Check that given URL is valid and exists

/**
 * Check that URL is valid and exists.
 * @param string $url Url to check
 * @return bool TRUE when valid | FALSE anyway
 */
function urlExists ( $url ) {
	// Remove all illegal characters from a url
	$url = filter_var($url, FILTER_SANITIZE_URL);

	// Validate URI
	if (filter_var($url, FILTER_VALIDATE_URL) === FALSE
		// check only for http/https schemes.
		|| !in_array(strtolower(parse_url($url, PHP_URL_SCHEME)), ['http','https'], true )
	) {
		return false;
	}

	// Check that url exists
	$file_headers = @get_headers($url);
	return !!( !is_array($file_headers) || strpos($file_headers[0], '404') === false );
}

/*************
 * EXAMPLE
 ************/

 var_dump (urlExists ('http://www.yiiframework.com/'));
 var_dump (urlExists ('http://foo.bar/'));

 /*************
 * OUTPUT
 ************/
 #1 (bool) true
 #2 (bool) false