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function s3_api_private_url($file, $bucket, $lifetime_in_seconds = 7200) {
  // key
  $aws_s3_key = variable_get('s3_api_key', "");
  // password
  $aws_s3_secret = variable_get('s3_api_skey', "");

//  $object = $file;

  if(strlen($file) == 0)
    return;
  //get filename
  $s3_filename = $file->filename;

  $string_to_sign = "GET\n\n\n{$lifetime_in_seconds}\n/{$bucket}/{$s3_filename}";
  $signature = urlencode(base64_encode((hash_hmac("sha1", utf8_encode($string_to_sign), $aws_s3_secret, TRUE))));

  $authentication_params = "AWSAccessKeyId=" . $aws_s3_key;
  $authentication_params.= "&Expires={$lifetime_in_seconds}";
  $authentication_params.= "&Signature={$signature}";

  // Create the return filepath. We add the bucket file path if
  // the a custom domain is not being used
  // Create the return filepath.
  // We add the bucket file path if http(s)://s3.amazonaws.com is being used as the s3 url
  $default_s3_url = variable_get('s3_api_default_server_url', "https://s3.amazonaws.com/");
  preg_match('@^(?:https?://)?([^/]+)@i', $default_s3_url, $domain);
  if ($domain[1] == 's3.amazonaws.com') {
    $s3_filename = $bucket . '/' . $s3_filename;
  }
  return $default_s3_url . $s3_filename . "?{$authentication_params}";
}