Socket Io limiting only 6 connection in Node js

Question

So i came across a problem.I am trying to send {id} to my rest API (node js) and in response, I get data on the socket.

Problem: For first 5-6 time it works perfectly fine and display Id and send data back to socket.But after 6 time it does not get ID. I tried this https://github.com/socketio/socket.io/issues/1145 and https://github.com/socketio/socket.io/issues/1145 but didn't solve the problem. On re compiling the server it shows previous {ids} which i enter after 6 time.it like after 5-6 time it is storing id in some form of cache. Here is my API route. //this route only get {id} 5-6 times .After 5-6 times it does not display receing {id}.

const express = require("express");
var closeFlag = false;
const PORT = process.env.SERVER_PORT; //|| 3000; 
const app = express();
var count = 1;
http = require('http');
http.globalAgent.maxSockets = 100;
http.Agent.maxSockets = 100;
const serverTCP = http.createServer(app)

// const tcpsock = require("socket.io")(serverTCP)
const tcpsock = require('socket.io')(serverTCP, {
  cors: {
    origin: '*',
  }
  ,  perMessageDeflate: false 
});
app.post("/getchanneldata", (req, res) => {
  console.log("count : "+count)

  count++;// for debugging purpose
  closeFlag = false;
  var message = (req.body.val).toString()
  console.log("message : "+message);
  chanId = message;

  client = dgram.createSocket({ type: 'udp4', reuseAddr: true });
  client.on('listening', () => {
    const address = client.address();
  });


  client.on('message', function (message1, remote) {


    var arr = message1.toString().split(',');
    
    }
  }); 

  client.send(message, 0, message.length, UDP_PORT, UDP_HOST, function (err, bytes) {
    if (err) throw err;
    console.log(message);
    console.log('UDP client message sent to ' + UDP_HOST + ':' + UDP_PORT);
    // message="";
  });


  client.on('disconnect', (msg) => {
    client.Diconnected()
    client.log(client.client)


  })
}
);

jfriend00 · Accepted Answer · 2021-11-26 05:52:49Z

There are multiple issues here.

In your app.post() handler, you don't send any response to the incoming http request. That means that when the browser (or any client) sends a POST to your server, the client sits there waiting for a response, but that response never comes.

Meanwhile, the browser has a limit for how many requests it will send simultaneously to the same host (I think Chrome's limit is coincidentally 6). Once you hit that limit, the browser queues the request and and waits for one of the previous connections to return its response before sending another one. Eventually (after a long time), those connections will time out, but that takes awhile.

So, the first thing to fix is to send a response in your app.post() handler. Even if you just do res.send("ok");. That will allow the 7th and 8th and so on requests to be immediately sent to your server. Every incoming http request should have a response sent back to it, even if you have nothing to send, just do a res.end(). Otherwise, the http connection is left hanging, consuming resources and waiting to eventually time out.

On a separate note, your app.post() handler contains this:

client = dgram.createSocket({ type: 'udp4', reuseAddr: true });

This has a couple issues. First, you never declare the variable client so it becomes an implicit global (which is really bad in a server). That means successive calls to the app.post() handler will overwrite that variable.

Second, it is not clear from the included code when, if ever, you close that udp4 socket. It does not appear that the server itself ever closes it.

Third, you're recreating the same UDP socket on every single POST to /getchanneldata. Is that really the right design? If your server receives 20 of these requests, it will open up 20 separate UDP connections.

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