在Heroku部署Flask Websocket服务遇WebsocketMismatch错误求助

我用Godot制作回合制游戏，为防止作弊将服务部署在Heroku，选择Websocket方案并使用flask-sockets实现，但始终无法正常运行，Heroku日志中持续出现WebsocketMismatch错误。所有Websocket测试方法均无效，我确定是服务端存在问题。

Flask应用代码 #

from flask import Flask
from flask_sockets import Sockets

app = Flask(__name__)
sockets = Sockets(app)

@sockets.route('/reverse')
def echo_socket(ws):
    while not ws.closed:
        message = ws.receive()
        ws.send(message[::-1])

@app.route('/')
def hello():
    return "Hello World!"

Heroku日志错误信息 #

2022-08-10T01:13:42.934964+00:00 app[web.1]: Traceback (most recent call last):
2022-08-10T01:13:42.934997+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.9/site-packages/gevent/pywsgi.py", line 999, in handle_one_response
2022-08-10T01:13:42.934998+00:00 app[web.1]: self.run_application()
2022-08-10T01:13:42.935002+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.9/site-packages/geventwebsocket/handler.py", line 75, in run_application
2022-08-10T01:13:42.935002+00:00 app[web.1]: self.run_websocket()
2022-08-10T01:13:42.935004+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.9/site-packages/geventwebsocket/handler.py", line 52, in run_websocket
2022-08-10T01:13:42.935005+00:00 app[web.1]: list(self.application(self.environ, lambda s, h, e=None: []))
2022-08-10T01:13:42.935017+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.9/site-packages/flask/app.py", line 2548, in __call__
2022-08-10T01:13:42.935018+00:00 app[web.1]: return self.wsgi_app(environ, start_response)
2022-08-10T01:13:42.935029+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.9/site-packages/flask_sockets.py", line 40, in __call__
2022-08-10T01:13:42.935029+00:00 app[web.1]: handler, values = adapter.match()
2022-08-10T01:13:42.935039+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.9/site-packages/werkzeug/routing/map.py", line 622, in match
2022-08-10T01:13:42.935040+00:00 app[web.1]: raise WebsocketMismatch() from None
2022-08-10T01:13:42.935067+00:00 app[web.1]: werkzeug.routing.exceptions.WebsocketMismatch: 400 Bad Request: The browser (or proxy) sent a request that this server could not understand.
2022-08-10T01:13:42.935181+00:00 app[web.1]: 2022-08-10T01:13:42Z {'REMOTE_ADDR': '10.1.31.248', 'REMOTE_PORT': '12800', 'HTTP_HOST': 'reversertesterheroku.herokuapp.com', (hidden keys: 33)} failed with WebsocketMismatch

问题原因及解决方案 #

1. 修正WSGI服务器配置 #

Flask自带的开发服务器不支持Websocket，必须使用兼容的服务器。修改Procfile为：

web: gunicorn -k geventwebsocket.gunicorn.workers.GeventWebSocketWorker -w 1 app:app

同时确保requirements.txt包含以下依赖：

flask==2.2.2
flask-sockets==0.2.1
gevent==22.8.0
gevent-websocket==0.10.1
gunicorn==20.1.0

2. 强制使用WSS协议 #

Heroku强制使用HTTPS，Websocket请求必须用wss://而非ws://，否则会被重定向导致请求头丢失Websocket标识。客户端连接时务必使用wss://你的域名/reverse。

3. 替代方案：改用FastAPI+WebSocket #

Flask-Sockets维护状态较差，FastAPI对Websocket有原生支持，部署更简单。示例代码：

from fastapi import FastAPI, WebSocket
from fastapi.responses import HTMLResponse

app = FastAPI()

@app.websocket("/reverse")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()
        await websocket.send_text(data[::-1])

@app.get("/")
async def root():
    return HTMLResponse("Hello World!")

对应的Procfile配置：

web: uvicorn app:app --host 0.0.0.0 --port $PORT

requirements.txt依赖：

fastapi==0.95.2
uvicorn==0.22.0

内容的提问来源于stack exchange，提问作者user19731293