+  private static function get_info($url)
+  {
+    $ch = curl_init($url);
+    curl_setopt_array($ch, array(
+      CURLOPT_HEADER => TRUE,
+      CURLOPT_NOBODY => TRUE,
+      CURLOPT_FOLLOWLOCATION => TRUE,  // follow http redirects to get the real URL
+      CURLOPT_RETURNTRANSFER => TRUE,
+      CURLOPT_SSL_VERIFYHOST => FALSE,
+      CURLOPT_SSL_VERIFYPEER => FALSE,
+      CURLOPT_USERAGENT => Tweeper::$USER_AGENT,
+    ));
+    curl_exec($ch);
+    $url_info = curl_getinfo($ch);
+    curl_close($ch);
+
+    return $url_info;
+  }
+
+  public static function generate_enclosure($url)
+  {
+    $supported_content_types = array(
+      "application/ogg",
+      "audio/aac",
+      "audio/mp4",
+      "audio/mpeg",
+      "audio/ogg",
+      "audio/vorbis",
+      "audio/wav",
+      "audio/webm",
+      "audio/x-midi",
+      "image/gif",
+      "image/jpeg",
+      "video/avi",
+      "video/mp4",
+      "video/mpeg",
+      "video/ogg",
+    );
+
+    $url_info = Tweeper::get_info($url);
+
+    $supported = in_array($url_info['content_type'], $supported_content_types);
+    if (!$supported) {
+      error_log("Unsupported enclosure content type \"" . $url_info['content_type'] . "\" for URL: " . $url_info['url']);
+      return '';
+    }
+
+    $dom = new DomDocument();
+    $enc = $dom->createElement('enclosure');
+    $enc->setAttribute('url', $url_info['url']);
+    $enc->setAttribute('length', $url_info['download_content_length']);
+    $enc->setAttribute('type', $url_info['content_type']);
+
+    $dom->appendChild($enc);
+
+    return $dom->saveXML($enc);
+  }
+
+  /* Mimic the message from libxml.c::php_libxml_ctx_error_level() */
+  private function log_xml_error($error) {
+    $output = "";
+
+    switch ($error->level) {
+    case LIBXML_ERR_WARNING:
+      $output .= "Warning $error->code: ";
+      break;
+    case LIBXML_ERR_ERROR:
+      $output .= "Error $error->code: ";
+      break;
+    case LIBXML_ERR_FATAL:
+      $output .= "Fatal Error $error->code: ";
+      break;
+    }
+
+    $output .= trim($error->message);
+
+    if ($error->file) {
+      $output .= " in $error->file";
+    } else {
+      $output .= " in Entity,";
+    }
+
+    $output .=" line $error->line";
+
+    error_log($output);
+  }
+