Nodejs Websocket Close Event Called...Eventually

Question

I've been having some problems with the below code that I've pieced together. All the events work as advertised however, when a client drops off-line without first disconnecting the close event doesn't get call right away. If you give it a minute or so it will eventually get called. Also, I find if I continue to send data to the client it picks up a close event faster but never right away. Lastly, if the client gracefully disconnects, the end event is called just fine.

I understand this is related to the other listen events like upgrade and ondata.

I should also state that the client is an embedded device.

client http request:
GET /demo HTTP/1.1\r\n
Host: example.com\r\n
Upgrade: Websocket\r\n
Connection: Upgrade\r\n\r\n


//nodejs server (I'm using version 6.6)
var http = require('http');
var net = require('net');
var sys = require("util");

var srv = http.createServer(function (req, res){
});

srv.on('upgrade', function(req, socket, upgradeHead) {

  socket.write('HTTP/1.1 101 Web Socket Protocol Handshake\r\n' +
               'Upgrade: WebSocket\r\n' +
               'Connection: Upgrade\r\n' +
               '\r\n\r\n');

  sys.puts('upgraded');

  socket.ondata = function(data, start, end) {
    socket.write(data.toString('utf8', start, end), 'utf8'); // echo back
  }; 

  socket.addListener('end', function () {    
    sys.puts('end');  //works fine
  });

  socket.addListener('close', function () {
    sys.puts('close');  //eventually gets here
  });

});
srv.listen(3400);

Can anyone suggest a solution to pickup an immediate close event? I am trying to keep this simple without use of modules. Thanks in advance.

Answer 1

close event will be called once TCP socket connection is closed by one or another end with few complications of rare cases when system "not realising" that socket been already closed, but this are rare cases. As WebSockets start from HTTP request server might just keep-alive till it timeouts the socket. That involves the delay.

In your case you are trying to perform handshake and then send data back and forth, but WebSockets are a bit more complex process than that.
The handshake process requires some security procedure to validate both ends (server and client) and it is HTTP compatible headers. But different draft versions supported by different platforms and browsers do implement it in a different manner so your implementation should take this in account as well and follow official documentation on WebSockets specification based on versions you need to support.

Then sending and receiving data via WebSockets is not pure string. Actual data sent over WebSockets protocol has data-framing layer, which involves adding header to each message you send. This header has details over message you sending, masking (from client to server), length and many other things. data-framing depends on version of WebSockets again, so implementations will vary slightly.

I would encourage to use existing libraries as they already implement everything you need in nice and clean manner, and have been used extensively across commercial projects.
As your client is embedded platform, and server I assume is node.js as well, it is easy to use same library on both ends.

Best suit here would be ws - actual pure WebSockets.
Socket.IO is not good for your case, as it is much more complex and heavy library that has multiple list of protocols support with fallbacks and have some abstraction that might be not what you are looking for.