Socket IO keeps disconnecting and reconnecting

Question

I'm very very new to sockets and socket.io, so I apologize if this is an obvious question. I'm using the C# client for Socket.IO and have a local javascript server running. Here is my app.js:

var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);

io.on('connection', function(socket) {
   console.log('A user connected');

   socket.on('test', function () {
      console.log('Test run'); });


   socket.on('disconnect', function () {
      console.log('A user disconnected'); });

});

http.listen(3000, function() {
   console.log('listening on localhost:3000'); });

In my main C# class (it is a Windows Forms application) the only line of code I have relating to the sockets at all is the instance variable private Socket socket = IO.Socket("http://localhost:3000/");. Yet for some reason, the server repeatedly receives the connect and disconnect events. Here is a screenshot of my console: screenshot

This all happens automatically, as soon as I run my C# program, without any interaction, and stops as soon as I close it. Any ideas as to why it keeps connecting/disconnecting?

EDIT: For whatever reason the problem seems to go away when I remove Newtonsoft.json from the project. However, without it I cannot use the Emit function as well as others. Is there a workaround to this?

user_8527009 · Answer

To anyone encountering this issue, check if client & server speak the same protocol version.

On a high-level, this is likely to be caused by protocol version mismatch between server and client. I've had the same issue in JS app. Turned out I was using some older version of socket.io on the client and the latest on the server. In the repository you provided we can find:

// EngineIoClientDotNet/Src/EngineIoClientDotNet.mono/Parser/Parser.cs
public static readonly int Protocol = 3;

So this (now deprecated) client is using Engine.IO protocol v3. You didn't provide info which socket.io version you were using on the server, but it simply might've been using different revision on Engine.IO protocol.

As a side note, speaking more low-level: I guess that the client might be able to connect, but it does not respond to server's first ping command in a proper way (or the other way around). Therefore the connection is immediately dropped. Socket.IO has a history of breaking changes in how ping-pong mechanism is implemented, and this might be the underlying root cause.

Socket IO keeps disconnecting and reconnecting

1 Answers