WordPress/wp-admin/async-upload.php

<?php
/**
 * Accepts file uploads from swfupload or other asynchronous upload methods.
 *
 * @package WordPress
 * @subpackage Administration
 */

define('WP_ADMIN', true);

if ( defined('ABSPATH') )
	require_once(ABSPATH . 'wp-load.php');
else
	require_once('../wp-load.php');

if ( ! ( isset( $_REQUEST['action'] ) && 'upload-attachment' == $_REQUEST['action'] ) ) {
	// Flash often fails to send cookies with the POST or upload, so we need to pass it in GET or POST instead
	if ( is_ssl() && empty($_COOKIE[SECURE_AUTH_COOKIE]) && !empty($_REQUEST['auth_cookie']) )
		$_COOKIE[SECURE_AUTH_COOKIE] = $_REQUEST['auth_cookie'];
	elseif ( empty($_COOKIE[AUTH_COOKIE]) && !empty($_REQUEST['auth_cookie']) )
		$_COOKIE[AUTH_COOKIE] = $_REQUEST['auth_cookie'];
	if ( empty($_COOKIE[LOGGED_IN_COOKIE]) && !empty($_REQUEST['logged_in_cookie']) )
		$_COOKIE[LOGGED_IN_COOKIE] = $_REQUEST['logged_in_cookie'];
	unset($current_user);
}

require_once('./admin.php');

if ( !current_user_can('upload_files') )
	wp_die(__('You do not have permission to upload files.'));

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

if ( isset( $_REQUEST['action'] ) && 'upload-attachment' === $_REQUEST['action'] ) {
	define( 'DOING_AJAX', true );
	include ABSPATH . 'wp-admin/includes/ajax-actions.php';

	send_nosniff_header();
	nocache_headers();

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

// just fetch the detail form for that attachment
if ( isset($_REQUEST['attachment_id']) && ($id = intval($_REQUEST['attachment_id'])) && $_REQUEST['fetch'] ) {
	$post = get_post( $id );
	if ( 'attachment' != $post->post_type )
		wp_die( __( 'Unknown post type.' ) );
	$post_type_object = get_post_type_object( 'attachment' );
	if ( ! current_user_can( $post_type_object->cap->edit_post, $id ) )
		wp_die( __( 'You are not allowed to edit this item.' ) );

	switch ( $_REQUEST['fetch'] ) {
		case 3 :
			if ( $thumb_url = wp_get_attachment_image_src( $id, 'thumbnail', true ) )
				echo '<img class="pinkynail" src="' . esc_url( $thumb_url[0] ) . '" alt="" />';
			echo '<a class="edit-attachment" href="' . esc_url( get_edit_post_link( $id ) ) . '" target="_blank">' . _x( 'Edit', 'media item' ) . '</a>';
			$title = $post->post_title ? $post->post_title : wp_basename( $post->guid ); // title shouldn't ever be empty, but use filename just in cas.e
			echo '<div class="filename new"><span class="title">' . esc_html( wp_html_excerpt( $title, 60, '&hellip;' ) ) . '</span></div>';
			break;
		case 2 :
			add_filter('attachment_fields_to_edit', 'media_single_attachment_fields_to_edit', 10, 2);
			echo get_media_item($id, array( 'send' => false, 'delete' => 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) ) {
	echo '<div class="error-div">
	<a class="dismiss" href="#" onclick="jQuery(this).parents(\'div.media-item\').slideUp(200, function(){jQuery(this).remove();});">' . __('Dismiss') . '</a>
	<strong>' . sprintf(__('&#8220;%s&#8221; has failed to upload due to an error'), esc_html($_FILES['async-upload']['name']) ) . '</strong><br />' .
	esc_html($id->get_error_message()) . '</div>';
	exit;
}

if ( $_REQUEST['short'] ) {
	// short form response - attachment ID only
	echo $id;
} else {
	// long form response - big chunk o html
	$type = $_REQUEST['type'];
	echo apply_filters("async_upload_{$type}", $id);
}