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FastAPI Web框架教程第13章 WebSocket

news 2025/9/12 4:34:12

13-1 WebSocket是什么

WebSocket简介：

WebSocket是一种在单个TCP连接上进行全双工通信的协议。
WebSocket使得客户端和服务器之间的数据交换变得更加简单，允许服务端主动向客户端推送数据。
在WebSocket API中，浏览器和服务器只需要完成一次握手，两者之间就直接可以创建持久性的连接，并进行双向数据传输。

WebSocket和HTTP的相同点和不同点：

WebSocket和HTTP都是解决客户端-服务端通信的网络协议。
HTTP是单向的，客户端先发起请求，服务端收到请求后再处理这个请求返回响应结果；即先有请求再有响应，且是一个请求对应一个响应；请求时建立连接，响应后断开连接。
WebSocket是双向的，客户端发起请求经过三次握手连接后，客户端和服务端就会基于这个连接保持通信，都可以主动向对方发消息。任何一端都可以主动断开这个连接。
HTTP是无状态的，WebSocket是有状态的。即如果使用WebSocket，那么只要建立了连接，每次通信时，服务端都知道在和谁通信，不需要借助Cookie或seesion或jwt等登录认证方式。

参考：https://www.geeksforgeeks.org/what-is-web-socket-and-how-it-is-different-from-the-http/

WebSocket的应用：

实时web应用
游戏
聊天软件等等

13-2 WebSocket聊天室简易版

使用FastAPI演示浏览器和服务端基于WebSocket，建立连接并双向通信。
前端代码无需掌握，只要了解它在干什么事情即可。
示例中，我们使用 HTMLResponse，通过接口的方式把前端代码响应的浏览器上；但其实直接写一个html文件，手动打开也可以的。
后端使用WebSocket，需要使用WebSocket这个对象，常用如下三个协程函数。

await websocket.accept()				# 建立连接
data = await websocket.receive_text()	 # 收消息
await websocket.send_text()				# 发消息

想要在fastAPI中使用websocket 需要安装标准版的uvicorn

pip3 install uvicorn[standard]

实例：简单版聊天

from fastapi import FastAPI, WebSocket
from fastapi.responses import HTMLResponseapp = FastAPI()html = """
<!DOCTYPE html>
<html><head><title>Chat</title></head><body><h1>WebSocket Chat</h1><form action="" οnsubmit="sendMessage(event)"><input type="text" id="messageText" autocomplete="off"/><button>Send</button></form><ul id='messages'></ul><script>var ws = new WebSocket("ws://localhost:8000/ws");ws.onmessage = function(event) {var messages = document.getElementById('messages')var message = document.createElement('li')var content = document.createTextNode(event.data)message.appendChild(content)messages.appendChild(message)};function sendMessage(event) {var input = document.getElementById("messageText")ws.send(input.value)input.value = ''event.preventDefault()}</script></body>
</html>
"""@app.get("/")
async def get():return HTMLResponse(html)@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):await websocket.accept()while True:data = await websocket.receive_text()await websocket.send_text(f"Message text was: {data}")

13-3 WebSocket多人在线聊天室

实现多人在线聊天室
处理客户端下线通知
使用时间戳做客户端id

示例1：多人在线聊天室

from typing import Listfrom fastapi import FastAPI, WebSocket, WebSocketDisconnect
from fastapi.responses import HTMLResponseapp = FastAPI()html = """
<!DOCTYPE html>
<html><head><title>Chat</title></head><body><h1>WebSocket Chat</h1><h2>Your ID: <span id="ws-id"></span></h2><form action="" οnsubmit="sendMessage(event)"><input type="text" id="messageText" autocomplete="off"/><button>Send</button></form><ul id='messages'></ul><script>var client_id = Date.now()document.querySelector("#ws-id").textContent = client_id;var ws = new WebSocket(`ws://localhost:8000/ws/${client_id}`);ws.onmessage = function(event) {var messages = document.getElementById('messages')var message = document.createElement('li')var content = document.createTextNode(event.data)message.appendChild(content)messages.appendChild(message)};function sendMessage(event) {var input = document.getElementById("messageText")ws.send(input.value)input.value = ''event.preventDefault()}</script></body>
</html>
"""class ConnectionManager:def __init__(self):self.active_connections: List[WebSocket] = []async def connect(self, websocket: WebSocket):await websocket.accept()self.active_connections.append(websocket)def disconnect(self, websocket: WebSocket):self.active_connections.remove(websocket)async def send_personal_message(self, message: str, websocket: WebSocket):await websocket.send_text(message)async def broadcast(self, message: str):for connection in self.active_connections:await connection.send_text(message)manager = ConnectionManager()@app.get("/")
async def get():return HTMLResponse(html)@app.websocket("/ws/{client_id}")
async def websocket_endpoint(websocket: WebSocket, client_id: int):await manager.connect(websocket)	# 接收连接try:while True:data = await websocket.receive_text()		# 接收数据await manager.send_personal_message(f"You wrote: {data}", websocket)	# 自己发的消息自己看到await manager.broadcast(f"Client #{client_id} says: {data}")			# 广播，发给所有在线的客户端except WebSocketDisconnect:manager.disconnect(websocket)	# 断开连接await manager.broadcast(f"Client #{client_id} left the chat")	# 广播

示例2：优化自己发的消息不重复展示

from typing import Listfrom fastapi import FastAPI, WebSocket, WebSocketDisconnect
from fastapi.responses import HTMLResponseapp = FastAPI()html = """
<!DOCTYPE html>
<html><head><title>Chat</title></head><body><h1>WebSocket Chat</h1><h2>Your ID: <span id="ws-id"></span></h2><form action="" οnsubmit="sendMessage(event)"><input type="text" id="messageText" autocomplete="off"/><button>Send</button></form><ul id='messages'></ul><script>var client_id = Date.now()document.querySelector("#ws-id").textContent = client_id;var ws = new WebSocket(`ws://localhost:8000/ws/${client_id}`);ws.onmessage = function(event) {var messages = document.getElementById('messages')var message = document.createElement('li')var content = document.createTextNode(event.data)message.appendChild(content)messages.appendChild(message)};function sendMessage(event) {var input = document.getElementById("messageText")ws.send(input.value)input.value = ''event.preventDefault()}</script></body>
</html>
"""class ConnectionManager:def __init__(self):self.active_connections: List[WebSocket] = []async def connect(self, websocket: WebSocket):await websocket.accept()self.active_connections.append(websocket)	# 收集有所的在线客户端def disconnect(self, websocket: WebSocket):self.active_connections.remove(websocket)	# 当客户端断线时，更新在线客户端列表async def send_personal_message(self, message: str, websocket: WebSocket):await websocket.send_text(message)async def broadcast(self, message: str, websocket: WebSocket):for connection in self.active_connections:if connection == websocket:		# 判断下，如果是自己就不再发送消息continueawait connection.send_text(message)manager = ConnectionManager()@app.get("/")
async def get():return HTMLResponse(html)@app.websocket("/ws/{client_id}")
async def websocket_endpoint(websocket: WebSocket, client_id: int):await manager.connect(websocket)try:while True:data = await websocket.receive_text()await manager.send_personal_message(f"You wrote: {data}", websocket)await manager.broadcast(f"Client #{client_id} says: {data}", websocket)except WebSocketDisconnect:manager.disconnect(websocket)await manager.broadcast(f"Client #{client_id} left the chat", websocket)