Why NodeJS KeepAlive does not seem to work as expected?

Question

Quoted from TCP keepalive HowTo:

In order to understand what TCP keepalive (which we will just call keepalive) does, you need do nothing more than read the name: keep TCP alive. This means that you will be able to check your connected socket (also known as TCP sockets), and determine whether the connection is still up and running or if it has broken.

So why is the following code not throwing something when the internet connection is broken?

var tls = require('tls');

var socket = tls.connect(443, "google.com", function connected() {
  console.log('connected');
});

socket.setNoDelay(true);
socket.setKeepAlive(true, 0);
socket.setTimeout(0, function(){
  console.log('timeout');
});
socket.on('data', function(data) {
  console.log(data);
});
socket.on('close', function() {
  console.error("close");
});
socket.on('error', function(err) {
  console.error("error", err);
});

Tested on MacOS/Debian, with NodeJS v0.10.17

Answer 1

Quoting man 7 tcp:

tcp_keepalive_time (integer; default: 7200; since Linux 2.2)

The number of seconds a connection needs to be idle before TCP begins sending out keep-alive probes. Keep-alives are only sent when the SO_KEEPALIVE socket option is enabled. The default value is 7200 seconds (2 hours). An idle connection is terminated after approximately an additional 11 minutes (9 probes an interval of 75 seconds apart) when keep-alive is enabled.

So after ~10 minutes (on MacOS 10.8) node emitted an error:

error { [Error: read ETIMEDOUT] code: 'ETIMEDOUT', errno: 'ETIMEDOUT', syscall: 'read' }

Answer 2

https://www.npmjs.com/package/net-keepalive

Here is a module which lets you configure TCP_KEEPINTVL and TCP_KEEPCNT per-socket basis.

Provides high-level access to socket options like TCP_KEEPIDLE, TCP_KEEPINTVL, TCP_KEEPCNT

var Net = require('net')
  , NetKeepAlive = require('net-keepalive')
;

// Create a TCP Server
var srv = Net.createServer(function(s){>
  console.log('Connected %j', s.address())
  // Doesn't matter what it does
  s.pipe(s)
});

// Start on some port
srv.listen(1337, function(){
  console.log('Listening on %j', srv.address())
});

// Connect to that server
var s = Net.createConnection({port:1337}, function(){
  console.log('Connected to %j', s.address())

  //IMPORTANT: KeepAlive must be enabled for this to work
  s.setKeepAlive(true, 1000)

  // Set TCP_KEEPINTVL for this specific socket
  NetKeepAlive.setKeepAliveInterval(s, 1000)

  // and TCP_KEEPCNT
  NetKeepAlive.setKeepAliveProbes(s, 1)
});