Node JS Executed function twice

Question

New at stackoverflow and new with Node.

I have one simple socket server and one web server.

I want the web server to send a message to the socket server if someone connected the web server.

Browser <=> Web Server/Socket Client <=> Socket Server

I created the server like this :

var http = require('http');
var net = require('net');
var HOST = '192.168.1.254';
var PORT = 8888;
var client = new net.Socket();

http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n', function(){
      client.connect(PORT, HOST, function() {
        console.log('Connected To: ' + HOST + ':' + PORT);
        client.write('0109001' + "\n");
      });   

    // Add a 'data' event handler for the client socket
    // data is what the server sent to this socket
        client.on('data', function(data) {
            console.log('The Data: ' + data);
            client.destroy();
        });

        // Add a 'close' event handler for the client socket
        client.on('close', function() {
            console.log('Connection closed');
        });
  });
}).listen(1337, '127.0.0.1');
console.log('Server running at http://127.0.0.1:1337/');

This code works but the web server sending the message to the socket server twice. Did I do something wrong maybe with the callback or something? Any help would be appreciated.

are you sure you are sending only one request? Dont forget the favicon request every browser does — pfried, Mar 06 '13 at 07:56
Try adding [`console.log(req.url);`](http://nodejs.org/api/http.html#http_request_url). Does it output the same URL each time? — Jonathan Lonowski, Mar 06 '13 at 08:07

score 12 · Accepted Answer · answered Mar 06 '13 at 08:09

12

If you call this code by a browser it sends 2 requests to the server. One for the FavIcon and one for the page itself.

The code inside the callback is called twice because there are 2 requests.

As Matt mentioned: dont put the socket response handlers inside the callback, because you loose the reference to them and a new handler is attached for every request.

var http = require('http');
var net = require('net');
var HOST = '192.168.1.254';
var PORT = 8888;
var client = new net.Socket();
var url   = require('url');

http.createServer(function (req, res) {
  console.log(url.parse(req.url));
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n', function(){

        console.log('Connected To: ' + HOST + ':' + PORT);

  });
}).listen(1337, '127.0.0.1');
console.log('Server running at http://127.0.0.1:1337/');

answered Mar 06 '13 at 08:09

pfried

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Here's how you can ignore the favicon requests, at least while you're debugging: https://gist.github.com/kentbrew/763822 – Matt Browne Mar 06 '13 at 08:17
You are correct about the favicon, I forgot it that the http header from browser include the favicon request :) Anyway, thanks for pointing me out about the reference problem. – BigBoss Mar 06 '13 at 11:53
The above code is still giving two response in console – Mohammad Shahnawaz Aug 30 '18 at 11:07
@MohammadShahnawaz Sure it does because there are 2 requests, that was not the point – pfried Aug 30 '18 at 12:08

score 0 · Answer 2 · answered Mar 06 '13 at 07:59

0

The client.on() calls shouldn't be inside the res.end() callback - that's causing the event handler to be attached multiple times, meaning that every time data is received, it's getting called multiple times.

Try this instead:

http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n', function(){
      client.connect(PORT, HOST, function() {
        console.log('Connected To: ' + HOST + ':' + PORT);
        client.write('0109001' + "\n");
      });   
  });
}).listen(1337, '127.0.0.1');

// Add a 'data' event handler for the client socket
// data is what the server sent to this socket
client.on('data', function(data) {
    console.log('The Data: ' + data);
    client.destroy();
});

// Add a 'close' event handler for the client socket
client.on('close', function() {
    console.log('Connection closed');
});

answered Mar 06 '13 at 07:59

Matt Browne

12,169
4
59
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2

are you sure this is the problem? I think it is attached for every request. It is a zombie handler, but i dont think it is causing the problem of 2 requests on the other server the socket connects to – pfried Mar 06 '13 at 08:01
@pfried I think you may be right...now that you mention it, it seems that the socket is only being written to by the client.write() line – Matt Browne Mar 06 '13 at 08:09
I forgot it that the http header from browser include the favicon request :) Thanks for pointing me out to place the event handler outside of the callback – BigBoss Mar 06 '13 at 11:54

Node JS Executed function twice

2 Answers2