Flask-SocketIO结合蓝图使用时客户端无法接收服务端emit消息

此前曾提过类似问题，现单独发帖求助：在采用工厂应用原则构建且使用蓝图的Flask应用中集成Flask-SocketIO，Socket连接正常（connect事件已触发），但手动调用含emit()的函数时，客户端无法接收消息。

简化代码示例 #

init.py #

from flask import Flask
from flask_socketio import SocketIO
import os

gv_socketio = SocketIO(logger=True, engineio_logger=True)

def create_app():
    # instance_relative_config=True --> 实例文件夹位于主目录（此处为'spotr'）外
    app = Flask(__name__, instance_relative_config=True)

    # 默认配置，'spotr.sqlite'将存放在实例文件夹中
    app.config.from_mapping(
        SECRET_KEY='dev',
        DATABASE=os.path.join(app.instance_path, 'spotr.sqlite'),
    )

    # 用'config.py'中的值覆盖默认配置（不存在则静默失败）
    app.config.from_pyfile('config.py', silent=True)

    # 初始化SocketIO扩展
    gv_socketio.init_app(app)

    # 确保实例文件夹存在
    try:
        os.makedirs(app.instance_path)
    except OSError:
        pass

    with app.app_context():
        # 注册蓝图
        from . import watchlist, home, database

        app.register_blueprint(watchlist.bp_watchlist)
        app.register_blueprint(home.bp_home)
        app.register_blueprint(database.bp_database)

    return app

watchlist.py #

from flask import Blueprint, request, render_template
from flask_socketio import emit
from . import gv_socketio

bp_watchlist = Blueprint('watchlist', __name__, url_prefix="/watchlist")

def sendStatusViaSocket(note):
    gv_socketio.emit('updateStatus', {"data": note}, namespace='/watchlist')

@bp_watchlist.route("/", methods=["GET","POST"])
def watchlist_main():
    args = request.args       

    # 页面加载逻辑
    if request.method == "GET" and not ("addArtist" in args):
        sendStatusViaSocket("11111111111111")
        return render_template('watchlist.html')

watchlist.html #

{% extends 'base.html' %}

{% block title %} 
    Watchlist
{% endblock %}

{% block content %}
    <!-- socketio 接口 -->
    <script src="https://cdnjs.cloudflare.com/ajax/libs/socket.io/4.5.1/socket.io.js"></script>
    <script>
        socket = io();
        socket.connect('http://' + document.domain + ':' + location.port + '/watchlist');

        socket.on('updateStatus',function(data){
            console.log('HEY');
            // console.log(data.data);
        })

        socket.on('connect',function(){
            console.log('CONNECT');
        })

        socket.on('message',function(msg){
            console.log("MESSAGE");
        })
    </script>
    <!-- 其他页面内容 -->
    ....
{% endblock %}

问题现象 #

预期触发watchlist_main()函数时，sendStatusViaSocket()会向客户端（watchlist.html）发送updateStatus事件，但客户端无任何响应，仅控制台打印CONNECT，浏览器调试中updateStatus和message事件均未触发。

Socket日志 #

127.0.0.1 - - [21/Aug/2022 13:29:35] "GET /watchlist/ HTTP/1.1" 200 -
127.0.0.1 - - [21/Aug/2022 13:29:35] "GET /static/style.css HTTP/1.1" 304 -
**The WebSocket transport is not available, you must install a WebSocket server that is compatible with your async mode to enable it. See the documentation for details. (further occurrences of this error will be logged with level INFO)**
bYHyaOm5DEHy1S5XAAAA: Sending packet OPEN data {'sid': 'bYHyaOm5DEHy1S5XAAAA', 'upgrades': [], 'pingTimeout': 20000, 'pingInterval': 25000}
127.0.0.1 - - [21/Aug/2022 13:29:35] "GET /socket.io/?EIO=4&transport=polling&t=OB0AbE6 HTTP/1.1" 200 -
bYHyaOm5DEHy1S5XAAAA: Received packet MESSAGE data 0
CONNNNECT
bYHyaOm5DEHy1S5XAAAA: Sending packet MESSAGE data 0{"sid":"Q941dFU3MYnD-ydkAAAB"}
127.0.0.1 - - [21/Aug/2022 13:29:35] "GET /socket.io/?EIO=4&transport=polling&t=OB0AbHH&sid=bYHyaOm5DEHy1S5XAAAA HTTP/1.1" 200 -
127.0.0.1 - - [21/Aug/2022 13:29:35] "POST /socket.io/?EIO=4&transport=polling&t=OB0AbHG&sid=bYHyaOm5DEHy1S5XAAAA HTTP/1.1" 200 -
bYHyaOm5DEHy1S5XAAAA: Received packet MESSAGE data 2["done"]
received event "done" from Q941dFU3MYnD-ydkAAAB [/]
127.0.0.1 - - [21/Aug/2022 13:29:35] "POST /socket.io/?EIO=4&transport=polling&t=OB0AbI0&sid=bYHyaOm5DEHy1S5XAAAA HTTP/1.1" 200 -

已尝试的解决 #

参考'Flask-SocketIO-Chat'仓库排查问题，尝试安装gevent-websocket和eventlet，但仍存在'WebSocket传输不可用'的警告，问题未解决。

内容的提问来源于stack exchange，提问作者user3592897