HTML Exception Error

Just wanted to report a small issue I’ve had. Basically, the plugin was throwing an error as below:

[03-May-2025 08:16:36 UTC] PHP Fatal error: Uncaught ValueError: DOMDocument::loadHTML(): Argument #1 ($source) must not be empty in /var/www/html/wp-content/plugins/fix-alt-text/inc/Scan.php:532
Stack trace:
#0 /var/www/html/wp-content/plugins/fix-alt-text/inc/Scan.php(532): DOMDocument->loadHTML()
#1 /var/www/html/wp-content/plugins/fix-alt-text/inc/Scan.php(273): FixAltText\Scan::get_from_html()
#2 /var/www/html/wp-content/plugins/fix-alt-text/library/_helpers-library/inc/Scan_Process_Library.php(779): FixAltText\Scan::scan_post()
#3 /var/www/html/wp-content/plugins/fix-alt-text/library/_helpers-library/inc/Scan_Process_Library.php(462): FixAltText\HelpersLibrary\Scan_Process_Library->process()
#4 /var/www/html/wp-content/plugins/fix-alt-text/library/_helpers-library/inc/Scan_Process_Library.php(1536): FixAltText\HelpersLibrary\Scan_Process_Library->handle()
#5 /var/www/html/wp-includes/class-wp-hook.php(324): FixAltText\HelpersLibrary\Scan_Process_Library->maybe_handle()
#6 /var/www/html/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
#7 /var/www/html/wp-includes/plugin.php(517): WP_Hook->do_action()
#8 /var/www/html/wp-admin/admin-ajax.php(192): do_action()
#9 {main}
thrown in /var/www/html/wp-content/plugins/fix-alt-text/inc/Scan.php on line 532

This was causing the progress to get stuck. Turns out the issue was due to effectively empty html (so for example ” ” (single space) not being detected on some post types. I think this is because the site it’s installed on uses ACF extensively and doesn’t always have main content.

I fixed it by adding a catch to the block as below:

public static function get_from_html( string $html, array $args = [] ): array {

    // Must have something to scan
    if ( empty( $args ) ) {
        return [];
    }

    // Require HTML
    if ( empty( $html ) ) {
        return [];
    }

    // Empty array to hold all links to return
    $all_references = [];

    // Create DOM structure so we can reliably grab all img tags
    $dom = new DOMDocument();

    // Silence warnings
    libxml_use_internal_errors( true );

    // Ensure we are using UTF-8 Encoding
    $html = htmlspecialchars_decode( htmlentities( $html, ENT_COMPAT, 'utf-8', false ) );

    try {
        // Load the URL's content into the DOM
        $dom->loadHTML( $html, LIBXML_HTML_NODEFDTD | LIBXML_HTML_NOIMPLIED );

        $images = $dom->getElementsByTagName( 'img' );
        $image_index = 0;

        // Ensure we have default values
        $args['from_post_id'] = $args['from_post_id'] ?? 0;
        $args['from_post_type'] = $args['from_post_type'] ?? '';
        $args['from_where'] = $args['from_where'] ?? '';
        $args['from_where_key'] = $args['from_where_key'] ?? '';

        // Loop through each <img> tag in the dom and add it to the link array
        foreach ( $images as $img ) {

            // Inherit base details from args
            $ref = $args;

            // Fixing legacy code from breaking Gutenburg Editor
            $img->removeAttribute( 'id' );

            $ref['image_index'] = $image_index;
            $ref['image_url'] = $img->getAttribute( 'src' );
            $ref['image_alt_text'] = $img->getAttribute( 'alt' );

            $all_references[] = new Reference( $ref );

            ++ $image_index;

        }
    } catch ( \Throwable $e ) {
        error_log( print_r( $html, 1 ) );
        // Deliberately empty.
    }

    // Done silencing errors
    libxml_clear_errors();

    //Return the links
    return $all_references;
}

Anyway, I know its not really a support issue but wanted to report it so you could hopefully include in the next release of what is a great little plugin! I’m going to leave a 5 star review for you now!

Thanks for all the hard work guys!

Steve