Local caching helper for GTM containers

getgtm.php

<?php
/******************************************************************
Helper for locally cached GTM container: update local GTM cache and
enable optional live container loading for debugging 
******************************************************************/

//path and filename for local GTM container cache, relative
//to this PHP file or as absolute server path     
$gtm_save_path = "../js/gtm.js"; 

//ID for GTM container to be cached in local file specified above
$gtm_id = "GTM-XYZABC";

//NOTE: better use a .htaccess secured file for this or somethin similar. 
//As an example for minimum security you _could_ use a constant key as 
//GET parameter - which is definitely not the best way to secure this 
//helper that downloads an external file and places it on your server!
if ($_GET['secretkey'] !== 'mysecretpassword') die('go away!');

//load container JS and store locally and enable live container 
//loading for debugging. To use live container, just type 
//document.cookie='dbglive=1'
//in your browser`s console  
try {
  $fp = fopen($gtm_save_path, 'wb');
  $ld = "\nif (document.cookie.indexOf('dbglive=1') >= 0) {".
        "\nvar s=document.createElement('script');s.type='text/javascript';".
        "s.src='https://www.googletagmanager.com/gtm.js?id=$gtm_id';".
        "document.getElementsByTagName('head')[0].appendChild(s);\n} else {\n";

  $ch = curl_init("https://www.googletagmanager.com/gtm.js?id=$gtm_id");
  $fp = fopen($gtm_save_path, 'wb');
  fwrite($fp,"//**Cached GTM** last update:".date("Y-m-d H:i:s").$ld); 
  curl_setopt($ch, CURLOPT_FILE, $fp);
  curl_setopt($ch, CURLOPT_HEADER, 0);
  curl_exec($ch);
  curl_close($ch);
  fwrite($fp,"\n}"); 
  echo "cache updated";
} catch (Exception $ex) {
	echo $ex->getMessage();
} finally {
  fclose($fp);
}  
?>