FreeSR/FreeSR.Gateserver/Network/Handlers/Decoder/StarRailHeaderDecoder.cs

namespace FreeSR.Gateserver.Network.Handlers.Decoder
{
    using DotNetty.Buffers;
    using DotNetty.Codecs;
    using DotNetty.Transport.Channels;

    internal class StarRailHeaderDecoder : ByteToMessageDecoder
    {
        private IByteBuffer _current;

        public StarRailHeaderDecoder()
        {
            _current = Unpooled.Buffer();
        }

        protected override void Decode(IChannelHandlerContext context, IByteBuffer input, List<object> output)
        {
            var allocated = Unpooled.Buffer();
            allocated.WriteBytes(_current);
            allocated.WriteBytes(input);
            _current = allocated;

            byte[] lands = new byte[_current.ReadableBytes];
            _current.ReadBytes(lands);
            _current.ResetReaderIndex();

            IByteBuffer packet;
            while ((packet = Process()) != null)
                output.Add(packet);
        }

        private IByteBuffer Process()
        {
            if (_current.ReadableBytes < 12)
                return null;

            _current.ReadInt(); // headMagic
            _current.ReadShort(); // CmdID
            int headerLength = _current.ReadShort();
            int payloadLength = _current.ReadInt();

            int totalLength = 12 + headerLength + payloadLength + 4;
            _current.ResetReaderIndex();
            if (_current.ReadableBytes < totalLength)
                return null;

            IByteBuffer result = _current.ReadBytes(totalLength);
            _current = _current.ReadBytes(_current.ReadableBytes);

            return result;
        }
    }
}