How to get files from loop for zip

Question

I am working on a button which will download the images as a zip on specific posts. It works if I leave the files array in functions.php with a few hard-coded img links. But when I move the array to the custom post where the images I need to zip are already being looped and displayed, I can still download via button, but opening the downloaded zip I get error "Unable to expand archive. It is in an unsupported format"

I have tried moving different parts of the code back and forth, like all of the code in the custom post, and all of the code in functions.php, to no avail. I must be not getting the img file urls properly but I'm not sure how.

This is all of the mentioned code, only in functions.php (except the download button), with the hard-coded image links, which works as intended:

$image1 = 'https://com.tripletigers/wp-content/uploads/homesweet_nowords-1920x1920.jpg';
$image2 = 'https://com.tripletigers/wp-content/uploads/V3-1920x2880.jpg';
$image3 = 'https://com.tripletigers/wp-content/uploads/SM_Single-Cover_Damn-Strait-1920x1920.jpg';

$files = array($image1, $image2, $image3);


$tmpFile = tempnam('/tmp', '');

$zip = new ZipArchive;
$zip->open($tmpFile, ZipArchive::CREATE);
foreach ($files as $file) {
    // download file
    $fileContent = file_get_contents($file);

    $zip->addFromString(basename($file), $fileContent);
}
$zip->close();

// Download Created Zip file from button via form submit
if(isset($_POST['download'])){

    header('Content-Type: application/zip');
    header('Content-disposition: attachment; filename=artist-photos.zip');
    header('Content-Length: ' . filesize($tmpFile));
    readfile($tmpFile);

    unlink($tmpFile);
}

This is what leads to the error, trying to get the images from the otherwise working loop in the custom post:

foreach( $list_posts as $list_item ) :
    if ( $list_item->post_type == 'crb_photo' ):
        if ( has_post_thumbnail( $list_item->ID ) ) {
            $img_url = get_the_post_thumbnail_url( $list_item->ID, 'crb_full_width' );              
             // this var i created for the zip, to add each image url to the array
            $getImage =  esc_url($img_url);
            // testing: prints image url. Why is that url not getting to the zip?
            echo '<h6>' . $img_url . '</h6>';
            
            // create array for zip - tried both = and .=   
            $files[] .= $getImage;
            // same result as above
            // $files[] = $getImage;
        } ?>
                            
            <li>
                <div>
                   <?php if ( ! empty( $img_url ) ) : ?>
                        <a href="<?php echo esc_url( $img_url ); ?>"></a>
                   <?php endif; ?>
                </div>
            </li>
    <?php endif; ?>

The functions.php used with above (same as first snippet but without hard-coded array)

$tmpFile = tempnam('/tmp', '');

$zip = new ZipArchive;
$zip->open($tmpFile, ZipArchive::CREATE);
foreach ($files as $file) {
    // download file
    $fileContent = file_get_contents($file);

    $zip->addFromString(basename($file), $fileContent);
}
$zip->close();

// Download Created Zip file
if(isset($_POST['download'])){

    header('Content-Type: application/zip');
    header('Content-disposition: attachment; filename=artist-photos.zip');
    header('Content-Length: ' . filesize($tmpFile));
    readfile($tmpFile);

    unlink($tmpFile);
}

When trying to open zip via command line:

What am i missing in order to get those images into the zip properly?

Answer 1

As the files are within the same WP installation (not a remote), you don't need to download the file using get_file_contents(), try to add the file using its absolute path of the attachment.

if(isset($_POST['download'])){
    $tmpFile = tempnam('/tmp', '');
    $zip = new ZipArchive();
    $zip->open($tmpFile, ZipArchive::CREATE);

    
    foreach( $list_posts as $list_item ) :
      if ( $list_item->post_type == 'crb_photo' ):
        if ( has_post_thumbnail( $list_item->ID ) ) {
          $zip->addFile(get_attached_file(get_post_thumbnail_id($list_item->ID )));
        }
      }
    }

    $zip->close();

    header('Content-Type: application/zip');
    header('Content-disposition: attachment; filename=artist-photos.zip');
    header('Content-Length: ' . filesize($tmpFile));
    readfile($tmpFile);

    unlink($tmpFile);
}

Note typed the code in this editor, may contain syntax error.