Netty UDP 報文截取問題

問題

• 最近在寫一個 syslog udp 日志接收器，然后發(fā)現(xiàn)接收過大的日志數(shù)據(jù)會被截斷，拿到的信息不完整

源碼追蹤

創(chuàng)建 udp server 的示例代碼

       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 初始化源碼追蹤

channel 使用 NioDatagramChannel ，追蹤 NioDatagramChannel 源碼

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

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

• 調(diào)用構(gòu)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;
    }

• 調(diào)用父類構(gòu)造方法
  io.netty.channel.socket.DefaultDatagramChannelConfig#DefaultDatagramChannelConfig

    public DefaultDatagramChannelConfig(DatagramChannel channel, DatagramSocket javaSocket) {
        // 初始化 2048 字節(jié)的固定長度的接收緩沖區(qū)
        super(channel, new FixedRecvByteBufAllocator(2048));
        this.javaSocket = ObjectUtil.checkNotNull(javaSocket, "javaSocket");
    }

原因

NioDatagramChannel 默認(rèn)緩沖區(qū)大小只給了 2048 ，開發(fā)一個 Syslog UDP 協(xié)議服務(wù)，日志大小其實就不止這么點，所以日志被截取一部分導(dǎo)致問題出現(xiàn)

解決方法

構(gòu)建 Bootstrap 增加參數(shù)選項，把默認(rèn) 2048 固定緩沖區(qū)調(diào)大

實際構(gòu)建代碼如下：

       def b = new Bootstrap()
        group = new NioEventLoopGroup()
        b.group(group)
                .channel(NioDatagramChannel.class)
                .localAddress(config.udp.port)
                // 增加下面這一行代碼 固定 64 k大小，這個根據(jù)實際情況調(diào)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()