How to get remote file size without downloading file using PHP?

Here is a function to get the size of a remote file. Note that HEAD requests don’t get the actual body of the request, they just retrieve the headers. So making a HEAD request to a resource that is 100MB will take the same amount of time as a HEAD request to a resource that is 1KB.

function curl_get_file_size($url) {
  // Assume failure.
  $result = -1;

  $curl = curl_init($url);

  // Issue a HEAD request and follow any redirects.
  curl_setopt($curl, CURLOPT_NOBODY, true);
  curl_setopt($curl, CURLOPT_HEADER, true);
  curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
  curl_setopt($curl, CURLOPT_FOLLOWLOCATION, true);
  curl_setopt($curl, CURLOPT_USERAGENT, get_user_agent_string());

  $data = curl_exec($curl);
  curl_close($curl);

  if ($data) {
    $content_length = "unknown";
    $status = "unknown";

    if (preg_match("/^HTTP\/1\.[01] (\d\d\d)/", $data, $matches)) {
      $status = (int)$matches[1];
    }

    if (preg_match("/Content-Length: (\d+)/", $data, $matches)) {
      $content_length = (int)$matches[1];
    }

    // http://en.wikipedia.org/wiki/List_of_HTTP_status_codes
    if ($status === 200 || ($status > 300 && $status <= 308)) {
      $result = $content_length;
    }
  }

  return $result;
}

Usage:

$file_size = curl_get_file_size("https://www.example.com/test.txt");