Correctly capture an error Socket.io

Question

I am building a simple chat. I am using the websocket lib socket.io because it has a great server/client implementation.

My client is on mobile and therefore has a very unstable network connection. I have read something about acknowledgment functions which could be passed with an emit, to execute code once the socket "transaction" is done. But building an error handling on top of that would be very uggly.

I have also read about the .on('error' implementation that catches errors.

The problem here is: how do I seperate between an unsuccessfuly sent message (.emit) and a temporarily lost socketconnection. I dont care about losing the socketconnection because i set it up to reconnect once its lost.

I hope my situation got clear. Thanks in advance.

EDIT:

What I am looking for is something like this on the clientside:

socket.on('error', function(data){
   alert(data.emitData.msg+' could not be sent: '+data.emitID);
});

I am going to start taking a closer look at the API myself in the meantime

Community · Accepted Answer · 2017-05-23 10:33:29Z

2

Message acknowledgement is covered here in the socket.io docs. Here's the relevant part of that docs:

Sometimes, you might want to get a callback when the client confirmed the message reception.

To do this, simply pass a function as the last parameter of .send or .emit. What’s more, when you use .emit, the acknowledgement is done by you, which means you can also pass data along:

Server (app.js)
var io = require('socket.io').listen(80);

io.sockets.on('connection', function (socket) {
  socket.on('ferret', function (name, fn) {
    fn('woot');
  });
});
Client (index.html)
<script>
  var socket = io(); // TIP: io() with no args does auto-discovery
  socket.on('connect', function () { // TIP: you can avoid listening on `connect` and listen on events directly too!
    socket.emit('ferret', 'tobi', function (data) {
      console.log(data); // data will be 'woot'
    });
  });
</script>

And, another example shown here: Acknowledgment for socket.io custom event

edited May 23, 2017 at 10:33

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answered Dec 8, 2014 at 18:08

jfriend00

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11 Comments

Max Bumaye Over a year ago

thanks for explaining acknoledgments in more detail - but how do you think this could help me find out what message actually was not delivered to the server. No connection to the server = no acknowlogment cb

jfriend00 Over a year ago

@MaxBumaye - what I described is the acknowledgement confirmation. If the packet is not delivered, you will get an error on the websocket and you can listen for errors by listening for the error message. TCP is a reliable protocol so you will either get a confirmation or an error - one or the other.

Max Bumaye Over a year ago

Oh, okay, do I understand this correctly that I dont actually need the acknowledgement func to do anything?

Max Bumaye Over a year ago

Pass an empty acknowledgement function that emits "error" if it doesnt get called?

jfriend00 Over a year ago

@MaxBumaye - if you only want errors, then just listen for the error message and process that. No need for an acknowledgement function if you don't want acknowledgement. The protocol is reliable either way. It will either deliver the message to the server or give you an error.

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