PHP Proxy to a specified domain, used for retrieving .atom feeds from shopify and avoid cross-domain issues.

proxy.php

<?php
  
  // Location where we are storing the cache
  $CACHE_DIRECTORY = dirname(dirname(__FILE__)) ."/statics";
  
  // Set the lifetime of cached pages
  $CACHE_LIFETIME = (24 * 60 * 60); // 24 Hours * 60 Minutes (per hour) * 60 Seconds (per minute)
  
  // Grab the URL to proxy, strip out the host as a security measure
  $url = null;
  $start = strpos($_SERVER['REQUEST_URI']);
  if ($start !== FALSE) {
    $url = substr($_SERVER['REQUEST_URI'], $start + 4);
  }
  else {
    header("HTTP/1.0 400 Bad Request");
    echo "Missing parameter URL";
    exit();
  }
  
  $cached_file = $CACHE_DIRECTORY . str_replace('.atom', '.xml', $url);
  $cache_invalid = FALSE;
  
  if (file_exists($cached_file) && $cache_mtime = filemtime($cached_file)) {
    $cache_invalid = time() - $cache_mtime > $CACHE_LIFETIME;
  }
  else {
    $cache_invalid = TRUE;
  }
  
  if ($cache_invalid) {
    // Request the page and update the cache prior to redirecting
    $remote_url = "http://shop.liftcaregiving.com". $url;
    $ch = curl_init($remote_url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
    $resp = curl_exec($ch);
    $status = curl_getinfo($ch, CURLINFO_HTTP_CODE);
    
    if ($status == 200) {
      // Verify the directory for the cache exists
      $parts = explode('/', $cached_file);
      array_shift($parts);
      array_pop($parts);
      $path = '/'. implode("/", $parts);
      
      if(!file_exists($path)) {
        // Create the directory
        if(!mkdir($path, 0775, TRUE)) {
          header("HTTP/1.0 500 Internal Server Error");
          echo "FAILED TO WRITE CACHE Directory: Could not make directory '$path'";
          exit();
        }
      }
      
      // We have a valid response cache it
      $fh = fopen($cached_file, 'w');
      if ($fh === FALSE) {
        header("HTTP/1.0 500 Internal Server Error");
        echo "FAILED TO WRITE CACHE: Could not open file '$cached_file'";
        exit();
      }
      else {
        fwrite($fh, $resp);
        fclose($fh);
      }
    }
    else {
      header("HTTP/1.0 ". $status);
      echo "Remote Error Encountered";
      exit();
    }
  }
  
  // Redirect to the cached page
  $cache_url = 'http://'. $_SERVER['HTTP_HOST']. '/statics'. str_replace('.atom', '.xml', $url);
  header("Location: ". $cache_url);

?>