java - Netty 客户端只能与 Netty 服务器一起使用吗？

Question

我正在尝试开发一个客户端来使用自定义协议(protocol)与生物识别设备进行通信，但似乎没有任何效果。我使用 MessageToByteEncoder 和 MessageToByteDecoder 来处理输入和输出数据:

public class PacketDecoder extends ByteToMessageDecoder {
    @Override
    protected void decode(ChannelHandlerContext context, ByteBuf input, List<Object> out) throws Exception {
        System.out.println("readable bytes: " + input.readableBytes());
        if (input.readableBytes() >= 1) {
            if (input.getByte(0) != DataCodes.START_BYTE) {
                input.readByte();
                return;
            }
        }
        if (input.readableBytes() >= 3) {
            byte command = input.getByte(2);
            boolean extendedLenght = (command & 0x80) == 0x80;
            short dataLength;
            int headerLength;
            if (extendedLenght) {
                byte[] dataLengthBytes = new byte[2];
                input.getBytes(3, dataLengthBytes);
                dataLength = Utils.getShort(dataLengthBytes);
                headerLength = 5;
            } else {
                dataLength = input.getByte(3);
                headerLength = 4;
            }

            int totalLength = headerLength + dataLength + 16;
            if (input.readableBytes() >= totalLength) {
               byte[] packetBytes = input.readBytes(totalLength).array();
                Packet packet = PacketConverter.decode(packetBytes);
                System.out.println("packet decoded");
                out.add(packet);
            }
        }
    }
}


public class PacketEncoder extends MessageToByteEncoder<Packet> {
    @Override
    protected void encode(ChannelHandlerContext context, Packet packet, ByteBuf out) throws Exception {
        byte[] packetBytes = PacketConverter.encode(packet);
        out.writeBytes(packetBytes);
    }
}

和连接类:

public class Connection implements PacketListener {
    private final byte deviceAddress;
    private ChannelFuture channelFuture;
    private EventLoopGroup workerGroup;
    private final Object readLock = new Object();
    private Packet responsePacket;

    public Connection(byte deviceAddress) {
        this.deviceAddress = deviceAddress;
    }

    public void connect(String address, int port) {
        workerGroup = new NioEventLoopGroup();
        Bootstrap b = new Bootstrap();
        b.group(workerGroup);
        b.channel(NioSocketChannel.class);
        b.option(ChannelOption.SO_KEEPALIVE, true);
        b.handler(new ChannelInitializer<SocketChannel>() {
            @Override
            protected void initChannel(SocketChannel socketChannel) throws Exception {
                socketChannel.pipeline().addLast(
                        new PacketEncoder(),
                        new PacketDecoder(),
                        new PacketHandler(Connection.this)
                );
            }
        });

        channelFuture = b.connect(address, port);
    }

    public void disconnect() {
        channelFuture.channel().disconnect().syncUninterruptibly();
        workerGroup.shutdownGracefully();
    }

    @Override
    public void receive(Packet packet) {
        synchronized (readLock) {
            this.responsePacket = packet;
            readLock.notify();
        }
    }

    public Response send(Command command, int responseTimeout) throws TimeOutException {
        Packet packet = new Packet();
        packet.setCommand(command.getCommandCode());
        packet.setData(command.getCommandData());
        packet.setAddress(deviceAddress);

        synchronized (readLock) {
            responsePacket = null;
            channelFuture.channel().writeAndFlush(packet).syncUninterruptibly();
            try {
                readLock.wait(responseTimeout);
            } catch (InterruptedException e) {
            }
            if (responsePacket == null)
                throw new TimeOutException();
            return Response.get(responsePacket);
        }
    }
}

在解码器上，它带有 0 个可读字节，我不确定编码器是否正在发送任何数据。我唯一的猜测是服务器需要是 Netty 实现。

Answer 1

Does a Netty client work with a netty server only?

没有。一般来说，Netty 提供网络抽象和事件循环结构来减轻您自己的痛苦和陷阱。

虽然您的示例相对简单，但我建议您根据工作示例构建代码，然后在各个部分变得更有意义后添加功能/结构。例如查看echo examples 。尝试使用此结构，并且不必担心获得干净的类层次结构(同步、超时等)，直到您可以发送/接收一些字节。

此外，通常在使用 ByteBuf 接口(interface)时要小心。您的 input.getByte(..) 调用使用绝对索引，该索引不基于 readerIndex()，这可能会导致越界异常。请引用ByteBuf javadocs但您可能只想坚持使用 readByte() 或至少使用 readerIndex()。

其他一些常见故障排除问题:

1) 您是否已验证您发送的信息是否正确并且设备正在接收该信息？

2) 您是否已确认设备正在按照预期响应进行响应？