WP_Import::handle_upload PHP Method

        function handle_upload()
        {
            $file = wp_import_handle_upload();
            if (isset($file['error'])) {
                echo '<p><strong>' . __('Sorry, there has been an error.', 'wordpress-importer') . '</strong><br />';
                echo esc_html($file['error']) . '</p>';
                return false;
            } else {
                if (!file_exists($file['file'])) {
                    echo '<p><strong>' . __('Sorry, there has been an error.', 'wordpress-importer') . '</strong><br />';
                    printf(__('The export file could not be found at <code>%s</code>. It is likely that this was caused by a permissions problem.', 'wordpress-importer'), esc_html($file['file']));
                    echo '</p>';
                    return false;
                }
            }
            $this->id = (int) $file['id'];
            $import_data = $this->parse($file['file']);
            if (is_wp_error($import_data)) {
                echo '<p><strong>' . __('Sorry, there has been an error.', 'wordpress-importer') . '</strong><br />';
                echo esc_html($import_data->get_error_message()) . '</p>';
                return false;
            }
            $this->version = $import_data['version'];
            if ($this->version > $this->max_wxr_version) {
                echo '<div class="error"><p><strong>';
                printf(__('This WXR file (version %s) may not be supported by this version of the importer. Please consider updating.', 'wordpress-importer'), esc_html($import_data['version']));
                echo '</strong></p></div>';
            }
            $this->get_authors_from_import($import_data);
            return true;
        }