Creating a private chat between a key using a node.js and socket.io

SURE: Simply,

This is what you need :

 io.to(socket.id).emit("event", data);

whenever a user joined to the server,socket details will be generated including ID.This is the ID really helps to send a message to particular people.

first we need to store all the socket.ids in array,

   var people={};

   people[name] =  socket.id;

here name is the reciever name. Example:

  people["ccccc"]=2387423cjhgfwerwer23;

So, now we can get that socket.id with the reciever name whenever we are sending message:

for this we need to know the recievername.You need to emit reciever name to the server.

final thing is:

  socket.on('chat message', function(data){
 io.to(people[data.reciever]).emit('chat message', data.msg);
 });

Hope this works well for you.!!Good Luck

You have to create a room with conversation_id and make users to subscribe to that room, so that you can emit a private message to that room it by,

client

var socket = io.connect('http://ip:port');

socket.emit('subscribe', conversation_id);

socket.emit('send message', {
    room: conversation_id,
    message: "Some message"
});

socket.on('conversation private post', function(data) {
    //display data.message
});

Server

socket.on('subscribe', function(room) {
    console.log('joining room', room);
    socket.join(room);
});

socket.on('send message', function(data) {
    console.log('sending room post', data.room);
    socket.broadcast.to(data.room).emit('conversation private post', {
        message: data.message
    });
});

Here is the docs and example for creating a room, subscribing to the room and Emit message to a room:

1. Socket.io Rooms
2. Socket.IO subscribe to multiple channels
3. Socket.io rooms difference between broadcast.to and sockets.in