random image swap

kloy

I'm using this code on this site to randomly swap out 6 header images.
I've wrestling with this for the last 2 weeks. For some reason, more often than not it seems to get stuck on one. Then I realized that it swaps them out when I reload the page...as opposed to going to a new page. Obviously visitors won't be reloading the page as much as going to different pages. Is there any way to fix this?

Here's the site it's on
www.newseminary.org

<?php
/*


*/// Make this the relative path to the images, like "../img" or "random/images/".
// If the images are in the same directory, leave it blank.
$folder = '';

// Space seperated list of extensions, you probably won't have to change this.
$exts = 'jpg jpeg png gif';

$files = array(); $i = -1; // Initialize some variables
if ('' == $folder) $folder = './';

$handle = opendir($folder);
$exts = explode(' ', $exts);
while (false !== ($file = readdir($handle))) {
foreach($exts as $ext) { // for each extension check the extension
if (preg_match('/\.'.$ext.'$/i', $file, $test)) { // faster than ereg, case insensitive
$files[] = $file; // it's good
++$i;
}
}
}
closedir($handle); // We're not using it anymore
mt_srand((double)microtime()*1000000); // seed for PHP < 4.2
$rand = mt_rand(0, $i); // $i was incremented as we went along

header('Location: '.$folder.$files[$rand]); // Voila!
?>

laserlight

It looks like you are using mt_rand() correctly, though you might want to account for the possibility that a configuration error could lead to $files being empty. Furthermore, you should indent your code better.

My guess is that your "more often than not it seems to get stuck on one" observation is psychological, much like how some web game players complain that the pseudorandom number generator is actively trying to make them lose just when they need to win.

Weedpacket

kloy wrote:

// We're not using it anymore
mt_srand((double)microtime()*1000000); // seed for PHP < 4.2

This line shouldn't be necessary - if you're still using something older than v4.2 then a misbehaving RNG is likely to be the least of your issues.

Even before 4.2 it would have been a pretty poor choice of initialiser, restricting the generator to choosing one out of only a million different sequences instead of one out of a couple of billion.

kloy

Thanks for your replies and trying to help.
I took out that line of code.

I think that b/c I built this in a CMS, the header just doesn't reload on every page click.
When a link is clicked, sometimes the entire page re-loads and sometime only the content area that needs to change, changes. Though what really seems random is when it chooses to reload the entire page and when it just load the new content area.

Does that make sense? Maybe I'm grasping at straws here?

Thanks

Weedpacket

If it's just refreshing the content area, and the image (rather, the header area that contains it) is not in the content area, then they won't be refreshed, no. I don't know the details of how that's working, of course, but if there is some way to explain to the CMS that when the content area is refreshed then the header (at least that part of it containing the image) should be refreshed as well then you might have a bit more luck.

One problem I've just noticed is that the 'Location:' header that's generated isn't entirely kosher. It should be a URL, not a file path. If the CMS does anything to rewrite URLs so that they don't match up perfectly with the file system then there could be hazards there: what needs to go in that header should be the same URL that you would use if you were using a conventional image.

On second thought, that header and the corresponding redirection shouldn't even be necessary: you already have the image - why not just give it to them now instead of just asking them to ask for it? Actually I just answered that one for myself: the browser cache. It can cache the images as it gets them. Each time this script is run it gets given the URL to a random image. If it's one it hasn't seen before it downloads it and displays it; otherwise it can fetch the cached version and avoid requesting it again.

So on third thought the redirection ought to remain. Unless the CMS is doing some weird voodoo that changes the HTTP response code for the output of this script then the browser cache will be normal. The URL given in the Location really ought to be fixed, though.

Anyway; in light of all that I thought I'd do a rewrite just to see what I get:

<?php
$folder = '';
$exts = 'jpg,jpeg,png,gif'; // Notice the commas
if('' == $folder) $folder = './';

$files = glob($folder.'{'.$exts.'}', GLOB_BRACE);

$image = $files[array_rand($files)];

//From http://www.php.net/header
$host  = $_SERVER['HTTP_HOST'];
$uri   = rtrim(dirname($_SERVER['PHP_SELF']), '/\\');
$url = "http://$host$uri/$image";
header("Location: $url");
?>
<html><body><a href="<?php echo $url?>"><?php echo basename($image);?></a></body></html>

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