SocketIO emit with callback fails while upgrading 0.9.16 to 1.3.5

Question

In 0.9.16, I use socket.emit with callback so that the chat server return some data and I can handle the result as per the acknowledgement. But after the upgrade to 1.3.5 I've found a error in console like this

Uncaught TypeError: Cannot read property 'apply' of undefined.

I've done something like this,

From web

socket.emit('userToUser', { 'usename': 'John',
'message': 'hi'
}, function(callback){
//callback handled
});

Chat Server

socket.on('userToUser', function(content, callback){
//do something
if(callback) return callback({'result':'success', 'messageid':content.messageid, 'chatid':content.chatid});
});

When I removed the callback from client side, there is no error. So I believe there will be some changes to be done in the callback.

I'm getting the acknowledgement and the chat is working properly, but my concern is about the console error which leads to socketio.js

Socket.prototype.onack = function(packet){
  debug('calling ack %s with %j', packet.id, packet.data);
  var fn = this.acks[packet.id];
  fn.apply(this, packet.data);
  delete this.acks[packet.id];
};

Guys, please help

score 6 · Accepted Answer · edited Nov 27 '17 at 10:20

Finally I've fixed the issue. It was a mistake in my code , I've done multiple callbacks in the chat server. like this:

socket.on('userToUser', function(content, callback){

  mysql.insertChat(content, function(err, data){
      return callback({'result':'1'})   //first callback
  })  
  sendToUser(content, function(errm successData){
      return callback({'result':'success','chatid':content.chatid});
      //second callback ->wrong
  })

});

In the previous versions it was a warning, now its an error !! That's it. So please avoid multiple callbacks

Please have a look at this and might be useful for every nodejs developer: http://www.toptal.com/nodejs/top-10-common-nodejs-developer-mistakes/#remote-developer-job

Thanks guys for upvoting !

Just an FYI it worked before because of a memory leak in Socket.IO 0.9.x - The handlers were never cleaned up correctly (and thus leaking memory and actually making your server/client vulnerable for attacks) which allowed you to continuously call the callback. — 3rdEden, May 11 '15 at 09:53

nilakshdas · Answer 2 · 2015-05-06T07:58:05.767

EDIT: ~~This is not how callbacks work with socket.io v1.3.5. In fact, the emit function does not accept any callbacks at all.~~

I'm guessing you want to send an acknowledgement to the sending node that its message has been received. To accomplish that, you need to make another socket.emit call from the server (on the server, socket variable represents the connection to a specific node in the network whereas on the client, the socket variable represents the connection to the server). Consequently, on the client, you need to handle the acknowledgement with a socket.on which is where you'll put your callback.

To broadcast the acknowledgement to ALL nodes in the network, you should use io.emit.

Code sample for a chat application using socket.io is available here.

I think you are wrong, because socketio support callback, see this socket.io/docs/#sending-and-getting-data-(acknowledgements) — Tony Jose, May 05 '15 at 06:25

SocketIO emit with callback fails while upgrading 0.9.16 to 1.3.5

2 Answers2