Untitled

<?php

/**
 * Server-side file.
 * This file is an infinitive loop. Seriously.
 * It gets the file data.txt's last-changed timestamp, checks if this is larger than the timestamp of the
 * AJAX-submitted timestamp (time of last ajax request), and if so, it sends back a JSON with the data from
 * data.txt (and a timestamp). If not, it waits for one seconds and then start the next while step.
 *
 * Note: This returns a JSON, containing the content of data.txt and the timestamp of the last data.txt change.
 * This timestamp is used by the client's JavaScript for the next request, so THIS server-side script here only
 * serves new content after the last file change. Sounds weird, but try it out, you'll get into it really fast!
 */

// set php runtime to unlimited
set_time_limit(0);

// where does the data come from ? In real world this would be a SQL query or something
$data_source_file = 'data.txt';

// main loop
while (true) {

    // if ajax request has send a timestamp, then $last_ajax_call = timestamp, else $last_ajax_call = null
    $last_ajax_call = isset($_GET['timestamp']) ? (int)$_GET['timestamp'] : null;

    // PHP caches file data, like requesting the size of a file, by default. clearstatcache() clears that cache
    clearstatcache();
    // get timestamp of when file has been changed the last time
    $last_change_in_data_file = filemtime($data_source_file);

    // if no timestamp delivered via ajax or data.txt has been changed SINCE last ajax timestamp
    if ($last_ajax_call == null || $last_change_in_data_file > $last_ajax_call) {

        // get content of data.txt
        $data = file_get_contents($data_source_file);

        // put data.txt's content and timestamp of last data.txt change into array
        $result = array(
            'data_from_file' => $data,
            'timestamp' => $last_change_in_data_file
        );

        // encode to JSON, render the result (for AJAX)
        $json = json_encode($result);
        echo $json;

        // leave this loop step
        break;

    } else {
        // wait for 1 sec (not very sexy as this blocks the PHP/Apache process, but that's how it goes)
        sleep( 1 );
        continue;
    }
}

/**
 * AJAX long-polling
 *
 * 1. sends a request to the server (without a timestamp parameter)
 * 2. waits for an answer from server.php (which can take forever)
 * 3. if server.php responds (whenever), put data_from_file into #response
 * 4. and call the function again
 *
 * @param timestamp
 */
function getContent(timestamp)
{
    var queryString = {'timestamp' : timestamp};

    $.ajax(
        {
            type: 'GET',
            url: '../server/server.php',
            data: queryString,
            success: function(data){
                // put result data into "obj"
                var obj = jQuery.parseJSON(data);
                // put the data_from_file into #response
                $('#response').html(obj.data_from_file);
                // call the function again, this time with the timestamp we just got from server.php
                getContent(obj.timestamp);
            }
        }
    );
}

// initialize jQuery
$(function() {
    getContent();
});

<html>
    <head>
        <script type="text/javascript" src="../../../../JS/jquery.min.js"></script>
        <script type="text/javascript" src="client.js"></script>
    </head>
    <body>
        <h1>Response from server:</h1>
        <div id="response" >


        </div>
    </body>
</html>