Socks4ServerDecoder Class — netty Architecture

Source Code

codec-socks/src/main/java/io/netty/handler/codec/socksx/v4/Socks4ServerDecoder.java lines 38–136

public class Socks4ServerDecoder extends ReplayingDecoder<State> {

    private static final int MAX_FIELD_LENGTH = 255;

    @UnstableApi
    public enum State {
        START,
        READ_USERID,
        READ_DOMAIN,
        SUCCESS,
        FAILURE
    }

    private Socks4CommandType type;
    private String dstAddr;
    private int dstPort;
    private String userId;

    public Socks4ServerDecoder() {
        super(State.START);
        setSingleDecode(true);
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        try {
            switch (state()) {
            case START: {
                final int version = in.readUnsignedByte();
                if (version != SocksVersion.SOCKS4a.byteValue()) {
                    throw new DecoderException("unsupported protocol version: " + version);
                }

                type = Socks4CommandType.valueOf(in.readByte());
                dstPort = ByteBufUtil.readUnsignedShortBE(in);
                dstAddr = NetUtil.intToIpAddress(ByteBufUtil.readIntBE(in));
                checkpoint(State.READ_USERID);
            }
            case READ_USERID: {
                userId = readString("userid", in);
                checkpoint(State.READ_DOMAIN);
            }
            case READ_DOMAIN: {
                // Check for Socks4a protocol marker 0.0.0.x
                if (!"0.0.0.0".equals(dstAddr) && dstAddr.startsWith("0.0.0.")) {
                    dstAddr = readString("dstAddr", in);
                }
                out.add(new DefaultSocks4CommandRequest(type, dstAddr, dstPort, userId));
                checkpoint(State.SUCCESS);
            }
            case SUCCESS: {
                int readableBytes = actualReadableBytes();
                if (readableBytes > 0) {
                    out.add(in.readRetainedSlice(readableBytes));
                }
                break;
            }
            case FAILURE: {
                in.skipBytes(actualReadableBytes());
                break;
            }
            }
        } catch (Exception e) {
            fail(out, e);
        }
    }

    private void fail(List<Object> out, Exception cause) {
        if (!(cause instanceof DecoderException)) {
            cause = new DecoderException(cause);
        }

        Socks4CommandRequest m = new DefaultSocks4CommandRequest(
                type != null? type : Socks4CommandType.CONNECT,
                dstAddr != null? dstAddr : "",
                dstPort != 0? dstPort : 65535,
                userId != null? userId : "");

        m.setDecoderResult(DecoderResult.failure(cause));
        out.add(m);