Netty 客户端是否仅与 Netty 服务器一起使用？

Question

我正在尝试开发一个客户端以使用自定义协议与生物识别设备进行通信，但似乎没有任何效果。 我正在使用 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 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

Netty 客户端是否只能与 Netty 服务器一起使用？

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

虽然您的示例相对简单，但我建议您从一个工作示例构建您的代码，然后在这些部分更有意义时添加功能/结构。例如查看echo examples。尝试使用这种结构，不要担心获得一个干净的类层次结构（同步、超时等），直到您可以发送/接收一些字节。

通常在使用ByteBuf 接口时也要小心。您的 input.getByte(..) 调用使用了不基于 readerIndex() 的绝对索引，这可能导致超出范围的异常。请参考ByteBuf javadocs，但您可能只想坚持使用readByte()，或者至少使用readerIndex()。

其他一些常见的故障排除问题：

1) 您是否确认您发送的信息正确且设备正在接收信息？

2) 您是否已验证设备的响应是否符合预期？