为什么我在这里收到连接重置错误

Question

我是Python 3的新手，正在玩asyncio。因此，我在以下服务器端代码中遇到了奇怪的行为：

import asyncio

@asyncio.coroutine
def handle_client(reader, writer):
    print('Client connected.')
    client_connected = True
    while client_connected:
        print('Waiting for client event.')
        line = yield from reader.readline()
        if line:
            print('Got: {}'.format(line))
            if line.decode() == 'echon':
                print('Sending back echo.')
                writer.write(line)
            else:
                print('Not sending back anything.')
        else:
            print('Client disconnected.')
            client_connected = False

if __name__ == '__main__':
    asyncio.async(asyncio.start_server(handle_client, 'localhost', 8888))
    asyncio.get_event_loop().run_forever()

当我运行此客户端代码时（编辑：客户端代码手动输入到 IPython 会话中，服务器肯定有时间在我关闭套接字之前写入）...

import socket
client = socket.create_connection(('localhost', 8888))
client.sendall('echon'.encode())
client.close()

。我从服务器收到错误回溯：

C:UsersGnarAnaconda3python.exe C:/Users/Gnar/Code/echo.py
Client connected.
Waiting for client event.
Got: b'echon'
Sending back echo.
Waiting for client event.
Task exception was never retrieved
future: <Task finished coro=<handle_client() done, defined at C:/Users/Gnar/Code/echo.py:4> exception=ConnectionResetError(10054, 'An existing connection was forcibly closed by the remote host', None, 10054, None)>
Traceback (most recent call last):
  File "C:UsersGnarAnaconda3libasynciotasks.py", line 234, in _step
    result = coro.throw(exc)
  File "C:/Users/Gnar/Code/echo.py", line 10, in handle_client
    line = yield from reader.readline()
  File "C:UsersGnarAnaconda3libasynciostreams.py", line 425, in readline
    yield from self._wait_for_data('readline')
  File "C:UsersGnarAnaconda3libasynciostreams.py", line 393, in _wait_for_data
    yield from self._waiter
  File "C:UsersGnarAnaconda3libasynciofutures.py", line 386, in __iter__
    yield self  # This tells Task to wait for completion.
  File "C:UsersGnarAnaconda3libasynciotasks.py", line 287, in _wakeup
    value = future.result()
  File "C:UsersGnarAnaconda3libasynciofutures.py", line 275, in result
    raise self._exception
  File "C:UsersGnarAnaconda3libasyncioselector_events.py", line 662, in _read_ready
    data = self._sock.recv(self.max_size)
ConnectionResetError: [WinError 10054] An existing connection was forcibly closed by the remote host

问题必须以某种方式与writer.write有关，因为当我调用以下客户端代码（使服务器跳过写入）时，没有错误：

import socket
client = socket.create_connection(('localhost', 8888))
client.sendall('foon'.encode())
client.close()

相应的服务器日志：

C:UsersGnarAnaconda3python.exe C:/Users/Gnar/Code/echo.py
Client connected.
Waiting for client event.
Got: b'foon'
Not sending back anything.
Waiting for client event.
Client disconnected.

我错过了什么？我是否错误地使用了异步？

谢谢！

Answer 1

您

收到异常是因为您尝试将一些数据写回服务器端的客户端，但客户端在发送'echo'后立即关闭socket，而实际上没有收到来自服务器的响应。如果套接字连接在线路上有未接收的数据时关闭，您将在发送端收到错误，以便您知道远程端可能没有收到您上次发送的任何内容。

如果在调用socket.close()之前在客户端添加对socket.recv(1024)的调用，则问题就会消失，以便客户端在关闭套接字之前等待服务器的响应。如果您只想优雅地处理异常，即使客户端做了错误的事情，您也可以在服务器端的写入调用周围使用 try/except。