protected override void Decode(IChannelHandlerContext context, IByteBuffer input, List <object> output)
        {
            try
            {
                switch (State)
                {
                case Socks4ServerDecoderState.Start:
                    var version = input.ReadByte();
                    if (version != (byte)SocksVersion.Socks4A)
                    {
                        throw new DecoderException("unsupported protocol version: " + version);
                    }

                    _type    = Socks4CommandType.ValueOf(input.ReadByte());
                    _dstPort = input.ReadUnsignedShort();
                    _dstAddr = new IPAddress(input.ReadInt()).ToString();
                    Checkpoint(Socks4ServerDecoderState.ReadUserid);
                    break;

                case Socks4ServerDecoderState.ReadUserid:
                    _userId = ReadString("userid", input);
                    Checkpoint(Socks4ServerDecoderState.ReadDomain);

                    break;

                case Socks4ServerDecoderState.ReadDomain:

                    // Check for Socks4a protocol marker 0.0.0.x
                    if (_dstAddr != "0.0.0.0" && _dstAddr.StartsWith("0.0.0."))
                    {
                        _dstAddr = ReadString("dstAddr", input);
                    }

                    output.Add(new DefaultSocks4CommandRequest(_type, _dstAddr, _dstPort, _userId));
                    Checkpoint(Socks4ServerDecoderState.Success);
                    break;

                case Socks4ServerDecoderState.Success:
                    var readableBytes = ActualReadableBytes;
                    if (readableBytes > 0)
                    {
                        output.Add(input.ReadRetainedSlice(readableBytes));
                    }

                    break;

                case Socks4ServerDecoderState.Failure:
                    input.SkipBytes(ActualReadableBytes);
                    break;
                }
            }
            catch (Exception e)
            {
                Fail(output, e);
            }
        }
        /**
         * Creates a new instance.
         *
         * @param type the type of the request
         * @param dstAddr the {@code DSTIP} field of the request
         * @param dstPort the {@code DSTPORT} field of the request
         */

        /**
         * Creates a new instance.
         *
         * @param type the type of the request
         * @param dstAddr the {@code DSTIP} field of the request
         * @param dstPort the {@code DSTPORT} field of the request
         * @param userId the {@code USERID} field of the request
         */
        public DefaultSocks4CommandRequest(Socks4CommandType type, string dstAddr, int dstPort, string userId = "")
        {
            if (dstPort <= 0 || dstPort >= 65536)
            {
                throw new ArgumentException("dstPort: " + dstPort + " (expected: 1~65535)");
            }

            UserId  = userId;
            Type    = type;
            DstAddr = Idn.GetAscii(dstAddr);
            DstPort = dstPort;
        }