Jetpack::upload_handler PHP Method

    function upload_handler()
    {
        if ('POST' !== strtoupper($_SERVER['REQUEST_METHOD'])) {
            return new Jetpack_Error(405, get_status_header_desc(405), 405);
        }
        $user = wp_authenticate('', '');
        if (!$user || is_wp_error($user)) {
            return new Jetpack_Error(403, get_status_header_desc(403), 403);
        }
        wp_set_current_user($user->ID);
        if (!current_user_can('upload_files')) {
            return new Jetpack_Error('cannot_upload_files', 'User does not have permission to upload files', 403);
        }
        if (empty($_FILES)) {
            return new Jetpack_Error('no_files_uploaded', 'No files were uploaded: nothing to process', 400);
        }
        foreach (array_keys($_FILES) as $files_key) {
            if (!isset($_POST["_jetpack_file_hmac_{$files_key}"])) {
                return new Jetpack_Error('missing_hmac', 'An HMAC for one or more files is missing', 400);
            }
        }
        $media_keys = array_keys($_FILES['media']);
        $token = Jetpack_Data::get_access_token(get_current_user_id());
        if (!$token || is_wp_error($token)) {
            return new Jetpack_Error('unknown_token', 'Unknown Jetpack token', 403);
        }
        $uploaded_files = array();
        $global_post = isset($GLOBALS['post']) ? $GLOBALS['post'] : null;
        unset($GLOBALS['post']);
        foreach ($_FILES['media']['name'] as $index => $name) {
            $file = array();
            foreach ($media_keys as $media_key) {
                $file[$media_key] = $_FILES['media'][$media_key][$index];
            }
            list($hmac_provided, $salt) = explode(':', $_POST['_jetpack_file_hmac_media'][$index]);
            $hmac_file = hash_hmac_file('sha1', $file['tmp_name'], $salt . $token->secret);
            if ($hmac_provided !== $hmac_file) {
                $uploaded_files[$index] = (object) array('error' => 'invalid_hmac', 'error_description' => 'The corresponding HMAC for this file does not match');
                continue;
            }
            $_FILES['.jetpack.upload.'] = $file;
            $post_id = isset($_POST['post_id'][$index]) ? absint($_POST['post_id'][$index]) : 0;
            if (!current_user_can('edit_post', $post_id)) {
                $post_id = 0;
            }
            $attachment_id = media_handle_upload('.jetpack.upload.', $post_id, array(), array('action' => 'jetpack_upload_file'));
            if (!$attachment_id) {
                $uploaded_files[$index] = (object) array('error' => 'unknown', 'error_description' => 'An unknown problem occurred processing the upload on the Jetpack site');
            } elseif (is_wp_error($attachment_id)) {
                $uploaded_files[$index] = (object) array('error' => 'attachment_' . $attachment_id->get_error_code(), 'error_description' => $attachment_id->get_error_message());
            } else {
                $attachment = get_post($attachment_id);
                $uploaded_files[$index] = (object) array('id' => (string) $attachment_id, 'file' => $attachment->post_title, 'url' => wp_get_attachment_url($attachment_id), 'type' => $attachment->post_mime_type, 'meta' => wp_get_attachment_metadata($attachment_id));
                // Zip files uploads are not supported unless they are done for installation purposed
                // lets delete them in case something goes wrong in this whole process
                if ('application/zip' === $attachment->post_mime_type) {
                    // Schedule a cleanup for 2 hours from now in case of failed install.
                    wp_schedule_single_event(time() + 2 * HOUR_IN_SECONDS, 'upgrader_scheduled_cleanup', array($attachment_id));
                }
            }
        }
        if (!is_null($global_post)) {
            $GLOBALS['post'] = $global_post;
        }
        return $uploaded_files;
    }