Mplex: change message channel size to 8

To avoid infinity sized channel, and to conform to the go
implementation.

libp2p/stream_muxer/mplex/mplex.py

@@ -1,5 +1,4 @@
 import logging
-import math
 from typing import Dict, Optional, Tuple
 
 import trio
@@ -24,6 +23,8 @@ from .exceptions import MplexUnavailable
 from .mplex_stream import MplexStream
 
 MPLEX_PROTOCOL_ID = TProtocol("/mplex/6.7.0")
+# Ref: https://github.com/libp2p/go-mplex/blob/master/multiplex.go#L115
+MPLEX_MESSAGE_CHANNEL_SIZE = 8
 
 logger = logging.getLogger("libp2p.stream_muxer.mplex.mplex")
 
@@ -109,9 +110,9 @@ class Mplex(IMuxedConn):
         return next_id
 
     async def _initialize_stream(self, stream_id: StreamID, name: str) -> MplexStream:
-        # Use an unbounded buffer, to avoid `handle_incoming` being blocked when doing
-        # `send_channel.send`.
-        send_channel, receive_channel = trio.open_memory_channel[bytes](math.inf)
+        send_channel, receive_channel = trio.open_memory_channel[bytes](
+            MPLEX_MESSAGE_CHANNEL_SIZE
+        )
         stream = MplexStream(name, stream_id, self, receive_channel)
         async with self.streams_lock:
             self.streams[stream_id] = stream
@@ -145,7 +146,7 @@ class Mplex(IMuxedConn):
         """
         sends a message over the connection.
 
-        :param header: header to use
+        :param flag: header to use
         :param data: data to send in the message
         :param stream_id: stream the message is in
         """
@@ -270,9 +271,15 @@ class Mplex(IMuxedConn):
                 # TODO: Warn "Received data from remote after stream was closed by them. (len = %d)"  # noqa: E501
                 return
         try:
-            await send_channel.send(message)
+            send_channel.send_nowait(message)
         except (trio.BrokenResourceError, trio.ClosedResourceError):
             raise MplexUnavailable
+        except trio.WouldBlock:
+            # `send_channel` is full, reset this stream.
+            logger.warning(
+                "message channel of stream %s is full: stream is reset", stream_id
+            )
+            await stream.reset()
 
     async def _handle_close(self, stream_id: StreamID) -> None:
         async with self.streams_lock: