使用 asyncio 的 Python 简单套接字客户端/服务器

Question

我想使用 asyncio 协程而不是多线程来重新实现我的代码。

server.py

def handle_client(client):
    request = None
    while request != 'quit':
        request = client.recv(255).decode('utf8')
        response = cmd.run(request)
        client.send(response.encode('utf8'))
    client.close()

server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server.bind(('localhost', 15555))
server.listen(8)

try:
    while True:
        client, _ = server.accept()
        threading.Thread(target=handle_client, args=(client,)).start()
except KeyboardInterrupt:
    server.close()

client.py

server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server.connect(('localhost', 15555))
request = None

try:
    while request != 'quit':
        request = input('>> ')
        if request:
            server.send(request.encode('utf8'))
            response = server.recv(255).decode('utf8')
            print(response)
except KeyboardInterrupt:
    server.close()

我知道有一些合适的异步网络库可以做到这一点。但我只是想在这个案例上只使用 asyncio 核心库，以便更好地理解它。

在处理客户端定义之前只添加 async 关键字会非常好...这里有一段代码似乎可以工作，但我仍然对实现感到困惑。

asyncio_server.py

def handle_client(client):
    request = None
    while request != 'quit':
        request = client.recv(255).decode('utf8')
        response = cmd.run(request)
        client.send(response.encode('utf8'))
    client.close()

def run_server(server):
    client, _ = server.accept()
    handle_client(client)

server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server.bind(('localhost', 15555))
server.listen(8)

loop = asyncio.get_event_loop()
asyncio.async(run_server(server))
try:
    loop.run_forever()
except KeyboardInterrupt:
    server.close()

如何以最佳方式适应这一点并使用 async await 关键字。

Answer 1

线程代码的最接近的字面翻译将像以前一样创建套接字，使其非阻塞，并使用asyncio low-level socket operations 来实现服务器。这是一个示例，坚持更相关的服务器部分（客户端是单线程的，可能原样正常）：

import asyncio, socket

async def handle_client(client):
    loop = asyncio.get_event_loop()
    request = None
    while request != 'quit':
        request = (await loop.sock_recv(client, 255)).decode('utf8')
        response = str(eval(request)) + '\n'
        await loop.sock_sendall(client, response.encode('utf8'))
    client.close()

async def run_server():
    server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server.bind(('localhost', 15555))
    server.listen(8)
    server.setblocking(False)

    loop = asyncio.get_event_loop()

    while True:
        client, _ = await loop.sock_accept(server)
        loop.create_task(handle_client(client))

asyncio.run(run_server())

上述方法有效，但不是使用asyncio 的预期方式。它是非常低级的，因此容易出错，需要您记住在套接字上设置适当的标志。此外，没有缓冲，所以像从客户端读取一行这样简单的事情变得令人厌烦。此 API 级别实际上仅适用于替代事件循环的实现者，它们将提供sock_recv、sock_sendall 等的他们的实现。

Asyncio 的公共 API 提供了两个用于消费的抽象层：以 Twisted 为模型的旧的 transport/protocol layer 和较新的 streams layer。在新代码中，您几乎肯定想要使用流 API，即调用 asyncio.start_server 并避免使用原始套接字。这显着减少了行数：

import asyncio, socket

async def handle_client(reader, writer):
    request = None
    while request != 'quit':
        request = (await reader.read(255)).decode('utf8')
        response = str(eval(request)) + '\n'
        writer.write(response.encode('utf8'))
        await writer.drain()
    writer.close()

async def run_server():
    server = await asyncio.start_server(handle_client, 'localhost', 15555)
    async with server:
        await server.serve_forever()

asyncio.run(run_server())

Answer 2

我已经阅读了上面的答案和 cmets，试图弄清楚如何将asynchio lib 用于套接字。 正如 Python 经常发生的那样，官方文档和示例是有用信息的最佳来源。 我从支持文章末尾提供的示例中了解了Transports and Protocols（低级 API）和Streams（高级 API）。

例如 TCP Echo 服务器：

import asyncio


class EchoServerProtocol(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):
        message = data.decode()
        print('Data received: {!r}'.format(message))

        print('Send: {!r}'.format(message))
        self.transport.write(data)

        print('Close the client socket')
        self.transport.close()


async def main():
    # Get a reference to the event loop as we plan to use
    # low-level APIs.
    loop = asyncio.get_running_loop()

    server = await loop.create_server(
        lambda: EchoServerProtocol(),
        '127.0.0.1', 8888)

    async with server:
        await server.serve_forever()


asyncio.run(main())

和 TCP Echo 客户端：

import asyncio


class EchoClientProtocol(asyncio.Protocol):
    def __init__(self, message, on_con_lost):
        self.message = message
        self.on_con_lost = on_con_lost

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

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

    def connection_lost(self, exc):
        print('The server closed the connection')
        self.on_con_lost.set_result(True)


async def main():
    # Get a reference to the event loop as we plan to use
    # low-level APIs.
    loop = asyncio.get_running_loop()

    on_con_lost = loop.create_future()
    message = 'Hello World!'

    transport, protocol = await loop.create_connection(
        lambda: EchoClientProtocol(message, on_con_lost),
        '127.0.0.1', 8888)

    # Wait until the protocol signals that the connection
    # is lost and close the transport.
    try:
        await on_con_lost
    finally:
        transport.close()


asyncio.run(main())

希望对搜索asynchio的简单解释的人有所帮助。