esc_url( string $url, string[] $protocols = null, string $_context = ‘display’ )

检查并清除URL。
Checks and cleans a URL.

目录锚点：#说明#参数#返回#源码#笔记

说明（Description）

从URL中删除了一些字符。如果URL用于显示（默认行为），则还将替换与号。“clean_url”筛选器将应用于返回的已清除url。

参数（Parameters）

返回（Return）

（string）应用“clean_url”筛选器后清除的$url。

源码（Source）

/**
 * Checks and cleans a URL.
 *
 * A number of characters are removed from the URL. If the URL is for displaying
 * (the default behaviour) ampersands are also replaced. The 'clean_url' filter
 * is applied to the returned cleaned URL.
 *
 * @since 2.8.0
 *
 * @param string $url       The URL to be cleaned.
 * @param array  $protocols Optional. An array of acceptable protocols.
 *		                    Defaults to return value of wp_allowed_protocols()
 * @param string $_context  Private. Use esc_url_raw() for database usage.
 * @return string The cleaned $url after the 'clean_url' filter is applied.
 */
function esc_url( $url, $protocols = null, $_context = 'display' ) {
	$original_url = $url;

	if ( '' == $url )
		return $url;
	$url = preg_replace('|[^a-z0-9-~+_.?#=!&;,/:%@$|*'()x80-xff]|i', '', $url);
	if ( 0 !== stripos( $url, 'mailto:' ) ) {
		$strip = array('%0d', '%0a', '%0D', '%0A');
		$url = _deep_replace($strip, $url);
	}
	$url = str_replace(';//', '://', $url);
	/* If the URL doesn't appear to contain a scheme, we
	 * presume it needs http:// appended (unless a relative
	 * link starting with /, # or ? or a php file).
	 */
	if ( strpos($url, ':') === false && ! in_array( $url[0], array( '/', '#', '?' ) ) &&
		! preg_match('/^[a-z0-9-]+?.php/i', $url) )
		$url = 'http://' . $url;

	// Replace ampersands and single quotes only when displaying.
	if ( 'display' == $_context ) {
		$url = wp_kses_normalize_entities( $url );
		$url = str_replace( '&', '&', $url );
		$url = str_replace( "'", ''', $url );
	}

	if ( '/' === $url[0] ) {
		$good_protocol_url = $url;
	} else {
		if ( ! is_array( $protocols ) )
			$protocols = wp_allowed_protocols();
		$good_protocol_url = wp_kses_bad_protocol( $url, $protocols );
		if ( strtolower( $good_protocol_url ) != strtolower( $url ) )
			return '';
	}

	/**
	 * Filter a string cleaned and escaped for output as a URL.
	 *
	 * @since 2.3.0
	 *
	 * @param string $good_protocol_url The cleaned URL to be returned.
	 * @param string $original_url      The URL prior to cleaning.
	 * @param string $_context          If 'display', replace ampersands and single quotes only.
	 */
	return apply_filters( 'clean_url', $good_protocol_url, $original_url, $_context );
}

笔记（Notes）

添加指向主页的链接
如果URI协议不是允许的协议之一，则esc_url（）的结果是空字符串。WordPress允许的默认协议列表可以用以下代码扩展：