public function read($bytesRequested)
    {
      $len = strlen($this->_sourceString);
      if($this->_bytesRead == $len) {
          return FALSE;
      } else if($bytesRequested > $len - $this->_bytesRead) {
          $bytesRequested = $len - $this->_bytesRead;
      }

      $buffer = substr($this->_sourceString, $this->_bytesRead, $bytesRequested);
      $this->_bytesRead += $bytesRequested;

      return $buffer;
    }