
-                'Trying to use `breakpoint()` eh?\n'
+                'Trying to use `breakpoint()` eh?\n\n'
                 'Welp, `tractor` blocks `breakpoint()` built-in calls by default!\n'
                 'If you need to use it please install `greenback` and set '
                 '`debug_mode=True` when opening the runtime '
@@ -131,11 +145,13 @@ async def open_root_actor(
             )
 
         sys.breakpointhook = block_bps
-        # os.environ['PYTHONBREAKPOINT'] = None
+        # lol ok,
+        # https://docs.python.org/3/library/sys.html#sys.breakpointhook
+        os.environ['PYTHONBREAKPOINT'] = "0"
 
     # attempt to retreive ``trio``'s sigint handler and stash it
     # on our debugger lock state.
-    _debug.Lock._trio_handler = signal.getsignal(signal.SIGINT)
+    _debug.DebugStatus._trio_handler = signal.getsignal(signal.SIGINT)
 
     # mark top most level process as root actor
     _state._runtime_vars['_is_root'] = True
@@ -201,6 +217,7 @@ async def open_root_actor(
         ):
             loglevel = 'PDB'
 
+
     elif debug_mode:
         raise RuntimeError(
             "Debug mode is only supported for the `trio` backend!"
@@ -254,7 +271,9 @@ async def open_root_actor(
 
         except OSError:
             # TODO: make this a "discovery" log level?
-            logger.warning(f'No actor registry found @ {addr}')
+            logger.info(
+                f'No actor registry found @ {addr}\n'
+            )
 
     async with trio.open_nursery() as tn:
         for addr in registry_addrs:
@@ -268,7 +287,6 @@ async def open_root_actor(
     # Create a new local root-actor instance which IS NOT THE
     # REGISTRAR
     if ponged_addrs:
-
         if ensure_registry:
             raise RuntimeError(
                  f'Failed to open `{name}`@{ponged_addrs}: '
@@ -355,19 +373,25 @@ async def open_root_actor(
             )
             try:
                 yield actor
-
             except (
                 Exception,
                 BaseExceptionGroup,
             ) as err:
-
-                entered: bool = await _debug._maybe_enter_pm(err)
+                # XXX NOTE XXX see equiv note inside
+                # `._runtime.Actor._stream_handler()` where in the
+                # non-root or root-that-opened-this-mahually case we
+                # wait for the local actor-nursery to exit before
+                # exiting the transport channel handler.
+                entered: bool = await _debug._maybe_enter_pm(
+                    err,
+                    api_frame=inspect.currentframe(),
+                )
                 if (
                     not entered
                     and
                     not is_multi_cancelled(err)
                 ):
-                    logger.exception('Root actor crashed:\n')
+                    logger.exception('Root actor crashed\n')
 
                 # ALWAYS re-raise any error bubbled up from the
                 # runtime!
@@ -392,14 +416,20 @@ async def open_root_actor(
         _state._last_actor_terminated = actor
 
         # restore built-in `breakpoint()` hook state
-        if debug_mode:
+        if (
+            debug_mode
+            and
+            maybe_enable_greenback
+        ):
             if builtin_bp_handler is not None:
                 sys.breakpointhook = builtin_bp_handler
+
             if orig_bp_path is not None:
                 os.environ['PYTHONBREAKPOINT'] = orig_bp_path
+
             else:
                 # clear env back to having no entry
-                os.environ.pop('PYTHONBREAKPOINT')
+                os.environ.pop('PYTHONBREAKPOINT', None)
 
         logger.runtime("Root actor terminated")
 

tractor/_spawn.py

@@ -43,12 +43,16 @@ from tractor._state import (
     is_main_process,
     is_root_process,
     debug_mode,
+    _runtime_vars,
 )
 from tractor.log import get_logger
 from tractor._portal import Portal
 from tractor._runtime import Actor
 from tractor._entry import _mp_main
 from tractor._exceptions import ActorFailure
+from tractor.msg.types import (
+    SpawnSpec,
+)
 
 
 if TYPE_CHECKING:
@@ -139,11 +143,13 @@ async def exhaust_portal(
     '''
     __tracebackhide__ = True
     try:
-        log.debug(f"Waiting on final result from {actor.uid}")
+        log.debug(
+            f'Waiting on final result from {actor.uid}'
+        )
 
         # XXX: streams should never be reaped here since they should
         # always be established and shutdown using a context manager api
-        final: Any = await portal.result()
+        final: Any = await portal.wait_for_result()
 
     except (
         Exception,
@@ -192,7 +198,10 @@ async def cancel_on_completion(
     # if this call errors we store the exception for later
     # in ``errors`` which will be reraised inside
     # an exception group and we still send out a cancel request
-    result: Any|Exception = await exhaust_portal(portal, actor)
+    result: Any|Exception = await exhaust_portal(
+        portal,
+        actor,
+    )
     if isinstance(result, Exception):
         errors[actor.uid]: Exception = result
         log.cancel(
@@ -214,8 +223,8 @@ async def cancel_on_completion(
 
 async def hard_kill(
     proc: trio.Process,
-    terminate_after: int = 1.6,
 
+    terminate_after: int = 1.6,
     # NOTE: for mucking with `.pause()`-ing inside the runtime
     # whilst also hacking on it XD
     # terminate_after: int = 99999,
@@ -241,8 +250,9 @@ async def hard_kill(
 
     '''
     log.cancel(
-        'Terminating sub-proc:\n'
-        f'|_{proc}\n'
+        'Terminating sub-proc\n'
+        f'>x)\n'
+        f' |_{proc}\n'
     )
     # NOTE: this timeout used to do nothing since we were shielding
     # the ``.wait()`` inside ``new_proc()`` which will pretty much
@@ -288,14 +298,13 @@ async def hard_kill(
         log.critical(
             # 'Well, the #ZOMBIE_LORD_IS_HERE# to collect\n'
             '#T-800 deployed to collect zombie B0\n'
-            f'|\n'
-            f'|_{proc}\n'
+            f'>x)\n'
+            f' |_{proc}\n'
         )
         proc.kill()
 
 
 async def soft_kill(
-
     proc: ProcessType,
     wait_func: Callable[
         [ProcessType],
@@ -318,13 +327,26 @@ async def soft_kill(
     uid: tuple[str, str] = portal.channel.uid
     try:
         log.cancel(
-            'Soft killing sub-actor via `Portal.cancel_actor()`\n'
-            f'|_{proc}\n'
+            'Soft killing sub-actor via portal request\n'
+            f'c)> {portal.chan.uid}\n'
+            f' |_{proc}\n'
         )
         # wait on sub-proc to signal termination
         await wait_func(proc)
 
     except trio.Cancelled:
+        with trio.CancelScope(shield=True):
+            await maybe_wait_for_debugger(
+                child_in_debug=_runtime_vars.get(
+                    '_debug_mode', False
+                ),
+                header_msg=(
+                    'Delaying `soft_kill()` subproc reaper while debugger locked..\n'
+                ),
+                # TODO: need a diff value then default?
+                # poll_steps=9999999,
+            )
+
         # if cancelled during a soft wait, cancel the child
         # actor before entering the hard reap sequence
         # below. This means we try to do a graceful teardown
@@ -452,10 +474,9 @@ async def trio_proc(
     proc: trio.Process|None = None
     try:
         try:
-            # TODO: needs ``trio_typing`` patch?
-            proc = await trio.lowlevel.open_process(spawn_cmd)
+            proc: trio.Process = await trio.lowlevel.open_process(spawn_cmd)
             log.runtime(
-                'Started new sub-proc\n'
+                'Started new child\n'
                 f'|_{proc}\n'
             )
 
@@ -493,14 +514,17 @@ async def trio_proc(
             portal,
         )
 
-        # send additional init params
-        await chan.send({
-            '_parent_main_data': subactor._parent_main_data,
-            'enable_modules': subactor.enable_modules,
-            'reg_addrs': subactor.reg_addrs,
-            'bind_addrs': bind_addrs,
-            '_runtime_vars': _runtime_vars,
-        })
+        # send a "spawning specification" which configures the
+        # initial runtime state of the child.
+        await chan.send(
+            SpawnSpec(
+                _parent_main_data=subactor._parent_main_data,
+                enable_modules=subactor.enable_modules,
+                reg_addrs=subactor.reg_addrs,
+                bind_addrs=bind_addrs,
+                _runtime_vars=_runtime_vars,
+            )
+        )
 
         # track subactor in current nursery
         curr_actor: Actor = current_actor()
@@ -534,8 +558,9 @@ async def trio_proc(
             # cancel result waiter that may have been spawned in
             # tandem if not done already
             log.cancel(
-                'Cancelling existing result waiter task for '
-                f'{subactor.uid}'
+                'Cancelling portal result reaper task\n'
+                f'>c)\n'
+                f' |_{subactor.uid}\n'
             )
             nursery.cancel_scope.cancel()
 
@@ -544,9 +569,13 @@ async def trio_proc(
         # allowed! Do this **after** cancellation/teardown to avoid
         # killing the process too early.
         if proc:
-            log.cancel(f'Hard reap sequence starting for {subactor.uid}')
-            with trio.CancelScope(shield=True):
+            log.cancel(
+                f'Hard reap sequence starting for subactor\n'
+                f'>x)\n'
+                f' |_{subactor}@{subactor.uid}\n'
+            )
 
+            with trio.CancelScope(shield=True):
                 # don't clobber an ongoing pdb
                 if cancelled_during_spawn:
                     # Try again to avoid TTY clobbering.

tractor/_state.py

@@ -19,13 +19,19 @@ Per process state
 
 """
 from __future__ import annotations
+from contextvars import (
+    ContextVar,
+)
 from typing import (
     Any,
     TYPE_CHECKING,
 )
 
+from trio.lowlevel import current_task
+
 if TYPE_CHECKING:
     from ._runtime import Actor
+    from ._context import Context
 
 
 _current_actor: Actor|None = None  # type: ignore # noqa
@@ -38,7 +44,7 @@ _runtime_vars: dict[str, Any] = {
     '_root_mailbox': (None, None),
     '_registry_addrs': [],
 
-    # for `breakpoint()` support
+    # for `tractor.pause_from_sync()` & `breakpoint()` support
     'use_greenback': False,
 }
 
@@ -66,7 +72,7 @@ def current_actor(
         err_on_no_runtime
         and _current_actor is None
     ):
-        msg: str = 'No local actor has been initialized yet'
+        msg: str = 'No local actor has been initialized yet?\n'
         from ._exceptions import NoRuntime
 
         if last := last_actor():
@@ -79,8 +85,8 @@ def current_actor(
         # this process.
         else:
             msg += (
-                'No last actor found?\n'
-                'Did you forget to open one of:\n\n'
+                # 'No last actor found?\n'
+                '\nDid you forget to call one of,\n'
                 '- `tractor.open_root_actor()`\n'
                 '- `tractor.open_nursery()`\n'
             )
@@ -110,3 +116,26 @@ def debug_mode() -> bool:
 
 def is_root_process() -> bool:
     return _runtime_vars['_is_root']
+
+
+_ctxvar_Context: ContextVar[Context] = ContextVar(
+    'ipc_context',
+    default=None,
+)
+
+
+def current_ipc_ctx(
+    error_on_not_set: bool = False,
+) -> Context|None:
+    ctx: Context = _ctxvar_Context.get()
+
+    if (
+        not ctx
+        and error_on_not_set
+    ):
+        from ._exceptions import InternalError
+        raise InternalError(
+            'No IPC context has been allocated for this task yet?\n'
+            f'|_{current_task()}\n'
+        )
+    return ctx

tractor/_streaming.py

@@ -26,6 +26,7 @@ import inspect
 from pprint import pformat
 from typing import (
     Any,
+    AsyncGenerator,
     Callable,
     AsyncIterator,
     TYPE_CHECKING,
@@ -35,17 +36,25 @@ import warnings
 import trio
 
 from ._exceptions import (
-    _raise_from_no_key_in_msg,
     ContextCancelled,
+    RemoteActorError,
 )
 from .log import get_logger
 from .trionics import (
     broadcast_receiver,
     BroadcastReceiver,
 )
+from tractor.msg import (
+    # Return,
+    # Stop,
+    MsgType,
+    Yield,
+)
 
 if TYPE_CHECKING:
+    from ._runtime import Actor
     from ._context import Context
+    from ._ipc import Channel
 
 
 log = get_logger(__name__)
@@ -59,10 +68,10 @@ log = get_logger(__name__)
 class MsgStream(trio.abc.Channel):
     '''
     A bidirectional message stream for receiving logically sequenced
-    values over an inter-actor IPC ``Channel``.
+    values over an inter-actor IPC `Channel`.
 
     This is the type returned to a local task which entered either
-    ``Portal.open_stream_from()`` or ``Context.open_stream()``.
+    `Portal.open_stream_from()` or `Context.open_stream()`.
 
     Termination rules:
 
@@ -78,7 +87,7 @@ class MsgStream(trio.abc.Channel):
         self,
         ctx: Context,  # typing: ignore # noqa
         rx_chan: trio.MemoryReceiveChannel,
-        _broadcaster: BroadcastReceiver | None = None,
+        _broadcaster: BroadcastReceiver|None = None,
 
     ) -> None:
         self._ctx = ctx
@@ -89,35 +98,44 @@ class MsgStream(trio.abc.Channel):
         self._eoc: bool|trio.EndOfChannel = False
         self._closed: bool|trio.ClosedResourceError = False
 
+    @property
+    def ctx(self) -> Context:
+        '''
+        A read-only ref to this stream's inter-actor-task `Context`.
+
+        '''
+        return self._ctx
+
+    @property
+    def chan(self) -> Channel:
+        '''
+        Ref to the containing `Context`'s transport `Channel`.
+
+        '''
+        return self._ctx.chan
+
+    # TODO: could we make this a direct method bind to `PldRx`?
+    # -> receive_nowait = PldRx.recv_pld
+    # |_ means latter would have to accept `MsgStream`-as-`self`?
+    #  => should be fine as long as,
+    #  -[ ] both define `._rx_chan`
+    #  -[ ] .ctx is bound into `PldRx` using a `@cm`?
+    #
     # delegate directly to underlying mem channel
     def receive_nowait(
         self,
-        allow_msg_keys: list[str] = ['yield'],
+        expect_msg: MsgType = Yield,
     ):
-        msg: dict = self._rx_chan.receive_nowait()
-        for (
-            i,
-            key,
-        ) in enumerate(allow_msg_keys):
-            try:
-                return msg[key]
-            except KeyError as kerr:
-                if i < (len(allow_msg_keys) - 1):
-                    continue
-
-                _raise_from_no_key_in_msg(
-                    ctx=self._ctx,
-                    msg=msg,
-                    src_err=kerr,
-                    log=log,
-                    expect_key=key,
-                    stream=self,
-                )
+        ctx: Context = self._ctx
+        return ctx._pld_rx.recv_pld_nowait(
+            ipc=self,
+            expect_msg=expect_msg,
+        )
 
     async def receive(
         self,
 
-        hide_tb: bool = True,
+        hide_tb: bool = False,
     ):
         '''
         Receive a single msg from the IPC transport, the next in
@@ -127,9 +145,8 @@ class MsgStream(trio.abc.Channel):
         '''
         __tracebackhide__: bool = hide_tb
 
-        # NOTE: `trio.ReceiveChannel` implements
-        # EOC handling as follows (aka uses it
-        # to gracefully exit async for loops):
+        # NOTE FYI: `trio.ReceiveChannel` implements EOC handling as
+        # follows (aka uses it to gracefully exit async for loops):
         #
         # async def __anext__(self) -> ReceiveType:
         #     try:
@@ -147,62 +164,29 @@ class MsgStream(trio.abc.Channel):
 
         src_err: Exception|None = None  # orig tb
         try:
-            try:
-                msg = await self._rx_chan.receive()
-                return msg['yield']
-
-            except KeyError as kerr:
-                src_err = kerr
-
-                # NOTE: may raise any of the below error types
-                # includg EoC when a 'stop' msg is found.
-                _raise_from_no_key_in_msg(
-                    ctx=self._ctx,
-                    msg=msg,
-                    src_err=kerr,
-                    log=log,
-                    expect_key='yield',
-                    stream=self,
-                )
+            ctx: Context = self._ctx
+            return await ctx._pld_rx.recv_pld(ipc=self)
 
         # XXX: the stream terminates on either of:
-        # - via `self._rx_chan.receive()` raising  after manual closure
-        #   by the rpc-runtime OR,
-        # - via a received `{'stop': ...}` msg from remote side.
-        #   |_ NOTE: previously this was triggered by calling
-        #   ``._rx_chan.aclose()`` on the send side of the channel inside
-        #   `Actor._push_result()`, but now the 'stop' message handling
-        #   has been put just above inside `_raise_from_no_key_in_msg()`.
-        except (
-            trio.EndOfChannel,
-        ) as eoc:
-            src_err = eoc
+        # - `self._rx_chan.receive()` raising  after manual closure
+        #   by the rpc-runtime,
+        #   OR
+        # - via a `Stop`-msg received from remote peer task.
+        #   NOTE
+        #   |_ previously this was triggered by calling
+        #   ``._rx_chan.aclose()`` on the send side of the channel
+        #   inside `Actor._deliver_ctx_payload()`, but now the 'stop'
+        #   message handling gets delegated to `PldRFx.recv_pld()`
+        #   internals.
+        except trio.EndOfChannel as eoc:
+            # a graceful stream finished signal
             self._eoc = eoc
+            src_err = eoc
 
-            # TODO: Locally, we want to close this stream gracefully, by
-            # terminating any local consumers tasks deterministically.
-            # Once we have broadcast support, we **don't** want to be
-            # closing this stream and not flushing a final value to
-            # remaining (clone) consumers who may not have been
-            # scheduled to receive it yet.
-            # try:
-            #     maybe_err_msg_or_res: dict = self._rx_chan.receive_nowait()
-            #     if maybe_err_msg_or_res:
-            #         log.warning(
-            #             'Discarding un-processed msg:\n'
-            #             f'{maybe_err_msg_or_res}'
-            #         )
-            # except trio.WouldBlock:
-            #     # no queued msgs that might be another remote
-            #     # error, so just raise the original EoC
-            #     pass
-
-            # raise eoc
-
-        # a ``ClosedResourceError`` indicates that the internal
-        # feeder memory receive channel was closed likely by the
-        # runtime after the associated transport-channel
-        # disconnected or broke.
+        # a `ClosedResourceError` indicates that the internal feeder
+        # memory receive channel was closed likely by the runtime
+        # after the associated transport-channel disconnected or
+        # broke.
         except trio.ClosedResourceError as cre:  # by self._rx_chan.receive()
             src_err = cre
             log.warning(
@@ -214,47 +198,57 @@ class MsgStream(trio.abc.Channel):
         # terminated and signal this local iterator to stop
         drained: list[Exception|dict] = await self.aclose()
         if drained:
+            # ?TODO? pass these to the `._ctx._drained_msgs: deque`
+            # and then iterate them as part of any `.wait_for_result()` call?
+            #
             # from .devx import pause
             # await pause()
             log.warning(
-                'Drained context msgs during closure:\n'
+                'Drained context msgs during closure\n\n'
                 f'{drained}'
             )
-        # TODO: pass these to the `._ctx._drained_msgs: deque`
-        # and then iterate them as part of any `.result()` call?
 
         # NOTE XXX: if the context was cancelled or remote-errored
         # but we received the stream close msg first, we
         # probably want to instead raise the remote error
         # over the end-of-stream connection error since likely
         # the remote error was the source cause?
-        ctx: Context = self._ctx
+        # ctx: Context = self._ctx
         ctx.maybe_raise(
             raise_ctxc_from_self_call=True,
+            from_src_exc=src_err,
         )
 
-        # propagate any error but hide low-level frame details
-        # from the caller by default for debug noise reduction.
+        # propagate any error but hide low-level frame details from
+        # the caller by default for console/debug-REPL noise
+        # reduction.
         if (
             hide_tb
+            and (
 
-            # XXX NOTE XXX don't reraise on certain
-            # stream-specific internal error types like,
-            #
-            # - `trio.EoC` since we want to use the exact instance
-            #   to ensure that it is the error that bubbles upward
-            #   for silent absorption by `Context.open_stream()`.
-            and not self._eoc
+                # XXX NOTE special conditions: don't reraise on
+                # certain stream-specific internal error types like,
+                #
+                # - `trio.EoC` since we want to use the exact instance
+                #   to ensure that it is the error that bubbles upward
+                #   for silent absorption by `Context.open_stream()`.
+                not self._eoc
 
-            # - `RemoteActorError` (or `ContextCancelled`) if it gets
-            #   raised from `_raise_from_no_key_in_msg()` since we
-            #   want the same (as the above bullet) for any
-            #   `.open_context()` block bubbled error raised by
-            #   any nearby ctx API remote-failures.
-            # and not isinstance(src_err, RemoteActorError)
+                # - `RemoteActorError` (or subtypes like ctxc)
+                #    since we want to present the error as though it is
+                #    "sourced" directly from this `.receive()` call and
+                #    generally NOT include the stack frames raised from
+                #    inside the `PldRx` and/or the transport stack
+                #    layers.
+                or isinstance(src_err, RemoteActorError)
+            )
         ):
             raise type(src_err)(*src_err.args) from src_err
         else:
+            # for any non-graceful-EOC we want to NOT hide this frame
+            if not self._eoc:
+                __tracebackhide__: bool = False
+
             raise src_err
 
     async def aclose(self) -> list[Exception|dict]:
@@ -292,7 +286,8 @@ class MsgStream(trio.abc.Channel):
         while not drained:
             try:
                 maybe_final_msg = self.receive_nowait(
-                    allow_msg_keys=['yield', 'return'],
+                    # allow_msgs=[Yield, Return],
+                    expect_msg=Yield,
                 )
                 if maybe_final_msg:
                     log.debug(
@@ -377,14 +372,15 @@ class MsgStream(trio.abc.Channel):
         #         await rx_chan.aclose()
 
         if not self._eoc:
-            log.cancel(
-                'Stream closed before it received an EoC?\n'
-                'Setting eoc manually..\n..'
-            )
-            self._eoc: bool = trio.EndOfChannel(
-                f'Context stream closed by {self._ctx.side}\n'
+            message: str = (
+                f'Stream self-closed by {self._ctx.side!r}-side before EoC\n'
+                # } bc a stream is a "scope"/msging-phase inside an IPC
+                f'x}}>\n'
                 f'|_{self}\n'
             )
+            log.cancel(message)
+            self._eoc = trio.EndOfChannel(message)
+
         # ?XXX WAIT, why do we not close the local mem chan `._rx_chan` XXX?
         # => NO, DEFINITELY NOT! <=
         # if we're a bi-dir ``MsgStream`` BECAUSE this same
@@ -469,6 +465,9 @@ class MsgStream(trio.abc.Channel):
                 self,
                 # use memory channel size by default
                 self._rx_chan._state.max_buffer_size,  # type: ignore
+
+                # TODO: can remove this kwarg right since
+                # by default behaviour is to do this anyway?
                 receive_afunc=self.receive,
             )
 
@@ -515,11 +514,10 @@ class MsgStream(trio.abc.Channel):
 
         try:
             await self._ctx.chan.send(
-                payload={
-                    'yield': data,
-                    'cid': self._ctx.cid,
-                },
-                # hide_tb=hide_tb,
+                payload=Yield(
+                    cid=self._ctx.cid,
+                    pld=data,
+                ),
             )
         except (
             trio.ClosedResourceError,
@@ -533,6 +531,224 @@ class MsgStream(trio.abc.Channel):
             else:
                 raise
 
+    # TODO: msg capability context api1
+    # @acm
+    # async def enable_msg_caps(
+    #     self,
+    #     msg_subtypes: Union[
+    #         list[list[Struct]],
+    #         Protocol,   # hypothetical type that wraps a msg set
+    #     ],
+    # ) -> tuple[Callable, Callable]:  # payload enc, dec pair
+    #     ...
+
+
+@acm
+async def open_stream_from_ctx(
+    ctx: Context,
+    allow_overruns: bool|None = False,
+    msg_buffer_size: int|None = None,
+
+) -> AsyncGenerator[MsgStream, None]:
+    '''
+    Open a `MsgStream`, a bi-directional msg transport dialog
+    connected to the cross-actor peer task for an IPC `Context`.
+
+    This context manager must be entered in both the "parent" (task
+    which entered `Portal.open_context()`) and "child" (RPC task
+    which is decorated by `@context`) tasks for the stream to
+    logically be considered "open"; if one side begins sending to an
+    un-opened peer, depending on policy config, msgs will either be
+    queued until the other side opens and/or a `StreamOverrun` will
+    (eventually) be raised.
+
+                         ------ - ------
+
+    Runtime semantics design:
+
+    A `MsgStream` session adheres to "one-shot use" semantics,
+    meaning if you close the scope it **can not** be "re-opened".
+
+    Instead you must re-establish a new surrounding RPC `Context`
+    (RTC: remote task context?) using `Portal.open_context()`.
+
+    In the future this *design choice* may need to be changed but
+    currently there seems to be no obvious reason to support such
+    semantics..
+
+    - "pausing a stream" can be supported with a message implemented
+      by the `tractor` application dev.
+
+    - any remote error will normally require a restart of the entire
+      `trio.Task`'s scope due to the nature of `trio`'s cancellation
+      (`CancelScope`) system and semantics (level triggered).
+
+    '''
+    actor: Actor = ctx._actor
+
+    # If the surrounding context has been cancelled by some
+    # task with a handle to THIS, we error here immediately
+    # since it likely means the surrounding lexical-scope has
+    # errored, been `trio.Cancelled` or at the least
+    # `Context.cancel()` was called by some task.
+    if ctx._cancel_called:
+
+        # XXX NOTE: ALWAYS RAISE any remote error here even if
+        # it's an expected `ContextCancelled` due to a local
+        # task having called `.cancel()`!
+        #
+        # WHY: we expect the error to always bubble up to the
+        # surrounding `Portal.open_context()` call and be
+        # absorbed there (silently) and we DO NOT want to
+        # actually try to stream - a cancel msg was already
+        # sent to the other side!
+        ctx.maybe_raise(
+            raise_ctxc_from_self_call=True,
+        )
+        # NOTE: this is diff then calling
+        # `._maybe_raise_remote_err()` specifically
+        # because we want to raise a ctxc on any task entering this `.open_stream()`
+        # AFTER cancellation was already been requested,
+        # we DO NOT want to absorb any ctxc ACK silently!
+        # if ctx._remote_error:
+        #     raise ctx._remote_error
+
+        # XXX NOTE: if no `ContextCancelled` has been responded
+        # back from the other side (yet), we raise a different
+        # runtime error indicating that this task's usage of
+        # `Context.cancel()` and then `.open_stream()` is WRONG!
+        task: str = trio.lowlevel.current_task().name
+        raise RuntimeError(
+            'Stream opened after `Context.cancel()` called..?\n'
+            f'task: {actor.uid[0]}:{task}\n'
+            f'{ctx}'
+        )
+
+    if (
+        not ctx._portal
+        and not ctx._started_called
+    ):
+        raise RuntimeError(
+            'Context.started()` must be called before opening a stream'
+        )
+
+    # NOTE: in one way streaming this only happens on the
+    # parent-ctx-task side (on the side that calls
+    # `Actor.start_remote_task()`) so if you try to send
+    # a stop from the caller to the callee in the
+    # single-direction-stream case you'll get a lookup error
+    # currently.
+    ctx: Context = actor.get_context(
+        chan=ctx.chan,
+        cid=ctx.cid,
+        nsf=ctx._nsf,
+        # side=ctx.side,
+
+        msg_buffer_size=msg_buffer_size,
+        allow_overruns=allow_overruns,
+    )
+    ctx._allow_overruns: bool = allow_overruns
+    assert ctx is ctx
+
+    # XXX: If the underlying channel feeder receive mem chan has
+    # been closed then likely client code has already exited
+    # a ``.open_stream()`` block prior or there was some other
+    # unanticipated error or cancellation from ``trio``.
+
+    if ctx._rx_chan._closed:
+        raise trio.ClosedResourceError(
+            'The underlying channel for this stream was already closed!\n'
+        )
+
+    # NOTE: implicitly this will call `MsgStream.aclose()` on
+    # `.__aexit__()` due to stream's parent `Channel` type!
+    #
+    # XXX NOTE XXX: ensures the stream is "one-shot use",
+    # which specifically means that on exit,
+    # - signal ``trio.EndOfChannel``/``StopAsyncIteration`` to
+    #   the far end indicating that the caller exited
+    #   the streaming context purposefully by letting
+    #   the exit block exec.
+    # - this is diff from the cancel/error case where
+    #   a cancel request from this side or an error
+    #   should be sent to the far end indicating the
+    #   stream WAS NOT just closed normally/gracefully.
+    async with MsgStream(
+        ctx=ctx,
+        rx_chan=ctx._rx_chan,
+    ) as stream:
+
+        # NOTE: we track all existing streams per portal for
+        # the purposes of attempting graceful closes on runtime
+        # cancel requests.
+        if ctx._portal:
+            ctx._portal._streams.add(stream)
+
+        try:
+            ctx._stream_opened: bool = True
+            ctx._stream = stream
+
+            # XXX: do we need this?
+            # ensure we aren't cancelled before yielding the stream
+            # await trio.lowlevel.checkpoint()
+            yield stream
+
+            # XXX: (MEGA IMPORTANT) if this is a root opened process we
+            # wait for any immediate child in debug before popping the
+            # context from the runtime msg loop otherwise inside
+            # ``Actor._deliver_ctx_payload()`` the msg will be discarded and in
+            # the case where that msg is global debugger unlock (via
+            # a "stop" msg for a stream), this can result in a deadlock
+            # where the root is waiting on the lock to clear but the
+            # child has already cleared it and clobbered IPC.
+            #
+            # await maybe_wait_for_debugger()
+
+            # XXX TODO: pretty sure this isn't needed (see
+            # note above this block) AND will result in
+            # a double `.send_stop()` call. The only reason to
+            # put it here would be to due with "order" in
+            # terms of raising any remote error (as per
+            # directly below) or bc the stream's
+            # `.__aexit__()` block might not get run
+            # (doubtful)? Either way if we did put this back
+            # in we also need a state var to avoid the double
+            # stop-msg send..
+            #
+            # await stream.aclose()
+
+        # NOTE: absorb and do not raise any
+        # EoC received from the other side such that
+        # it is not raised inside the surrounding
+        # context block's scope!
+        except trio.EndOfChannel as eoc:
+            if (
+                eoc
+                and
+                stream.closed
+            ):
+                # sanity, can remove?
+                assert eoc is stream._eoc
+
+                log.warning(
+                    'Stream was terminated by EoC\n\n'
+                    # NOTE: won't show the error <Type> but
+                    # does show txt followed by IPC msg.
+                    f'{str(eoc)}\n'
+                )
+
+        finally:
+            if ctx._portal:
+                try:
+                    ctx._portal._streams.remove(stream)
+                except KeyError:
+                    log.warning(
+                        f'Stream was already destroyed?\n'
+                        f'actor: {ctx.chan.uid}\n'
+                        f'ctx id: {ctx.cid}'
+                    )
+
+
 
 def stream(func: Callable) -> Callable:
     '''
@@ -541,7 +757,7 @@ def stream(func: Callable) -> Callable:
     '''
     # TODO: apply whatever solution ``mypy`` ends up picking for this:
     # https://github.com/python/mypy/issues/2087#issuecomment-769266912
-    func._tractor_stream_function = True  # type: ignore
+    func._tractor_stream_function: bool = True  # type: ignore
 
     sig = inspect.signature(func)
     params = sig.parameters

tractor/_supervise.py

@@ -80,15 +80,19 @@ class ActorNursery:
     '''
     def __init__(
         self,
+        # TODO: maybe def these as fields of a struct looking type?
         actor: Actor,
         ria_nursery: trio.Nursery,
         da_nursery: trio.Nursery,
         errors: dict[tuple[str, str], BaseException],
+
     ) -> None:
         # self.supervisor = supervisor  # TODO
         self._actor: Actor = actor
-        self._ria_nursery = ria_nursery
+
+        # TODO: rename to `._tn` for our conventional "task-nursery"
         self._da_nursery = da_nursery
+
         self._children: dict[
             tuple[str, str],
             tuple[
@@ -97,13 +101,12 @@ class ActorNursery:
                 Portal | None,
             ]
         ] = {}
-        # portals spawned with ``run_in_actor()`` are
-        # cancelled when their "main" result arrives
-        self._cancel_after_result_on_exit: set = set()
+
         self.cancelled: bool = False
         self._join_procs = trio.Event()
         self._at_least_one_child_in_debug: bool = False
         self.errors = errors
+        self._scope_error: BaseException|None = None
         self.exited = trio.Event()
 
         # NOTE: when no explicit call is made to
@@ -114,24 +117,43 @@ class ActorNursery:
         # and syncing purposes to any actor opened nurseries.
         self._implicit_runtime_started: bool = False
 
+        # TODO: remove the `.run_in_actor()` API and thus this 2ndary
+        # nursery when that API get's moved outside this primitive!
+        self._ria_nursery = ria_nursery
+        # portals spawned with ``run_in_actor()`` are
+        # cancelled when their "main" result arrives
+        self._cancel_after_result_on_exit: set = set()
+
     async def start_actor(
         self,
         name: str,
+
         *,
+
         bind_addrs: list[tuple[str, int]] = [_default_bind_addr],
         rpc_module_paths: list[str]|None = None,
         enable_modules: list[str]|None = None,
         loglevel: str|None = None,  # set log level per subactor
-        nursery: trio.Nursery|None = None,
         debug_mode: bool|None = None,
         infect_asyncio: bool = False,
+
+        # TODO: ideally we can rm this once we no longer have
+        # a `._ria_nursery` since the dependent APIs have been
+        # removed!
+        nursery: trio.Nursery|None = None,
+
     ) -> Portal:
         '''
         Start a (daemon) actor: an process that has no designated
         "main task" besides the runtime.
 
         '''
-        loglevel = loglevel or self._actor.loglevel or get_loglevel()
+        __runtimeframe__: int = 1  # noqa
+        loglevel: str = (
+            loglevel
+            or self._actor.loglevel
+            or get_loglevel()
+        )
 
         # configure and pass runtime state
         _rtv = _state._runtime_vars.copy()
@@ -184,6 +206,14 @@ class ActorNursery:
             )
         )
 
+    # TODO: DEPRECATE THIS:
+    # -[ ] impl instead as a hilevel wrapper on
+    #   top of a `@context` style invocation.
+    #  |_ dynamic @context decoration on child side
+    #  |_ implicit `Portal.open_context() as (ctx, first):`
+    #    and `return first` on parent side.
+    #  |_ mention how it's similar to `trio-parallel` API?
+    # -[ ] use @api_frame on the wrapper
     async def run_in_actor(
         self,
 
@@ -209,13 +239,14 @@ class ActorNursery:
         the actor is terminated.
 
         '''
+        __runtimeframe__: int = 1  # noqa
         mod_path: str = fn.__module__
 
         if name is None:
             # use the explicit function name if not provided
             name = fn.__name__
 
-        portal = await self.start_actor(
+        portal: Portal = await self.start_actor(
             name,
             enable_modules=[mod_path] + (
                 enable_modules or rpc_module_paths or []
@@ -244,19 +275,24 @@ class ActorNursery:
         )
         return portal
 
+    # @api_frame
     async def cancel(
         self,
         hard_kill: bool = False,
 
     ) -> None:
         '''
-        Cancel this nursery by instructing each subactor to cancel
-        itself and wait for all subactors to terminate.
+        Cancel this actor-nursery by instructing each subactor's
+        runtime to cancel and wait for all underlying sub-processes
+        to terminate.
 
-        If ``hard_killl`` is set to ``True`` then kill the processes
-        directly without any far end graceful ``trio`` cancellation.
+        If `hard_kill` is set then kill the processes directly using
+        the spawning-backend's API/OS-machinery without any attempt
+        at (graceful) `trio`-style cancellation using our
+        `Actor.cancel()`.
 
         '''
+        __runtimeframe__: int = 1  # noqa
         self.cancelled = True
 
         # TODO: impl a repr for spawn more compact
@@ -337,11 +373,15 @@ class ActorNursery:
 @acm
 async def _open_and_supervise_one_cancels_all_nursery(
     actor: Actor,
+    tb_hide: bool = False,
 
 ) -> typing.AsyncGenerator[ActorNursery, None]:
 
-    # TODO: yay or nay?
-    __tracebackhide__ = True
+    # normally don't need to show user by default
+    __tracebackhide__: bool = tb_hide
+
+    outer_err: BaseException|None = None
+    inner_err: BaseException|None = None
 
     # the collection of errors retreived from spawned sub-actors
     errors: dict[tuple[str, str], BaseException] = {}
@@ -351,7 +391,7 @@ async def _open_and_supervise_one_cancels_all_nursery(
     # handling errors that are generated by the inner nursery in
     # a supervisor strategy **before** blocking indefinitely to wait for
     # actors spawned in "daemon mode" (aka started using
-    # ``ActorNursery.start_actor()``).
+    # `ActorNursery.start_actor()`).
 
     # errors from this daemon actor nursery bubble up to caller
     async with trio.open_nursery() as da_nursery:
@@ -386,7 +426,8 @@ async def _open_and_supervise_one_cancels_all_nursery(
                     )
                     an._join_procs.set()
 
-                except BaseException as inner_err:
+                except BaseException as _inner_err:
+                    inner_err = _inner_err
                     errors[actor.uid] = inner_err
 
                     # If we error in the root but the debugger is
@@ -464,8 +505,10 @@ async def _open_and_supervise_one_cancels_all_nursery(
             Exception,
             BaseExceptionGroup,
             trio.Cancelled
+        ) as _outer_err:
+            outer_err = _outer_err
 
-        ) as err:
+            an._scope_error = outer_err or inner_err
 
             # XXX: yet another guard before allowing the cancel
             # sequence in case a (single) child is in debug.
@@ -480,7 +523,7 @@ async def _open_and_supervise_one_cancels_all_nursery(
             if an._children:
                 log.cancel(
                     'Actor-nursery cancelling due error type:\n'
-                    f'{err}\n'
+                    f'{outer_err}\n'
                 )
                 with trio.CancelScope(shield=True):
                     await an.cancel()
@@ -507,11 +550,19 @@ async def _open_and_supervise_one_cancels_all_nursery(
                 else:
                     raise list(errors.values())[0]
 
+            # show frame on any (likely) internal error
+            if (
+                not an.cancelled
+                and an._scope_error
+            ):
+                __tracebackhide__: bool = False
+
         # da_nursery scope end - nursery checkpoint
     # final exit
 
 
 @acm
+# @api_frame
 async def open_nursery(
     **kwargs,
 
@@ -531,6 +582,7 @@ async def open_nursery(
     which cancellation scopes correspond to each spawned subactor set.
 
     '''
+    __tracebackhide__: bool = True
     implicit_runtime: bool = False
     actor: Actor = current_actor(err_on_no_runtime=False)
     an: ActorNursery|None = None
@@ -581,13 +633,25 @@ async def open_nursery(
                 an.exited.set()
 
     finally:
+        # show frame on any internal runtime-scope error
+        if (
+            an
+            and not an.cancelled
+            and an._scope_error
+        ):
+            __tracebackhide__: bool = False
+
         msg: str = (
             'Actor-nursery exited\n'
             f'|_{an}\n'
         )
 
-        # shutdown runtime if it was started
         if implicit_runtime:
+            # shutdown runtime if it was started and report noisly
+            # that we're did so.
             msg += '=> Shutting down actor runtime <=\n'
+            log.info(msg)
 
-        log.info(msg)
+        else:
+            # keep noise low during std operation.
+            log.runtime(msg)

tractor/_testing/__init__.py

@@ -26,6 +26,9 @@ import tractor
 from .pytest import (
     tractor_test as tractor_test
 )
+from .fault_simulation import (
+    break_ipc as break_ipc,
+)
 
 
 def repodir() -> pathlib.Path:

tractor/_testing/fault_simulation.py

@@ -0,0 +1,92 @@
+# tractor: structured concurrent "actors".
+# Copyright 2018-eternity Tyler Goodlet.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+'''
+`pytest` utils helpers and plugins for testing `tractor`'s runtime
+and applications.
+
+'''
+
+from tractor import (
+    MsgStream,
+)
+
+async def break_ipc(
+    stream: MsgStream,
+    method: str|None = None,
+    pre_close: bool = False,
+
+    def_method: str = 'socket_close',
+
+) -> None:
+    '''
+    XXX: close the channel right after an error is raised
+    purposely breaking the IPC transport to make sure the parent
+    doesn't get stuck in debug or hang on the connection join.
+    this more or less simulates an infinite msg-receive hang on
+    the other end.
+
+    '''
+    # close channel via IPC prot msging before
+    # any transport breakage
+    if pre_close:
+        await stream.aclose()
+
+    method: str = method or def_method
+    print(
+        '#################################\n'
+        'Simulating CHILD-side IPC BREAK!\n'
+        f'method: {method}\n'
+        f'pre `.aclose()`: {pre_close}\n'
+        '#################################\n'
+    )
+
+    match method:
+        case 'socket_close':
+            await stream._ctx.chan.transport.stream.aclose()
+
+        case 'socket_eof':
+            # NOTE: `trio` does the following underneath this
+            # call in `src/trio/_highlevel_socket.py`:
+            # `Stream.socket.shutdown(tsocket.SHUT_WR)`
+            await stream._ctx.chan.transport.stream.send_eof()
+
+        # TODO: remove since now this will be invalid with our
+        # new typed msg spec?
+        # case 'msg':
+        #     await stream._ctx.chan.send(None)
+
+        # TODO: the actual real-world simulated cases like
+        # transport layer hangs and/or lower layer 2-gens type
+        # scenarios..
+        #
+        # -[ ] already have some issues for this general testing
+        # area:
+        #  - https://github.com/goodboy/tractor/issues/97
+        #  - https://github.com/goodboy/tractor/issues/124
+        #   - PR from @guille:
+        #     https://github.com/goodboy/tractor/pull/149
+        # case 'hang':
+        # TODO: framework research:
+        #
+        # - https://github.com/GuoTengda1993/pynetem
+        # - https://github.com/shopify/toxiproxy
+        # - https://manpages.ubuntu.com/manpages/trusty/man1/wirefilter.1.html
+
+        case _:
+            raise RuntimeError(
+                f'IPC break method unsupported: {method}'
+            )

tractor/devx/__init__.py

@@ -27,21 +27,23 @@ from ._debug import (
     pause as pause,
     pause_from_sync as pause_from_sync,
     shield_sigint_handler as shield_sigint_handler,
-    MultiActorPdb as MultiActorPdb,
     open_crash_handler as open_crash_handler,
     maybe_open_crash_handler as maybe_open_crash_handler,
+    maybe_init_greenback as maybe_init_greenback,
     post_mortem as post_mortem,
+    mk_pdb as mk_pdb,
 )
 from ._stackscope import (
     enable_stack_on_sig as enable_stack_on_sig,
 )
-# from .pformat import (
-#     add_div as add_div,
-#     pformat_caller_frame as pformat_caller_frame,
-#     pformat_boxed_tb as pformat_boxed_tb,
-# )
+from .pformat import (
+    add_div as add_div,
+    pformat_caller_frame as pformat_caller_frame,
+    pformat_boxed_tb as pformat_boxed_tb,
+)
 
 
+# TODO, move this to a new `.devx._pdbp` mod?
 def _enable_readline_feats() -> str:
     '''
     Handle `readline` when compiled with `libedit` to avoid breaking
@@ -73,5 +75,4 @@ def _enable_readline_feats() -> str:
         return 'readline'
 
 
-# TODO, move this to a new `.devx._pdbp` mod?
 _enable_readline_feats()

tractor/devx/_frame_stack.py

@@ -20,9 +20,8 @@ as it pertains to improving the grok-ability of our runtime!
 
 '''
 from __future__ import annotations
+from functools import partial
 import inspect
-# import msgspec
-# from pprint import pformat
 from types import (
     FrameType,
     FunctionType,
@@ -30,9 +29,8 @@ from types import (
     # CodeType,
 )
 from typing import (
-    # Any,
+    Any,
     Callable,
-    # TYPE_CHECKING,
     Type,
 )
 
@@ -40,6 +38,7 @@ from tractor.msg import (
     pretty_struct,
     NamespacePath,
 )
+import wrapt
 
 
 # TODO: yeah, i don't love this and we should prolly just
@@ -81,6 +80,31 @@ def get_class_from_frame(fr: FrameType) -> (
     return None
 
 
+def get_ns_and_func_from_frame(
+    frame: FrameType,
+) -> Callable:
+    '''
+    Return the corresponding function object reference from
+    a `FrameType`, and return it and it's parent namespace `dict`.
+
+    '''
+    ns: dict[str, Any]
+
+    # for a method, go up a frame and lookup the name in locals()
+    if '.' in (qualname := frame.f_code.co_qualname):
+        cls_name, _, func_name = qualname.partition('.')
+        ns = frame.f_back.f_locals[cls_name].__dict__
+
+    else:
+        func_name: str = frame.f_code.co_name
+        ns = frame.f_globals
+
+    return (
+        ns,
+        ns[func_name],
+    )
+
+
 def func_ref_from_frame(
     frame: FrameType,
 ) -> Callable:
@@ -96,34 +120,63 @@ def func_ref_from_frame(
             )
 
 
-# TODO: move all this into new `.devx._code`!
-# -[ ] prolly create a `@runtime_api` dec?
-# -[ ] ^- make it capture and/or accept buncha optional
-#     meta-data like a fancier version of `@pdbp.hideframe`.
-#
 class CallerInfo(pretty_struct.Struct):
-    rt_fi: inspect.FrameInfo
-    call_frame: FrameType
+    # https://docs.python.org/dev/reference/datamodel.html#frame-objects
+    # https://docs.python.org/dev/library/inspect.html#the-interpreter-stack
+    _api_frame: FrameType
 
     @property
-    def api_func_ref(self) -> Callable|None:
-        return func_ref_from_frame(self.rt_fi.frame)
+    def api_frame(self) -> FrameType:
+        try:
+            self._api_frame.clear()
+        except RuntimeError:
+            # log.warning(
+            print(
+                f'Frame {self._api_frame} for {self.api_func} is still active!'
+            )
+
+        return self._api_frame
+
+    _api_func: Callable
+
+    @property
+    def api_func(self) -> Callable:
+        return self._api_func
+
+    _caller_frames_up: int|None = 1
+    _caller_frame: FrameType|None = None  # cached after first stack scan
 
     @property
     def api_nsp(self) -> NamespacePath|None:
-        func: FunctionType = self.api_func_ref
+        func: FunctionType = self.api_func
         if func:
             return NamespacePath.from_ref(func)
 
         return '<unknown>'
 
     @property
-    def caller_func_ref(self) -> Callable|None:
-        return func_ref_from_frame(self.call_frame)
+    def caller_frame(self) -> FrameType:
+
+        # if not already cached, scan up stack explicitly by
+        # configured count.
+        if not self._caller_frame:
+            if self._caller_frames_up:
+                for _ in range(self._caller_frames_up):
+                    caller_frame: FrameType|None = self.api_frame.f_back
+
+                if not caller_frame:
+                    raise ValueError(
+                        'No frame exists {self._caller_frames_up} up from\n'
+                        f'{self.api_frame} @ {self.api_nsp}\n'
+                    )
+
+            self._caller_frame = caller_frame
+
+        return self._caller_frame
 
     @property
     def caller_nsp(self) -> NamespacePath|None:
-        func: FunctionType = self.caller_func_ref
+        func: FunctionType = self.api_func
         if func:
             return NamespacePath.from_ref(func)
 
@@ -170,8 +223,66 @@ def find_caller_info(
                 call_frame = call_frame.f_back
 
             return CallerInfo(
-                rt_fi=fi,
-                call_frame=call_frame,
+                _api_frame=rt_frame,
+                _api_func=func_ref_from_frame(rt_frame),
+                _caller_frames_up=go_up_iframes,
             )
 
     return None
+
+
+_frame2callerinfo_cache: dict[FrameType, CallerInfo] = {}
+
+
+# TODO: -[x] move all this into new `.devx._code`!
+# -[ ] consider rename to _callstack?
+# -[ ] prolly create a `@runtime_api` dec?
+#   |_ @api_frame seems better?
+# -[ ] ^- make it capture and/or accept buncha optional
+#     meta-data like a fancier version of `@pdbp.hideframe`.
+#
+def api_frame(
+    wrapped: Callable|None = None,
+    *,
+    caller_frames_up: int = 1,
+
+) -> Callable:
+
+    # handle the decorator called WITHOUT () case,
+    # i.e. just @api_frame, NOT @api_frame(extra=<blah>)
+    if wrapped is None:
+        return partial(
+            api_frame,
+            caller_frames_up=caller_frames_up,
+        )
+
+    @wrapt.decorator
+    async def wrapper(
+        wrapped: Callable,
+        instance: object,
+        args: tuple,
+        kwargs: dict,
+    ):
+        # maybe cache the API frame for this call
+        global _frame2callerinfo_cache
+        this_frame: FrameType = inspect.currentframe()
+        api_frame: FrameType = this_frame.f_back
+
+        if not _frame2callerinfo_cache.get(api_frame):
+            _frame2callerinfo_cache[api_frame] = CallerInfo(
+                _api_frame=api_frame,
+                _api_func=wrapped,
+                _caller_frames_up=caller_frames_up,
+            )
+
+        return wrapped(*args, **kwargs)
+
+    # annotate the function as a "api function", meaning it is
+    # a function for which the function above it in the call stack should be
+    # non-`tractor` code aka "user code".
+    #
+    # in the global frame cache for easy lookup from a given
+    # func-instance
+    wrapped._call_infos: dict[FrameType, CallerInfo] = _frame2callerinfo_cache
+    wrapped.__api_func__: bool = True
+    return wrapper(wrapped)

tractor/devx/pformat.py

@@ -0,0 +1,168 @@
+# tractor: structured concurrent "actors".
+# Copyright 2018-eternity Tyler Goodlet.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+'''
+Pretty formatters for use throughout the code base.
+Mostly handy for logging and exception message content.
+
+'''
+import textwrap
+import traceback
+
+from trio import CancelScope
+
+
+def add_div(
+    message: str,
+    div_str: str = '------ - ------',
+
+) -> str:
+    '''
+    Add a "divider string" to the input `message` with
+    a little math to center it underneath.
+
+    '''
+    div_offset: int = (
+        round(len(message)/2)+1
+        -
+        round(len(div_str)/2)+1
+    )
+    div_str: str = (
+        '\n' + ' '*div_offset + f'{div_str}\n'
+    )
+    return div_str
+
+
+def pformat_boxed_tb(
+    tb_str: str,
+    fields_str: str|None = None,
+    field_prefix: str = ' |_',
+
+    tb_box_indent: int|None = None,
+    tb_body_indent: int = 1,
+
+) -> str:
+    '''
+    Create a "boxed" looking traceback string.
+
+    Useful for emphasizing traceback text content as being an
+    embedded attribute of some other object (like
+    a `RemoteActorError` or other boxing remote error shuttle
+    container).
+
+    Any other parent/container "fields" can be passed in the
+    `fields_str` input along with other prefix/indent settings.
+
+    '''
+    if (
+        fields_str
+        and
+        field_prefix
+    ):
+        fields: str = textwrap.indent(
+            fields_str,
+            prefix=field_prefix,
+        )
+    else:
+        fields = fields_str or ''
+
+    tb_body = tb_str
+    if tb_body_indent:
+        tb_body: str = textwrap.indent(
+            tb_str,
+            prefix=tb_body_indent * ' ',
+        )
+
+    tb_box: str = (
+        f'|\n'
+        f' ------ - ------\n'
+        f'{tb_body}'
+        f' ------ - ------\n'
+        f'_|\n'
+    )
+    tb_box_indent: str = (
+        tb_box_indent
+        or
+        1
+
+        # (len(field_prefix))
+        # ? ^-TODO-^ ? if you wanted another indent level
+    )
+    if tb_box_indent > 0:
+        tb_box: str = textwrap.indent(
+            tb_box,
+            prefix=tb_box_indent * ' ',
+        )
+
+    return (
+        fields
+        +
+        tb_box
+    )
+
+
+def pformat_caller_frame(
+    stack_limit: int = 1,
+    box_tb: bool = True,
+) -> str:
+    '''
+    Capture and return the traceback text content from
+    `stack_limit` call frames up.
+
+    '''
+    tb_str: str = (
+        '\n'.join(
+            traceback.format_stack(limit=stack_limit)
+        )
+    )
+    if box_tb:
+        tb_str: str = pformat_boxed_tb(
+            tb_str=tb_str,
+            field_prefix='  ',
+            indent='',
+        )
+    return tb_str
+
+
+def pformat_cs(
+    cs: CancelScope,
+    var_name: str = 'cs',
+    field_prefix: str = ' |_',
+) -> str:
+    '''
+    Pretty format info about a `trio.CancelScope` including most
+    of its public state and `._cancel_status`.
+
+    The output can be modified to show a "var name" for the
+    instance as a field prefix, just a simple str before each
+    line more or less.
+
+    '''
+
+    fields: str = textwrap.indent(
+        (
+            f'cancel_called = {cs.cancel_called}\n'
+            f'cancelled_caught = {cs.cancelled_caught}\n'
+            f'_cancel_status = {cs._cancel_status}\n'
+            f'shield = {cs.shield}\n'
+        ),
+        prefix=field_prefix,
+    )
+    return (
+        f'{var_name}: {cs}\n'
+        +
+        fields
+    )

tractor/log.py

@@ -54,11 +54,12 @@ LOG_FORMAT = (
 DATE_FORMAT = '%b %d %H:%M:%S'
 
 # FYI, ERROR is 40
+# TODO: use a `bidict` to avoid the :155 check?
 CUSTOM_LEVELS: dict[str, int] = {
     'TRANSPORT': 5,
     'RUNTIME': 15,
     'DEVX': 17,
-    'CANCEL': 18,
+    'CANCEL': 22,
     'PDB': 500,
 }
 STD_PALETTE = {
@@ -147,6 +148,8 @@ class StackLevelAdapter(LoggerAdapter):
         Delegate a log call to the underlying logger, after adding
         contextual information from this adapter instance.
 
+        NOTE: all custom level methods (above) delegate to this!
+
         '''
         if self.isEnabledFor(level):
             stacklevel: int = 3

tractor/msg/__init__.py

@@ -18,9 +18,56 @@
 Built-in messaging patterns, types, APIs and helpers.
 
 '''
+from typing import (
+    TypeAlias,
+)
 from .ptr import (
     NamespacePath as NamespacePath,
 )
-from .types import (
+from .pretty_struct import (
     Struct as Struct,
 )
+from ._codec import (
+    _def_msgspec_codec as _def_msgspec_codec,
+    _ctxvar_MsgCodec as _ctxvar_MsgCodec,
+
+    apply_codec as apply_codec,
+    mk_codec as mk_codec,
+    MsgCodec as MsgCodec,
+    MsgDec as MsgDec,
+    current_codec as current_codec,
+)
+# currently can't bc circular with `._context`
+# from ._ops import (
+#     PldRx as PldRx,
+#     _drain_to_final_msg as _drain_to_final_msg,
+# )
+
+from .types import (
+    PayloadMsg as PayloadMsg,
+
+    Aid as Aid,
+    SpawnSpec as SpawnSpec,
+
+    Start as Start,
+    StartAck as StartAck,
+
+    Started as Started,
+    Yield as Yield,
+    Stop as Stop,
+    Return as Return,
+    CancelAck as CancelAck,
+
+    Error as Error,
+
+    # type-var for `.pld` field
+    PayloadT as PayloadT,
+
+    # full msg class set from above as list
+    __msg_types__ as __msg_types__,
+
+    # type-alias for union of all msgs
+    MsgType as MsgType,
+)
+
+__msg_spec__: TypeAlias = MsgType

tractor/msg/_codec.py

@@ -0,0 +1,660 @@
+# tractor: structured concurrent "actors".
+# Copyright 2018-eternity Tyler Goodlet.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+'''
+IPC msg interchange codec management.
+
+Supported backend libs:
+- `msgspec.msgpack`
+
+ToDo: backends we prolly should offer:
+
+- see project/lib list throughout GH issue discussion comments:
+  https://github.com/goodboy/tractor/issues/196
+
+- `capnproto`: https://capnproto.org/rpc.html
+   - https://capnproto.org/language.html#language-reference
+
+'''
+from __future__ import annotations
+from contextlib import (
+    contextmanager as cm,
+)
+from contextvars import (
+    ContextVar,
+    Token,
+)
+import textwrap
+from typing import (
+    Any,
+    Callable,
+    Type,
+    TYPE_CHECKING,
+    Union,
+)
+from types import ModuleType
+
+import msgspec
+from msgspec import (
+    msgpack,
+    Raw,
+)
+# TODO: see notes below from @mikenerone..
+# from tricycle import TreeVar
+
+from tractor.msg.pretty_struct import Struct
+from tractor.msg.types import (
+    mk_msg_spec,
+    MsgType,
+)
+from tractor.log import get_logger
+
+if TYPE_CHECKING:
+    from tractor._context import Context
+
+log = get_logger(__name__)
+
+
+# TODO: unify with `MsgCodec` by making `._dec` part this?
+class MsgDec(Struct):
+    '''
+    An IPC msg (payload) decoder.
+
+    Normally used to decode only a payload: `MsgType.pld:
+    PayloadT` field before delivery to IPC consumer code.
+
+    '''
+    _dec: msgpack.Decoder
+
+    @property
+    def dec(self) -> msgpack.Decoder:
+        return self._dec
+
+    def __repr__(self) -> str:
+
+        speclines: str = self.spec_str
+
+        # in multi-typed spec case we stick the list
+        # all on newlines after the |__pld_spec__:,
+        # OW it's prolly single type spec-value
+        # so just leave it on same line.
+        if '\n' in speclines:
+            speclines: str = '\n' + textwrap.indent(
+                speclines,
+                prefix=' '*3,
+            )
+
+        body: str = textwrap.indent(
+            f'|_dec_hook: {self.dec.dec_hook}\n'
+            f'|__pld_spec__: {speclines}\n',
+            prefix=' '*2,
+        )
+        return (
+            f'<{type(self).__name__}(\n'
+            f'{body}'
+            ')>'
+        )
+
+    # struct type unions
+    # https://jcristharif.com/msgspec/structs.html#tagged-unions
+    #
+    # ^-TODO-^: make a wrapper type for this such that alt
+    # backends can be represented easily without a `Union` needed,
+    # AND so that we have better support for wire transport.
+    #
+    # -[ ] maybe `FieldSpec` is a good name since msg-spec
+    #   better applies to a `MsgType[FieldSpec]`?
+    #
+    # -[ ] both as part of the `.open_context()` call AND as part of the
+    #     immediate ack-reponse (see similar below)
+    #     we should do spec matching and fail if anything is awry?
+    #
+    # -[ ] eventually spec should be generated/parsed from the
+    #     type-annots as # desired in GH issue:
+    #     https://github.com/goodboy/tractor/issues/365
+    #
+    # -[ ] semantics of the mismatch case
+    #   - when caller-callee specs we should raise
+    #    a `MsgTypeError` or `MsgSpecError` or similar?
+    #
+    # -[ ] wrapper types for both spec types such that we can easily
+    #     IPC transport them?
+    #     - `TypeSpec: Union[Type]`
+    #      * also a `.__contains__()` for doing `None in
+    #      TypeSpec[None|int]` since rn you need to do it on
+    #      `.__args__` for unions..
+    #     - `MsgSpec: Union[MsgType]
+    #
+    # -[ ] auto-genning this from new (in 3.12) type parameter lists Bo
+    # |_ https://docs.python.org/3/reference/compound_stmts.html#type-params
+    # |_ historical pep 695: https://peps.python.org/pep-0695/
+    # |_ full lang spec: https://typing.readthedocs.io/en/latest/spec/
+    # |_ on annotation scopes:
+    #    https://docs.python.org/3/reference/executionmodel.html#annotation-scopes
+    # |_ 3.13 will have subscriptable funcs Bo
+    #    https://peps.python.org/pep-0718/
+    @property
+    def spec(self) -> Union[Type[Struct]]:
+        # NOTE: defined and applied inside `mk_codec()`
+        return self._dec.type
+
+    # no difference, as compared to a `MsgCodec` which defines the
+    # `MsgType.pld: PayloadT` part of its spec separately
+    pld_spec = spec
+
+    # TODO: would get moved into `FieldSpec.__str__()` right?
+    @property
+    def spec_str(self) -> str:
+        return pformat_msgspec(
+            codec=self,
+            join_char='|',
+        )
+
+    pld_spec_str = spec_str
+
+    def decode(
+        self,
+        raw: Raw|bytes,
+    ) -> Any:
+        return self._dec.decode(raw)
+
+    @property
+    def hook(self) -> Callable|None:
+        return self._dec.dec_hook
+
+
+def mk_dec(
+    spec: Union[Type[Struct]]|Any = Any,
+    dec_hook: Callable|None = None,
+
+) -> MsgDec:
+
+    return MsgDec(
+        _dec=msgpack.Decoder(
+            type=spec,  # like `MsgType[Any]`
+            dec_hook=dec_hook,
+        )
+    )
+
+
+def mk_msgspec_table(
+    dec: msgpack.Decoder,
+    msg: MsgType|None = None,
+
+) -> dict[str, MsgType]|str:
+    '''
+    Fill out a `dict` of `MsgType`s keyed by name
+    for a given input `msgspec.msgpack.Decoder`
+    as defined by its `.type: Union[Type]` setting.
+
+    If `msg` is provided, only deliver a `dict` with a single
+    entry for that type.
+
+    '''
+    msgspec: Union[Type]|Type = dec.type
+
+    if not (msgtypes := getattr(msgspec, '__args__', False)):
+        msgtypes = [msgspec]
+
+    msgt_table: dict[str, MsgType] = {
+        msgt: str(msgt.__name__)
+        for msgt in msgtypes
+    }
+    if msg:
+        msgt: MsgType = type(msg)
+        str_repr: str = msgt_table[msgt]
+        return {msgt: str_repr}
+
+    return msgt_table
+
+
+def pformat_msgspec(
+    codec: MsgCodec|MsgDec,
+    msg: MsgType|None = None,
+    join_char: str = '\n',
+
+) -> str:
+    dec: msgpack.Decoder = getattr(codec, 'dec', codec)
+    return join_char.join(
+        mk_msgspec_table(
+            dec=dec,
+            msg=msg,
+        ).values()
+    )
+
+# TODO: overall IPC msg-spec features (i.e. in this mod)!
+#
+# -[ ] API changes towards being interchange lib agnostic!
+#   -[ ] capnproto has pre-compiled schema for eg..
+#    * https://capnproto.org/language.html
+#    * http://capnproto.github.io/pycapnp/quickstart.html
+#     * https://github.com/capnproto/pycapnp/blob/master/examples/addressbook.capnp
+#
+# -[ ] struct aware messaging coders as per:
+#   -[x] https://github.com/goodboy/tractor/issues/36
+#   -[ ] https://github.com/goodboy/tractor/issues/196
+#   -[ ] https://github.com/goodboy/tractor/issues/365
+#
+class MsgCodec(Struct):
+    '''
+    A IPC msg interchange format lib's encoder + decoder pair.
+
+    Pretty much nothing more then delegation to underlying
+    `msgspec.<interchange-protocol>.Encoder/Decoder`s for now.
+
+    '''
+    _enc: msgpack.Encoder
+    _dec: msgpack.Decoder
+    _pld_spec: Type[Struct]|Raw|Any
+
+    def __repr__(self) -> str:
+        speclines: str = textwrap.indent(
+            pformat_msgspec(codec=self),
+            prefix=' '*3,
+        )
+        body: str = textwrap.indent(
+            f'|_lib = {self.lib.__name__!r}\n'
+            f'|_enc_hook: {self.enc.enc_hook}\n'
+            f'|_dec_hook: {self.dec.dec_hook}\n'
+            f'|_pld_spec: {self.pld_spec_str}\n'
+            # f'|\n'
+            f'|__msg_spec__:\n'
+            f'{speclines}\n',
+            prefix=' '*2,
+        )
+        return (
+            f'<{type(self).__name__}(\n'
+            f'{body}'
+            ')>'
+        )
+
+    @property
+    def pld_spec(self) -> Type[Struct]|Raw|Any:
+        return self._pld_spec
+
+    @property
+    def pld_spec_str(self) -> str:
+
+        # TODO: could also use match: instead?
+        spec: Union[Type]|Type = self.pld_spec
+
+        # `typing.Union` case
+        if getattr(spec, '__args__', False):
+            return str(spec)
+
+        # just a single type
+        else:
+            return spec.__name__
+
+    # struct type unions
+    # https://jcristharif.com/msgspec/structs.html#tagged-unions
+    @property
+    def msg_spec(self) -> Union[Type[Struct]]:
+        # NOTE: defined and applied inside `mk_codec()`
+        return self._dec.type
+
+    # TODO: some way to make `pretty_struct.Struct` use this
+    # wrapped field over the `.msg_spec` one?
+    @property
+    def msg_spec_str(self) -> str:
+        return pformat_msgspec(self.msg_spec)
+
+    lib: ModuleType = msgspec
+
+    # TODO: use `functools.cached_property` for these ?
+    # https://docs.python.org/3/library/functools.html#functools.cached_property
+    @property
+    def enc(self) -> msgpack.Encoder:
+        return self._enc
+
+    # TODO: reusing encode buffer for perf?
+    # https://jcristharif.com/msgspec/perf-tips.html#reusing-an-output-buffer
+    _buf: bytearray = bytearray()
+
+    def encode(
+        self,
+        py_obj: Any,
+
+        use_buf: bool = False,
+        # ^-XXX-^ uhh why am i getting this?
+        # |_BufferError: Existing exports of data: object cannot be re-sized
+
+    ) -> bytes:
+        '''
+        Encode input python objects to `msgpack` bytes for
+        transfer on a tranport protocol connection.
+
+        When `use_buf == True` use the output buffer optimization:
+        https://jcristharif.com/msgspec/perf-tips.html#reusing-an-output-buffer
+
+        '''
+        if use_buf:
+            self._enc.encode_into(py_obj, self._buf)
+            return self._buf
+        else:
+            return self._enc.encode(py_obj)
+
+    @property
+    def dec(self) -> msgpack.Decoder:
+        return self._dec
+
+    def decode(
+        self,
+        msg: bytes,
+    ) -> Any:
+        '''
+        Decode received `msgpack` bytes into a local python object
+        with special `msgspec.Struct` (or other type) handling
+        determined by the 
+
+        '''
+        # https://jcristharif.com/msgspec/usage.html#typed-decoding
+        return self._dec.decode(msg)
+
+
+# [x] TODO: a sub-decoder system as well? => No!
+#
+# -[x] do we still want to try and support the sub-decoder with
+# `.Raw` technique in the case that the `Generic` approach gives
+# future grief?
+# => NO, since we went with the `PldRx` approach instead B)
+#
+# IF however you want to see the code that was staged for this
+# from wayyy back, see the pure removal commit.
+
+
+def mk_codec(
+    # struct type unions set for `Decoder`
+    # https://jcristharif.com/msgspec/structs.html#tagged-unions
+    ipc_pld_spec: Union[Type[Struct]]|Any = Any,
+
+    # TODO: offering a per-msg(-field) type-spec such that
+    # the fields can be dynamically NOT decoded and left as `Raw`
+    # values which are later loaded by a sub-decoder specified
+    # by `tag_field: str` value key?
+    # payload_msg_specs: dict[
+    #     str,  # tag_field value as sub-decoder key
+    #     Union[Type[Struct]]  # `MsgType.pld` type spec
+    # ]|None = None,
+
+    libname: str = 'msgspec',
+
+    # proxy as `Struct(**kwargs)` for ad-hoc type extensions
+    # https://jcristharif.com/msgspec/extending.html#mapping-to-from-native-types
+    # ------ - ------
+    dec_hook: Callable|None = None,
+    enc_hook: Callable|None = None,
+    # ------ - ------
+    #
+    # Encoder:
+    # write_buffer_size=write_buffer_size,
+    #
+    # Decoder:
+    # ext_hook: ext_hook_sig
+
+) -> MsgCodec:
+    '''
+    Convenience factory for creating codecs eventually meant
+    to be interchange lib agnostic (i.e. once we support more then just
+    `msgspec` ;).
+
+    '''
+    # (manually) generate a msg-payload-spec for all relevant
+    # god-boxing-msg subtypes, parameterizing the `PayloadMsg.pld: PayloadT`
+    # for the decoder such that all sub-type msgs in our SCIPP
+    # will automatically decode to a type-"limited" payload (`Struct`)
+    # object (set).
+    (
+        ipc_msg_spec,
+        msg_types,
+    ) = mk_msg_spec(
+        payload_type_union=ipc_pld_spec,
+    )
+    assert len(ipc_msg_spec.__args__) == len(msg_types)
+    assert ipc_msg_spec
+
+    # TODO: use this shim instead?
+    # bc.. unification, err somethin?
+    # dec: MsgDec = mk_dec(
+    #     spec=ipc_msg_spec,
+    #     dec_hook=dec_hook,
+    # )
+
+    dec = msgpack.Decoder(
+        type=ipc_msg_spec,
+        dec_hook=dec_hook,
+    )
+    enc = msgpack.Encoder(
+       enc_hook=enc_hook,
+    )
+
+    codec = MsgCodec(
+        _enc=enc,
+        _dec=dec,
+        _pld_spec=ipc_pld_spec,
+    )
+
+    # sanity on expected backend support
+    assert codec.lib.__name__ == libname
+
+    return codec
+
+
+# instance of the default `msgspec.msgpack` codec settings, i.e.
+# no custom structs, hooks or other special types.
+_def_msgspec_codec: MsgCodec = mk_codec(ipc_pld_spec=Any)
+
+# The built-in IPC `Msg` spec.
+# Our composing "shuttle" protocol which allows `tractor`-app code
+# to use any `msgspec` supported type as the `PayloadMsg.pld` payload,
+# https://jcristharif.com/msgspec/supported-types.html
+#
+_def_tractor_codec: MsgCodec = mk_codec(
+    # TODO: use this for debug mode locking prot?
+    # ipc_pld_spec=Any,
+    ipc_pld_spec=Raw,
+)
+# TODO: IDEALLY provides for per-`trio.Task` specificity of the
+# IPC msging codec used by the transport layer when doing
+# `Channel.send()/.recv()` of wire data.
+
+# ContextVar-TODO: DIDN'T WORK, kept resetting in every new task to default!?
+# _ctxvar_MsgCodec: ContextVar[MsgCodec] = ContextVar(
+
+# TreeVar-TODO: DIDN'T WORK, kept resetting in every new embedded nursery
+# even though it's supposed to inherit from a parent context ???
+#
+# _ctxvar_MsgCodec: TreeVar[MsgCodec] = TreeVar(
+#
+# ^-NOTE-^: for this to work see the mods by @mikenerone from `trio` gitter:
+#
+# 22:02:54 <mikenerone> even for regular contextvars, all you have to do is:
+#    `task: Task = trio.lowlevel.current_task()`
+#    `task.parent_nursery.parent_task.context.run(my_ctx_var.set, new_value)`
+#
+# From a comment in his prop code he couldn't share outright:
+# 1. For every TreeVar set in the current task (which covers what
+#    we need from SynchronizerFacade), walk up the tree until the
+#    root or finding one where the TreeVar is already set, setting
+#    it in all of the contexts along the way.
+# 2. For each of those, we also forcibly set the values that are
+#    pending for child nurseries that have not yet accessed the
+#    TreeVar.
+# 3. We similarly set the pending values for the child nurseries
+#    of the *current* task.
+#
+_ctxvar_MsgCodec: ContextVar[MsgCodec] = ContextVar(
+    'msgspec_codec',
+    default=_def_tractor_codec,
+)
+
+
+@cm
+def apply_codec(
+    codec: MsgCodec,
+
+    ctx: Context|None = None,
+
+) -> MsgCodec:
+    '''
+    Dynamically apply a `MsgCodec` to the current task's runtime
+    context such that all (of a certain class of payload
+    containing i.e. `MsgType.pld: PayloadT`) IPC msgs are
+    processed with it for that task.
+
+    Uses a `contextvars.ContextVar` to ensure the scope of any
+    codec setting matches the current `Context` or
+    `._rpc.process_messages()` feeder task's prior setting without
+    mutating any surrounding scope.
+
+    When a `ctx` is supplied, only mod its `Context.pld_codec`.
+
+    matches the `@cm` block and DOES NOT change to the original
+    (default) value in new tasks (as it does for `ContextVar`).
+
+    '''
+    __tracebackhide__: bool = True
+
+    if ctx is not None:
+        var: ContextVar = ctx._var_pld_codec
+    else:
+        # use IPC channel-connection "global" codec
+        var: ContextVar = _ctxvar_MsgCodec
+
+    orig: MsgCodec = var.get()
+
+    assert orig is not codec
+    if codec.pld_spec is None:
+        breakpoint()
+
+    log.info(
+        'Applying new msg-spec codec\n\n'
+        f'{codec}\n'
+    )
+    token: Token = var.set(codec)
+
+    # ?TODO? for TreeVar approach which copies from the
+    # cancel-scope of the prior value, NOT the prior task
+    # See the docs:
+    # - https://tricycle.readthedocs.io/en/latest/reference.html#tree-variables
+    # - https://github.com/oremanj/tricycle/blob/master/tricycle/_tests/test_tree_var.py
+    #   ^- see docs for @cm `.being()` API
+    # with _ctxvar_MsgCodec.being(codec):
+    #     new = _ctxvar_MsgCodec.get()
+    #     assert new is codec
+    #     yield codec
+
+    try:
+        yield var.get()
+    finally:
+        var.reset(token)
+        log.info(
+            'Reverted to last msg-spec codec\n\n'
+            f'{orig}\n'
+        )
+        assert var.get() is orig
+
+
+def current_codec() -> MsgCodec:
+    '''
+    Return the current `trio.Task.context`'s value
+    for `msgspec_codec` used by `Channel.send/.recv()`
+    for wire serialization.
+
+    '''
+    return _ctxvar_MsgCodec.get()
+
+
+@cm
+def limit_msg_spec(
+    payload_spec: Union[Type[Struct]],
+
+    # TODO: don't need this approach right?
+    # -> related to the `MsgCodec._payload_decs` stuff above..
+    # tagged_structs: list[Struct]|None = None,
+
+    **codec_kwargs,
+
+) -> MsgCodec:
+    '''
+    Apply a `MsgCodec` that will natively decode the SC-msg set's
+    `PayloadMsg.pld: Union[Type[Struct]]` payload fields using
+    tagged-unions of `msgspec.Struct`s from the `payload_types`
+    for all IPC contexts in use by the current `trio.Task`.
+
+    '''
+    __tracebackhide__: bool = True
+    curr_codec: MsgCodec = current_codec()
+    msgspec_codec: MsgCodec = mk_codec(
+        ipc_pld_spec=payload_spec,
+        **codec_kwargs,
+    )
+    with apply_codec(msgspec_codec) as applied_codec:
+        assert applied_codec is msgspec_codec
+        yield msgspec_codec
+
+    assert curr_codec is current_codec()
+
+
+# XXX: msgspec won't allow this with non-struct custom types
+# like `NamespacePath`!@!
+# @cm
+# def extend_msg_spec(
+#     payload_spec: Union[Type[Struct]],
+
+# ) -> MsgCodec:
+#     '''
+#     Extend the current `MsgCodec.pld_spec` (type set) by extending
+#     the payload spec to **include** the types specified by
+#     `payload_spec`.
+
+#     '''
+#     codec: MsgCodec = current_codec()
+#     pld_spec: Union[Type] = codec.pld_spec
+#     extended_spec: Union[Type] = pld_spec|payload_spec
+
+#     with limit_msg_spec(payload_types=extended_spec) as ext_codec:
+#         # import pdbp; pdbp.set_trace()
+#         assert ext_codec.pld_spec == extended_spec
+#         yield ext_codec
+
+
+# TODO: make something similar to this inside `._codec` such that
+# user can just pass a type table of some sort?
+# -[ ] we would need to decode all msgs to `pretty_struct.Struct`
+#     and then call `.to_dict()` on them?
+# -[x] we're going to need to re-impl all the stuff changed in the
+#    runtime port such that it can handle dicts or `Msg`s?
+#
+# def mk_dict_msg_codec_hooks() -> tuple[Callable, Callable]:
+#     '''
+#     Deliver a `enc_hook()`/`dec_hook()` pair which does
+#     manual convertion from our above native `Msg` set
+#     to `dict` equivalent (wire msgs) in order to keep legacy compat
+#     with the original runtime implementation.
+#
+#     Note: this is is/was primarly used while moving the core
+#     runtime over to using native `Msg`-struct types wherein we
+#     start with the send side emitting without loading
+#     a typed-decoder and then later flipping the switch over to
+#     load to the native struct types once all runtime usage has
+#     been adjusted appropriately.
+#
+#     '''
+#     return (
+#         # enc_to_dict,
+#         dec_from_dict,
+#     )

tractor/msg/_ops.py

@@ -0,0 +1,842 @@
+# tractor: structured concurrent "actors".
+# Copyright 2018-eternity Tyler Goodlet.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+'''
+Near-application abstractions for `MsgType.pld: PayloadT|Raw`
+delivery, filtering and type checking as well as generic
+operational helpers for processing transaction flows.
+
+'''
+from __future__ import annotations
+from contextlib import (
+    asynccontextmanager as acm,
+    contextmanager as cm,
+)
+from typing import (
+    Any,
+    Callable,
+    Type,
+    TYPE_CHECKING,
+    Union,
+)
+# ------ - ------
+from msgspec import (
+    msgpack,
+    Raw,
+    Struct,
+    ValidationError,
+)
+import trio
+# ------ - ------
+from tractor.log import get_logger
+from tractor._exceptions import (
+    MessagingError,
+    InternalError,
+    _raise_from_unexpected_msg,
+    MsgTypeError,
+    _mk_recv_mte,
+    pack_error,
+)
+from tractor._state import current_ipc_ctx
+from ._codec import (
+    mk_dec,
+    MsgDec,
+    MsgCodec,
+    current_codec,
+)
+from .types import (
+    CancelAck,
+    Error,
+    MsgType,
+    PayloadT,
+    Return,
+    Started,
+    Stop,
+    Yield,
+    pretty_struct,
+)
+
+
+if TYPE_CHECKING:
+    from tractor._context import Context
+    from tractor._streaming import MsgStream
+
+
+log = get_logger(__name__)
+
+
+_def_any_pldec: MsgDec[Any] = mk_dec()
+
+
+class PldRx(Struct):
+    '''
+    A "msg payload receiver".
+
+    The pairing of a "feeder" `trio.abc.ReceiveChannel` and an
+    interchange-specific (eg. msgpack) payload field decoder. The
+    validation/type-filtering rules are runtime mutable and allow
+    type constraining the set of `MsgType.pld: Raw|PayloadT`
+    values at runtime, per IPC task-context.
+
+    This abstraction, being just below "user application code",
+    allows for the equivalent of our `MsgCodec` (used for
+    typer-filtering IPC dialog protocol msgs against a msg-spec)
+    but with granular control around payload delivery (i.e. the
+    data-values user code actually sees and uses (the blobs that
+    are "shuttled" by the wrapping dialog prot) such that invalid
+    `.pld: Raw` can be decoded and handled by IPC-primitive user
+    code (i.e. that operates on `Context` and `Msgstream` APIs)
+    without knowledge of the lower level `Channel`/`MsgTransport`
+    primitives nor the `MsgCodec` in use. Further, lazily decoding
+    payload blobs allows for topical (and maybe intentionally
+    "partial") encryption of msg field subsets.
+
+    '''
+    # TODO: better to bind it here?
+    # _rx_mc: trio.MemoryReceiveChannel
+    _pld_dec: MsgDec
+    _ctx: Context|None = None
+    _ipc: Context|MsgStream|None = None
+
+    @property
+    def pld_dec(self) -> MsgDec:
+        return self._pld_dec
+
+    # TODO: a better name?
+    # -[ ] when would this be used as it avoids needingn to pass the
+    #   ipc prim to every method
+    @cm
+    def wraps_ipc(
+        self,
+        ipc_prim: Context|MsgStream,
+
+    ) -> PldRx:
+        '''
+        Apply this payload receiver to an IPC primitive type, one
+        of `Context` or `MsgStream`.
+
+        '''
+        self._ipc = ipc_prim
+        try:
+            yield self
+        finally:
+            self._ipc = None
+
+    @cm
+    def limit_plds(
+        self,
+        spec: Union[Type[Struct]],
+        **dec_kwargs,
+
+    ) -> MsgDec:
+        '''
+        Type-limit the loadable msg payloads via an applied
+        `MsgDec` given an input spec, revert to prior decoder on
+        exit.
+
+        '''
+        orig_dec: MsgDec = self._pld_dec
+        limit_dec: MsgDec = mk_dec(
+            spec=spec,
+            **dec_kwargs,
+        )
+        try:
+            self._pld_dec = limit_dec
+            yield limit_dec
+        finally:
+            self._pld_dec = orig_dec
+
+    @property
+    def dec(self) -> msgpack.Decoder:
+        return self._pld_dec.dec
+
+    def recv_pld_nowait(
+        self,
+        # TODO: make this `MsgStream` compat as well, see above^
+        # ipc_prim: Context|MsgStream,
+        ipc: Context|MsgStream,
+
+        ipc_msg: MsgType|None = None,
+        expect_msg: Type[MsgType]|None = None,
+        hide_tb: bool = False,
+        **dec_pld_kwargs,
+
+    ) -> Any|Raw:
+        __tracebackhide__: bool = hide_tb
+
+        msg: MsgType = (
+            ipc_msg
+            or
+
+            # sync-rx msg from underlying IPC feeder (mem-)chan
+            ipc._rx_chan.receive_nowait()
+        )
+        return self.decode_pld(
+            msg,
+            ipc=ipc,
+            expect_msg=expect_msg,
+            hide_tb=hide_tb,
+            **dec_pld_kwargs,
+        )
+
+    async def recv_pld(
+        self,
+        ipc: Context|MsgStream,
+        ipc_msg: MsgType|None = None,
+        expect_msg: Type[MsgType]|None = None,
+        hide_tb: bool = True,
+
+        **dec_pld_kwargs,
+
+    ) -> Any|Raw:
+        '''
+        Receive a `MsgType`, then decode and return its `.pld` field.
+
+        '''
+        __tracebackhide__: bool = hide_tb
+        msg: MsgType = (
+            ipc_msg
+            or
+            # async-rx msg from underlying IPC feeder (mem-)chan
+            await ipc._rx_chan.receive()
+        )
+        return self.decode_pld(
+            msg=msg,
+            ipc=ipc,
+            expect_msg=expect_msg,
+            **dec_pld_kwargs,
+        )
+
+    def decode_pld(
+        self,
+        msg: MsgType,
+        ipc: Context|MsgStream,
+        expect_msg: Type[MsgType]|None,
+
+        raise_error: bool = True,
+        hide_tb: bool = True,
+
+        # XXX for special (default?) case of send side call with
+        # `Context.started(validate_pld_spec=True)`
+        is_started_send_side: bool = False,
+
+    ) -> PayloadT|Raw:
+        '''
+        Decode a msg's payload field: `MsgType.pld: PayloadT|Raw` and
+        return the value or raise an appropriate error.
+
+        '''
+        __tracebackhide__: bool = hide_tb
+        src_err: BaseException|None = None
+        match msg:
+            # payload-data shuttle msg; deliver the `.pld` value
+            # directly to IPC (primitive) client-consumer code.
+            case (
+                Started(pld=pld)  # sync phase
+                |Yield(pld=pld)  # streaming phase
+                |Return(pld=pld)  # termination phase
+            ):
+                try:
+                    pld: PayloadT = self._pld_dec.decode(pld)
+                    log.runtime(
+                        'Decoded msg payload\n\n'
+                        f'{msg}\n'
+                        f'where payload decoded as\n'
+                        f'|_pld={pld!r}\n'
+                    )
+                    return pld
+
+                # XXX pld-value type failure
+                except ValidationError as valerr:
+                    # pack mgterr into error-msg for
+                    # reraise below; ensure remote-actor-err
+                    # info is displayed nicely?
+                    mte: MsgTypeError = _mk_recv_mte(
+                        msg=msg,
+                        codec=self.pld_dec,
+                        src_validation_error=valerr,
+                        is_invalid_payload=True,
+                        expected_msg=expect_msg,
+                    )
+                    # NOTE: just raise the MTE inline instead of all
+                    # the pack-unpack-repack non-sense when this is
+                    # a "send side" validation error.
+                    if is_started_send_side:
+                        raise mte
+
+                    # NOTE: the `.message` is automatically
+                    # transferred into the message as long as we
+                    # define it as a `Error.message` field.
+                    err_msg: Error = pack_error(
+                        exc=mte,
+                        cid=msg.cid,
+                        src_uid=(
+                            ipc.chan.uid
+                            if not is_started_send_side
+                            else ipc._actor.uid
+                        ),
+                    )
+                    mte._ipc_msg = err_msg
+
+                    # XXX override the `msg` passed to
+                    # `_raise_from_unexpected_msg()` (below) so so
+                    # that we're effectively able to use that same
+                    # func to unpack and raise an "emulated remote
+                    # `Error`" of this local MTE.
+                    msg = err_msg
+                    # XXX NOTE: so when the `_raise_from_unexpected_msg()`
+                    # raises the boxed `err_msg` from above it raises
+                    # it from the above caught interchange-lib
+                    # validation error.
+                    src_err = valerr
+
+            # a runtime-internal RPC endpoint response.
+            # always passthrough since (internal) runtime
+            # responses are generally never exposed to consumer
+            # code.
+            case CancelAck(
+                pld=bool(cancelled)
+            ):
+                return cancelled
+
+            case Error():
+                src_err = MessagingError(
+                    'IPC ctx dialog terminated without `Return`-ing a result\n'
+                    f'Instead it raised {msg.boxed_type_str!r}!'
+                )
+                # XXX NOTE XXX another super subtle runtime-y thing..
+                #
+                # - when user code (transitively) calls into this
+                #   func (usually via a `Context/MsgStream` API) we
+                #   generally want errors to propagate immediately
+                #   and directly so that the user can define how it
+                #   wants to handle them.
+                #
+                #  HOWEVER,
+                #
+                # - for certain runtime calling cases, we don't want to
+                #   directly raise since the calling code might have
+                #   special logic around whether to raise the error
+                #   or supress it silently (eg. a `ContextCancelled`
+                #   received from the far end which was requested by
+                #   this side, aka a self-cancel).
+                #
+                # SO, we offer a flag to control this.
+                if not raise_error:
+                    return src_err
+
+            case Stop(cid=cid):
+                ctx: Context = getattr(ipc, 'ctx', ipc)
+                message: str = (
+                    f'{ctx.side!r}-side of ctx received stream-`Stop` from '
+                    f'{ctx.peer_side!r} peer ?\n'
+                    f'|_cid: {cid}\n\n'
+
+                    f'{pretty_struct.pformat(msg)}\n'
+                )
+                if ctx._stream is None:
+                    explain: str = (
+                        f'BUT, no `MsgStream` (was) open(ed) on this '
+                        f'{ctx.side!r}-side of the IPC ctx?\n'
+                        f'Maybe check your code for streaming phase race conditions?\n'
+                    )
+                    log.warning(
+                        message
+                        +
+                        explain
+                    )
+                    # let caller decide what to do when only one
+                    # side opened a stream, don't raise.
+                    return msg
+
+                else:
+                    explain: str = (
+                        'Received a `Stop` when it should NEVER be possible!?!?\n'
+                    )
+                    # TODO: this is constructed inside
+                    # `_raise_from_unexpected_msg()` but maybe we
+                    # should pass it in?
+                    # src_err = trio.EndOfChannel(explain)
+                    src_err = None
+
+            case _:
+                src_err = InternalError(
+                    'Invalid IPC msg ??\n\n'
+                    f'{msg}\n'
+                )
+
+        # TODO: maybe use the new `.add_note()` from 3.11?
+        # |_https://docs.python.org/3.11/library/exceptions.html#BaseException.add_note
+        #
+        # fallthrough and raise from `src_err`
+        try:
+            _raise_from_unexpected_msg(
+                ctx=getattr(ipc, 'ctx', ipc),
+                msg=msg,
+                src_err=src_err,
+                log=log,
+                expect_msg=expect_msg,
+                hide_tb=hide_tb,
+            )
+        except UnboundLocalError:
+            # XXX if there's an internal lookup error in the above
+            # code (prolly on `src_err`) we want to show this frame
+            # in the tb!
+            __tracebackhide__: bool = False
+            raise
+
+    dec_msg = decode_pld
+
+    async def recv_msg_w_pld(
+        self,
+        ipc: Context|MsgStream,
+        expect_msg: MsgType,
+
+        # NOTE: generally speaking only for handling `Stop`-msgs that
+        # arrive during a call to `drain_to_final_msg()` above!
+        passthrough_non_pld_msgs: bool = True,
+        hide_tb: bool = True,
+        **kwargs,
+
+    ) -> tuple[MsgType, PayloadT]:
+        '''
+        Retrieve the next avail IPC msg, decode it's payload, and return
+        the pair of refs.
+
+        '''
+        __tracebackhide__: bool = hide_tb
+        msg: MsgType = await ipc._rx_chan.receive()
+
+        if passthrough_non_pld_msgs:
+            match msg:
+                case Stop():
+                    return msg, None
+
+        # TODO: is there some way we can inject the decoded
+        # payload into an existing output buffer for the original
+        # msg instance?
+        pld: PayloadT = self.decode_pld(
+            msg,
+            ipc=ipc,
+            expect_msg=expect_msg,
+            hide_tb=hide_tb,
+            **kwargs,
+        )
+        return msg, pld
+
+
+@cm
+def limit_plds(
+    spec: Union[Type[Struct]],
+    **dec_kwargs,
+
+) -> MsgDec:
+    '''
+    Apply a `MsgCodec` that will natively decode the SC-msg set's
+    `PayloadMsg.pld: Union[Type[Struct]]` payload fields using
+    tagged-unions of `msgspec.Struct`s from the `payload_types`
+    for all IPC contexts in use by the current `trio.Task`.
+
+    '''
+    __tracebackhide__: bool = True
+    try:
+        curr_ctx: Context = current_ipc_ctx()
+        rx: PldRx = curr_ctx._pld_rx
+        orig_pldec: MsgDec = rx.pld_dec
+
+        with rx.limit_plds(
+            spec=spec,
+            **dec_kwargs,
+        ) as pldec:
+            log.runtime(
+                'Applying payload-decoder\n\n'
+                f'{pldec}\n'
+            )
+            yield pldec
+    finally:
+        log.runtime(
+            'Reverted to previous payload-decoder\n\n'
+            f'{orig_pldec}\n'
+        )
+        # sanity on orig settings
+        assert rx.pld_dec is orig_pldec
+
+
+@acm
+async def maybe_limit_plds(
+    ctx: Context,
+    spec: Union[Type[Struct]]|None = None,
+    dec_hook: Callable|None = None,
+    **kwargs,
+
+) -> MsgDec|None:
+    '''
+    Async compat maybe-payload type limiter.
+
+    Mostly for use inside other internal `@acm`s such that a separate
+    indent block isn't needed when an async one is already being
+    used.
+
+    '''
+    if (
+        spec is None
+        and
+        dec_hook is None
+    ):
+        yield None
+        return
+
+    # sanity check on IPC scoping
+    curr_ctx: Context = current_ipc_ctx()
+    assert ctx is curr_ctx
+
+    with ctx._pld_rx.limit_plds(
+        spec=spec,
+        dec_hook=dec_hook,
+        **kwargs,
+    ) as msgdec:
+        yield msgdec
+
+    # when the applied spec is unwound/removed, the same IPC-ctx
+    # should still be in scope.
+    curr_ctx: Context = current_ipc_ctx()
+    assert ctx is curr_ctx
+
+
+async def drain_to_final_msg(
+    ctx: Context,
+
+    hide_tb: bool = True,
+    msg_limit: int = 6,
+
+) -> tuple[
+    Return|None,
+    list[MsgType]
+]:
+    '''
+    Drain IPC msgs delivered to the underlying IPC context's
+    rx-mem-chan (i.e. from `Context._rx_chan`) in search for a final
+    `Return` or `Error` msg.
+
+    Deliver the `Return` + preceding drained msgs (`list[MsgType]`)
+    as a pair unless an `Error` is found, in which unpack and raise
+    it.
+
+    The motivation here is to always capture any remote error relayed
+    by the remote peer task during a ctxc condition.
+
+    For eg. a ctxc-request may be sent to the peer as part of the
+    local task's (request for) cancellation but then that same task
+    **also errors** before executing the teardown in the
+    `Portal.open_context().__aexit__()` block. In such error-on-exit
+    cases we want to always capture and raise any delivered remote
+    error (like an expected ctxc-ACK) as part of the final
+    `ctx.wait_for_result()` teardown sequence such that the
+    `Context.outcome` related state always reflect what transpired
+    even after ctx closure and the `.open_context()` block exit.
+
+    '''
+    __tracebackhide__: bool = hide_tb
+    raise_overrun: bool = not ctx._allow_overruns
+
+    # wait for a final context result by collecting (but
+    # basically ignoring) any bi-dir-stream msgs still in transit
+    # from the far end.
+    pre_result_drained: list[MsgType] = []
+    result_msg: Return|Error|None = None
+    while not (
+        ctx.maybe_error
+        and not ctx._final_result_is_set()
+    ):
+        try:
+            # receive all msgs, scanning for either a final result
+            # or error; the underlying call should never raise any
+            # remote error directly!
+            msg, pld = await ctx._pld_rx.recv_msg_w_pld(
+                ipc=ctx,
+                expect_msg=Return,
+                raise_error=False,
+                hide_tb=hide_tb,
+            )
+            # ^-TODO-^ some bad ideas?
+            # -[ ] wrap final outcome .receive() in a scope so
+            #     it can be cancelled out of band if needed?
+            # |_with trio.CancelScope() as res_cs:
+            #       ctx._res_scope = res_cs
+            #       msg: dict = await ctx._rx_chan.receive()
+            #   if res_cs.cancelled_caught:
+            #
+            # -[ ] make sure pause points work here for REPLing
+            #   the runtime itself; i.e. ensure there's no hangs!
+            # |_from tractor.devx._debug import pause
+            #   await pause()
+
+        # NOTE: we get here if the far end was
+        # `ContextCancelled` in 2 cases:
+        # 1. we requested the cancellation and thus
+        #    SHOULD NOT raise that far end error,
+        # 2. WE DID NOT REQUEST that cancel and thus
+        #    SHOULD RAISE HERE!
+        except trio.Cancelled as _taskc:
+            taskc: trio.Cancelled = _taskc
+
+            # report when the cancellation wasn't (ostensibly) due to
+            # RPC operation, some surrounding parent cancel-scope.
+            if not ctx._scope.cancel_called:
+                task: trio.lowlevel.Task = trio.lowlevel.current_task()
+                rent_n: trio.Nursery = task.parent_nursery
+                if (
+                    (local_cs := rent_n.cancel_scope).cancel_called
+                ):
+                    log.cancel(
+                        'RPC-ctx cancelled by local-parent scope during drain!\n\n'
+                        f'c}}>\n'
+                        f' |_{rent_n}\n'
+                        f'   |_.cancel_scope = {local_cs}\n'
+                        f'   |_>c}}\n'
+                        f'      |_{ctx.pformat(indent=" "*9)}'
+                        # ^TODO, some (other) simpler repr here?
+                    )
+                    __tracebackhide__: bool = False
+
+            # CASE 2: mask the local cancelled-error(s)
+            # only when we are sure the remote error is
+            # the source cause of this local task's
+            # cancellation.
+            ctx.maybe_raise(
+                hide_tb=hide_tb,
+                from_src_exc=taskc,
+                # ?TODO? when *should* we use this?
+            )
+
+            # CASE 1: we DID request the cancel we simply
+            # continue to bubble up as normal.
+            raise taskc
+
+        match msg:
+
+            # final result arrived!
+            case Return():
+                log.runtime(
+                    'Context delivered final draining msg:\n'
+                    f'{pretty_struct.pformat(msg)}'
+                )
+                ctx._result: Any = pld
+                result_msg = msg
+                break
+
+            # far end task is still streaming to us so discard
+            # and report depending on local ctx state.
+            case Yield():
+                pre_result_drained.append(msg)
+                if (
+                    (ctx._stream.closed
+                     and (reason := 'stream was already closed')
+                    )
+                    or (ctx.cancel_acked
+                        and (reason := 'ctx cancelled other side')
+                    )
+                    or (ctx._cancel_called
+                        and (reason := 'ctx called `.cancel()`')
+                    )
+                    or (len(pre_result_drained) > msg_limit
+                        and (reason := f'"yield" limit={msg_limit}')
+                    )
+                ):
+                    log.cancel(
+                        'Cancelling `MsgStream` drain since '
+                        f'{reason}\n\n'
+                        f'<= {ctx.chan.uid}\n'
+                        f'  |_{ctx._nsf}()\n\n'
+                        f'=> {ctx._task}\n'
+                        f'  |_{ctx._stream}\n\n'
+
+                        f'{pretty_struct.pformat(msg)}\n'
+                    )
+                    break
+
+                # drain up to the `msg_limit` hoping to get
+                # a final result or error/ctxc.
+                else:
+                    log.warning(
+                        'Ignoring "yield" msg during `ctx.result()` drain..\n'
+                        f'<= {ctx.chan.uid}\n'
+                        f'  |_{ctx._nsf}()\n\n'
+                        f'=> {ctx._task}\n'
+                        f'  |_{ctx._stream}\n\n'
+
+                        f'{pretty_struct.pformat(msg)}\n'
+                    )
+                    continue
+
+            # stream terminated, but no result yet..
+            #
+            # TODO: work out edge cases here where
+            # a stream is open but the task also calls
+            # this?
+            # -[ ] should be a runtime error if a stream is open right?
+            # Stop()
+            case Stop():
+                pre_result_drained.append(msg)
+                log.runtime(  # normal/expected shutdown transaction
+                    'Remote stream terminated due to "stop" msg:\n\n'
+                    f'{pretty_struct.pformat(msg)}\n'
+                )
+                continue
+
+            # remote error msg, likely already handled inside
+            # `Context._deliver_msg()`
+            case Error():
+                # TODO: can we replace this with `ctx.maybe_raise()`?
+                # -[ ]  would this be handier for this case maybe?
+                # |_async with maybe_raise_on_exit() as raises:
+                #       if raises:
+                #           log.error('some msg about raising..')
+                #
+                re: Exception|None = ctx._remote_error
+                if re:
+                    assert msg is ctx._cancel_msg
+                    # NOTE: this solved a super duper edge case XD
+                    # this was THE super duper edge case of:
+                    # - local task opens a remote task,
+                    # - requests remote cancellation of far end
+                    #   ctx/tasks,
+                    # - needs to wait for the cancel ack msg
+                    #   (ctxc) or some result in the race case
+                    #   where the other side's task returns
+                    #   before the cancel request msg is ever
+                    #   rxed and processed,
+                    # - here this surrounding drain loop (which
+                    #   iterates all ipc msgs until the ack or
+                    #   an early result arrives) was NOT exiting
+                    #   since we are the edge case: local task
+                    #   does not re-raise any ctxc it receives
+                    #   IFF **it** was the cancellation
+                    #   requester..
+                    #
+                    # XXX will raise if necessary but ow break
+                    # from loop presuming any supressed error
+                    # (ctxc) should terminate the context!
+                    ctx._maybe_raise_remote_err(
+                        re,
+                        # NOTE: obvi we don't care if we
+                        # overran the far end if we're already
+                        # waiting on a final result (msg).
+                        # raise_overrun_from_self=False,
+                        raise_overrun_from_self=raise_overrun,
+                    )
+                    result_msg = msg
+                    break  # OOOOOF, yeah obvi we need this..
+
+                else:
+                    # bubble the original src key error
+                    raise
+
+            # XXX should pretty much never get here unless someone
+            # overrides the default `MsgType` spec.
+            case _:
+                pre_result_drained.append(msg)
+                # It's definitely an internal error if any other
+                # msg type without a`'cid'` field arrives here!
+                report: str = (
+                    f'Invalid or unknown msg type {type(msg)!r}!?\n'
+                )
+                if not msg.cid:
+                    report += (
+                        '\nWhich also has no `.cid` field?\n'
+                    )
+
+                raise MessagingError(
+                    report
+                    +
+                    f'\n{msg}\n'
+                )
+
+    else:
+        log.cancel(
+            'Skipping `MsgStream` drain since final outcome is set\n\n'
+            f'{ctx.outcome}\n'
+        )
+
+    return (
+        result_msg,
+        pre_result_drained,
+    )
+
+
+def validate_payload_msg(
+    pld_msg: Started|Yield|Return,
+    pld_value: PayloadT,
+    ipc: Context|MsgStream,
+
+    raise_mte: bool = True,
+    strict_pld_parity: bool = False,
+    hide_tb: bool = True,
+
+) -> MsgTypeError|None:
+    '''
+    Validate a `PayloadMsg.pld` value with the current
+    IPC ctx's `PldRx` and raise an appropriate `MsgTypeError`
+    on failure.
+
+    '''
+    __tracebackhide__: bool = hide_tb
+    codec: MsgCodec = current_codec()
+    msg_bytes: bytes = codec.encode(pld_msg)
+    try:
+        roundtripped: Started = codec.decode(msg_bytes)
+        ctx: Context = getattr(ipc, 'ctx', ipc)
+        pld: PayloadT = ctx.pld_rx.decode_pld(
+            msg=roundtripped,
+            ipc=ipc,
+            expect_msg=Started,
+            hide_tb=hide_tb,
+            is_started_send_side=True,
+        )
+        if (
+            strict_pld_parity
+            and
+            pld != pld_value
+        ):
+            # TODO: make that one a mod func too..
+            diff = pretty_struct.Struct.__sub__(
+                roundtripped,
+                pld_msg,
+            )
+            complaint: str = (
+                'Started value does not match after roundtrip?\n\n'
+                f'{diff}'
+            )
+            raise ValidationError(complaint)
+
+    # raise any msg type error NO MATTER WHAT!
+    except ValidationError as verr:
+        try:
+            mte: MsgTypeError = _mk_recv_mte(
+                msg=roundtripped,
+                codec=codec,
+                src_validation_error=verr,
+                verb_header='Trying to send ',
+                is_invalid_payload=True,
+            )
+        except BaseException:
+            __tracebackhide__: bool = False
+            raise
+
+        if not raise_mte:
+            return mte
+
+        raise mte from verr

tractor/msg/pretty_struct.py

@@ -0,0 +1,292 @@
+# tractor: structured concurrent "actors".
+# Copyright 2018-eternity Tyler Goodlet.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+'''
+Prettified version of `msgspec.Struct` for easier console grokin.
+
+'''
+from __future__ import annotations
+from collections import UserList
+from typing import (
+    Any,
+    Iterator,
+)
+
+from msgspec import (
+    msgpack,
+    Struct as _Struct,
+    structs,
+)
+from pprint import (
+    saferepr,
+)
+
+from tractor.log import get_logger
+
+log = get_logger()
+# TODO: auto-gen type sig for input func both for
+# type-msgs and logging of RPC tasks?
+# taken and modified from:
+# https://stackoverflow.com/a/57110117
+# import inspect
+# from typing import List
+
+# def my_function(input_1: str, input_2: int) -> list[int]:
+#     pass
+
+# def types_of(func):
+#     specs = inspect.getfullargspec(func)
+#     return_type = specs.annotations['return']
+#     input_types = [t.__name__ for s, t in specs.annotations.items() if s != 'return']
+#     return f'{func.__name__}({": ".join(input_types)}) -> {return_type}'
+
+# types_of(my_function)
+
+
+class DiffDump(UserList):
+    '''
+    Very simple list delegator that repr() dumps (presumed) tuple
+    elements of the form `tuple[str, Any, Any]` in a nice
+    multi-line readable form for analyzing `Struct` diffs.
+
+    '''
+    def __repr__(self) -> str:
+        if not len(self):
+            return super().__repr__()
+
+        # format by displaying item pair's ``repr()`` on multiple,
+        # indented lines such that they are more easily visually
+        # comparable when printed to console when printed to
+        # console.
+        repstr: str = '[\n'
+        for k, left, right in self:
+            repstr += (
+                f'({k},\n'
+                f'\t{repr(left)},\n'
+                f'\t{repr(right)},\n'
+                ')\n'
+            )
+        repstr += ']\n'
+        return repstr
+
+
+def iter_fields(struct: Struct) -> Iterator[
+    tuple[
+        structs.FieldIinfo,
+        str,
+        Any,
+    ]
+]:
+    '''
+    Iterate over all non-@property fields of this struct.
+
+    '''
+    fi: structs.FieldInfo
+    for fi in structs.fields(struct):
+        key: str = fi.name
+        val: Any = getattr(struct, key)
+        yield (
+            fi,
+            key,
+            val,
+        )
+
+
+def pformat(
+    struct: Struct,
+    field_indent: int = 2,
+    indent: int = 0,
+
+) -> str:
+    '''
+    Recursion-safe `pprint.pformat()` style formatting of
+    a `msgspec.Struct` for sane reading by a human using a REPL.
+
+    '''
+    # global whitespace indent
+    ws: str = ' '*indent
+
+    # field whitespace indent
+    field_ws: str = ' '*(field_indent + indent)
+
+    # qtn: str = ws + struct.__class__.__qualname__
+    qtn: str = struct.__class__.__qualname__
+
+    obj_str: str = ''  # accumulator
+    fi: structs.FieldInfo
+    k: str
+    v: Any
+    for fi, k, v in iter_fields(struct):
+
+        # TODO: how can we prefer `Literal['option1',  'option2,
+        # ..]` over .__name__ == `Literal` but still get only the
+        # latter for simple types like `str | int | None` etc..?
+        ft: type = fi.type
+        typ_name: str = getattr(ft, '__name__', str(ft))
+
+        # recurse to get sub-struct's `.pformat()` output Bo
+        if isinstance(v, Struct):
+            val_str: str =  v.pformat(
+                indent=field_indent + indent,
+                field_indent=indent + field_indent,
+            )
+
+        else:  # the `pprint` recursion-safe format:
+            # https://docs.python.org/3.11/library/pprint.html#pprint.saferepr
+            try:
+                val_str: str = saferepr(v)
+            except Exception:
+                log.exception(
+                    'Failed to `saferepr({type(struct)})` !?\n'
+                )
+            return _Struct.__repr__(struct)
+
+        # TODO: LOLOL use `textwrap.indent()` instead dawwwwwg!
+        obj_str += (field_ws + f'{k}: {typ_name} = {val_str},\n')
+
+    return (
+        f'{qtn}(\n'
+        f'{obj_str}'
+        f'{ws})'
+    )
+
+
+class Struct(
+    _Struct,
+
+    # https://jcristharif.com/msgspec/structs.html#tagged-unions
+    # tag='pikerstruct',
+    # tag=True,
+):
+    '''
+    A "human friendlier" (aka repl buddy) struct subtype.
+
+    '''
+    def to_dict(
+        self,
+        include_non_members: bool = True,
+
+    ) -> dict:
+        '''
+        Like it sounds.. direct delegation to:
+        https://jcristharif.com/msgspec/api.html#msgspec.structs.asdict
+
+        BUT, by default we pop all non-member (aka not defined as
+        struct fields) fields by default.
+
+        '''
+        asdict: dict = structs.asdict(self)
+        if include_non_members:
+            return asdict
+
+        # only return a dict of the struct members
+        # which were provided as input, NOT anything
+        # added as type-defined `@property` methods!
+        sin_props: dict = {}
+        fi: structs.FieldInfo
+        for fi, k, v in iter_fields(self):
+            sin_props[k] = asdict[k]
+
+        return sin_props
+
+    pformat = pformat
+    # __repr__ = pformat
+    # __str__ = __repr__ = pformat
+    # TODO: use a pprint.PrettyPrinter instance around ONLY rendering
+    # inside a known tty?
+    # def __repr__(self) -> str:
+    #     ...
+    def __repr__(self) -> str:
+        try:
+            return pformat(self)
+        except Exception:
+            log.exception(
+                f'Failed to `pformat({type(self)})` !?\n'
+            )
+            return _Struct.__repr__(self)
+
+    def copy(
+        self,
+        update: dict | None = None,
+
+    ) -> Struct:
+        '''
+        Validate-typecast all self defined fields, return a copy of
+        us with all such fields.
+
+        NOTE: This is kinda like the default behaviour in
+        `pydantic.BaseModel` except a copy of the object is
+        returned making it compat with `frozen=True`.
+
+        '''
+        if update:
+            for k, v in update.items():
+                setattr(self, k, v)
+
+        # NOTE: roundtrip serialize to validate
+        # - enode to msgpack binary format,
+        # - decode that back to a struct.
+        return msgpack.Decoder(type=type(self)).decode(
+            msgpack.Encoder().encode(self)
+        )
+
+    def typecast(
+        self,
+
+        # TODO: allow only casting a named subset?
+        # fields: set[str] | None = None,
+
+    ) -> None:
+        '''
+        Cast all fields using their declared type annotations
+        (kinda like what `pydantic` does by default).
+
+        NOTE: this of course won't work on frozen types, use
+        ``.copy()`` above in such cases.
+
+        '''
+        # https://jcristharif.com/msgspec/api.html#msgspec.structs.fields
+        fi: structs.FieldInfo
+        for fi in structs.fields(self):
+            setattr(
+                self,
+                fi.name,
+                fi.type(getattr(self, fi.name)),
+            )
+
+    def __sub__(
+        self,
+        other: Struct,
+
+    ) -> DiffDump[tuple[str, Any, Any]]:
+        '''
+        Compare fields/items key-wise and return a ``DiffDump``
+        for easy visual REPL comparison B)
+
+        '''
+        diffs: DiffDump[tuple[str, Any, Any]] = DiffDump()
+        for fi in structs.fields(self):
+            attr_name: str = fi.name
+            ours: Any = getattr(self, attr_name)
+            theirs: Any = getattr(other, attr_name)
+            if ours != theirs:
+                diffs.append((
+                    attr_name,
+                    ours,
+                    theirs,
+                ))
+
+        return diffs

tractor/msg/ptr.py

@@ -76,9 +76,11 @@ class NamespacePath(str):
         return self._ref
 
     @staticmethod
-    def _mk_fqnp(ref: type | object) -> tuple[str, str]:
+    def _mk_fqnp(
+        ref: type|object,
+    ) -> tuple[str, str]:
         '''
-        Generate a minial ``str`` pair which describes a python
+        Generate a minial `str` pair which describes a python
         object's namespace path and object/type name.
 
         In more precise terms something like:
@@ -87,10 +89,9 @@ class NamespacePath(str):
             of THIS type XD
 
         '''
-        if (
-            isfunction(ref)
-        ):
+        if isfunction(ref):
             name: str = getattr(ref, '__name__')
+            mod_name: str = ref.__module__
 
         elif ismethod(ref):
             # build out the path manually i guess..?
@@ -99,15 +100,19 @@ class NamespacePath(str):
                 type(ref.__self__).__name__,
                 ref.__func__.__name__,
             ])
+            mod_name: str = ref.__self__.__module__
 
         else:  # object or other?
             # isinstance(ref, object)
             # and not isfunction(ref)
             name: str = type(ref).__name__
+            mod_name: str = ref.__module__
 
+        # TODO: return static value direactly?
+        #
         # fully qualified namespace path, tuple.
         fqnp: tuple[str, str] = (
-            ref.__module__,
+            mod_name,
             name,
         )
         return fqnp
@@ -115,7 +120,7 @@ class NamespacePath(str):
     @classmethod
     def from_ref(
         cls,
-        ref: type | object,
+        ref: type|object,
 
     ) -> NamespacePath:
 

tractor/msg/types.py

@@ -15,256 +15,716 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 '''
-Extensions to built-in or (heavily used but 3rd party) friend-lib
-types.
+Define our strictly typed IPC message spec for the SCIPP:
+
+that is,
+
+the "Structurred-Concurrency-Inter-Process-(dialog)-(un)Protocol".
 
 '''
 from __future__ import annotations
-from collections import UserList
-from pprint import (
-    saferepr,
-)
+import types
 from typing import (
     Any,
-    Iterator,
+    Generic,
+    Literal,
+    Type,
+    TypeVar,
+    TypeAlias,
+    Union,
 )
 
 from msgspec import (
-    msgpack,
-    Struct as _Struct,
-    structs,
+    defstruct,
+    # field,
+    Raw,
+    Struct,
+    # UNSET,
+    # UnsetType,
 )
 
-# TODO: auto-gen type sig for input func both for
-# type-msgs and logging of RPC tasks?
-# taken and modified from:
-# https://stackoverflow.com/a/57110117
-# import inspect
-# from typing import List
-
-# def my_function(input_1: str, input_2: int) -> list[int]:
-#     pass
-
-# def types_of(func):
-#     specs = inspect.getfullargspec(func)
-#     return_type = specs.annotations['return']
-#     input_types = [t.__name__ for s, t in specs.annotations.items() if s != 'return']
-#     return f'{func.__name__}({": ".join(input_types)}) -> {return_type}'
-
-# types_of(my_function)
+from tractor.msg import (
+    pretty_struct,
+)
+from tractor.log import get_logger
 
 
-class DiffDump(UserList):
-    '''
-    Very simple list delegator that repr() dumps (presumed) tuple
-    elements of the form `tuple[str, Any, Any]` in a nice
-    multi-line readable form for analyzing `Struct` diffs.
+log = get_logger('tractor.msgspec')
 
-    '''
-    def __repr__(self) -> str:
-        if not len(self):
-            return super().__repr__()
-
-        # format by displaying item pair's ``repr()`` on multiple,
-        # indented lines such that they are more easily visually
-        # comparable when printed to console when printed to
-        # console.
-        repstr: str = '[\n'
-        for k, left, right in self:
-            repstr += (
-                f'({k},\n'
-                f'\t{repr(left)},\n'
-                f'\t{repr(right)},\n'
-                ')\n'
-            )
-        repstr += ']\n'
-        return repstr
+# type variable for the boxed payload field `.pld`
+PayloadT = TypeVar('PayloadT')
 
 
-class Struct(
-    _Struct,
+class PayloadMsg(
+    Struct,
+    Generic[PayloadT],
 
     # https://jcristharif.com/msgspec/structs.html#tagged-unions
-    # tag='pikerstruct',
-    # tag=True,
+    tag=True,
+    tag_field='msg_type',
+
+    # https://jcristharif.com/msgspec/structs.html#field-ordering
+    # kw_only=True,
+
+    # https://jcristharif.com/msgspec/structs.html#equality-and-order
+    # order=True,
+
+    # https://jcristharif.com/msgspec/structs.html#encoding-decoding-as-arrays
+    # as_array=True,
 ):
     '''
-    A "human friendlier" (aka repl buddy) struct subtype.
+    An abstract payload boxing/shuttling IPC msg type.
+
+    Boxes data-values passed to/from user code
+
+    (i.e. any values passed by `tractor` application code using any of
+
+      |_ `._streaming.MsgStream.send/receive()`
+      |_ `._context.Context.started/result()`
+      |_ `._ipc.Channel.send/recv()`
+
+     aka our "IPC primitive APIs")
+
+    as message "payloads" set to the `.pld` field and uses
+    `msgspec`'s "tagged unions" feature to support a subset of our
+    "SC-transitive shuttle protocol" specification with
+    a `msgspec.Struct` inheritance tree.
 
     '''
-    def _sin_props(self) -> Iterator[
-        tuple[
-            structs.FieldIinfo,
-            str,
-            Any,
-        ]
-    ]:
-        '''
-        Iterate over all non-@property fields of this struct.
+    cid: str  # call/context-id
+    # ^-TODO-^: more explicit type?
+    # -[ ] use UNSET here?
+    #  https://jcristharif.com/msgspec/supported-types.html#unset
+    #
+    # -[ ] `uuid.UUID` which has multi-protocol support
+    #  https://jcristharif.com/msgspec/supported-types.html#uuid
 
-        '''
-        fi: structs.FieldInfo
-        for fi in structs.fields(self):
-            key: str = fi.name
-            val: Any = getattr(self, key)
-            yield fi, key, val
+    # The msg's "payload" (spelled without vowels):
+    # https://en.wikipedia.org/wiki/Payload_(computing)
+    pld: Raw
 
-    def to_dict(
-        self,
-        include_non_members: bool = True,
+    # ^-NOTE-^ inherited from any `PayloadMsg` (and maybe type
+    # overriden via the `._ops.limit_plds()` API), but by default is
+    # parameterized to be `Any`.
+    #
+    # XXX this `Union` must strictly NOT contain `Any` if
+    # a limited msg-type-spec is intended, such that when
+    # creating and applying a new `MsgCodec` its 
+    # `.decoder: Decoder` is configured with a `Union[Type[Struct]]` which
+    # restricts the allowed payload content (this `.pld` field) 
+    # by type system defined loading constraints B)
+    #
+    # TODO: could also be set to `msgspec.Raw` if the sub-decoders
+    # approach is preferred over the generic parameterization 
+    # approach as take by `mk_msg_spec()` below.
 
-    ) -> dict:
-        '''
-        Like it sounds.. direct delegation to:
-        https://jcristharif.com/msgspec/api.html#msgspec.structs.asdict
 
-        BUT, by default we pop all non-member (aka not defined as
-        struct fields) fields by default.
+# TODO: complete rename
+Msg = PayloadMsg
 
-        '''
-        asdict: dict = structs.asdict(self)
-        if include_non_members:
-            return asdict
 
-        # only return a dict of the struct members
-        # which were provided as input, NOT anything
-        # added as type-defined `@property` methods!
-        sin_props: dict = {}
-        fi: structs.FieldInfo
-        for fi, k, v in self._sin_props():
-            sin_props[k] = asdict[k]
+class Aid(
+    Struct,
+    tag=True,
+    tag_field='msg_type',
+):
+    '''
+    Actor-identity msg.
 
-        return sin_props
+    Initial contact exchange enabling an actor "mailbox handshake"
+    delivering the peer identity (and maybe eventually contact)
+    info.
 
-    def pformat(
-        self,
-        field_indent: int = 2,
-        indent: int = 0,
+    Used by discovery protocol to register actors as well as
+    conduct the initial comms (capability) filtering.
 
-    ) -> str:
-        '''
-        Recursion-safe `pprint.pformat()` style formatting of
-        a `msgspec.Struct` for sane reading by a human using a REPL.
+    '''
+    name: str
+    uuid: str
+    # TODO: use built-in support for UUIDs?
+    # -[ ] `uuid.UUID` which has multi-protocol support
+    #  https://jcristharif.com/msgspec/supported-types.html#uuid
 
-        '''
-        # global whitespace indent
-        ws: str = ' '*indent
 
-        # field whitespace indent
-        field_ws: str = ' '*(field_indent + indent)
+class SpawnSpec(
+    pretty_struct.Struct,
+    tag=True,
+    tag_field='msg_type',
+):
+    '''
+    Initial runtime spec handed down from a spawning parent to its
+    child subactor immediately following first contact via an
+    `Aid` msg.
 
-        # qtn: str = ws + self.__class__.__qualname__
-        qtn: str = self.__class__.__qualname__
+    '''
+    # TODO: similar to the `Start` kwargs spec needed below, we need
+    # a hard `Struct` def for all of these fields!
+    _parent_main_data: dict
+    _runtime_vars: dict[str, Any]
 
-        obj_str: str = ''  # accumulator
-        fi: structs.FieldInfo
-        k: str
-        v: Any
-        for fi, k, v in self._sin_props():
+    # module import capability
+    enable_modules: dict[str, str]
 
-            # TODO: how can we prefer `Literal['option1',  'option2,
-            # ..]` over .__name__ == `Literal` but still get only the
-            # latter for simple types like `str | int | None` etc..?
-            ft: type = fi.type
-            typ_name: str = getattr(ft, '__name__', str(ft))
+    # TODO: not just sockaddr pairs?
+    # -[ ] abstract into a `TransportAddr` type?
+    reg_addrs: list[tuple[str, int]]
+    bind_addrs: list[tuple[str, int]]
 
-            # recurse to get sub-struct's `.pformat()` output Bo
-            if isinstance(v, Struct):
-                val_str: str =  v.pformat(
-                    indent=field_indent + indent,
-                    field_indent=indent + field_indent,
-                )
 
-            else:  # the `pprint` recursion-safe format:
-                # https://docs.python.org/3.11/library/pprint.html#pprint.saferepr
-                val_str: str = saferepr(v)
+# TODO: caps based RPC support in the payload?
+#
+# -[ ] integration with our ``enable_modules: list[str]`` caps sys.
+#   ``pkgutil.resolve_name()`` internally uses
+#   ``importlib.import_module()`` which can be filtered by
+#   inserting a ``MetaPathFinder`` into ``sys.meta_path`` (which
+#   we could do before entering the ``Actor._process_messages()``
+#   loop)?
+#   - https://github.com/python/cpython/blob/main/Lib/pkgutil.py#L645
+#   - https://stackoverflow.com/questions/1350466/preventing-python-code-from-importing-certain-modules
+#   - https://stackoverflow.com/a/63320902
+#   - https://docs.python.org/3/library/sys.html#sys.meta_path
+#
+# -[ ] can we combine .ns + .func into a native `NamespacePath` field?
+#
+# -[ ] better name, like `Call/TaskInput`?
+#
+# -[ ] XXX a debugger lock msg transaction with payloads like,
+#   child -> `.pld: DebugLock` -> root
+#   child <- `.pld: DebugLocked` <- root
+#   child -> `.pld: DebugRelease` -> root
+#
+#   WHY => when a pld spec is provided it might not allow for
+#   debug mode msgs as they currently are (using plain old `pld.
+#   str` payloads) so we only when debug_mode=True we need to
+#   union in this debugger payload set?
+#
+#   mk_msg_spec(
+#       MyPldSpec,
+#       debug_mode=True,
+#   ) -> (
+#       Union[MyPldSpec]
+#      | Union[DebugLock, DebugLocked, DebugRelease]
+#   )
 
-            # TODO: LOLOL use `textwrap.indent()` instead dawwwwwg!
-            obj_str += (field_ws + f'{k}: {typ_name} = {val_str},\n')
+# class Params(
+#     Struct,
+#     Generic[PayloadT],
+# ):
+#     spec: PayloadT|ParamSpec
+#     inputs: InputsT|dict[str, Any]
 
-        return (
-            f'{qtn}(\n'
-            f'{obj_str}'
-            f'{ws})'
+    # TODO: for eg. we could stringently check the target
+    # task-func's type sig and enforce it?
+    # as an example for an IPTC,
+    # @tractor.context
+    # async def send_back_nsp(
+    #     ctx: Context,
+    #     expect_debug: bool,
+    #     pld_spec_str: str,
+    #     add_hooks: bool,
+    #     started_msg_dict: dict,
+    # ) -> <WhatHere!>:
+
+    # TODO: figure out which of the `typing` feats we want to
+    # support:
+    # - plain ol `ParamSpec`:
+    #   https://docs.python.org/3/library/typing.html#typing.ParamSpec
+    # - new in 3.12 type parameter lists Bo
+    # |_ https://docs.python.org/3/reference/compound_stmts.html#type-params
+    # |_ historical pep 695: https://peps.python.org/pep-0695/
+    # |_ full lang spec: https://typing.readthedocs.io/en/latest/spec/
+    # |_ on annotation scopes:
+    #    https://docs.python.org/3/reference/executionmodel.html#annotation-scopes
+    # spec: ParamSpec[
+    #     expect_debug: bool,
+    #     pld_spec_str: str,
+    #     add_hooks: bool,
+    #     started_msg_dict: dict,
+    # ]
+
+
+# TODO: possibly sub-type for runtime method requests?
+# -[ ] `Runtime(Start)` with a `.ns: str = 'self' or
+#     we can just enforce any such method as having a strict
+#     ns for calling funcs, namely the `Actor` instance?
+class Start(
+    Struct,
+    tag=True,
+    tag_field='msg_type',
+):
+    '''
+    Initial request to remotely schedule an RPC `trio.Task` via
+    `Actor.start_remote_task()`.
+
+    It is called by all the following public APIs:
+
+    - `ActorNursery.run_in_actor()`
+
+    - `Portal.run()`
+          `|_.run_from_ns()`
+          `|_.open_stream_from()`
+          `|_._submit_for_result()`
+
+    - `Context.open_context()`
+
+    '''
+    cid: str
+
+    ns: str
+    func: str
+
+    # TODO: make this a sub-struct which can be further
+    # type-limited, maybe `Inputs`?
+    # => SEE ABOVE <=
+    kwargs: dict[str, Any]
+    uid: tuple[str, str]  # (calling) actor-id
+
+    # TODO: enforcing a msg-spec in terms `Msg.pld`
+    # parameterizable msgs to be used in the appls IPC dialog.
+    # => SEE `._codec.MsgDec` for more <=
+    pld_spec: str = str(Any)
+
+
+class StartAck(
+    Struct,
+    tag=True,
+    tag_field='msg_type',
+):
+    '''
+    Init response to a `Cmd` request indicating the far
+    end's RPC spec, namely its callable "type".
+
+    '''
+    cid: str
+    # TODO: maybe better names for all these?
+    # -[ ] obvi ^ would need sync with `._rpc`
+    functype: Literal[
+        'asyncfunc',
+        'asyncgen',
+        'context',  # TODO: the only one eventually?
+    ]
+
+    # import typing
+    # eval(str(Any), {}, {'typing': typing})
+    # started_spec: str = str(Any)
+    # return_spec
+
+
+class Started(
+    PayloadMsg,
+    Generic[PayloadT],
+):
+    '''
+    Packet to shuttle the "first value" delivered by
+    `Context.started(value: Any)` from a `@tractor.context`
+    decorated IPC endpoint.
+
+    '''
+    pld: PayloadT|Raw
+
+
+# TODO: cancel request dedicated msg?
+# -[ ] instead of using our existing `Start`?
+#
+# class Cancel:
+#     cid: str
+
+
+class Yield(
+    PayloadMsg,
+    Generic[PayloadT],
+):
+    '''
+    Per IPC transmission of a value from `await MsgStream.send(<value>)`.
+
+    '''
+    pld: PayloadT|Raw
+
+
+class Stop(
+    Struct,
+    tag=True,
+    tag_field='msg_type',
+):
+    '''
+    Stream termination signal much like an IPC version 
+    of `StopAsyncIteration`.
+
+    '''
+    cid: str
+    # TODO: do we want to support a payload on stop?
+    # pld: UnsetType = UNSET
+
+
+# TODO: is `Result` or `Out[come]` a better name?
+class Return(
+    PayloadMsg,
+    Generic[PayloadT],
+):
+    '''
+    Final `return <value>` from a remotely scheduled
+    func-as-`trio.Task`.
+
+    '''
+    pld: PayloadT|Raw
+
+
+class CancelAck(
+    PayloadMsg,
+    Generic[PayloadT],
+):
+    '''
+    Deliver the `bool` return-value from a cancellation `Actor`
+    method scheduled via and prior RPC request.
+
+    - `Actor.cancel()`
+       `|_.cancel_soon()`
+       `|_.cancel_rpc_tasks()`
+       `|_._cancel_task()`
+       `|_.cancel_server()`
+
+    RPCs to these methods must **always** be able to deliver a result
+    despite the currently configured IPC msg spec such that graceful
+    cancellation is always functional in the runtime.
+
+    '''
+    pld: bool
+
+
+# TODO: unify this with `._exceptions.RemoteActorError`
+# such that we can have a msg which is both raisable and
+# IPC-wire ready?
+# B~o
+class Error(
+    Struct,
+    tag=True,
+    tag_field='msg_type',
+
+    # TODO may omit defaults?
+    # https://jcristharif.com/msgspec/structs.html#omitting-default-values
+    # omit_defaults=True,
+):
+    '''
+    A pkt that wraps `RemoteActorError`s for relay and raising.
+
+    Fields are 1-to-1 meta-data as needed originally by
+    `RemoteActorError.msgdata: dict` but now are defined here.
+
+    Note: this msg shuttles `ContextCancelled` and `StreamOverrun`
+    as well is used to rewrap any `MsgTypeError` for relay-reponse
+    to bad `Yield.pld` senders during an IPC ctx's streaming dialog
+    phase.
+
+    '''
+    src_uid: tuple[str, str]
+    src_type_str: str
+    boxed_type_str: str
+    relay_path: list[tuple[str, str]]
+
+    # normally either both are provided or just
+    # a message for certain special cases where
+    # we pack a message for a locally raised
+    # mte or ctxc.
+    message: str|None = None
+    tb_str: str = ''
+
+    # TODO: only optionally include sub-type specfic fields?
+    # -[ ] use UNSET or don't include them via `omit_defaults` (see
+    #      inheritance-line options above)
+    #
+    # `ContextCancelled` reports the src cancelling `Actor.uid`
+    canceller: tuple[str, str]|None = None
+
+    # `StreamOverrun`-specific src `Actor.uid`
+    sender: tuple[str, str]|None = None
+
+    # `MsgTypeError` meta-data
+    cid: str|None = None
+    # when the receiver side fails to decode a delivered
+    # `PayloadMsg`-subtype; one and/or both the msg-struct instance
+    # and `Any`-decoded to `dict` of the msg are set and relayed
+    # (back to the sender) for introspection.
+    _bad_msg: Started|Yield|Return|None = None
+    _bad_msg_as_dict: dict|None = None
+
+
+def from_dict_msg(
+    dict_msg: dict,
+
+    msgT: MsgType|None = None,
+    tag_field: str = 'msg_type',
+    use_pretty: bool = False,
+
+) -> MsgType:
+    '''
+    Helper to build a specific `MsgType` struct from a "vanilla"
+    decoded `dict`-ified equivalent of the msg: i.e. if the
+    `msgpack.Decoder.type == Any`, the default when using
+    `msgspec.msgpack` and not "typed decoding" using
+    `msgspec.Struct`.
+
+    '''
+    msg_type_tag_field: str = (
+        msgT.__struct_config__.tag_field
+        if msgT is not None
+        else tag_field
+    )
+    # XXX ensure tag field is removed
+    msgT_name: str = dict_msg.pop(msg_type_tag_field)
+    msgT: MsgType = _msg_table[msgT_name]
+    if use_pretty:
+        msgT = defstruct(
+            name=msgT_name,
+            fields=[
+                (key, fi.type)
+                for fi, key, _
+                in pretty_struct.iter_fields(msgT)
+            ],
+            bases=(
+                pretty_struct.Struct,
+                msgT,
+            ),
+        )
+    return msgT(**dict_msg)
+
+# TODO: should be make a set of cancel msgs?
+# -[ ] a version of `ContextCancelled`?
+#     |_ and/or with a scope field?
+# -[ ] or, a full `ActorCancelled`?
+#
+# class Cancelled(MsgType):
+#     cid: str
+#
+# -[ ] what about overruns?
+#
+# class Overrun(MsgType):
+#     cid: str
+
+_runtime_msgs: list[Struct] = [
+
+    # identity handshake on first IPC `Channel` contact.
+    Aid,
+
+    # parent-to-child spawn specification passed as 2nd msg after
+    # handshake ONLY after child connects back to parent.
+    SpawnSpec,
+
+    # inter-actor RPC initiation
+    Start,  # schedule remote task-as-func
+    StartAck,  # ack the schedule request
+
+    # emission from `MsgStream.aclose()`
+    Stop,
+
+    # `Return` sub-type that we always accept from
+    # runtime-internal cancel endpoints
+    CancelAck,
+
+    # box remote errors, normally subtypes
+    # of `RemoteActorError`.
+    Error,
+]
+
+# the no-outcome-yet IAC (inter-actor-communication) sub-set which
+# can be `PayloadMsg.pld` payload field type-limited by application code
+# using `apply_codec()` and `limit_msg_spec()`.
+_payload_msgs: list[PayloadMsg] = [
+    # first <value> from `Context.started(<value>)`
+    Started,
+
+    # any <value> sent via `MsgStream.send(<value>)`
+    Yield,
+
+    # the final value returned from a `@context` decorated
+    # IPC endpoint.
+    Return,
+]
+
+# built-in SC shuttle protocol msg type set in
+# approx order of the IPC txn-state spaces.
+__msg_types__: list[MsgType] = (
+    _runtime_msgs
+    +
+    _payload_msgs
+)
+
+
+_msg_table: dict[str, MsgType] = {
+    msgT.__name__: msgT
+    for msgT in __msg_types__
+}
+
+# TODO: use new type declaration syntax for msg-type-spec
+# https://docs.python.org/3/library/typing.html#type-aliases
+# https://docs.python.org/3/reference/simple_stmts.html#type
+MsgType: TypeAlias = Union[*__msg_types__]
+
+
+def mk_msg_spec(
+    payload_type_union: Union[Type] = Any,
+
+    spec_build_method: Literal[
+        'indexed_generics',  # works
+        'defstruct',
+        'types_new_class',
+
+    ] = 'indexed_generics',
+
+) -> tuple[
+    Union[MsgType],
+    list[MsgType],
+]:
+    '''
+    Create a payload-(data-)type-parameterized IPC message specification.
+
+    Allows generating IPC msg types from the above builtin set
+    with a payload (field) restricted data-type, the `Msg.pld: PayloadT`.
+
+    This allows runtime-task contexts to use the python type system
+    to limit/filter payload values as determined by the input
+    `payload_type_union: Union[Type]`.
+
+    Notes: originally multiple approaches for constructing the
+    type-union passed to `msgspec` were attempted as selected via the
+    `spec_build_method`, but it turns out only the defaul method
+    'indexed_generics' seems to work reliably in all use cases. As
+    such, the others will likely be removed in the near future.
+
+    '''
+    submsg_types: list[MsgType] = Msg.__subclasses__()
+    bases: tuple = (
+        # XXX NOTE XXX the below generic-parameterization seems to
+        # be THE ONLY way to get this to work correctly in terms
+        # of getting ValidationError on a roundtrip?
+        Msg[payload_type_union],
+        Generic[PayloadT],
+    )
+    defstruct_bases: tuple = (
+        Msg, # [payload_type_union],
+        # Generic[PayloadT],
+        # ^-XXX-^: not allowed? lul..
+    )
+    ipc_msg_types: list[Msg] = []
+
+    idx_msg_types: list[Msg] = []
+    defs_msg_types: list[Msg] = []
+    nc_msg_types: list[Msg] = []
+
+    for msgtype in __msg_types__:
+
+        # for the NON-payload (user api) type specify-able
+        # msgs types, we simply aggregate the def as is
+        # for inclusion in the output type `Union`.
+        if msgtype not in _payload_msgs:
+            ipc_msg_types.append(msgtype)
+            continue
+
+        # check inheritance sanity
+        assert msgtype in submsg_types
+
+        # TODO: wait why do we need the dynamic version here?
+        # XXX ANSWER XXX -> BC INHERITANCE.. don't work w generics..
+        #
+        # NOTE previously bc msgtypes WERE NOT inheritting
+        # directly the `Generic[PayloadT]` type, the manual method
+        # of generic-paraming with `.__class_getitem__()` wasn't
+        # working..
+        #
+        # XXX but bc i changed that to make every subtype inherit
+        # it, this manual "indexed parameterization" method seems
+        # to work?
+        #
+        # -[x] paraming the `PayloadT` values via `Generic[T]`
+        #   does work it seems but WITHOUT inheritance of generics
+        #
+        # -[-] is there a way to get it to work at module level
+        #   just using inheritance or maybe a metaclass?
+        #  => thot that `defstruct` might work, but NOPE, see
+        #   below..
+        #
+        idxed_msg_type: Msg = msgtype[payload_type_union]
+        idx_msg_types.append(idxed_msg_type)
+
+        # TODO: WHY do we need to dynamically generate the
+        # subtype-msgs here to ensure the `.pld` parameterization
+        # propagates as well as works at all in terms of the
+        # `msgpack.Decoder()`..?
+        #
+        # dynamically create the payload type-spec-limited msg set.
+        newclass_msgtype: Type = types.new_class(
+            name=msgtype.__name__,
+            bases=bases,
+            kwds={},
+        )
+        nc_msg_types.append(
+            newclass_msgtype[payload_type_union]
         )
 
-    # TODO: use a pprint.PrettyPrinter instance around ONLY rendering
-    # inside a known tty?
-    # def __repr__(self) -> str:
-    #     ...
+        # with `msgspec.structs.defstruct`
+        # XXX ALSO DOESN'T WORK
+        defstruct_msgtype = defstruct(
+            name=msgtype.__name__,
+            fields=[
+                ('cid', str),
 
-    # __str__ = __repr__ = pformat
-    __repr__ = pformat
+                # XXX doesn't seem to work..
+                # ('pld', PayloadT),
 
-    def copy(
-        self,
-        update: dict | None = None,
-
-    ) -> Struct:
-        '''
-        Validate-typecast all self defined fields, return a copy of
-        us with all such fields.
-
-        NOTE: This is kinda like the default behaviour in
-        `pydantic.BaseModel` except a copy of the object is
-        returned making it compat with `frozen=True`.
-
-        '''
-        if update:
-            for k, v in update.items():
-                setattr(self, k, v)
-
-        # NOTE: roundtrip serialize to validate
-        # - enode to msgpack binary format,
-        # - decode that back to a struct.
-        return msgpack.Decoder(type=type(self)).decode(
-            msgpack.Encoder().encode(self)
+                ('pld', payload_type_union),
+            ],
+            bases=defstruct_bases,
         )
+        defs_msg_types.append(defstruct_msgtype)
 
-    def typecast(
-        self,
+        # assert index_paramed_msg_type == manual_paramed_msg_subtype
 
-        # TODO: allow only casting a named subset?
-        # fields: set[str] | None = None,
+        # paramed_msg_type = manual_paramed_msg_subtype
 
-    ) -> None:
-        '''
-        Cast all fields using their declared type annotations
-        (kinda like what `pydantic` does by default).
+        # ipc_payload_msgs_type_union |= index_paramed_msg_type
 
-        NOTE: this of course won't work on frozen types, use
-        ``.copy()`` above in such cases.
+    idx_spec: Union[Type[Msg]] = Union[*idx_msg_types]
+    def_spec: Union[Type[Msg]] = Union[*defs_msg_types]
+    nc_spec: Union[Type[Msg]] = Union[*nc_msg_types]
 
-        '''
-        # https://jcristharif.com/msgspec/api.html#msgspec.structs.fields
-        fi: structs.FieldInfo
-        for fi in structs.fields(self):
-            setattr(
-                self,
-                fi.name,
-                fi.type(getattr(self, fi.name)),
-            )
+    specs: dict[str, Union[Type[Msg]]] = {
+        'indexed_generics': idx_spec,
+        'defstruct': def_spec,
+        'types_new_class': nc_spec,
+    }
+    msgtypes_table: dict[str, list[Msg]] = {
+        'indexed_generics': idx_msg_types,
+        'defstruct': defs_msg_types,
+        'types_new_class': nc_msg_types,
+    }
 
-    def __sub__(
-        self,
-        other: Struct,
+    # XXX lol apparently type unions can't ever
+    # be equal eh?
+    # TODO: grok the diff here better..
+    #
+    # assert (
+    #     idx_spec
+    #     ==
+    #     nc_spec
+    #     ==
+    #     def_spec
+    # )
+    # breakpoint()
 
-    ) -> DiffDump[tuple[str, Any, Any]]:
-        '''
-        Compare fields/items key-wise and return a ``DiffDump``
-        for easy visual REPL comparison B)
-
-        '''
-        diffs: DiffDump[tuple[str, Any, Any]] = DiffDump()
-        for fi in structs.fields(self):
-            attr_name: str = fi.name
-            ours: Any = getattr(self, attr_name)
-            theirs: Any = getattr(other, attr_name)
-            if ours != theirs:
-                diffs.append((
-                    attr_name,
-                    ours,
-                    theirs,
-                ))
-
-        return diffs
+    pld_spec: Union[Type] = specs[spec_build_method]
+    runtime_spec: Union[Type] = Union[*ipc_msg_types]
+    ipc_spec = pld_spec | runtime_spec
+    log.runtime(
+        'Generating new IPC msg-spec\n'
+        f'{ipc_spec}\n'
+    )
+    assert (
+        ipc_spec
+        and
+        ipc_spec is not Any
+    )
+    return (
+        ipc_spec,
+        msgtypes_table[spec_build_method]
+        +
+        ipc_msg_types,
+    )

tractor/to_asyncio.py

@@ -577,14 +577,18 @@ def run_as_asyncio_guest(
                 log.runtime(f"trio_main finished: {main_outcome!r}")
 
         # start the infection: run trio on the asyncio loop in "guest mode"
-        log.info(f"Infecting asyncio process with {trio_main}")
+        log.runtime(
+            'Infecting `asyncio`-process with a `trio` guest-run of\n\n'
+            f'{trio_main!r}\n\n'
 
+            f'{trio_done_callback}\n'
+        )
         trio.lowlevel.start_guest_run(
             trio_main,
             run_sync_soon_threadsafe=loop.call_soon_threadsafe,
             done_callback=trio_done_callback,
         )
-        # ``.unwrap()`` will raise here on error
+        # NOTE `.unwrap()` will raise on error
         return (await trio_done_fut).unwrap()
 
     # might as well if it's installed.

tractor/trionics/_broadcast.py

@@ -156,11 +156,12 @@ class BroadcastState(Struct):
 
 class BroadcastReceiver(ReceiveChannel):
     '''
-    A memory receive channel broadcaster which is non-lossy for the
-    fastest consumer.
+    A memory receive channel broadcaster which is non-lossy for
+    the fastest consumer.
 
-    Additional consumer tasks can receive all produced values by registering
-    with ``.subscribe()`` and receiving from the new instance it delivers.
+    Additional consumer tasks can receive all produced values by
+    registering with ``.subscribe()`` and receiving from the new
+    instance it delivers.
 
     '''
     def __init__(

tractor/trionics/_mngrs.py

@@ -18,8 +18,12 @@
 Async context manager primitives with hard ``trio``-aware semantics
 
 '''
-from contextlib import asynccontextmanager as acm
+from __future__ import annotations
+from contextlib import (
+    asynccontextmanager as acm,
+)
 import inspect
+from types import ModuleType
 from typing import (
     Any,
     AsyncContextManager,
@@ -30,13 +34,16 @@ from typing import (
     Optional,
     Sequence,
     TypeVar,
+    TYPE_CHECKING,
 )
 
 import trio
-
 from tractor._state import current_actor
 from tractor.log import get_logger
 
+if TYPE_CHECKING:
+    from tractor import ActorNursery
+
 
 log = get_logger(__name__)
 
@@ -46,8 +53,10 @@ T = TypeVar("T")
 
 @acm
 async def maybe_open_nursery(
-    nursery: trio.Nursery | None = None,
+    nursery: trio.Nursery|ActorNursery|None = None,
     shield: bool = False,
+    lib: ModuleType = trio,
+
 ) -> AsyncGenerator[trio.Nursery, Any]:
     '''
     Create a new nursery if None provided.
@@ -58,13 +67,12 @@ async def maybe_open_nursery(
     if nursery is not None:
         yield nursery
     else:
-        async with trio.open_nursery() as nursery:
+        async with lib.open_nursery() as nursery:
             nursery.cancel_scope.shield = shield
             yield nursery
 
 
 async def _enter_and_wait(
-
     mngr: AsyncContextManager[T],
     unwrapped: dict[int, T],
     all_entered: trio.Event,
@@ -91,7 +99,6 @@ async def _enter_and_wait(
 
 @acm
 async def gather_contexts(
-
     mngrs: Sequence[AsyncContextManager[T]],
 
 ) -> AsyncGenerator[
@@ -102,15 +109,17 @@ async def gather_contexts(
     None,
 ]:
     '''
-    Concurrently enter a sequence of async context managers, each in
-    a separate ``trio`` task and deliver the unwrapped values in the
-    same order once all managers have entered. On exit all contexts are
-    subsequently and concurrently exited.
+    Concurrently enter a sequence of async context managers (acms),
+    each from a separate `trio` task and deliver the unwrapped
+    `yield`-ed values in the same order once all managers have entered.
 
-    This function is somewhat similar to common usage of
-    ``contextlib.AsyncExitStack.enter_async_context()`` (in a loop) in
-    combo with ``asyncio.gather()`` except the managers are concurrently
-    entered and exited, and cancellation just works.
+    On exit, all acms are subsequently and concurrently exited.
+
+    This function is somewhat similar to a batch of non-blocking
+    calls to `contextlib.AsyncExitStack.enter_async_context()`
+    (inside a loop) *in combo with* a `asyncio.gather()` to get the
+    `.__aenter__()`-ed values, except the managers are both
+    concurrently entered and exited and *cancellation just works*(R).
 
     '''
     seed: int = id(mngrs)
@@ -210,9 +219,10 @@ async def maybe_open_context(
 
 ) -> AsyncIterator[tuple[bool, T]]:
     '''
-    Maybe open a context manager if there is not already a _Cached
-    version for the provided ``key`` for *this* actor. Return the
-    _Cached instance on a _Cache hit.
+    Maybe open an async-context-manager (acm) if there is not already
+    a `_Cached` version for the provided (input) `key` for *this* actor.
+
+    Return the `_Cached` instance on a _Cache hit.
 
     '''
     fid = id(acm_func)
@@ -271,8 +281,16 @@ async def maybe_open_context(
         yield False, yielded
 
     else:
-        log.info(f'Reusing _Cached resource for {ctx_key}')
         _Cache.users += 1
+        log.runtime(
+            f'Re-using cached resource for user {_Cache.users}\n\n'
+            f'{ctx_key!r} -> {type(yielded)}\n'
+
+            # TODO: make this work with values but without
+            # `msgspec.Struct` causing frickin crashes on field-type
+            # lookups..
+            # f'{ctx_key!r} -> {yielded!r}\n'
+        )
         lock.release()
         yield True, yielded