How to check if the user is online?

Question

I am developing a project in PHP and using Mysql as a database. I only have one question about how to chat: How to know which users are online at that exact moment?

Answer 1

You can use a set of techniques to get this information.

On the client’s side:

• Listen to the closing event of the browser window, and when the user closes, send a signal to the server, indicating that the user has a less open window, and on the server will have to count how many pages the user has opened

• Listen to mouse movement event, and if you stay for a while without moving the mouse, then the user is considered offline

To implement the chat:

• the option that will give you the widest range in terms of browsers, is called long-time, but it is also the one that will give more work. See more about the technique: http://rberaldo.com.br/server-push-long-polling-php-ios/

• another option that will be easier, is to use websocket, and create a server connection, which will be able to send messages when some chat event occurs... like send a message

Answer 2

The question has already been marked as answered, but as a reference for those who stop here in the future: use websockets, they have been around for some time and are the most suitable solution for real-time communication between browsers and Servers (a chat for example). Their basic idea is to keep a constantly open connection between clients and the server to allow real-time communication, you could emulate this using ajax and long-time, however the difference in performance is relevant (worse in this case) and long-Polling is an alternative solution that is usually preferred only in the absence of better mechanisms.

One of the only problems with the use of websockets would be the lack of support in browsers, a virtually irrelevant problem since now almost all major already has support and most (if not all) websockets libraries provide automatic fallback to long-Polling if necessary.

In case the problem of verifying who is online would be simple, see an example using socket.:

// código do servidor realtime
var onlineClients = {};
io.on('connection', function (socket) {
    onlineClients[socket.id] = socket;

    // on disconnected, unregister
    socket.on('disconnect', function() {
        delete onlineClients[socket.id];
    });

    // usado em um exemplo mais abaixo
    socket.on('enviarMensagem', function(mensagem) {
        io.emit('novaMensagem', mensagem);
    });
});

// código do cliente (browser)
<script>
  var socket = io();

  // usado em um exemplo mais abaixo
  socket.on('novaMensagem', function(mensagem) {
      alert(mensagem);
  });
</script>

When a client connects or disconnects your server is instantly aware and you can take action based on this. Let’s say for example that you want from PHP to send a "hello" to everyone who is on:

// código do servidor php, usando a elephant.io lib
$elephant = new Client($socketServerUrl);
$elephant->initialize();
$elephant->emit('enviarMensagem', 'ola');

Your php server would send a 'send' event to your Realtime nodejs server, which in turn would send the 'newMensage' event to all connected clients, when arriving at them would be fired a alert(mensagem); with the message sent (see code snippet with the comment "used in an example below").

Answer 3

Give preference to using websocket, but if you have a shared host other than this support follow something that can help.

if if you create a field(EX: time) and in each text message it updates this field with php team value ( EX: $tempo=time() ) in the area where you will get the result use the following select

$query = "SELECT * FROM users WHERE tempo > UNIX_TIMESTAMP() - 300";

in the case UNIX_TIMESTAMP() - 300 means 5 minutes plus vc can change to the time you want in seconds EX: UNIX_TIMESTAMP() - 60 = 1 minute

Answer 4

The ideal would be to use Node.js (with the chat inside an iframe, connecting to Node.js which would be a separate PHP server), and Sockets.io as basic technology. There are even several example chats written in socket.io that could be used as a basis (example: http://socket.io/demos/chat/)