Flask-SocketIO reconnects Websocket after HTTP request

[BillyHesse]

Flask-SocketIO reconnects Websocket after HTTP request

Hey Python Webdev's!

I'm currently working on a Flask-Webserver (with Flask-Login, Flask-SocketIO and Flask-Session) to control relais for static and also flashing lights. Using uWSGI with Gevent-Websocket for deployment i am encountering the problem, that the User who triggers an HTTP request gets disconnected from the Websocket. After 4-8 seconds the Websocket reconnects the User with a new SID and everything works again. While all other Users (anonymous and also authenticated) just recieve the data from the socket instantly as supposed to. I already studied logs and tried everything to solve this problem in the past 10 days and couldn't find any error.

[miguelgrinberg]

Is the hardware code that you are using compatible with gevent? Most hardware control libraries aren't.

[BillyHesse]

I've looked deeply into SocketIO.run() and the Flask.run() method and found out, maybe the working development-server version was using wsgi with eventlet and greenlet. To be honest, i didn't note down any of the choices SocketIO.run() made, but i can remember reading "Werkzeug runinng on". Just to make shure this isn't a dejavue i'll give the wsgi server with green(threads) a go.

My main guess is, that the standard threading with gevent could cause this problem.

The function that gets executed on a button click is shown above: update_relais_mode(RX)
I really, really made shure there is only non-blocking code.

[miguelgrinberg]

Gevent and eventlet are both incompatible with GPIO, unless your library has been specifically designed for async use.

You have avoided my question though. What happens when the user clicks the button? Does the browser reload the page? That's where the problem likely is, not in the server.

[BillyHesse]

When clicking a button the browser doesn't reload. I've tried MS Edge, Chrome and Samsung Browser.

I thought "return ("", 204)" doesn't trigger any reloading

[miguelgrinberg]

What are you doing to prevent the browser from reloading? I think this is likely a misunderstanding on your part regarding how the browser works.

[BillyHesse]

You're right seems like the page is reloading.

I think i understood your reply now. You may be right with the reloading-issue because i am using JS with window.location.href to follow the btn link.

At this point the HTML side does this (for every button)

body

img src="/static/btn_rd_light_active.png" id="btn_rd_light_active" class="btn_rd_light_active">

JS

rd_light = function(event) {
window.location.href = "/btnchg/btn_rd_light";}

From Stackoverflow

The internet suggests not using JS to make the HTTP request. Instead i should use button> or input type="button"/>#
https://stackoverflow.com/questions/1878264/how-do-i-make-an-html-button-not-reload-the-page