Python websocket库

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2023-03-14

Python websockets库是用于在Python中构建WebSocket服务器和客户端的库。
如果可能，应该使用最新版本的Python。如果使用的是旧版本，请注意，对于每个次要版本(3.x)，仅官方支持最新的错误修复版本(3.x.y)。

为了获得最佳体验，应该从Python≥3.6以上版本。asyncio在Python 3.4和3.6之间做了很大的改进。

注意：本文档是为Python≥3.6编写的。

安装websockets

$ pip install websockets

基本的例子

下面是一个WebSocket服务器示例。它从客户端读取名称，发送问候语，然后关闭连接。参考以下实现代码 -

#!/usr/bin/env python

# WS server example

import asyncio
import websockets

async def hello(websocket, path):
    name = await websocket.recv()
    print(f"< {name}")

    greeting = f"Hello {name}!"

    await websocket.send(greeting)
    print(f"> {greeting}")

start_server = websockets.serve(hello, 'localhost', 8765)

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

在服务器端，websockets为每个WebSocket连接执行一次处理协同程序hello。它在处理协同程序返回时关闭连接。

下面是一个相应的WebSocket客户端示例。

#!/usr/bin/env python

# WS client example

import asyncio
import websockets

async def hello():
    async with websockets.connect('ws://localhost:8765') as websocket:
        name = input("What's your name? ")

        await websocket.send(name)
        print(f"> {name}")

        greeting = await websocket.recv()
        print(f"< {greeting}")

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

使用connect()作为异步上下文管理器可确保在退出hello协同程序之前关闭连接。

安全示例

安全的WebSocket连接可以提高机密性和可靠性，因为它们可以降低不良代理干扰的风险。WSS协议是WS到HTTPS的HTTP：连接是用TLS加密的。WSS需要像HTTPS这样的TLS证书。以下是使用Python≥3.6中提供的API来调整服务器示例以提供安全连接的方法。
请参阅ssl模块的文档以安全地配置上下文或将代码调整为较旧的Python版本。

#!/usr/bin/env python

# WSS (WS over TLS) server example, with a self-signed certificate

import asyncio
import pathlib
import ssl
import websockets

async def hello(websocket, path):
    name = await websocket.recv()
    print(f"< {name}")

    greeting = f"Hello {name}!"

    await websocket.send(greeting)
    print(f"> {greeting}")

ssl_context = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
ssl_context.load_cert_chain(
    pathlib.Path(__file__).with_name('localhost.pem'))

start_server = websockets.serve(
    hello, 'localhost', 8765, ssl=ssl_context)

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

以下是调整客户端代码，也适用于Python≥3.6。

#!/usr/bin/env python

# WSS (WS over TLS) client example, with a self-signed certificate

import asyncio
import pathlib
import ssl
import websockets

ssl_context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
ssl_context.load_verify_locations(
    pathlib.Path(__file__).with_name('localhost.pem'))

async def hello():
    async with websockets.connect(
            'wss://localhost:8765', ssl=ssl_context) as websocket:
        name = input("What's your name? ")

        await websocket.send(name)
        print(f"> {name}")

        greeting = await websocket.recv()
        print(f"< {greeting}")

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

此客户端需要上下文，因为服务器使用自签名证书。

连接到具有有效证书的安全WebSocket服务器的客户端(即由您的Python安装信任的CA签名)可以简单地将ssl = True传递给connect()而不是构建上下文。

基于浏览器的示例

这是一个如何运行WebSocket服务器并从浏览器连接的示例。

在控制台中运行此脚本：

#!/usr/bin/env python

# WS server that sends messages at random intervals

import asyncio
import datetime
import random
import websockets

async def time(websocket, path):
    while True:
        now = datetime.datetime.utcnow().isoformat() + 'Z'
        await websocket.send(now)
        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()

然后在浏览器中打开此HTML文件。

<!DOCTYPE html>
<html>
    <head>
        <title>WebSocket demo</title>
    </head>
    <body>
        <script>
            var ws = new WebSocket("ws://127.0.0.1:5678/"),
                messages = document.createElement('ul');
            ws.onmessage = function (event) {
                var messages = document.getElementsByTagName('ul')[0],
                    message = document.createElement('li'),
                    content = document.createTextNode(event.data);
                message.appendChild(content);
                messages.appendChild(message);
            };
            document.body.appendChild(messages);
        </script>
    </body>
</html>

同步示例

WebSocket服务器可以从客户端接收事件，处理它们以更新应用程序状态，并在客户端之间同步结果状态。

这是一个示例，任何客户端都可以递增或递减计数器。更新将传播到所有连接的客户端。

asyncio的并发模型保证更新被序列化。

在控制台中运行此脚本：

#!/usr/bin/env python

# WS server example that synchronizes state across clients

import asyncio
import json
import logging
import websockets

logging.basicConfig()

STATE = {'value': 0}

USERS = set()

def state_event():
    return json.dumps({'type': 'state', **STATE})

def users_event():
    return json.dumps({'type': 'users', 'count': len(USERS)})

async def notify_state():
    if USERS:       # asyncio.wait doesn't accept an empty list
        message = state_event()
        await asyncio.wait([user.send(message) for user in USERS])

async def notify_users():
    if USERS:       # asyncio.wait doesn't accept an empty list
        message = users_event()
        await asyncio.wait([user.send(message) for user in USERS])

async def register(websocket):
    USERS.add(websocket)
    await notify_users()

async def unregister(websocket):
    USERS.remove(websocket)
    await notify_users()

async def counter(websocket, path):
    # register(websocket) sends user_event() to websocket
    await register(websocket)
    try:
        await websocket.send(state_event())
        async for message in websocket:
            data = json.loads(message)
            if data['action'] == 'minus':
                STATE['value'] -= 1
                await notify_state()
            elif data['action'] == 'plus':
                STATE['value'] += 1
                await notify_state()
            else:
                logging.error(
                    "unsupported event: {}", data)
    finally:
        await unregister(websocket)

asyncio.get_event_loop().run_until_complete(
    websockets.serve(counter, 'localhost', 6789))
asyncio.get_event_loop().run_forever()

然后在几个浏览器中打开此HTML文件。

<!DOCTYPE html>
<html>
    <head>
        <title>WebSocket demo</title>
        <style type="text/css">
            body {
                font-family: "Courier New", sans-serif;
                text-align: center;
            }
            .buttons {
                font-size: 4em;
                display: flex;
                justify-content: center;
            }
            .button, .value {
                line-height: 1;
                padding: 2rem;
                margin: 2rem;
                border: medium solid;
                min-height: 1em;
                min-width: 1em;
            }
            .button {
                cursor: pointer;
                user-select: none;
            }
            .minus {
                color: red;
            }
            .plus {
                color: green;
            }
            .value {
                min-width: 2em;
            }
            .state {
                font-size: 2em;
            }
        </style>
    </head>
    <body>
        <div class="buttons">
            <div class="minus button">-</div>
            <div class="value">?</div>
            <div class="plus button">+</div>
        </div>
        <div class="state">
            <span class="users">?</span> online
        </div>
        <script>
            var minus = document.querySelector('.minus'),
                plus = document.querySelector('.plus'),
                value = document.querySelector('.value'),
                users = document.querySelector('.users'),
                websocket = new WebSocket("ws://127.0.0.1:6789/");
            minus.onclick = function (event) {
                websocket.send(JSON.stringify({action: 'minus'}));
            }
            plus.onclick = function (event) {
                websocket.send(JSON.stringify({action: 'plus'}));
            }
            websocket.onmessage = function (event) {
                data = JSON.parse(event.data);
                switch (data.type) {
                    case 'state':
                        value.textContent = data.value;
                        break;
                    case 'users':
                        users.textContent = (
                            data.count.toString() + " user" +
                            (data.count == 1 ? "" : "s"));
                        break;
                    default:
                        console.error(
                            "unsupported event", data);
                }
            };
        </script>
    </body>
</html>