Question

我正在使用asyncio.Protocol服务器，其目的是让客户端调用服务器，但等待，直到服务器响应并在停止客户端循环之前返回数据。

基于asyncio doc Echo Client和Server：https://docs.python.org/3/library/asyncio-protocol.html#protocol-example-tcp-echo-server-and-client，在调用时会立即返回transport.write（...）的结果。

根据经验，使用loop.run_until_complete(coroutine)

调用RuntimeError: Event loop is running.失败

在服务器的asyncio.sleep(n)方法中运行data_received()也没有任何效果。

<{1}} yield from asyncio.sleep(n)和yield from asyncio.async(asyncio.sleep(n)) data_received()都挂起了服务器。

我的问题是，如何让我的客户端在回馈控制权之前等待服务器编写响应？

Answer 1

您不必更改客户端代码。

<强> echo-client.py

#!/usr/bin/env python3.4
import asyncio

class EchoClient(asyncio.Protocol):
    message = 'Client Echo'

    def connection_made(self, transport):
        transport.write(self.message.encode())
        print('data sent: {}'.format(self.message))

    def data_received(self, data):
        print('data received: {}'.format(data.decode()))

    def connection_lost(self, exc):
        print('server closed the connection')
        asyncio.get_event_loop().stop()

loop = asyncio.get_event_loop()
coro = loop.create_connection(EchoClient, '127.0.0.1', 8888)
loop.run_until_complete(coro)
loop.run_forever()
loop.close()

诀窍是将代码（包括self.transport方法）放入协程并使用wait_for()方法，在需要返回值的语句前面加yield from语句，或者需要一段时间才能完成的事情：

<强> echo-server.py

#!/usr/bin/env python3.4
import asyncio

class EchoServer(asyncio.Protocol):
    def connection_made(self, transport):
        peername = transport.get_extra_info('peername')
        print('connection from {}'.format(peername))
        self.transport = transport

    def data_received(self, data):
        print('data received: {}'.format(data.decode()))
        fut = asyncio.async(self.sleeper())
        result = asyncio.wait_for(fut, 60)

    @asyncio.coroutine
    def sleeper(self):
        yield from asyncio.sleep(2)
        self.transport.write("Hello World".encode())
        self.transport.close()

loop = asyncio.get_event_loop()
coro = loop.create_server(EchoServer, '127.0.0.1', 8888)
server = loop.run_until_complete(coro)
print('serving on {}'.format(server.sockets[0].getsockname()))

try:
    loop.run_forever()
except KeyboardInterrupt:
    print("exit")
finally:
    server.close()
    loop.close()

调用echo-server.py然后调用echo-client.py，客户端将按asyncio.sleep确定等待2秒，然后停止。

Answer 2

我想永远不要直接使用传输/协议对。

asyncio具有用于高级编程的Streams API。

客户端代码可能如下所示：

@asyncio.coroutine
def communicate():
    reader, writer = yield from asyncio.open_connection(HOST, PORT)
    writer.write(b'data')
    yield from writer.drain()
    answer = yield from reader.read()
    # process answer, maybe send new data back to server and wait for answer again
    writer.close()

如何让我的asyncio客户端调用套接字服务器并等待响应

2 个答案: