物联网 基于netty核心实战-心跳保活机制
简述
心跳保活是MQTT连接的生命线------它并不是连接瞬间发起的，而是在整个长连接期间持续运行的后台守护机制
源码(netty-sample-05-idle)
https://gitee.com/kcnf-iot/iot-sample/tree/master/netty/netty-sample-05
为什么需要心跳保活机制
MQTT 协议运行在 TCP/IP 之上，当网络连接长时间没有数据交互时，可能会被防火墙或中间网络设备断开，导致连接"假死"。心跳机制可以让客户端定期发送 PINGREQ 心跳包，服务端回复 PINGRESP，双方以此确认对方仍然存活
| 角色 | 职责 | 保活周期 |
|---|---|---|
| 客户端 | 发送 PINGREQ 请求 | KeepAlive（如 60 秒），即客户端每 KeepAlive 秒主动发一次 PINGREQ |
| 服务端 | 响应 PINGRESP | 接收客户端任何报文（PUBLISH/PINGREQ等），若 1.5 倍 KeepAlive 内无任何报文则断开连接 |
双端超时机制的区别
- 客户端按 KeepAlive 间隔主动发送 PINGREQ；若发送 PINGREQ 后一段时间内未收到 PINGRESP，则断开。
- 服务端计算"从客户端收到的最近一次任何报文"（不限于 PINGREQ）至今的时间，若超过 1.5 倍 KeepAlive 则断开。
说明：KeepAlive 参数由客户端在 CONNECT 报文可变头中指定，服务端据此计算两种超时阈值
源码
server
package com.jysemel.iot;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
public class MqttServer {
private static final int PORT = 1883;
private static final long DEFAULT_KEEP_ALIVE_SECONDS = 30;
public static void main(String[] args) throws Exception {
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.option(ChannelOption.SO_BACKLOG, 128)
.childOption(ChannelOption.SO_KEEPALIVE, true)
.childHandler(new MqttServerInitializer(DEFAULT_KEEP_ALIVE_SECONDS));
ChannelFuture future = bootstrap.bind(PORT).sync();
System.out.println("╔════════════════════════════════════════╗");
System.out.println("║ MQTT 心跳保活服务端已启动 ║");
System.out.println("║ 监听端口: " + String.format("%-22d", PORT) + "║");
System.out.println("║ 默认KeepAlive: " + String.format("%-16d", DEFAULT_KEEP_ALIVE_SECONDS) + "║");
System.out.println("╚════════════════════════════════════════╝");
future.channel().closeFuture().sync();
} finally {
workerGroup.shutdownGracefully();
bossGroup.shutdownGracefully();
System.out.println("MQTT 服务端已关闭");
}
}
}client
package com.jysemel.iot;
import com.jysemel.iot.handler.MqttHeartbeatClientHandler;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.mqtt.MqttDecoder;
import io.netty.handler.codec.mqtt.MqttEncoder;
import io.netty.handler.timeout.IdleStateHandler;
import java.util.concurrent.TimeUnit;
public class MqttHeartbeatClient {
private static final String HOST = "127.0.0.1";
private static final int PORT = 1883;
private static final int KEEP_ALIVE_SECONDS = 10;
public static void main(String[] args) throws Exception {
EventLoopGroup group = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.group(group)
.channel(NioSocketChannel.class)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast("mqttDecoder", new MqttDecoder(65536));
pipeline.addLast("mqttEncoder", MqttEncoder.INSTANCE);
pipeline.addLast("idleStateHandler",
new IdleStateHandler(0, KEEP_ALIVE_SECONDS, 0, TimeUnit.SECONDS));
pipeline.addLast("clientHandler", new MqttHeartbeatClientHandler(KEEP_ALIVE_SECONDS));
}
});
ChannelFuture future = bootstrap.connect(HOST, PORT).sync();
System.out.println("╔════════════════════════════════════════╗");
System.out.println("║ MQTT 心跳客户端已启动 ║");
System.out.println("║ 服务器: " + String.format("%-22s", HOST + ":" + PORT) + "║");
System.out.println("║ KeepAlive: " + String.format("%-19d", KEEP_ALIVE_SECONDS) + "║");
System.out.println("║ 说明: 每" + KEEP_ALIVE_SECONDS + "秒发送一次PINGREQ ║");
System.out.println("╚════════════════════════════════════════╝");
future.channel().closeFuture().sync();
} finally {
group.shutdownGracefully();
System.out.println("MQTT 客户端已关闭");
}
}
}消息类型标记
private void handlePingReq(ChannelHandlerContext ctx) {
System.out.println(">>> 收到 PINGREQ，回复 PINGRESP");
MqttFixedHeader pingRespHeader = new MqttFixedHeader(
MqttMessageType.PINGRESP, false, MqttQoS.AT_MOST_ONCE, false, 0);
ctx.writeAndFlush(new MqttMessage(pingRespHeader));
}
if (event.state() == IdleState.WRITER_IDLE && isConnected) {
pingCount++;
System.out.println(">>> [" + pingCount + "] 写空闲超时，发送 PINGREQ");
MqttFixedHeader pingReqHeader = new MqttFixedHeader(
MqttMessageType.PINGREQ, false, MqttQoS.AT_MOST_ONCE, false, 0);
ctx.writeAndFlush(new MqttMessage(pingReqHeader));
}验证结果
