Raise a `MessagingError` from the src error on msging edge cases

tractor/_streaming.py

@@ -23,6 +23,7 @@ The machinery and types behind ``Context.open_stream()``
 from __future__ import annotations
 import inspect
 from contextlib import asynccontextmanager as acm
+from pprint import pformat
 from typing import (
     Any,
     Callable,
@@ -35,6 +36,7 @@ import trio
 
 from ._exceptions import (
     unpack_error,
+    MessagingError,
 )
 from .log import get_logger
 from .trionics import (
@@ -66,6 +68,8 @@ def _raise_from_no_yield_msg(
     `'yield'` field.
 
     '''
+    __tracebackhide__: bool = True
+
     # internal error should never get here
     assert msg.get('cid'), ("Received internal error at portal?")
 
@@ -73,18 +77,22 @@ def _raise_from_no_yield_msg(
     # - 'stop'
     # - 'error'
     # possibly just handle msg['stop'] here!
+    # breakpoint()
 
     if stream._closed:
         raise trio.ClosedResourceError('This stream was closed')
 
-    if msg.get('stop') or stream._eoc:
-        log.debug(f"{stream} was stopped at remote end")
+    if (
+        msg.get('stop')
+        or stream._eoc
+    ):
+        log.debug(f'{stream} was stopped at remote end')
 
         # XXX: important to set so that a new ``.receive()``
         # call (likely by another task using a broadcast receiver)
         # doesn't accidentally pull the ``return`` message
         # value out of the underlying feed mem chan!
-        stream._eoc = True
+        stream._eoc: bool = True
 
         # # when the send is closed we assume the stream has
         # # terminated and signal this local iterator to stop
@@ -93,20 +101,24 @@ def _raise_from_no_yield_msg(
         # XXX: this causes ``ReceiveChannel.__anext__()`` to
         # raise a ``StopAsyncIteration`` **and** in our catch
         # block below it will trigger ``.aclose()``.
-        raise trio.EndOfChannel from src_err
+        raise trio.EndOfChannel(
+                'Stream ended due to msg:\n'
+                f'{pformat(msg)}'
+        ) from src_err
 
     # TODO: test that shows stream raising an expected error!!!
     elif msg.get('error'):
         # raise the error message
         raise unpack_error(msg, stream._ctx.chan)
 
-    # always re-raise the source error if no translation error
-    # case is activated above.
-    raise src_err
-    # raise RuntimeError(
-    #     'Unknown non-yield stream msg?\n'
-    #     f'{msg}'
-    # )
+    # always re-raise the source error if no translation error case
+    # is activated above.
+    raise MessagingError(
+        f'Context received unexpected non-error msg!?\n'
+        f'cid: {cid}\n'
+        'received msg:\n'
+        f'{pformat(msg)}'
+    ) from src_err
 
 
 class MsgStream(trio.abc.Channel):
@@ -161,6 +173,16 @@ class MsgStream(trio.abc.Channel):
         determined by the underlying protocol).
 
         '''
+        # NOTE: `trio.ReceiveChannel` implements
+        # EOC handling as follows (aka uses it
+        # to gracefully exit async for loops):
+        #
+        # async def __anext__(self) -> ReceiveType:
+        #     try:
+        #         return await self.receive()
+        #     except trio.EndOfChannel:
+        #         raise StopAsyncIteration
+
         # see ``.aclose()`` for notes on the old behaviour prior to
         # introducing this
         if self._eoc: