Netty UDP 报文截取问题

问题

• 最近在写一个 syslog udp 日志接收器，然后发现接收过大的日志数据会被截断，拿到的信息不完整

源码追踪

创建 udp server 的示例代码

       def b = new Bootstrap()
        group = new NioEventLoopGroup()
        b.group(group)
                .channel(NioDatagramChannel.class)
                .localAddress(config.udp.port)
                .handler(new ChannelInitializer<DatagramChannel>() {
                    @Override
                    protected void initChannel(DatagramChannel datagramChannel) throws Exception {
                        ChannelPipeline channelPipeline = datagramChannel.pipeline()
                        channelPipeline.addLast(
                                new UDPSyslogMessageDecoder(),
                                new SyslogMessageHandler()
                        )

                        if (config.log) {
                            channelPipeline.addLast(new SyslogMessageLogHandler())
                        }

                        channelPipeline.addLast(new QianxinLogHandler(vertx,config))
                    }
                })

        startFuture = b.bind().sync()

NioDatagramChannel 初始化源码追踪

channel 使用 NioDatagramChannel ，追踪 NioDatagramChannel 源码

• 初始化 NioDatagramChannel
io.netty.channel.socket.nio.NioDatagramChannel.NioDatagramChannel()

    public NioDatagramChannel() {
        this(newSocket(DEFAULT_SELECTOR_PROVIDER));
    }

• 调用构造方法
  io.netty.channel.socket.nio.NioDatagramChannel#NioDatagramChannel(java.nio.channels.DatagramChannel)

    public NioDatagramChannel(DatagramChannel socket) {
        super(null, socket, SelectionKey.OP_READ);
        config = new NioDatagramChannelConfig(this, socket);
    }

• 初始化 NioDatagramChannelConfig 配置信息
  io.netty.channel.socket.nio.NioDatagramChannelConfig.NioDatagramChannelConfig

    NioDatagramChannelConfig(NioDatagramChannel channel, DatagramChannel javaChannel) {
        super(channel, javaChannel.socket());
        this.javaChannel = javaChannel;
    }

• 调用父类构造方法
  io.netty.channel.socket.DefaultDatagramChannelConfig#DefaultDatagramChannelConfig

    public DefaultDatagramChannelConfig(DatagramChannel channel, DatagramSocket javaSocket) {
        // 初始化 2048 字节的固定长度的接收缓冲区
        super(channel, new FixedRecvByteBufAllocator(2048));
        this.javaSocket = ObjectUtil.checkNotNull(javaSocket, "javaSocket");
    }

原因

NioDatagramChannel 默认缓冲区大小只给了 2048 ，开发一个 Syslog UDP 协议服务，日志大小其实就不止这么点，所以日志被截取一部分导致问题出现

解决方法

构建 Bootstrap 增加参数选项，把默认 2048 固定缓冲区调大

实际构建代码如下：

       def b = new Bootstrap()
        group = new NioEventLoopGroup()
        b.group(group)
                .channel(NioDatagramChannel.class)
                .localAddress(config.udp.port)
                // 增加下面这一行代码 固定 64 k大小，这个根据实际情况调整
                .option(ChannelOption.RCVBUF_ALLOCATOR, new FixedRecvByteBufAllocator(65535))
                .handler(new ChannelInitializer<DatagramChannel>() {
                    @Override
                    protected void initChannel(DatagramChannel datagramChannel) throws Exception {
                        ChannelPipeline channelPipeline = datagramChannel.pipeline()
                        channelPipeline.addLast(
                                new UDPSyslogMessageDecoder(),
                                new SyslogMessageHandler()
                        )

                        if (config.log) {
                            channelPipeline.addLast(new SyslogMessageLogHandler())
                        }

                        channelPipeline.addLast(new QianxinLogHandler(vertx,config))
                    }
                })

        startFuture = b.bind().sync()