Permessage-Deflate Extension Breaks Socket.io WebSocket Communication (400 Bad Request)-CodePudding

I need to enable compression for websocket communication (using socketio). I did this by setting the perMessageDeflate to true which worked fine in my development environment and on a staging server (verified with Wireshark). However, on our production server the websocket connection fails and socketio (v4.4.1) falls back to polling. Both use nginx as a reverse proxy with the same configuration. Chromium console shows

WebSocket connection to 'wss://***/ws-test/socket.io/?EIO=4&transport=websocket&sid=9P4EelJhF0CcxvwNAAAE' failed: Error during WebSocket handshake: Unexpected response code: 400

I created a minimal sample that shows the same behaviour. Nodejs app on the server:

const express = require('express');
const app = express();
const http = require('http');
const server = http.createServer(app);
const { Server } = require("socket.io");

const io = new Server(server, {
    perMessageDeflate: true
});

app.get('/', (req, res) => {
    res.sendFile(__dirname   '/index.html');
});

server.listen(3001, () => {
    console.log('listening on *:3001');
});

Client:

    ...
    <script src="socket.io/socket.io.js"></script>
    <script>
      var socketio_path = window.location.pathname   'socket.io';
      var socket = io( { path: socketio_path } );
    </script>
</body>

The error 400 seems to come from the nodejs server, not from nginx. I enabled all kinds of logging but couldn't find any related messages. Software versions are also reasonably close and up-to-date: nginx 1.18.0 on both (staging and production), nodejs 14.19.0/14.18.1 (staging/prod). Do you have any ideas that could help making this work on the production server?

CodePudding user response：

It turned out, the issue is the Azure Application Gateway used on the production server. When it's bypassed, the websocket connection (with perMessageDeflate enabled) works fine.

Switching to a newer version of the Azure Application Gateway (v2 instead of v1) solved the issue in the end.