simple PHP proxy for Google Analytics hits

gaproxy.php

<?php
/******************************************************************************************************/
//send hits to GA- or GTM tag-server: use this file via transport_url 
//more info: https://developers.google.com/tag-manager/serverside/send-data
/******************************************************************************************************/

//define destination for tracking hits - either on www.google-analytics.com 
//or own tag server like https://trk.myserver.com/collect or 
//https://gtm-xxxxxx-xxxx.xx.x.appspot.com/collect  :
$endpoint = "https://www.google-analytics.com/collect";

/******************************************************************************************************/

function get_domain_from_host($h) {
  $hst = explode(".", $h);
  return $hst[count($hst)-2] . "." . $hst[count($hst)-1];
}

function send_hit($url) {
  $ch = cURL_init($url);
  cURL_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
  cURL_setopt($ch, CURLOPT_FRESH_CONNECT, true);
  cURL_setopt($ch, CURLOPT_TIMEOUT_MS, 100);
  
  //optional: send cookie values (if your own client on the tag 
  //server needs them - maybe increase timeout as well) 
  /*
  curl_setopt($ch, CURLOPT_HEADER, 1);
  $cookie_string = "" ;
  foreach($_COOKIE as $key => $value) {
    $cookie_string .= "$key=$value;";
  }
  curl_setopt($ch,CURLOPT_COOKIE, $cookie_string);
  */

  curl_exec($ch);
  //you might want to persist cookies here 
  //if your GTM tag server client sends cookies in the response
  cURL_close($ch);
  return true ;
}

/******************************************************************************************************/

$params = $_SERVER['QUERY_STRING'];
$call_from = strtolower(get_domain_from_host(parse_url($_SERVER['HTTP_REFERER'], PHP_URL_HOST)));
$this_domain = strtolower(get_domain_from_host($_SERVER['SERVER_NAME']));

//only accept requests from same domain - comment out if not needed or running on a different host
if ($call_from != $this_domain) $params = ""; 

if ($params != "") {
  $collect_url = $endpoint."?".$params;
  send_hit($collect_url);
  header('Content-Type: image/gif');
  echo(hex2bin('47494638396101000100900000ff000000000021f90405100000002c00000000010001000002020401003b'));
} else {
  header('HTTP/1.0 403 Forbidden');
  echo "No!";
}
?>

loaduascript.php

<?php
/******************************************************************************************************/
//loading of analytics.js - in a (too) simple way. do not use like this in a productive environment ;)
/******************************************************************************************************/
$scriptcode = file_get_contents('https://www.google-analytics.com/analytics.js');
header("Content-type: text/javascript");
header("cache-control: public, max-age=7200");
header("content-length: ".strlen($scriptcode));
echo $scriptcode;
?>