WebSockets接收中断信号后无法通信的问题及解决咨询

服务端代码 #

import websockets
async def handler(ws):
  async for message in ws:
    print(message)
    await ws.send('received' + message)
server = await websockets.serve(handler, 'localhost', 22235)

客户端代码 #

import websockets
import asyncio
import json

async def keep_recv():
  ws = await websockets.connect('ws://localhost:22235')
  while True:
    try:
      response = await ws.recv()
      print(f"Received from server: {response}")
      await asyncio.create_task(asyncio.sleep(10000))
    finally:
      print('cancelled')
      await ws.send('client cancelled')
      response = await ws.recv()
      print(f"Received from server: {response}")
      break

asyncio.run(keep_recv())

预期输出 #

客户端预期输出 #

cancelled
Received from server: client cancelled

服务端预期输出 #

client cancelled

实际输出 #

客户端实际输出 #

cancelled

随后客户端卡在ws.send操作，一段时间后抛出KeyboardInterrupt错误退出。

服务端实际输出 #

无即时输出，一段时间后打印错误信息：

websockets.exceptions.ConnectionClosedError: no close frame received or sent

之后服务端继续运行。

核心问题 #

1. WebSockets在程序接收中断信号后是否会停止通信？该如何解决此问题？
2. 尝试在客户端用except Exception捕获异常时，为何不会打印asyncio.CancelledError，而是直接进入finally块？

问题原因与解决方法 #

问题1：捕获不到CancelledError的原因 #

asyncio.CancelledError继承自BaseException而非Exception，所以except Exception无法捕获它，会直接进入finally块。

问题2：中断后WebSocket通信失败的原因 #

按下Ctrl+C时，asyncio.run()会触发KeyboardInterrupt，进而引发任务的CancelledError。此时事件循环处于待关闭状态，finally块中的WebSocket操作（send/recv）会因连接状态异常或事件循环资源不足而阻塞，最终超时报错。

具体解决方案 #

1. 正确捕获CancelledError并处理WebSocket通信

修改客户端代码，直接捕获CancelledError，并在通信时添加超时和连接状态检查：

import websockets
import asyncio

async def keep_recv():
  ws = await websockets.connect('ws://localhost:22235')
  while True:
    try:
      response = await ws.recv()
      print(f"Received from server: {response}")
      await asyncio.sleep(10000)  # 无需用create_task，确保sleep能被中断
    except asyncio.CancelledError:
      print("任务被取消")
    except Exception as e:
      print(f"其他异常: {e}")
    finally:
      print('cancelled')
      try:
        # 先检查连接是否仍处于打开状态
        if ws.open:
          await ws.send('client cancelled')
          # 给recv设置超时，避免无限等待
          response = await asyncio.wait_for(ws.recv(), timeout=5)
          print(f"Received from server: {response}")
      except (websockets.exceptions.ConnectionClosed, asyncio.TimeoutError):
        print("通信失败或超时")
      finally:
        await ws.close()
        break

asyncio.run(keep_recv())

2. 优雅处理中断信号

通过注册信号处理器，确保收到Ctrl+C时能完成必要通信再退出：

import websockets
import asyncio
import signal

async def keep_recv():
  ws = await websockets.connect('ws://localhost:22235')
  loop = asyncio.get_running_loop()
  # 注册SIGINT和SIGTERM信号处理
  for sig in (signal.SIGINT, signal.SIGTERM):
    loop.add_signal_handler(sig, lambda: asyncio.create_task(shutdown(ws)))
  
  try:
    while True:
      response = await ws.recv()
      print(f"Received from server: {response}")
      await asyncio.sleep(10000)
  except asyncio.CancelledError:
    pass

async def shutdown(ws):
  print('cancelled')
  try:
    if ws.open:
      await ws.send('client cancelled')
      response = await asyncio.wait_for(ws.recv(), timeout=5)
      print(f"Received from server: {response}")
  except (websockets.exceptions.ConnectionClosed, asyncio.TimeoutError):
    print("通信失败或超时")
  finally:
    await ws.close()
    asyncio.get_running_loop().stop()

asyncio.run(keep_recv())

3. 服务端添加异常处理

给服务端补充连接关闭的异常捕获，避免不必要的错误输出：

import websockets
import asyncio

async def handler(ws):
  try:
    async for message in ws:
      print(message)
      await ws.send('received' + message)
  except websockets.exceptions.ConnectionClosed:
    print("客户端连接已关闭")

async def main():
  server = await websockets.serve(handler, 'localhost', 22235)
  await server.wait_closed()

asyncio.run(main())

内容的提问来源于stack exchange，提问作者Donny