Undefined variable '$fwrite'

[horaciocastro7]

protected function _fwrite($buffer)
{
    $buffer_length = strlen($buffer);
    for ($written = 0; $written < $buffer_length; $written += $fwrite) {
        $fwrite = fwrite($this->socket, substr($buffer, $written));
        if ($fwrite === false) {
            return false;
        }
    }
    return $buffer_length;
}