Python websockets onclose

Question

In javascript, we have WebSocket.onclose() for doing some stuff when a websocket connection is closed by the server. Is there a way to do the same in a Python server when the connection is closed by the client device? The server is run using the websockets module itself using the websockets.serve() method. Both the .Connected & .ConnectionClosed aren’t attributes of WebSocketServerProtocol (or so the error says). Any help would be appreciated.

Asked By: Vishal DS

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Answer 1

Both recv() and send() will raise a websockets.exceptions.ConnectionClosed on a closed connection. Handle your cleanup there. See https://websockets.readthedocs.io/en/stable/howto/cheatsheet.html

Here’s a slight modification of the websocket web example from the docs:

import asyncio
import datetime
import random
import websockets

async def time(websocket, path):
    while True:
        now = datetime.datetime.utcnow().isoformat() + "Z"
        try:
            await websocket.send(now)
        except websockets.exceptions.ConnectionClosed:
            print("Client disconnected.  Do cleanup")
            break             
        await asyncio.sleep(random.random() * 3)

start_server = websockets.serve(time, "127.0.0.1", 5678)

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

Example client:

import asyncio
import websockets

async def hello():
    uri = "ws://localhost:5678"
    count = 5
    async with websockets.connect(uri) as websocket:
        while count > 0:
            greeting = await websocket.recv()
            print(f"< {greeting}")
            count = count - 1

asyncio.get_event_loop().run_until_complete(hello())

Answered By: clockwatcher

Python websockets onclose

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