Question

I want to build a chat, based on JavaScript (jQuery will be used for AJAX) and PHP.

I’ve heard a good way of doing this is to use long-polling.

I do understand the idea, but I don’t know how to implement it on the server side.

An infinite loop sounds like a bad idea.

Answer 1

You don’t want to create an infinite loop, but you can set a timeout. Basically loop for X second waiting for some sort of data, and if that doesn’t happen send a response to the client telling it that it needs to initiate a new request, which will have the same timeout period.

$source; // some data source - db, etc
$data = null; // our return data
$timeout = 30; // timeout in seconds
$now = time(); // start time

// loop for $timeout seconds from $now until we get $data
while((time() - $now) < $timeout) {
    // fetch $data
    $data = $source->getData();

    // if we got $data, break the loop
    if (!empty($data)) break;

    // wait 1 sec to check for new $data
    usleep(10000);
}

// if there is no $data, tell the client to re-request (arbitrary status message)
if (empty($data)) $data = array('status'=>'no-data');

// send $data response to client
echo json_encode($data);