Wordpress page template for JSON sitemaps

page-sitemap.php

<?php
/*
Template Name: sitemap.json
*/

$args = array();
$args['post_per_page'] = -1;
$args['nopaging'] = true;

query_posts( $args );

// The Loop
$data = array();

$fst = true;

while ( have_posts() ) : the_post();
	$o = array();
	$o['date'] = get_the_time("Y/m/d");
	$o['title'] = get_the_title();
	$o['url'] = get_permalink(get_the_id());
	$tags = array();
	if ($posttags) foreach($posttags as $tag) {
		$tags[] = $tag->name; 
  	}
	$o['tags'] = join(',',$tags);
	$data[] = $o;
endwhile;

wp_reset_query();

header('content-type: application/json; charset=utf-8');

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);
}

$json = json_encode($data);

# JSON if no callback
if( ! isset($_GET['callback']))
    exit($json);

# JSONP if valid callback
if(is_valid_callback($_GET['callback']))
    exit("{$_GET['callback']}($json)");

# Otherwise, bad request
header('status: 400 Bad Request', true, 400);

?>