FastAPI（56）- 使用 Websocket 打造一个迷你聊天室

背景

• 在实际项目中，可能会通过前端框架使用 WebSocket 和后端进行通信
• 这里就来详细讲解下 FastAPI 是如何操作 WebSocket 的

模拟 WebSocket 客户端

#!usr/bin/env python
# -*- coding:utf-8 _*-
"""
# author: 小菠萝测试笔记
# blog:  https://www.cnblogs.com/poloyy/
# time: 2021/10/5 5:26 下午
# file: 46_websocket.py
"""
import uvicorn
from fastapi import FastAPI, WebSocket

from fastapi.responses import HTMLResponse

app = FastAPI()

html = """
<!DOCTYPE html>
<html>
    <head>
        <title>小菠萝聊天室</title>
    </head>
    <body>
        <h1>小菠萝聊天室</h1>
        <form action="" onsubmit="sendMessage(event)">
            <input type="text" id="messageText" autocomplete="off"/>
            <button>Send</button>
        </form>
        <ul id='messages'>
        </ul>
        <script>
            // 加载页面，自动创建一个 WebSocket 连接
            var ws = new WebSocket("ws://localhost:8080/ws");

            // 收到消息
            ws.onmessage = function(event) {
                // 获取输入框的值
                var messages = document.getElementById('messages')
                // 创建一个 li 元素
                var message = document.createElement('li')
                // 接收 event 的 data
                var content = document.createTextNode(event.data)
                message.appendChild(content)
                messages.appendChild(message)
            };

            // 发送消息方法
            function sendMessage(event) {
                var input = document.getElementById("messageText")
                ws.send(input.value)
                input.value = ''
                event.preventDefault()
            }
        </script>
    </body>
</html>
"""

# 返回一段 HTML 代码给前端
@app.get("/")
async def get():
    return HTMLResponse(html)

@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    # 1、ws 连接
    await websocket.accept()
    while True:
        # 2、接收客户端发送的内容
        data = await websocket.receive_text()

        # 3、服务端发送内容
        await websocket.send_text(f"小菠萝收到的消息是: {data}")

if __name__ == '__main__':
    uvicorn.run(app="46_websocket:app", reload=True, host="127.0.0.1", port=8080)

启动 uvicorn 服务器，访问 127.0.0.1:8080/

客户端、服务端建立 WebSocket 连接成功

发送聊天信息

每发一条消息，均会显示在列表中

可以在其他地方使用 WebSocket

• Depends
• Security
• Cookie
• Header
• Path
• Query

在依赖项中使用 WebSocket

from typing import Optional
import uvicorn
from fastapi import FastAPI, WebSocket, Cookie, Query, status, Depends

from fastapi.responses import HTMLResponse

app = FastAPI()

html = """
<!DOCTYPE html>
<html>
    <head>
        <title>Chat</title>
    </head>
    <body>
        <h1>小菠萝聊天室</h1>
        <form action="" onsubmit="sendMessage(event)">
            <label>Item ID: <input type="text" id="itemId" autocomplete="off" value="foo"/></label>
            <label>Token: <input type="text" id="token" autocomplete="off" value="some-key-token"/></label>
            <button onclick="connect(event)">Connect</button>
            <hr>
            <label>Message: <input type="text" id="messageText" autocomplete="off"/></label>
            <button>Send</button>
        </form>
        <ul id='messages'>
        </ul>
        <script>
        var ws = null;
            function connect(event) {
                var itemId = document.getElementById("itemId")
                var token = document.getElementById("token")
                ws = new WebSocket("ws://localhost:8080/items/" + itemId.value + "/ws?token=" + token.value);
                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)
                };
                event.preventDefault()
            }
            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)

async def get_cookie_or_token(
        websocket: WebSocket,
        session: Optional[str] = Cookie(None),
        token: Optional[str] = Query(None)
):
    # 模拟：如果 session 和 token 都为空，则关闭 websocket
    if session or token:
        return session or token
    await websocket.close(code=status.WS_1008_POLICY_VIOLATION)

@app.websocket("/items/{item_id}/ws")
async def websocket_depends(
        websocket: WebSocket,
        item_id: str,
        q: Optional[str] = None,
        # 依赖项
        cookie_or_token: str = Depends(get_cookie_or_token)
):
    # 1、创建 websocket 连接
    await websocket.accept()

    while True:
        # 2、接收客户端发送的内容
        data = await websocket.receive_text()
        # 3、服务端发送内容
        await websocket.send_text(f"cookie or token value is:{cookie_or_token}")
        if q:
            # 4、如果有传查询参数 q，则再发一条
            await websocket.send_text(f"query param value is:{q}")
        # 5、最后再发一条信息
        await websocket.send_text(f"Message text was: {data}, for item ID: {item_id}")

if __name__ == '__main__':
    uvicorn.run(app="46_websocket:app", reload=True, host="127.0.0.1", port=8080)

发送聊天信息

不带查询参数 q

带查询参数 q

当 WebSocket 连接关闭时

await websocket.receive_text()  将引发 WebSocketDisconnect 异常，这不是期望看到的结果

处理断开连接和多个客户端

from typing import List

import uvicorn
from fastapi import FastAPI, WebSocket, WebSocketDisconnect, status

from fastapi.responses import HTMLResponse

app = 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="" onsubmit="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:8080/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>
"""

# 返回一段 HTML 代码给前端
@app.get("/")
async def get():
    return HTMLResponse(html)

# 处理和广播消息到多个 WebSocket 连接
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.websocket("/ws/{client_id}")
async def websocket_endpoint(client_id: str, websocket: WebSocket):
    # 1、客户端、服务端建立 ws 连接
    await manager.connect(websocket)
    # 2、广播某个客户端进入聊天室
    await manager.broadcast(f"{client_id} 进入了聊天室")
    try:
        while True:
            # 3、服务端接收客户端发送的内容
            data = await websocket.receive_text()
            # 4、广播某个客户端发送的消息
            await manager.broadcast(f"{client_id} 发送消息：{data}")
            # 5、服务端回复客户端
            await manager.send_personal_message(f"服务端回复{client_id}：你发送的信息是：{data}", websocket)
    except WebSocketDisconnect:
        # 6、若有客户端断开连接，广播某个客户端离开了
        manager.disconnect(websocket)
        await manager.broadcast(f"{client_id} 离开了聊天室")

if __name__ == '__main__':
    uvicorn.run(app="48_websocket_handler:app", reload=True, host="127.0.0.1", port=8080)

• 模拟一个小型聊天室的场景
• 新的客户端进来，所有人都会收到新客户端进入聊天室的消息
• 某个客户端发送消息，所有人都能看到
• 某个客户端退出了（关闭浏览器），所有人都会收到该客户端退出聊天室的消息

浏览器打开三个 tab 均访问 127.0.0.1:8080

关掉其中一个客户端（tab）