staylor / WordPress

	if ( isset( $_REQUEST['post_id'] ) ) {

		$post_id = $_REQUEST['post_id'];

		if ( ! current_user_can( 'edit_post', $post_id ) ) {

			echo wp_json_encode( array(

				'success' => false,

				'data'    => array(

					'message'  => __( "You don't have permission to attach files to this post." ),

					'filename' => $_FILES['async-upload']['name'],

				)

			) );

			wp_die();

		}

	} else {

		$post_id = null;

	}

	// If the context is custom header or background, make sure the uploaded file is an image.

	if ( isset( $post_data['context'] ) && in_array( $post_data['context'], array( 'custom-header', 'custom-background' ) ) ) {

		$wp_filetype = wp_check_filetype_and_ext( $_FILES['async-upload']['tmp_name'], $_FILES['async-upload']['name'] );

		if ( ! wp_match_mime_types( 'image', $wp_filetype['type'] ) ) {

			echo wp_json_encode( array(

				'success' => false,

				'data'    => array(

					'message'  => __( 'The uploaded file is not a valid image. Please try again.' ),

					'filename' => $_FILES['async-upload']['name'],

				)

			) );

			wp_die();

		}

	}

	$attachment_id = media_handle_upload( 'async-upload', $post_id, $post_data );