JsonpHelper.php

<?php
class JsonpHelper {

	private static function is_valid_callback($subject)
	{
	    $identifier_syntax
	      = '/^[$_\p{L}][$_\p{L}\p{Mn}\p{Mc}\p{Nd}\p{Pc}\x{200C}\x{200D}]*+$/u';

	    $reserved_words = array('break', 'do', 'instanceof', 'typeof', 'case',
	      'else', 'new', 'var', 'catch', 'finally', 'return', 'void', 'continue', 
	      'for', 'switch', 'while', 'debugger', 'function', 'this', 'with', 
	      'default', 'if', 'throw', 'delete', 'in', 'try', 'class', 'enum', 
	      'extends', 'super', 'const', 'export', 'import', 'implements', 'let', 
	      'private', 'public', 'yield', 'interface', 'package', 'protected', 
	      'static', 'null', 'true', 'false');

	    return preg_match($identifier_syntax, $subject)
	        && ! in_array(mb_strtolower($subject, 'UTF-8'), $reserved_words);
	}

	private static function set_header($format) {
		if ($format === "json") {
			header("Content-type: application/json");
		} else if ($format === "xml") {
			header("Content-type: text/xml");
		} else {
			header('status: 400 Bad Request', true, 400);
		}
	}
	
	
	public static function output($string, $format) {
		if ($format === "json") {
			$xml = simplexml_load_string($string);
			$string = json_encode($xml);
		}
		# JSON if no callback
		if( ! isset($_GET['callback']) ) {
			JsonpHelper::set_header($format);
		  print($string);
		}
		//$string = str_replace("\n", " ", str_replace("'", '"', $string));
		# JSONP if valid callback
		else if(JsonpHelper::is_valid_callback($_GET['callback'])) {
			header("Content-type: application/javascript");
		  print("{$_GET['callback']}($string);");
		} else {
			# Otherwise, bad request
			JsonpHelper::set_header("badrequest");

		}
	}
}