public function read($len = null)
    {
        if (!$this->getInitialized()) {
            $this->_initialize();
            $this->setInitialized(true);
        }

        $buffer = $this->in->read($len);

        if ($buffer === -1) {
            return -1;
        }

        $lines = explode("\n", $buffer);
        $filtered = [];

        foreach ($lines as $line) {
            $line = $this->_prefix . $line;
            $filtered[] = $line;
        }

        $filtered_buffer = implode("\n", $filtered);

        return $filtered_buffer;
    }