Add pre-stream open error conditions

tractor/_streaming.py

@@ -15,7 +15,7 @@ import warnings
 import trio
 
 from ._ipc import Channel
-from ._exceptions import unpack_error
+from ._exceptions import unpack_error, ContextCancelled
 from ._state import current_actor
 from .log import get_logger
 
@@ -135,16 +135,6 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
 
             raise  # propagate
 
-        # except trio.Cancelled:
-        #     if not self._shielded:
-        #         # if shielded we don't propagate a cancelled
-        #         raise
-
-        # except trio.Cancelled:
-        #     # relay cancels to the remote task
-        #     await self.aclose()
-        #     raise
-
     @contextmanager
     def shield(
         self
@@ -171,7 +161,7 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
         # https://trio.readthedocs.io/en/stable/reference-io.html#trio.abc.AsyncResource.aclose
         rx_chan = self._rx_chan
 
-        if rx_chan._closed: # or self._eoc:
+        if rx_chan._closed:
             log.warning(f"{self} is already closed")
 
             # this stream has already been closed so silently succeed as
@@ -440,19 +430,25 @@ class Context:
             self.cid
         )
 
-        # XXX: If the underlying receive mem chan has been closed then
-        # likely client code has already exited a ``.open_stream()``
-        # block prior. we error here until such a time that we decide
-        # allowing streams to be "re-connected" is supported and/or
-        # a good idea.
-        if recv_chan._closed:
+        # Likewise if the surrounding context has been cancelled we error here
+        # since it likely means the surrounding block was exited or
+        # killed
+
+        if self._cancel_called:
             task = trio.lowlevel.current_task().name
-            raise trio.ClosedResourceError(
-                f'stream for {actor.uid[0]}:{task} has already been closed.'
-                '\nRe-opening a closed stream is not yet supported!'
-                '\nConsider re-calling the containing `@tractor.context` func'
+            raise ContextCancelled(
+                f'Context around {actor.uid[0]}:{task} was already cancelled!'
             )
 
+        # 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 recv_chan._closed:
+            raise trio.ClosedResourceError(
+                'The underlying channel for this stream was already closed!?')
+
         async with MsgStream(
             ctx=self,
             rx_chan=recv_chan,