websockets.exceptions.ConnectionClosedError in very minimalistic example

[juergendrachta]

For getting to know the websockets package, I started with a very minimal example with fails with an ConnectionClosedError after ~10 s.
I'm using Python 3.7.
I suspected, that there might be somewhere a timeout, but I haven't found anything. As far as I understood the docs, the connection should stay alive?

server.py

import websockets
import asyncio


async def main(ws, _):
    while(True):
        msg = await ws.recv()
        print(msg)


start_server = websockets.serve(main, "localhost", "1236")

asyncio.get_event_loop().run_until_complete(start_server)
asyncio.get_event_loop().run_forever()

client.py

import asyncio
import websockets


async def main():
    uri = "ws://localhost:1236"
    async with websockets.connect(uri) as ws:
        while True:
            await ws.send(input())


asyncio.get_event_loop().run_until_complete(main())

The full error reads

Error in connection handler
Traceback (most recent call last):
  File "***lib/python3.7/site-packages/websockets/protocol.py", line 827, in transfer_data
    message = await self.read_message()
  File "***lib/python3.7/site-packages/websockets/protocol.py", line 895, in read_message
    frame = await self.read_data_frame(max_size=self.max_size)
  File "***lib/python3.7/site-packages/websockets/protocol.py", line 971, in read_data_frame
    frame = await self.read_frame(max_size)
  File "***lib/python3.7/site-packages/websockets/protocol.py", line 1051, in read_frame
    extensions=self.extensions,
  File "***lib/python3.7/site-packages/websockets/framing.py", line 105, in read
    data = await reader(2)
  File "***lib/python3.7/asyncio/streams.py", line 679, in readexactly
    await self._wait_for_data('readexactly')
  File "***lib/python3.7/asyncio/streams.py", line 473, in _wait_for_data
    await self._waiter
concurrent.futures._base.CancelledError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "***lib/python3.7/site-packages/websockets/server.py", line 191, in handler
    await self.ws_handler(self, path)
  File "/home/juergen/projects/poker/src/server/min_ex_server2.py", line 14, in main
    msg = await ws.recv()
  File "***lib/python3.7/site-packages/websockets/protocol.py", line 509, in recv
    await self.ensure_open()
  File "***lib/python3.7/site-packages/websockets/protocol.py", line 812, in ensure_open
    raise self.connection_closed_exc()
websockets.exceptions.ConnectionClosedError: code = 1006 (connection closed abnormally [internal]), no reason

[aaugustin]

Your example fails because input() blocks the event loop.

This is why main.py runs the event loop and the input() calls in separate threads. I believe this is the simplest solution with asyncio (even though it's a bit involved).