Send message to specific client with socket.io and node.js

Question

I'm working with socket.io and node.js and until now it seems pretty good, but I don't know how to send a message from the server to an specific client, something like this:

client.send(message, receiverSessionId)

But neither the .send() nor the .broadcast() methods seem to supply my need.

What I have found as a possible solution, is that the .broadcast() method accepts as a second parameter an array of SessionIds to which not send the message, so I could pass an array with all the SessionIds connected at that moment to the server, except the one I wish send the message, but I feel there must be a better solution.

Any ideas?

Answer 1

Ivo Wetzel's answer doesn't seem to be valid in Socket.io 0.9 anymore.

In short you must now save the socket.id and use io.sockets.socket(savedSocketId).emit(...) to send messages to it.

This is how I got this working in clustered Node.js server:

First you need to set Redis store as the store so that messages can go cross processes:

var express = require("express");
var redis = require("redis");
var sio = require("socket.io");

var client = redis.createClient()
var app = express.createServer();
var io = sio.listen(app);

io.set("store", new sio.RedisStore);


// In this example we have one master client socket 
// that receives messages from others.

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

  // Promote this socket as master
  socket.on("I'm the master", function() {

    // Save the socket id to Redis so that all processes can access it.
    client.set("mastersocket", socket.id, function(err) {
      if (err) throw err;
      console.log("Master socket is now" + socket.id);
    });
  });

  socket.on("message to master", function(msg) {

    // Fetch the socket id from Redis
    client.get("mastersocket", function(err, socketId) {
      if (err) throw err;
      io.sockets.socket(socketId).emit(msg);
    });
  });

});

I omitted the clustering code here, because it makes this more cluttered, but it's trivial to add. Just add everything to the worker code. More docs here http://nodejs.org/api/cluster.html