private function padContent($content)
    {
        // The request is part of a set of incremental uploads, so pad to the
        // required content length. This is not necessary if all operations for the
        // job are being uploaded in a single request.
        $numBytes = mb_strlen($content, '8bit');
        $remainder = $numBytes % self::$REQUIRED_CONTENT_BYTES_INCREMENT;
        if ($remainder > 0) {
            $targetLength = $numBytes +
                (self::$REQUIRED_CONTENT_BYTES_INCREMENT - $remainder);
            $content = str_pad($content, $targetLength, ' ');
        }

        return $content;
    }