Getting 200 code when using sockets in Flask

Question

I have Flask server, which handles HTTP requests but also WebSocket using flask-socketio. Code of server here:

from flask_socketio import SocketIO, emit
from flask import Flask

app = Flask(__name__)
socketio = SocketIO(app)

@socketio.on('response')
def message(data):  
    time.sleep(1)
    emit('sensor', {"data": "hello"})
    
@socketio.on('connect')
def connect():
    emit('after connect')

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

and script tag in html looks like this:

<script>
    var socket = io("ws://192.168.100.3:5000");
            
    socket.on('after connect', function(msg) {
        console.log('connected')
        socket.emit('response', msg)
    });
            
    socket.on('sensor', function(msg) {
        console.log(msg.data)
        socket.emit('response', msg)
    });     
</script>

Everything works, I got the communication, but one thing that concerning me is that in terminal where server run I get code 200 for GET and POST requests.

192.168.100.10 - - [17/Apr/2022 11:36:27] "GET /socket.io/?EIO=2&transport=polling&t=1650191787548-1094&sid=faed6806df0a437d8d17bd8a294f8754 HTTP/1.1" 200 -
192.168.100.10 - - [17/Apr/2022 11:36:27] "POST /socket.io/?EIO=2&transport=polling&t=1650191788570-1095&sid=faed6806df0a437d8d17bd8a294f8754 HTTP/1.1" 200 -

I get response in console I think communication is right. But with those request that I am "making" every second resources usage in web browser is getting bigger. Small amount but still. As far as I know WebSockets should not send HTTP requests to server, but it has to be TCP/IP constant connection.

What am I doing wrong, or it is my WebSockets understanding wrong?

better create minimal working code which we can copy and run. And add details about browser, python, SocketIO module - and put it in question, not in comments. Sometimes when it can't connect directly by socket then it can use standard HTTP for connection. — furas
– furas, Commented Apr 17, 2022 at 12:40
This is not question that resemble exact error in a code, rather question on how thing works. I do not see a reason to put here my .html as it is simple. My question is simple and I need explanation of theory behind not such a obvious solution. — Kaldesyvon
– Kaldesyvon, Commented Apr 17, 2022 at 17:11

Krerkkiat Chusap · Accepted Answer · 2022-04-18 06:03:06Z

2

The GET and POST requests are there because you are using Socket.IO. As stated in its documentation, Socket.IO starts with HTTP long-polling before it attempts to establish a WebSocket connection. It will also fallback to HTTP long-polling if it cannot use WebSocket.

answered Apr 18, 2022 at 6:03

Krerkkiat Chusap

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