socket.io emit when server is offline

Question

I was working with socket.io v1.3.6 (nodejs) and tried to emit the data from browser using the below code .

Client Code

var socket = io.connect('http://something.com:3300/');
function sendMessage(message) {
	socket.emit('message', message);    
}

Server Code

var io = require('socket.io').listen(3300);

io.sockets.on('connection', function (socket) {
  messageHandler(socket);
});

function messageHandler(socket) {
    socket.on('message', function (data) {	
	  console.log('Captured a message : ' + data);	
    });
}

my socket server http://something.com:3300/ is down initially , and tried to call few sendMessage() - (say around 10 calls)

As expected in the browser i will get the handshake error in console log.

I waited for 5 mins and started the socket server.

But surprisingly all the messages sent during offline are captured in the server, once the handshake is established.

My questions : 1) Is this offline logic as part of socket.io or WebSocket specification ? 2) I searched a lot of offline mode socket.io questions, and saw some special handling recommendations to capture offline messages. But how this works without those special offline checks ?

Answer 1

Yes, there is an 'offline' buffering for packages to be emitted before the first connect, see here the implementation of socket.js yourself:

https://github.com/socketio/socket.io-client/blob/master/lib/socket.js

(especiall check onconnect and emitBuffered functions/attribs)

Answer 2

I solved this problem with this little change on reconnecting:

mySocket.on('reconnect', function() {

  //Avoid that buffered emits getting send again
  mySocket.sendBuffer=[];

  ...
});

By setting the sendBuffer to an empty array you avoid sending the packages again on reconnect. Of course you should then handle the sending attempts on your own.