Change filename from URL when user downloads file

File links are all http://website.com/f/xxx.png/zip/txt and so on.
I need to set it up so that if a user downloads that file it would download with a different name.
I have seen how to do this on a normal page, but I have no clue how making it work when the image itself is linked to is done.

Appreciate any help :)

Edit: Using the rewrite Steven Jeffries posted,

header('Content-Disposition: inline; filename=' . $originalFileName . "'");
header("Content-Type:" . $mimeType);
$im = imagecreatefrompng($filePathOnServer);
imagepng($im);

to display images and

header('Content-Disposition: attachment; filename=' . $originalFileName . "'");
header("Content-Type:" . $mimeType);

to make other files download solved the issues I had.

Solution

I think an easy way to do this would be to redirect download links to another script that handles what to download, etc. Basically, I'd set up a download dir, add some rewrite rules, and then create a script to handle what gets output.

Something like this (untested):

/path-to-web-root/download/.htaccess

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^.* /downloads/handle-downloads.php

/path-to-web-root/download/handle-downloads.php

$url = trim($_SERVER['REQUEST_URI'], '/');

if (preg_match('^#downloads/(?<real_filename>.*?)/(?<options>.*)/(?<fake_filename>.*)$#', $url, $matches)) {
    // Double check my regex, but basically pull the real filename from the url here
    $actual_file = "/path-to-webroot/f/{$matches['real_filename']}";
    $options = explode('/', $matches['options']);
    if (in_array('zip', $options)) {
        // Handle zip, etc.
    }
    
    $fake_filename = $matches['fake_filename'];

    if (file_exists($actual_file)) {
        header('Content-Description: File Transfer');
        header('Content-Type: application/octet-stream');
        header('Content-Disposition: attachment; filename="'.basename($fake_filename).'"');
        header('Expires: 0');
        header('Cache-Control: must-revalidate');
        header('Pragma: public');
        header('Content-Length: ' . filesize($actual_file));
        readfile($actual_file);
        exit;
    }
}

Then, instead of having the download link being website.com/f/xxx.png/zip/txt, you could instead do website.com/download/xxx.png/zip/txt/new-filename.png. This would allow you to set the filename to whatever you wanted since the browser will just take what's at the end of the url.

Edit: I've included the relevant code from readfile's manual page.