wp_kses_bad_protocol

Sanitizes a string and removed disallowed URL protocols.

This function removes all non-allowed protocols from the beginning of the
string. It ignores whitespace and the case of the letters, and it does
understand HTML entities. It does its work recursively, so it won’t be
fooled by a string like `javascript:javascript:alert(57)`.

function wp_kses_bad_protocol( $string, $allowed_protocols ) {
	$string     = wp_kses_no_null( $string );
	$iterations = 0;

	do {
		$original_string = $string;
		$string          = wp_kses_bad_protocol_once( $string, $allowed_protocols );
	} while ( $original_string != $string && ++$iterations < 6 );

	if ( $original_string != $string ) {
		return '';
	}

	return $string;
}