title: node.js and socket.io chat with facebook friends
body: <p>I'm working on chat, where facebook friends can talk only with each other. I'm using redis so save relation: fb_user_id - user_socket_id. This is how my implementation looks like:</p>
  
  <ul>
  <li>getting friends from facebook;</li>
  <li>selecting socket ids of my friends from redis, creating local friends-sockets list in my node client;</li>
  <li>connecting to node server. Server saving my socket id to redis and notifying all my friends about new friend login (about me);</li>
  <li>all my friends updating local friends-sockets list;</li>
  <li>when someone sending chat message to server, this message comes with friends-sockets list, so server knows where need to send message (only for my friends).</li>
  </ul>
  
  <p>Question: it's better solution to send friends-sockets every time to server, or it's better to get this relation on server from redis (or create array of sockets in server). How to adapt my task for high availability?</p>
  
  <p>Any comments and suggestions are welcomed, thanks.</p>
  
  <p>Here is my code (socket.io 1.2.0)</p>
  
  <p>server.js</p>
  
  <pre><code>var app = require('express')();
  var http = require('http').Server(app);
  var io = require('socket.io')(http);
  
  var redis = require("redis"), client = redis.createClient();
  var parts;
  client.select(2, function() {});
  client.on("error", function (err) {
      console.log("Error " + err);
  });
  
  process.on('uncaughtException', function (err) {
      console.log(err);
  });
  
  app.get('/', function (req, res) {
      res.sendFile(__dirname + '/index.html');
  });
  
  io.on('connection', function (socket) {
  
      // on connect
      socket.on("join", function (data)
      {
          if (data) {
              // notify all friedns about new friend login
              if (data.to) {
                  if (data.to.length &gt; 0) {
                      for (x in data.to) {
                          io.to(data.to[x]['socket_id']).emit('new friend response', {uid: data.uid, sid: socket.id});
                      }
                  }
              }
  
              // save or update user socket id to redis
              parts = split_id(data.uid);
              client.hset(parts[1], parts[0], socket.id);
  
          }
      });
  
      // disconnect
      socket.on('disconnect', function () {
          console.log("user disconnected");
      });
  
      // send message by friends-sockets list
      socket.on('chat message', function (data) {
          if (data.to.length &gt; 0) {
              for (x in data.to) {
                  var message = data.msg;
                  io.to(data.to[x]['socket_id']).emit('chat message response', {msg: message, uid: data.uid});
              }
          }
      });
  });
  
  http.listen(3000, function () {
      console.log('listening on *:3000');
  });
  
  // split facebook uid in 2 parts (for redis saving)
  function split_id(str)
  {
      var n = str.length;
      var res1 = str.substr(n - 2, 2);
      var res2 = str.substr(0, n - 2);
      return [res1, res2];
  }
  </code></pre>
  
  <p>client.js</p>
  
  <pre><code>// friends socket list
  var friends_sockets = [];
  // my data from facebook
  var my_data;
  // my facebook uid
  var my_uid;
  
  function client() {
      socket = io('http://server.com:3000');
  
      // connect
      socket.on('connect', function () {
          // notify server about login
          socket.emit('join', {uid: my_uid, to: friends_sockets, from: my_data, type: 'web'});
      });
  
      // send chat message to my friends
      $('.enter_form button').click(function () {
          if (friends_sockets.length &gt; 0) {
              socket.emit('chat message', {msg: $('#m').val(), to: friends_sockets, from: my_data, uid: my_uid});
          }
          // add message to my chat
          $('#messages').append($('&lt;li&gt;').text(my_data.first_name + ' ' + my_data.last_name + ': ' + $('#m').val()));
          $('#m').val('');
          return false;
      });
  
      // new message listner (waiting for chat messages)
      socket.on('chat message response', function (data) {
          $('#messages').append($('&lt;li&gt;').text(data.msg));
      });
  
      // new friends lister (update list on friends login)
      socket.on('new friend response', function (data) {
          var found = false;
          if (friends_sockets.length &gt; 0) {
              for (x in friends_sockets) {
                  if (friends_sockets[x]['uid'] == data.uid) {
                      friends_sockets[x]['socket_id'] = data.sid;
                      found = true;
                  }
              }
          }
  
          if (found === false) {
              friends_sockets.push(data);
          }
      });
  }
  </code></pre>