Windows下运行Flask-SocketIO应用遇连接错误，寻求技术协助

问题概述 #

同一份 Flask-SocketIO 代码在 Ubuntu 上运行无问题，迁移到 Windows 10/11 后客户端抛出 socketio.exceptions.ConnectionError: One or more namespaces failed to connect 错误，但 HTTP 层面访问 localhost:5000 可正常返回响应。

代码片段 #

服务器代码 #

from flask import Flask
from flask_socketio import SocketIO

app = Flask(__name__)
app.config['SECRET_KEY'] = 'secret_key'
socketio = SocketIO(app=app, logging='DEBUG')

@socketio.on_error_default
def error_handler(e):
    print('An error occurred:', e)

@app.route('/')  # 注意：原代码遗漏了装饰器的@符号，已修正
def index():
    return 'Hello, Socket.IO Client!'

if __name__ == '__main__':
    socketio.run(app, port=5000)

客户端代码 #

import socketio
import logging

sio = socketio.Client()
logging.basicConfig(level=logging.DEBUG)

@sio.event
def connect():
    print('Connected to server')

@sio.event
def disconnect():
    print('Disconnected from server')

sio.connect('http://localhost:5000')

环境信息 #

• Python 版本：3.9.13
• 依赖包版本：
  • Flask==2.0.1
  • flask-restplus==0.13.0
  • Flask-SocketIO==5.1.0
  • python-engineio==4.2.0
  • python-socketio==5.3.0

已排查项 #

• Windows 10、11 均测试，问题一致
• 关闭防火墙、更换端口、管理员权限运行、改用 flask run 启动均无效
• Windows 主机的 Linux Docker 容器内运行正常
• 未修改网络设置或端口转发

日志信息 #

客户端完整日志 #

DEBUG:urllib3.connectionpool:Starting new HTTP connection (1): localhost:5000
DEBUG:urllib3.connectionpool:http://localhost:5000 "GET /socket.io/?transport=polling&EIO=4&t=1688031616.8050513 HTTP/1.1" 200 None
websocket-client package not installed, only polling transport is available
ERROR:engineio.client:websocket-client package not installed, only polling transport is available
DEBUG:urllib3.connectionpool:Resetting dropped connection: localhost
DEBUG:urllib3.connectionpool:Starting new HTTP connection (2): localhost:5000
Traceback (most recent call last):
  File "C:\Users\Matt\source\repos\data-art\hg-backend\Client.py", line 15, in <module>
    sio.connect('http://localhost:5000')
  File "C:\Users\Matt\source\repos\data-art\hg-backend\venv\lib\site-packages\socketio\client.py", line 323, in connect
    raise exceptions.ConnectionError(
socketio.exceptions.ConnectionError: One or more namespaces failed to connect
DEBUG:urllib3.connectionpool:http://localhost:5000 "POST /socket.io/?transport=polling&EIO=4&sid=XDn3Nhf3Wlaepe5fAAAA HTTP/1.1" 200 None
DEBUG:urllib3.connectionpool:http://localhost:5000 "GET /socket.io/?transport=polling&EIO=4&sid=XDn3Nhf3Wlaepe5fAAAA&t=1688031618.8611357 HTTP/1.1" 200 None
Connected to server

服务器完整日志 #

* Serving Flask app 'Server' (lazy loading)
* Environment: production
  WARNING: This is a development server. Do not use it in a production deployment.
  Use a production WSGI server instead.
* Debug mode: off
* Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
127.0.0.1 - - [29/Jun/2023 10:40:18] "GET /socket.io/?transport=polling&EIO=4&t=1688031616.8050513 HTTP/1.1" 200 -
127.0.0.1 - - [29/Jun/2023 10:40:20] "POST /socket.io/?transport=polling&EIO=4&sid=XDn3Nhf3Wlaepe5fAAAA HTTP/1.1" 200 -
127.0.0.1 - - [29/Jun/2023 10:40:20] "GET /socket.io/?transport=polling&EIO=4&sid=XDn3Nhf3Wlaepe5fAAAA&t=1688031618.8611357 HTTP/1.1" 200 -
127.0.0.1 - - [29/Jun/2023 10:41:20] "GET /socket.io/?EIO=4&transport=polling HTTP/1.1" 200 -

解决方法 #

1. 修复服务器路由装饰器：原代码中 app.route('/') 遗漏了 @ 符号，修正为 @app.route('/')，确保路由正常注册。

2. 安装 websocket-client 依赖：客户端日志提示缺少 websocket 支持，仅能使用轮询传输，Windows 下轮询易出现连接重置问题，安装依赖切换到更稳定的传输方式：

   pip install websocket-client
   

3. 强制使用 polling 传输并延长超时：若安装 websocket 后仍有问题，强制客户端使用 polling 并延长超时时间，避免误判连接失败：

   sio.connect('http://localhost:5000', transports=['polling'], wait_timeout=10)
   

4. 改用 IPv4 地址连接：Windows 下 localhost 可能优先解析到 IPv6，而服务器默认绑定 IPv4 的 127.0.0.1，修改客户端连接地址：

   sio.connect('http://127.0.0.1:5000')
   

5. 更新依赖包版本：当前依赖版本较旧，Windows 下可能存在已修复的兼容性问题，更新到稳定版本：

   pip install --upgrade Flask Flask-SocketIO python-engineio python-socketio
   

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