Ajax progress with PHP session

Question

I have an app that processes images and use jQuery to display progress to the user.
I done this with writing to a textfile each time and image is processed and than read this status with a setInterval.

Because no images are actually written in the processing (I do it in PHP's memory) I thought a log.txt would be a solution, but I am not sure about all the fopen and fread's. Is this prone to issues?

I tried also with PHP sessions, but can't seem to get it to work, I don't get why..

HTML:

<a class="download" href="#">request download</a>
<p class="message"></p>

JS:

$('a.download').click(function() {

    var queryData = {images : ["001.jpg", "002.jpg", "003.jpg"]};       
    $("p.message").html("initializing...");

    var progressCheck = function() {
        $.get("dynamic-session-progress.php",
            function(data) { 
                $("p.message").html(data); 
            }
        );
    };

    $.post('dynamic-session-process.php', queryData,
        function(intvalId) {
            return function(data) {
                $("p.message").html(data);
                clearInterval(intvalId);
            }
        } (setInterval(progressCheck, 1000))
    );

    return false;
});

process.php:

// session_start();

$arr = $_POST['images'];
$arr_cnt = count($arr);
$filename = "log.txt";

for ($i = 1; $i <= $arr_cnt; $i++) {
    $content = "processing $val ($i/$arr_cnt)";

    $handle = fopen($filename, 'w');
    fwrite($handle, $content);
    fclose($handle);

    // $_SESSION['counter'] = $content;

    sleep(3); // to mimic image processing
}

echo "<a href='#'>download zip</a>";

progress.php:

// session_start();

$filename = "log.txt";
$handle = fopen($filename, "r");
$contents = fread($handle, filesize($filename));
fclose($handle);

echo $contents;

// echo $_SESSION['counter'];

I don't know the exact solution to your problem but as a tip - in your process.php file you should move your fopen before you actually start the loop. You can fwrite() multiple times so long as you don't close the file (move the fclose() outside the end of the loop). You are opening the file each time you run through the loop. — Jarrod Nettles
– Jarrod Nettles, Commented May 20, 2010 at 19:07

baloo · Accepted Answer · 2010-05-20 19:07:44Z

2

What if two clients process images at the same time?

You can try adding session_write_close() between setting the new status in the session, so that the new session data is stored, otherwise it will only get stored once your script finishes.

Another solution would be to save the status in memcache or to use a database, perhaps separate the statuses with a userid or creating an md5 hash on the image data

answered May 20, 2010 at 19:07

baloo

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4 Comments

catchmeifyoutry Over a year ago

indeed, with multiple clients trying to open the same log.txt file for writing will fail, or present the same status message to all the clients.

TunaFFish Over a year ago

I didn't even think about multiple processing... Thanks for that. A solution could be to create logfiles for each client.

TunaFFish Over a year ago

Thanks for the link to session_write_close() Baloo. So I couldn't get the sessions method to work because the session would only be written at the end of the script?

TunaFFish Over a year ago

Okay I got it working now.. In the loop: session_start(); $content = "processing $val ($i/$arr_cnt)"; $_SESSION['counter'] = $content; session_write_close(); Thanks!!

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