@Override
protected Future<?> execute() {
    InetSocketAddress destinationAddress;
    try {
        destinationAddress = addressFor(serverHostAndPort, proxyServer);
    } catch (UnknownHostException e) {
        return channel.newFailedFuture(e);
    }

    DefaultSocks4CommandRequest connectRequest = new DefaultSocks4CommandRequest(
            Socks4CommandType.CONNECT, destinationAddress.getHostString(), destinationAddress.getPort());

    addFirstOrReplaceHandler(SOCKS_ENCODER_NAME, Socks4ClientEncoder.INSTANCE);
    addFirstOrReplaceHandler(SOCKS_DECODER_NAME, new Socks4ClientDecoder());
    return writeToChannel(connectRequest);
}
 

@Override
protected Object newInitialMessage(ChannelHandlerContext ctx) throws Exception {
    InetSocketAddress raddr = destinationAddress();
    String rhost;
    if (raddr.isUnresolved()) {
        rhost = raddr.getHostString();
    } else {
        rhost = raddr.getAddress().getHostAddress();
    }
    return new DefaultSocks4CommandRequest(
            Socks4CommandType.CONNECT, rhost, raddr.getPort(), username != null? username : "");
}
 

private boolean authenticate(ChannelHandlerContext ctx, Socks4CommandRequest req) {
    assertThat(req.type(), is(Socks4CommandType.CONNECT));

    if (testMode != TestMode.INTERMEDIARY) {
        ctx.pipeline().addBefore(ctx.name(), "lineDecoder", new LineBasedFrameDecoder(64, false, true));
    }

    boolean authzSuccess;
    if (username != null) {
        authzSuccess = username.equals(req.userId());
    } else {
        authzSuccess = true;
    }
    return authzSuccess;
}
 

@Override
protected void channelRead0(ChannelHandlerContext ctx, SocksMessage socksMessage)
        throws Exception {
    switch (socksMessage.version()) {
    case SOCKS4a:
        Socks4CommandRequest socksV4CmdRequest = (Socks4CommandRequest) socksMessage;
        if (socksV4CmdRequest.type() == Socks4CommandType.CONNECT) {
            onSocksSuccess(ctx, socksV4CmdRequest);
        } else {
            ctx.close();
        }
        break;
    case SOCKS5:
        if (socksMessage instanceof Socks5InitialRequest) {
            ctx.pipeline().addFirst(addChannelHandler(new Socks5CommandRequestDecoder()));
            ctx.writeAndFlush(new DefaultSocks5InitialResponse(Socks5AuthMethod.NO_AUTH));
        } else if (socksMessage instanceof Socks5PasswordAuthRequest) {
            ctx.pipeline().addFirst(addChannelHandler(new Socks5CommandRequestDecoder()));
            ctx.writeAndFlush(new DefaultSocks5PasswordAuthResponse(Socks5PasswordAuthStatus.SUCCESS));
        } else if (socksMessage instanceof Socks5CommandRequest) {
            Socks5CommandRequest socks5CmdRequest = (Socks5CommandRequest) socksMessage;
            if (socks5CmdRequest.type() == Socks5CommandType.CONNECT) {
                onSocksSuccess(ctx, socks5CmdRequest);
            } else {
                ctx.close();
            }
        } else {
            ctx.close();
        }
        break;
    case UNKNOWN:
        ctx.close();
        break;
    }
}
 

@Override
public void channelRead0(ChannelHandlerContext ctx, SocksMessage socksRequest) throws Exception {
    switch (socksRequest.version()) {
        case SOCKS4a:
            Socks4CommandRequest socksV4CmdRequest = (Socks4CommandRequest) socksRequest;
            if (socksV4CmdRequest.type() == Socks4CommandType.CONNECT) {
                ctx.pipeline().addLast(new SocksServerConnectHandler());
                ctx.pipeline().remove(this);
                ctx.fireChannelRead(socksRequest);
            } else {
                ctx.close();
            }
            break;
        case SOCKS5:
            if (socksRequest instanceof Socks5InitialRequest) {
                // auth support example
                //ctx.pipeline().addFirst(new Socks5PasswordAuthRequestDecoder());
                //ctx.write(new DefaultSocks5AuthMethodResponse(Socks5AuthMethod.PASSWORD));
                ctx.pipeline().addFirst(new Socks5CommandRequestDecoder());
                ctx.write(new DefaultSocks5InitialResponse(Socks5AuthMethod.NO_AUTH));
            } else if (socksRequest instanceof Socks5PasswordAuthRequest) {
                ctx.pipeline().addFirst(new Socks5CommandRequestDecoder());
                ctx.write(new DefaultSocks5PasswordAuthResponse(Socks5PasswordAuthStatus.SUCCESS));
            } else if (socksRequest instanceof Socks5CommandRequest) {
                Socks5CommandRequest socks5CmdRequest = (Socks5CommandRequest) socksRequest;
                if (socks5CmdRequest.type() == Socks5CommandType.CONNECT) {
                    ctx.pipeline().addLast(new SocksServerConnectHandler());
                    ctx.pipeline().remove(this);
                    ctx.fireChannelRead(socksRequest);
                } else {
                    ctx.close();
                }
            } else {
                ctx.close();
            }
            break;
        case UNKNOWN:
            ctx.close();
            break;
    }
}