Socket.io server to server (sending message to specific server) - node.js

Question

I have a specific situation. I have client (browser) which connects to server A. Server A is connected to server B and C. When client sends message to server A, I need to send message to specific server which means to one of the servers B or C, not both of them. Generally I need separated communication between servers but I have only broadcasted communication. Message from server A to another server can't be seen on all connected servers.
How can I send messages directly to one of the servers ? Here is my code snippet for servers. I just change ports for each server and connect them.
// Load requirements
var PORT = process.env.PORT || 8080;//just change port for other servers
var express = require("express");
var app = express();
var http = require("http").Server(app);
var io = require("socket.io")(http);
app.use(express.static(__dirname + '/public'));
var client = require('socket.io-client');
var socket1 = client.connect('http://localhost:8081', { reconnect: true });//connection to server B
var socket2 = client.connect('http://localhost:8082', { reconnect: true });//connection to server C
// Add a connect listener
io.on('connection', function (socket) {
console.log('Client connected.');
//when server receive message from client
socket.on('message_from_browser', function (message) {
console.log("Message from browser broadcasted: " + message.text);
var updated_message = {
text: message.text,
port: PORT
};
// send message to server B
socket1.emit('server_message', updated_message);//send message to server B
});
// Disconnect listener
socket.on('disconnect', function () {
console.log('Client disconnected.');
});
});
socket1.on('connect', function () {
socket1.on('server_message', function (message) {
console.log('RECEIVED MESSAGE FROM ANOTHER SERVER ON PORT '+ message.port + ": " + message.text);
});
//change server name
console.log('Connected to server B!');
});
socket2.on('connect', function () {
socket2.on('server_message', function (message) {
console.log('RECEIVED MESSAGE FROM ANOTHER SERVER ON PORT '+ message.port + ": " + message.text);
});
//change server name
console.log('Connected to server C!');
});
http.listen(PORT, function (req, res) {
console.log("Server Started on port: " + PORT);
});

Answer 1

You have a naming conflict with the variable name socket. It is defined as both your connection to server B and as an argument in your .on('connection', function(socket) {...}) callback.
To fix that, change this:
var socket = client.connect('http://localhost:8081', { reconnect: true });//connection to server B
var socket2 = client.connect('http://localhost:8082', { reconnect: true });//connection to server C
To this:
var socket1 = client.connect('http://localhost:8081', { reconnect: true });//connection to server B
var socket2 = client.connect('http://localhost:8082', { reconnect: true });//connection to server C
And, then refer to the server B connection as socket1, not socket.
The variable named socket is already defined as an argument in this so you cannot reach the outer socket variable when it has a conflicting name:
// Add a connect listener
io.on('connection', function (socket) {
// socket variable name ^^^^^^
console.log('Client connected.');
//when server receive message from client
socket.on('message_from_browser', function (message) {
console.log("Message from browser broadcasted: " + message.text);
var updated_message = {
text: message.text,
port: PORT
};
// send message to server B
socket1.emit('server_message', updated_message);//send message to server B
});
// Disconnect listener
socket.on('disconnect', function () {
console.log('Client disconnected.');
});
});
And there were no listeners for incoming server messages so you need to add listeners for socket1 and socket2.
io.on('connect', function(socket1){
socket1.on('server_message', function (message) {
console.log('RECEIVED MESSAGE FROM ANOTHER SERVER ON PORT '+ message.port + ": " + message.text);
});
});
io.on('connect', function(socket2){
socket2.on('server_message', function (message) {
console.log('RECEIVED MESSAGE FROM ANOTHER SERVER ON PORT '+ message.port + ": " + message.text);
});
});

Answer 2

Use one variable and configs to track others hosts, try:
Updated to fix some bugs:
// Load requirements
var PORT = process.env.PORT || 8081;//just change port for other servers
var express = require("express");
var app = express();
var http = require("http").Server(app);
var io = require("socket.io")(http);
var async = require('async'); // async is optional for this example ...
var client = require('socket.io-client');
app.use(express.static(__dirname + '/public'));
// save hosts here ...
var otherServers = {
server1: {
url: 'http://localhost:8082'
},
server2: {
url: 'http://localhost:8083'
},
};
// Add a connect listener
io.on('connection', function (socket) {
console.log('Client connected.');
//when server receive message from client
socket.on('message_from_browser', function (message) {
console.log("Message from browser broadcasted: " + message.text);
var updated_message = {
text: message.text,
port: PORT
};
// choice how server will receive this message ...
// then send it
otherServers.server1.client.broadcast.emit('server_message', updated_message);
});
// Disconnect listener
socket.on('disconnect', function () {
console.log('Client disconnected.');
});
});
async.each(otherServers, function forEachOtherServer(otherServer, next) {
//connect to another server
otherServer.client = client.connect(otherServer.url, { reconnect: true });
// to something more if need in every client connection ...
otherServer.client.on('connect', function (x) {
otherServer.client.on('server_message', function (message) {
console.log('RECEIVED MESSAGE FROM ANOTHER SERVER ON PORT '+ message.port + ": " + message.text);
//socket.broadcast.emit('message_from_server', message_server);
});
console.log('Connected!');
});
next();
}, function afterConnectInAllServers(err) {
if (err) throw err;
// to something after connect in all servers ...
});
http.listen(PORT, function (req, res) {
console.log("Server Started on port: " + PORT);
});