WordPress/wp-admin/includes/class-automatic-upgrader-skin.php

<?php
/**
 * Upgrader API: Automatic_Upgrader_Skin class
 *
 * @package WordPress
 * @subpackage Upgrader
 * @since 4.6.0
 */

/**
 * Upgrader Skin for Automatic WordPress Upgrades
 *
 * This skin is designed to be used when no output is intended, all output
 * is captured and stored for the caller to process and log/email/discard.
 *
 * @since 3.7.0
 */
class Automatic_Upgrader_Skin extends WP_Upgrader_Skin {
	protected $messages = array();

	/**
	 *
	 * @param bool   $error
	 * @param string $context
	 * @param bool   $allow_relaxed_file_ownership
	 * @return bool
	 */
	public function request_filesystem_credentials( $error = false, $context = '', $allow_relaxed_file_ownership = false ) {
		if ( $context ) {
			$this->options['context'] = $context;
		}
		// TODO: fix up request_filesystem_credentials(), or split it, to allow us to request a no-output version
		// This will output a credentials form in event of failure, We don't want that, so just hide with a buffer
		ob_start();
		$result = parent::request_filesystem_credentials( $error, $context, $allow_relaxed_file_ownership );
		ob_end_clean();
		return $result;
	}

	/**
	 * @access public
	 *
	 * @return array
	 */
	public function get_upgrade_messages() {
		return $this->messages;
	}

	/**
	 * @param string|array|WP_Error $data
	 */
	public function feedback( $data ) {
		if ( is_wp_error( $data ) ) {
			$string = $data->get_error_message();
		} elseif ( is_array( $data ) ) {
			return;
		} else {
			$string = $data;
		}
		if ( ! empty( $this->upgrader->strings[ $string ] ) )
			$string = $this->upgrader->strings[ $string ];

		if ( strpos( $string, '%' ) !== false ) {
			$args = func_get_args();
			$args = array_splice( $args, 1 );
			if ( ! empty( $args ) )
				$string = vsprintf( $string, $args );
		}

		$string = trim( $string );

		// Only allow basic HTML in the messages, as it'll be used in emails/logs rather than direct browser output.
		$string = wp_kses( $string, array(
			'a' => array(
				'href' => true
			),
			'br' => true,
			'em' => true,
			'strong' => true,
		) );

		if ( empty( $string ) )
			return;

		$this->messages[] = $string;
	}

	/**
	 * @access public
	 */
	public function header() {
		ob_start();
	}

	/**
	 * @access public
	 */
	public function footer() {
		$output = ob_get_clean();
		if ( ! empty( $output ) )
			$this->feedback( $output );
	}
}