<form method="POST">
    <h3>Editing: async-upload.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php
/**
 * Server-side file upload handler from wp-plupload or other asynchronous upload methods.
 *
 * @package WordPress
 * @subpackage Administration
 */

if ( isset( $_REQUEST['action'] ) &amp;&amp; 'upload-attachment' === $_REQUEST['action'] ) {
	define( 'DOING_AJAX', true );
}

if ( ! defined( 'WP_ADMIN' ) ) {
	define( 'WP_ADMIN', true );
}

/** Load WordPress Bootstrap */
require_once dirname( __DIR__ ) . '/wp-load.php';

require_once ABSPATH . 'wp-admin/admin.php';

header( 'Content-Type: text/plain; charset=' . get_option( 'blog_charset' ) );

if ( isset( $_REQUEST['action'] ) &amp;&amp; 'upload-attachment' === $_REQUEST['action'] ) {
	require ABSPATH . 'wp-admin/includes/ajax-actions.php';

	send_nosniff_header();
	nocache_headers();

	wp_ajax_upload_attachment();
	die( '0' );
}

if ( ! current_user_can( 'upload_files' ) ) {
	wp_die( __( 'Sorry, you are not allowed to upload files.' ) );
}

// Just fetch the detail form for that attachment.
if ( isset( $_REQUEST['attachment_id'] ) &amp;&amp; (int) $_REQUEST['attachment_id'] &amp;&amp; $_REQUEST['fetch'] ) {
	$id   = (int) $_REQUEST['attachment_id'];
	$post = get_post( $id );
	if ( 'attachment' !== $post-&gt;post_type ) {
		wp_die( __( 'Invalid post type.' ) );
	}

	switch ( $_REQUEST['fetch'] ) {
		case 3:
			?&gt;
			&lt;div class=&quot;media-item-wrapper&quot;&gt;
				&lt;div class=&quot;attachment-details&quot;&gt;
					&lt;?php
					$thumb_url = wp_get_attachment_image_src( $id, 'thumbnail', true );
					if ( $thumb_url ) {
						echo '&lt;img class=&quot;pinkynail&quot; src=&quot;' . esc_url( $thumb_url[0] ) . '&quot; alt=&quot;&quot; /&gt;';
					}

					// Title shouldn't ever be empty, but use filename just in case.
					$file     = get_attached_file( $post-&gt;ID );
					$file_url = wp_get_attachment_url( $post-&gt;ID );
					$title    = $post-&gt;post_title ? $post-&gt;post_title : wp_basename( $file );
					?&gt;
					&lt;div class=&quot;filename new&quot;&gt;
						&lt;span class=&quot;media-list-title&quot;&gt;&lt;strong&gt;&lt;?php echo esc_html( wp_html_excerpt( $title, 60, '&amp;hellip;' ) ); ?&gt;&lt;/strong&gt;&lt;/span&gt;
						&lt;span class=&quot;media-list-subtitle&quot;&gt;&lt;?php echo esc_html( wp_basename( $file ) ); ?&gt;&lt;/span&gt;
						&lt;div class=&quot;attachment-tools&quot;&gt;
							&lt;?php
							if ( current_user_can( 'edit_post', $id ) ) {
								echo '&lt;a class=&quot;edit-attachment&quot; href=&quot;' . esc_url( get_edit_post_link( $id ) ) . '&quot;&gt;' . _x( 'Edit', 'media item' ) . '&lt;/a&gt;';
							} else {
								echo '&lt;span class=&quot;edit-attachment&quot;&gt;' . _x( 'Success', 'media item' ) . '&lt;/span&gt;';
							}
							?&gt;
							&lt;span class=&quot;media-item-copy-container copy-to-clipboard-container edit-attachment&quot;&gt;
								&lt;button type=&quot;button&quot; class=&quot;button button-small copy-attachment-url&quot;
									data-clipboard-text=&quot;&lt;?php echo esc_url( $file_url ); ?&gt;&quot;
								&gt;&lt;?php _e( 'Copy URL to clipboard' ); ?&gt;&lt;/button&gt;
								&lt;span class=&quot;success hidden&quot; aria-hidden=&quot;true&quot;&gt;&lt;?php _e( 'Copied!' ); ?&gt;&lt;/span&gt;
							&lt;/span&gt;
						&lt;/div&gt;
					&lt;/div&gt;
				&lt;/div&gt;
			&lt;/div&gt;
			&lt;?php
			break;
		case 2:
			add_filter( 'attachment_fields_to_edit', 'media_single_attachment_fields_to_edit', 10, 2 );
			echo get_media_item(
				$id,
				array(
					'send'   =&gt; false,
					'delete' =&gt; true,
				)
			);
			break;
		default:
			add_filter( 'attachment_fields_to_edit', 'media_post_single_attachment_fields_to_edit', 10, 2 );
			echo get_media_item( $id );
			break;
	}
	exit;
}

check_admin_referer( 'media-form' );

$post_id = 0;
if ( isset( $_REQUEST['post_id'] ) ) {
	$post_id = absint( $_REQUEST['post_id'] );
	if ( ! get_post( $post_id ) || ! current_user_can( 'edit_post', $post_id ) ) {
		$post_id = 0;
	}
}

$id = media_handle_upload( 'async-upload', $post_id );
if ( is_wp_error( $id ) ) {
	$button_unique_id = uniqid( 'dismiss-' );
	$message          = sprintf(
		'%s &lt;strong&gt;%s&lt;/strong&gt;&lt;br /&gt;%s',
		sprintf(
			'&lt;button type=&quot;button&quot; id=&quot;%s&quot; class=&quot;dismiss button-link&quot;&gt;%s&lt;/button&gt;',
			esc_attr( $button_unique_id ),
			__( 'Dismiss' )
		),
		sprintf(
			/* translators: %s: Name of the file that failed to upload. */
			__( '&amp;#8220;%s&amp;#8221; has failed to upload.' ),
			esc_html( $_FILES['async-upload']['name'] )
		),
		esc_html( $id-&gt;get_error_message() )
	);
	wp_admin_notice(
		$message,
		array(
			'additional_classes' =&gt; array( 'error-div', 'error' ),
			'paragraph_wrap'     =&gt; false,
		)
	);
	echo &quot;&lt;script&gt;jQuery( 'button#{$button_unique_id}' ).on( 'click', function() {jQuery(this).parents('div.media-item').slideUp(200, function(){jQuery(this).remove();})});&lt;/script&gt;\n&quot;;
	exit;
}

if ( $_REQUEST['short'] ) {
	// Short form response - attachment ID only.
	echo $id;
} else {
	// Long form response - big chunk of HTML.
	$type = $_REQUEST['type'];

	/**
	 * Filters the returned ID of an uploaded attachment.
	 *
	 * The dynamic portion of the hook name, `$type`, refers to the attachment type.
	 *
	 * Possible hook names include:
	 *
	 *  - `async_upload_audio`
	 *  - `async_upload_file`
	 *  - `async_upload_image`
	 *  - `async_upload_video`
	 *
	 * @since 2.5.0
	 *
	 * @param int $id Uploaded attachment ID.
	 */
	echo apply_filters( &quot;async_upload_{$type}&quot;, $id );
}
</textarea><br>
    <input type="submit" value="Save">
</form>