前言：
现时看官们对“apachemqtt”大约比较关注，你们都想要了解一些“apachemqtt”的相关知识。那么小编也在网摘上网罗了一些关于“apachemqtt””的相关资讯，希望各位老铁们能喜欢，看官们快快来学习一下吧！本文分享自华为云社区《一文带你掌握物联网mqtt网关搭建背后的技术原理-云社区-华为云
》，作者：张俭。
前言
物联网是现在比较热门的软件领域，众多物联网厂商都有自己的物联网平台，而物联网平台其中一个核心的模块就是Mqtt网关。这篇文章的目的是手把手教大家写书写一个mqtt网关，后端存储支持Kafka/Pulsar，支持mqtt 连接、断链、发送消息、订阅消息。技术选型:
Netty java最流行的网络框架netty-codec-mqtt netty的子项目，mqtt编解码插件Pulsar/Kafka 流行的消息中间件作为后端存储
核心pom依赖如下
<dependency> <groupId>io.netty</groupId> <artifactId>netty-codec-mqtt</artifactId> </dependency> <dependency> <groupId>io.netty</groupId> <artifactId>netty-common</artifactId> </dependency> <dependency> <groupId>io.netty</groupId> <artifactId>netty-transport</artifactId> </dependency> <dependency> <groupId>org.apache.pulsar</groupId> <artifactId>pulsar-client-original</artifactId> <version>${pulsar.version}</version> </dependency> <dependency> <groupId>org.apache.kafka</groupId> <artifactId>kafka-clients</artifactId> <version>${kafka.version}</version> </dependency> <dependency> <groupId>org.eclipse.paho</groupId> <artifactId>org.eclipse.paho.client.mqttv3</artifactId> <version>${mqtt-client.version}</version> <scope>test</scope> </dependency>软件参数设计软件参数可谓是非常常见，复杂的开源项目，参数甚至可以达到上百个、配置文件长达数千行。我们需要的配置有
MqttServer监听的端口
监听端口的配置即使是写demo也非常必要，常常用在单元测试中，由于单元测试跑完之后，即使网络服务器关闭，操作系统也不会立即释放端口，所以单元测试的时候指定随机端口非常关键，在java中，我们可以通过这样的工具类来获取一个空闲的端口。未配置的话，我们就使用mqtt的默认端口1883。
package io.github.protocol.mqtt.broker.util;import java.io.IOException;import java.io.UncheckedIOException;import java.net.ServerSocket;public class SocketUtil { public static int getFreePort() { try (ServerSocket serverSocket = new ServerSocket(0)) { return serverSocket.getLocalPort(); } catch (IOException e) { throw new UncheckedIOException(e); } }}后端存储配置我们的mqtt网关是没有可靠的存储能力的，依赖后端的消息中间件来做持久化处理。后端规划支持Pulsar、Kafka两种类型。定义枚举类如下
public enum ProcessorType { KAFKA, PULSAR,}对应的KafkaProcessorConfig、PulsarProcessorConfig比较简单，包含基础的连接地址即可，如果后续要做性能调优、安全，这块还是会有更多的配置项
@Setter@Getterpublic class KafkaProcessorConfig { private String bootstrapServers = "localhost:9092"; public KafkaProcessorConfig() { }}@Setter@Getterpublic class PulsarProcessorConfig { private String httpUrl = ";; private String serviceUrl = "pulsar://localhost:6650"; public PulsarProcessorConfig() { }}启动netty MqttServer我们通过netty启动一个mqttServer，添加mqtt解码器
package io.github.protocol.mqtt.broker;import io.github.protocol.mqtt.broker.processor.KafkaProcessor;import io.github.protocol.mqtt.broker.processor.KafkaProcessorConfig;import io.github.protocol.mqtt.broker.processor.MqttProcessor;import io.github.protocol.mqtt.broker.processor.PulsarProcessor;import io.github.protocol.mqtt.broker.processor.PulsarProcessorConfig;import io.github.protocol.mqtt.broker.util.SocketUtil;import io.netty.bootstrap.ServerBootstrap;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelOption;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.NioServerSocketChannel;import io.netty.handler.codec.mqtt.MqttDecoder;import io.netty.handler.codec.mqtt.MqttEncoder;import io.netty.handler.logging.LogLevel;import io.netty.handler.logging.LoggingHandler;import lombok.extern.slf4j.Slf4j;@Slf4jpublic class MqttServer { private final MqttServerConfig mqttServerConfig; public MqttServer() { this(new MqttServerConfig()); } public MqttServer(MqttServerConfig mqttServerConfig) { this.mqttServerConfig = mqttServerConfig; if (mqttServerConfig.getPort() == 0) { mqttServerConfig.setPort(SocketUtil.getFreePort()); } } public void start() throws Exception { EventLoopGroup bossGroup = new NioEventLoopGroup(1); EventLoopGroup workerGroup = new NioEventLoopGroup(); try { ServerBootstrap b = new ServerBootstrap(); b.group(bossGroup, workerGroup) .channel(NioServerSocketChannel.class) .option(ChannelOption.SO_BACKLOG, 100) .handler(new LoggingHandler(LogLevel.INFO)) .childHandler(new ChannelInitializer<SocketChannel>() { @Override public void initChannel(SocketChannel ch) throws Exception { ChannelPipeline p = ch.pipeline(); // decoder p.addLast(new MqttDecoder()); p.addLast(MqttEncoder.INSTANCE); } }); // Start the server. ChannelFuture f = b.bind(mqttServerConfig.getPort()).sync(); // Wait until the server socket is closed. f.channel().closeFuture().sync(); } finally { // Shut down all event loops to terminate all threads. bossGroup.shutdownGracefully(); workerGroup.shutdownGracefully(); } } private MqttProcessor processor(MqttServerConfig config) { return switch (config.getProcessorType()) { case KAFKA -> new KafkaProcessor(config.getMqttAuth(), config.getKafkaProcessorConfig()); case PULSAR -> new PulsarProcessor(config.getMqttAuth(), config.getPulsarProcessorConfig()); }; } public int getPort() { return mqttServerConfig.getPort(); }}MqttserverStarter.java我们写一个简单的main函数用来启动mqttServer，方便调测
package io.github.protocol.mqtt.broker;public class MqttServerStarter { public static void main(String[] args) throws Exception { new MqttServer().start(); }}客户端使用eclipse mqtt client进行测试
package io.github.protocol.mqtt;import lombok.extern.log4j.Log4j2;import org.eclipse.paho.client.mqttv3.MqttClient;import org.eclipse.paho.client.mqttv3.MqttConnectOptions;import org.eclipse.paho.client.mqttv3.MqttException;import org.eclipse.paho.client.mqttv3.MqttMessage;import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;@Log4j2public class MqttClientPublishExample { public static void main(String[] args) throws Exception { String topic = "MQTT Examples"; String content = "Message from MqttPublishExample"; int qos = 2; String broker = "tcp://127.0.0.1:1883"; String clientId = "JavaSample"; MemoryPersistence persistence = new MemoryPersistence(); try { MqttClient sampleClient = new MqttClient(broker, clientId, persistence); MqttConnectOptions connOpts = new MqttConnectOptions(); connOpts.setCleanSession(true); log.info("Connecting to broker: {}", broker); sampleClient.connect(connOpts); log.info("Connected"); log.info("Publishing message: {}", content); MqttMessage message = new MqttMessage(content.getBytes()); message.setQos(qos); sampleClient.publish(topic, message); log.info("Message published"); sampleClient.disconnect(); log.info("Disconnected"); System.exit(0); } catch (MqttException me) { log.error("reason {} msg {}", me.getReasonCode(), me.getMessage(), me); } }}然后我们先运行MqttServer，再运行MqttClient，发现MqttClient卡住了
Connecting to broker: tcp://127.0.0.1:1883
这是为什么呢，我们通过抓包发现仅仅只有客户端发送了Mqtt connect信息，服务端并没有响应
但是根据mqtt标准协议，发送Connect消息，必须要有ConnAck响应
所以我们需要在接收到Connect后，返回connAck消息。我们创建一个MqttHandler，让他继承ChannelInboundHandlerAdapter, 用来接力MqttDecoder解码完成后的消息，这里要重点继承其中的channelRead方法，以及channelInactive方法，用来释放断链时需要释放的资源
package com.github.shoothzj.mqtt;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.ChannelInboundHandlerAdapter;import lombok.extern.slf4j.Slf4j;@Slf4jpublic class MqttHandler extends ChannelInboundHandlerAdapter { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { super.channelRead(ctx, msg); }}然后把这个handler加入到netty的职责链中，放到解码器的后面
在mqtt handler中插入我们的代码
@Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { super.channelRead(ctx, msg); if (msg instanceof MqttConnectMessage) { handleConnect(ctx, (MqttConnectMessage) msg); } else { log.error("Unsupported type msg [{}]", msg); } } private void handleConnect(ChannelHandlerContext ctx, MqttConnectMessage connectMessage) { log.info("connect msg is [{}]", connectMessage); }打印出connectMessage如下
[MqttConnectMessage[fixedHeader=MqttFixedHeader[messageType=CONNECT, isDup=false, qosLevel=AT_MOST_ONCE, isRetain=false, remainingLength=22], variableHeader=MqttConnectVariableHeader[name=MQTT, version=4, hasUserName=false, hasPassword=false, isWillRetain=false, isWillFlag=false, isCleanSession=true, keepAliveTimeSeconds=60], payload=MqttConnectPayload[clientIdentifier=JavaSample, willTopic=null, willMessage=null, userName=null, password=null]]]
通常，mqtt connect message中会包含qos、用户名、密码等信息，由于我们启动客户端的时候也没有携带用户名和密码，这里获取到的都为null，我们先不校验这些消息，直接给客户端返回connack消息，代表连接成功
final MqttConnAckMessage ackMessage = MqttMessageBuilders.connAck().returnCode(CONNECTION_ACCEPTED).build(); ctx.channel().writeAndFlush(ackMessage);
我们再运行起Server和Client，随后可以看到已经走过了Connect阶段，进入了publish message过程，接下来我们再实现更多的其他场景
附上此阶段的MqttHandler代码
package com.github.shoothzj.mqtt;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.ChannelInboundHandlerAdapter;import io.netty.handler.codec.mqtt.MqttConnAckMessage;import io.netty.handler.codec.mqtt.MqttConnectMessage;import io.netty.handler.codec.mqtt.MqttConnectPayload;import io.netty.handler.codec.mqtt.MqttConnectVariableHeader;import io.netty.handler.codec.mqtt.MqttFixedHeader;import io.netty.handler.codec.mqtt.MqttMessageBuilders;import lombok.extern.slf4j.Slf4j;import static io.netty.handler.codec.mqtt.MqttConnectReturnCode.CONNECTION_ACCEPTED;@Slf4jpublic class MqttHandler extends ChannelInboundHandlerAdapter { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { super.channelRead(ctx, msg); if (msg instanceof MqttConnectMessage) { handleConnect(ctx, (MqttConnectMessage) msg); } else { log.error("Unsupported type msg [{}]", msg); } } private void handleConnect(ChannelHandlerContext ctx, MqttConnectMessage connectMessage) { log.info("connect msg is [{}]", connectMessage); final MqttFixedHeader fixedHeader = connectMessage.fixedHeader(); final MqttConnectVariableHeader variableHeader = connectMessage.variableHeader(); final MqttConnectPayload connectPayload = connectMessage.payload(); final MqttConnAckMessage ackMessage = MqttMessageBuilders.connAck().returnCode(CONNECTION_ACCEPTED).build(); ctx.channel().writeAndFlush(ackMessage); }}我们当前把所有的逻辑都放在MqttHandler里面，不方便后续的扩展。抽象出一个MqttProcessor接口来处理具体的请求，MqttHandler负责解析MqttMessage的类型并分发。MqttProcess接口设计如下
package io.github.protocol.mqtt.broker.processor;import io.netty.channel.ChannelHandlerContext;import io.netty.handler.codec.mqtt.MqttConnAckMessage;import io.netty.handler.codec.mqtt.MqttConnectMessage;import io.netty.handler.codec.mqtt.MqttMessage;import io.netty.handler.codec.mqtt.MqttPubAckMessage;import io.netty.handler.codec.mqtt.MqttPublishMessage;import io.netty.handler.codec.mqtt.MqttSubAckMessage;import io.netty.handler.codec.mqtt.MqttSubscribeMessage;import io.netty.handler.codec.mqtt.MqttUnsubAckMessage;import io.netty.handler.codec.mqtt.MqttUnsubscribeMessage;public interface MqttProcessor { void processConnect(ChannelHandlerContext ctx, MqttConnectMessage msg) throws Exception; void processConnAck(ChannelHandlerContext ctx, MqttConnAckMessage msg) throws Exception; void processPublish(ChannelHandlerContext ctx, MqttPublishMessage msg) throws Exception; void processPubAck(ChannelHandlerContext ctx, MqttPubAckMessage msg) throws Exception; void processPubRec(ChannelHandlerContext ctx, MqttMessage msg) throws Exception; void processPubRel(ChannelHandlerContext ctx, MqttMessage msg) throws Exception; void processPubComp(ChannelHandlerContext ctx, MqttMessage msg) throws Exception; void processSubscribe(ChannelHandlerContext ctx, MqttSubscribeMessage msg) throws Exception; void processSubAck(ChannelHandlerContext ctx, MqttSubAckMessage msg) throws Exception; void processUnsubscribe(ChannelHandlerContext ctx, MqttUnsubscribeMessage msg) throws Exception; void processUnsubAck(ChannelHandlerContext ctx, MqttUnsubAckMessage msg) throws Exception; void processPingReq(ChannelHandlerContext ctx, MqttMessage msg) throws Exception; void processPingResp(ChannelHandlerContext ctx, MqttMessage msg) throws Exception; void processDisconnect(ChannelHandlerContext ctx) throws Exception; void processAuth(ChannelHandlerContext ctx, MqttMessage msg) throws Exception;}我们允许这些方法抛出异常，当遇到极难处理的故障时，把mqtt连接断掉（如后端存储故障），等待客户端的重连。
MqttHandler中来调用MqttProcessor，相关MqttHandler代码如下
Preconditions.checkArgument(message instanceof MqttMessage); MqttMessage msg = (MqttMessage) message; try { if (msg.decoderResult().isFailure()) { Throwable cause = msg.decoderResult().cause(); if (cause instanceof MqttUnacceptableProtocolVersionException) { // Unsupported protocol version MqttConnAckMessage connAckMessage = (MqttConnAckMessage) MqttMessageFactory.newMessage( new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0), new MqttConnAckVariableHeader( MqttConnectReturnCode.CONNECTION_REFUSED_UNACCEPTABLE_PROTOCOL_VERSION, false), null); ctx.writeAndFlush(connAckMessage); log.error("connection refused due to invalid protocol, client address [{}]", ctx.channel().remoteAddress()); ctx.close(); return; } else if (cause instanceof MqttIdentifierRejectedException) { // ineligible clientId MqttConnAckMessage connAckMessage = (MqttConnAckMessage) MqttMessageFactory.newMessage( new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0), new MqttConnAckVariableHeader(MqttConnectReturnCode.CONNECTION_REFUSED_IDENTIFIER_REJECTED, false), null); ctx.writeAndFlush(connAckMessage); log.error("ineligible clientId, client address [{}]", ctx.channel().remoteAddress()); ctx.close(); return; } throw new IllegalStateException(msg.decoderResult().cause().getMessage()); } MqttMessageType messageType = msg.fixedHeader().messageType(); if (log.isDebugEnabled()) { log.debug("Processing MQTT Inbound handler message, type={}", messageType); } switch (messageType) { case CONNECT: Preconditions.checkArgument(msg instanceof MqttConnectMessage); processor.processConnect(ctx, (MqttConnectMessage) msg); break; case CONNACK: Preconditions.checkArgument(msg instanceof MqttConnAckMessage); processor.processConnAck(ctx, (MqttConnAckMessage) msg); break; case PUBLISH: Preconditions.checkArgument(msg instanceof MqttPublishMessage); processor.processPublish(ctx, (MqttPublishMessage) msg); break; case PUBACK: Preconditions.checkArgument(msg instanceof MqttPubAckMessage); processor.processPubAck(ctx, (MqttPubAckMessage) msg); break; case PUBREC: processor.processPubRec(ctx, msg); break; case PUBREL: processor.processPubRel(ctx, msg); break; case PUBCOMP: processor.processPubComp(ctx, msg); break; case SUBSCRIBE: Preconditions.checkArgument(msg instanceof MqttSubscribeMessage); processor.processSubscribe(ctx, (MqttSubscribeMessage) msg); break; case SUBACK: Preconditions.checkArgument(msg instanceof MqttSubAckMessage); processor.processSubAck(ctx, (MqttSubAckMessage) msg); break; case UNSUBSCRIBE: Preconditions.checkArgument(msg instanceof MqttUnsubscribeMessage); processor.processUnsubscribe(ctx, (MqttUnsubscribeMessage) msg); break; case UNSUBACK: Preconditions.checkArgument(msg instanceof MqttUnsubAckMessage); processor.processUnsubAck(ctx, (MqttUnsubAckMessage) msg); break; case PINGREQ: processor.processPingReq(ctx, msg); break; case PINGRESP: processor.processPingResp(ctx, msg); break; case DISCONNECT: processor.processDisconnect(ctx); break; case AUTH: processor.processAuth(ctx, msg); break; default: throw new UnsupportedOperationException("Unknown MessageType: " + messageType); } } catch (Throwable ex) { ReferenceCountUtil.safeRelease(msg); log.error("Exception was caught while processing MQTT message, ", ex); ctx.close(); }这里的代码，主要是针对MqttMessage的不同类型，调用MqttProcessor的不同方法，值得一提的有两点
提前判断了一些解码异常，fast fail全局捕获异常，并进行断链处理维护MqttSession
维护Mqtt会话的session，主要用来持续跟踪客户端会话信息，跟踪在系统中占用的资源等，考虑到无论是何种后端实现，都需要维护Mqtt的Session，我们构筑一个AbstractMqttProcessor来维护MqttSession
package io.github.protocol.mqtt.broker.processor;import io.github.protocol.mqtt.broker.MqttSessionKey;import io.github.protocol.mqtt.broker.auth.MqttAuth;import io.github.protocol.mqtt.broker.util.ChannelUtils;import io.github.protocol.mqtt.broker.util.MqttMessageUtil;import io.netty.channel.ChannelHandlerContext;import io.netty.handler.codec.mqtt.MqttConnAckMessage;import io.netty.handler.codec.mqtt.MqttConnAckVariableHeader;import io.netty.handler.codec.mqtt.MqttConnectMessage;import io.netty.handler.codec.mqtt.MqttConnectReturnCode;import io.netty.handler.codec.mqtt.MqttFixedHeader;import io.netty.handler.codec.mqtt.MqttMessage;import io.netty.handler.codec.mqtt.MqttMessageFactory;import io.netty.handler.codec.mqtt.MqttMessageIdVariableHeader;import io.netty.handler.codec.mqtt.MqttMessageType;import io.netty.handler.codec.mqtt.MqttPubAckMessage;import io.netty.handler.codec.mqtt.MqttPublishMessage;import io.netty.handler.codec.mqtt.MqttQoS;import io.netty.handler.codec.mqtt.MqttSubAckMessage;import io.netty.handler.codec.mqtt.MqttSubAckPayload;import io.netty.handler.codec.mqtt.MqttSubscribeMessage;import io.netty.handler.codec.mqtt.MqttSubscribePayload;import io.netty.handler.codec.mqtt.MqttUnsubAckMessage;import io.netty.handler.codec.mqtt.MqttUnsubscribeMessage;import lombok.extern.slf4j.Slf4j;import org.apache.commons.lang3.StringUtils;import java.util.stream.IntStream;@Slf4jpublic abstract class AbstractProcessor implements MqttProcessor { protected final MqttAuth mqttAuth; public AbstractProcessor(MqttAuth mqttAuth) { this.mqttAuth = mqttAuth; } @Override public void processConnect(ChannelHandlerContext ctx, MqttConnectMessage msg) throws Exception { String clientId = msg.payload().clientIdentifier(); String username = msg.payload().userName(); byte[] pwd = msg.payload().passwordInBytes(); if (StringUtils.isBlank(clientId) || StringUtils.isBlank(username)) { MqttConnAckMessage connAckMessage = (MqttConnAckMessage) MqttMessageFactory.newMessage( new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0), new MqttConnAckVariableHeader(MqttConnectReturnCode.CONNECTION_REFUSED_IDENTIFIER_REJECTED, false), null); ctx.writeAndFlush(connAckMessage); log.error("the clientId username pwd cannot be empty, client address[{}]", ctx.channel().remoteAddress()); ctx.close(); return; } if (!mqttAuth.connAuth(clientId, username, pwd)) { MqttConnAckMessage connAckMessage = (MqttConnAckMessage) MqttMessageFactory.newMessage( new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0), new MqttConnAckVariableHeader(MqttConnectReturnCode.CONNECTION_REFUSED_BAD_USER_NAME_OR_PASSWORD, false), null); ctx.writeAndFlush(connAckMessage); log.error("the clientId username pwd cannot be empty, client address[{}]", ctx.channel().remoteAddress()); ctx.close(); return; } MqttSessionKey mqttSessionKey = new MqttSessionKey(); mqttSessionKey.setUsername(username); mqttSessionKey.setClientId(clientId); ChannelUtils.setMqttSession(ctx.channel(), mqttSessionKey); log.info("username {} clientId {} remote address {} connected", username, clientId, ctx.channel().remoteAddress()); onConnect(mqttSessionKey); MqttConnAckMessage mqttConnectMessage = (MqttConnAckMessage) MqttMessageFactory.newMessage( new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0), new MqttConnAckVariableHeader(MqttConnectReturnCode.CONNECTION_ACCEPTED, false), null); ctx.writeAndFlush(mqttConnectMessage); } protected void onConnect(MqttSessionKey mqttSessionKey) { } @Override public void processConnAck(ChannelHandlerContext ctx, MqttConnAckMessage msg) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("conn ack, client address {} not authed", ctx.channel().remoteAddress()); ctx.close(); } } @Override public void processPublish(ChannelHandlerContext ctx, MqttPublishMessage msg) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("publish, client address {} not authed", ctx.channel().remoteAddress()); ctx.close(); return; } if (msg.fixedHeader().qosLevel() == MqttQoS.FAILURE) { log.error("failure. clientId {}, username {} ", mqttSession.getClientId(), mqttSession.getUsername()); return; } if (msg.fixedHeader().qosLevel() == MqttQoS.EXACTLY_ONCE) { log.error("does not support QoS2 protocol. clientId {}, username {} ", mqttSession.getClientId(), mqttSession.getUsername()); return; } onPublish(ctx, mqttSession, msg); } protected void onPublish(ChannelHandlerContext ctx, MqttSessionKey mqttSessionKey, MqttPublishMessage msg) throws Exception { } @Override public void processPubAck(ChannelHandlerContext ctx, MqttPubAckMessage msg) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("pub ack, client address {} not authed", ctx.channel().remoteAddress()); ctx.close(); } } @Override public void processPubRec(ChannelHandlerContext ctx, MqttMessage msg) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("pub rec, client address {} not authed", ctx.channel().remoteAddress()); ctx.close(); } } @Override public void processPubRel(ChannelHandlerContext ctx, MqttMessage msg) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("pub rel, client address {} not authed", ctx.channel().remoteAddress()); ctx.close(); } } @Override public void processPubComp(ChannelHandlerContext ctx, MqttMessage msg) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("pub comp, client address {} not authed", ctx.channel().remoteAddress()); ctx.close(); } } @Override public void processSubscribe(ChannelHandlerContext ctx, MqttSubscribeMessage msg) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("sub, client address {} not authed", ctx.channel().remoteAddress()); ctx.close(); } onSubscribe(ctx, mqttSession, msg.payload()); MqttFixedHeader fixedHeader = new MqttFixedHeader(MqttMessageType.SUBACK, false, MqttQoS.AT_MOST_ONCE, false, 0); IntStream intStream = msg.payload().topicSubscriptions().stream().mapToInt(s -> s.qualityOfService().value()); MqttSubAckPayload payload = new MqttSubAckPayload(intStream.toArray()); ctx.writeAndFlush(MqttMessageFactory.newMessage( fixedHeader, MqttMessageIdVariableHeader.from(msg.variableHeader().messageId()), payload)); } protected void onSubscribe(ChannelHandlerContext ctx, MqttSessionKey mqttSessionKey, MqttSubscribePayload subscribePayload) throws Exception { } @Override public void processSubAck(ChannelHandlerContext ctx, MqttSubAckMessage msg) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("sub ack, client address {} not authed", ctx.channel().remoteAddress()); ctx.close(); } } @Override public void processUnsubscribe(ChannelHandlerContext ctx, MqttUnsubscribeMessage msg) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("unsub, client address {} not authed", ctx.channel().remoteAddress()); ctx.close(); } } @Override public void processUnsubAck(ChannelHandlerContext ctx, MqttUnsubAckMessage msg) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("unsub ack, client address {} not authed", ctx.channel().remoteAddress()); ctx.close(); } } @Override public void processPingReq(ChannelHandlerContext ctx, MqttMessage msg) throws Exception { ctx.writeAndFlush(MqttMessageUtil.pingResp()); } @Override public void processPingResp(ChannelHandlerContext ctx, MqttMessage msg) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("ping resp, client address {} not authed", ctx.channel().remoteAddress()); ctx.close(); } } @Override public void processDisconnect(ChannelHandlerContext ctx) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("disconnect, client address {} not authed", ctx.channel().remoteAddress()); } onDisconnect(mqttSession); } protected void onDisconnect(MqttSessionKey mqttSessionKey) { } @Override public void processAuth(ChannelHandlerContext ctx, MqttMessage msg) throws Exception { MqttSessionKey mqttSession = ChannelUtils.getMqttSession(ctx.channel()); if (mqttSession == null) { log.error("auth, client address {} not authed", ctx.channel().remoteAddress()); ctx.close(); } }}可以看到，这里的AbstractProcessor主要是维护了MqttSessionKey，校验MqttSessionKey，并拦截publish中不支持的Qos2、Failure。同时，也影响了mqtt心跳请求。同样的，我们允许在onPublish、onSubscribe中抛出异常。
基于消息队列实现的mqtt网关的基础思想也比较简单，简而言之就是，有publish消息的时候向消息队列中生产消息。有订阅的时候就从消息队列中拉取消息。由此延伸出来，我们可能需要维护每个mqtt topic和producer、consumer的对应关系，因为像kafka、pulsar这些消息中间件的消费者都是区分topic的，片段通用代码如下:
protected final ReentrantReadWriteLock.ReadLock rLock; protected final ReentrantReadWriteLock.WriteLock wLock; protected final Map<MqttSessionKey, List<MqttTopicKey>> sessionProducerMap; protected final Map<MqttSessionKey, List<MqttTopicKey>> sessionConsumerMap; protected final Map<MqttTopicKey, P> producerMap; protected final Map<MqttTopicKey, C> consumerMap; public AbstractMqProcessor(MqttAuth mqttAuth) { super(mqttAuth); ReentrantReadWriteLock lock = new ReentrantReadWriteLock(); rLock = lock.readLock(); wLock = lock.writeLock(); this.sessionProducerMap = new HashMap<>(); this.sessionConsumerMap = new HashMap<>(); this.producerMap = new HashMap<>(); this.consumerMap = new HashMap<>(); } @Override protected void onConnect(MqttSessionKey mqttSessionKey) { wLock.lock(); try { sessionProducerMap.put(mqttSessionKey, new ArrayList<>()); sessionConsumerMap.put(mqttSessionKey, new ArrayList<>()); } finally { wLock.unlock(); } } @Override protected void onDisconnect(MqttSessionKey mqttSessionKey) { wLock.lock(); try { // find producers List<MqttTopicKey> produceTopicKeys = sessionProducerMap.get(mqttSessionKey); if (produceTopicKeys != null) { for (MqttTopicKey mqttTopicKey : produceTopicKeys) { P producer = producerMap.get(mqttTopicKey); if (producer != null) { ClosableUtils.close(producer); producerMap.remove(mqttTopicKey); } } } sessionProducerMap.remove(mqttSessionKey); List<MqttTopicKey> consumeTopicKeys = sessionConsumerMap.get(mqttSessionKey); if (consumeTopicKeys != null) { for (MqttTopicKey mqttTopicKey : consumeTopicKeys) { C consumer = consumerMap.get(mqttTopicKey); if (consumer != null) { ClosableUtils.close(consumer); consumerMap.remove(mqttTopicKey); } } } sessionConsumerMap.remove(mqttSessionKey); } finally { wLock.unlock(); } }}kafka processor实现由于kafka producer不区分topic，我们可以在kafka processor中复用producer，在将来单个kafka producer的性能到达上限时，我们可以将kafka producer扩展为kafka producer列表进行轮询处理，消费者由于mqtt协议可能针对每个订阅topic有不同的行为，不合适复用同一个消费者实例。我们在构造函数中启动KafkaProducer
private final KafkaProcessorConfig kafkaProcessorConfig; private final KafkaProducer<String, ByteBuffer> producer; public KafkaProcessor(MqttAuth mqttAuth, KafkaProcessorConfig kafkaProcessorConfig) { super(mqttAuth); this.kafkaProcessorConfig = kafkaProcessorConfig; this.producer = createProducer(); } protected KafkaProducer<String, ByteBuffer> createProducer() { Properties properties = new Properties(); properties.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, kafkaProcessorConfig.getBootstrapServers()); properties.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class); properties.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, ByteBufferSerializer.class); return new KafkaProducer<>(properties); }处理MqttPublish消息，MqttPublish消息包含如下几个关键参数
MqttQoS mqttQoS = publishMessage.fixedHeader().qosLevel();String topic = publishMessage.variableHeader().topicName();ByteBuffer byteBuffer = publishMessage.payload().nioBuffer();
其中
qos代表这条消息的质量级别，0没有任何保障，1代表至少一次，2代表恰好一次。当前仅支持qos0、qos1topicName就是topic的名称ByteBuffer就是消息的内容
根据topic、qos发送消息，代码如下
String topic = msg.variableHeader().topicName(); ProducerRecord<String, ByteBuffer> record = new ProducerRecord<>(topic, msg.payload().nioBuffer()); switch (msg.fixedHeader().qosLevel()) { case AT_MOST_ONCE -> producer.send(record, (metadata, exception) -> { if (exception != null) { log.error("mqttSessionKey {} send message to kafka error", mqttSessionKey, exception); return; } log.debug("mqttSessionKey {} send message to kafka success, topic {}, partition {}, offset {}", mqttSessionKey, metadata.topic(), metadata.partition(), metadata.offset()); }); case AT_LEAST_ONCE -> { try { RecordMetadata recordMetadata = producer.send(record).get(); log.info("mqttSessionKey {} send message to kafka success, topic {}, partition {}, offset {}", mqttSessionKey, recordMetadata.topic(), recordMetadata.partition(), recordMetadata.offset()); ctx.writeAndFlush(MqttMessageUtil.pubAckMessage(msg.variableHeader().packetId())); } catch (Exception e) { log.error("mqttSessionKey {} send message to kafka error", mqttSessionKey, e); } } case EXACTLY_ONCE, FAILURE -> throw new IllegalStateException( String.format("mqttSessionKey %s can not reach here", mqttSessionKey)); }处理订阅消息，我们暂时仅根据订阅的topic，创建topic进行消费即可，由于kafka原生客户端建议的消费代码模式如下
while (true) { ConsumerRecords<String, byte[]> records = consumer.poll(Duration.ofSeconds(1)); for (ConsumerRecord<String, byte[]> record : records) { // do logic }}我们需要切换到其他线程对consumer进行消息，书写一个KafkaConsumerListenerWrapper的wrapper，转换为listener异步消费模型
package io.github.protocol.mqtt.broker.processor;import lombok.extern.slf4j.Slf4j;import org.apache.kafka.clients.admin.AdminClient;import org.apache.kafka.clients.admin.AdminClientConfig;import org.apache.kafka.clients.admin.KafkaAdminClient;import org.apache.kafka.clients.admin.NewTopic;import org.apache.kafka.clients.admin.TopicDescription;import org.apache.kafka.clients.consumer.ConsumerConfig;import org.apache.kafka.clients.consumer.ConsumerRecord;import org.apache.kafka.clients.consumer.ConsumerRecords;import org.apache.kafka.clients.consumer.KafkaConsumer;import org.apache.kafka.common.errors.UnknownTopicOrPartitionException;import org.apache.kafka.common.errors.WakeupException;import org.apache.kafka.common.serialization.ByteArrayDeserializer;import org.apache.kafka.common.serialization.StringDeserializer;import java.time.Duration;import java.util.Collections;import java.util.Properties;import java.util.concurrent.ExecutionException;@Slf4jpublic class KafkaConsumerListenerWrapper implements AutoCloseable { private final AdminClient adminClient; private final KafkaConsumer<String, byte[]> consumer; public KafkaConsumerListenerWrapper(KafkaProcessorConfig config, String username) { Properties adminProperties = new Properties(); adminProperties.put(AdminClientConfig.BOOTSTRAP_SERVERS_CONFIG, config.getBootstrapServers()); this.adminClient = KafkaAdminClient.create(adminProperties); Properties properties = new Properties(); properties.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, config.getBootstrapServers()); properties.put(ConsumerConfig.GROUP_ID_CONFIG, username); properties.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class); properties.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, ByteArrayDeserializer.class); this.consumer = new KafkaConsumer<>(properties); } public void start(String topic, KafkaMessageListener listener) throws Exception { try { TopicDescription topicDescription = adminClient.describeTopics(Collections.singletonList(topic)) .values().get(topic).get(); log.info("topic info is {}", topicDescription); } catch (ExecutionException ee) { if (ee.getCause() instanceof UnknownTopicOrPartitionException) { log.info("topic {} not exist, create it", topic); adminClient.createTopics(Collections.singletonList(new NewTopic(topic, 1, (short) 1))); } else { log.error("find topic info {} error", topic, ee); } } catch (Exception e) { throw new IllegalStateException("find topic info error", e); } consumer.subscribe(Collections.singletonList(topic)); log.info("consumer topic {} start", topic); new Thread(() -> { try { while (true) { ConsumerRecords<String, byte[]> records = consumer.poll(Duration.ofSeconds(1)); for (ConsumerRecord<String, byte[]> record : records) { listener.messageReceived(record); } } } catch (WakeupException we) { consumer.close(); } catch (Exception e) { log.error("consumer topic {} consume error", topic, e); consumer.close(); } }).start(); Thread.sleep(5_000); } @Override public void close() throws Exception { log.info("wake up {} consumer", consumer); consumer.wakeup(); }} @Override protected void onSubscribe(ChannelHandlerContext ctx, MqttSessionKey mqttSessionKey, MqttSubscribePayload subscribePayload) throws Exception { for (MqttTopicSubscription topicSubscription : subscribePayload.topicSubscriptions()) { KafkaConsumerListenerWrapper consumer = createConsumer(mqttSessionKey, topicSubscription.topicName()); subscribe(ctx, consumer, topicSubscription.topicName()); } } private KafkaConsumerListenerWrapper createConsumer(MqttSessionKey mqttSessionKey, String topic) { MqttTopicKey mqttTopicKey = new MqttTopicKey(); mqttTopicKey.setTopic(topic); mqttTopicKey.setMqttSessionKey(mqttSessionKey); wLock.lock(); try { KafkaConsumerListenerWrapper consumer = consumerMap.get(mqttTopicKey); if (consumer == null) { consumer = new KafkaConsumerListenerWrapper(kafkaProcessorConfig, mqttSessionKey.getUsername()); sessionConsumerMap.compute(mqttSessionKey, (mqttSessionKey1, mqttTopicKeys) -> { if (mqttTopicKeys == null) { mqttTopicKeys = new ArrayList<>(); } mqttTopicKeys.add(mqttTopicKey); return mqttTopicKeys; }); consumerMap.put(mqttTopicKey, consumer); } return consumer; } finally { wLock.unlock(); } } protected void subscribe(ChannelHandlerContext ctx, KafkaConsumerListenerWrapper consumer, String topic) throws Exception { BoundInt boundInt = new BoundInt(65535); consumer.start(topic, record -> { log.info("receive message from kafka, topic {}, partition {}, offset {}", record.topic(), record.partition(), record.offset()); MqttPublishMessage mqttPublishMessage = MqttMessageUtil.publishMessage( MqttQoS.AT_LEAST_ONCE, topic, boundInt.nextVal(), record.value()); ctx.writeAndFlush(mqttPublishMessage); }); }在上述的代码中，有一个需要通篇注意的点：日志打印的时候，注意要将关键的信息携带，比如：topic、mqtt username、mqtt clientId等，在写demo的时候没有感觉，但是海量请求下需要定位问题的时候，就知道这些信息的关键之处了。
使用BountInt这个简单的工具类来生成从0~65535的packageId，满足协议的要求
pulsar processor实现
pulsar相比kafka来说，更适合作为mqtt协议的代理。原因有如下几点：
pulsar支持百万topic、topic实现更轻量pulsar原生支持listener的消费模式，不需要每个消费者启动一个线程pulsar支持share的消费模式，消费模式更灵活pulsar消费者的subscribe可确保成功创建订阅，相比kafka的消费者没有这样的语义保障
protected final ReentrantReadWriteLock.ReadLock rLock; protected final ReentrantReadWriteLock.WriteLock wLock; protected final Map<MqttSessionKey, List<MqttTopicKey>> sessionProducerMap; protected final Map<MqttSessionKey, List<MqttTopicKey>> sessionConsumerMap; protected final Map<MqttTopicKey, Producer<byte[]>> producerMap; protected final Map<MqttTopicKey, Consumer<byte[]>> consumerMap; private final PulsarProcessorConfig pulsarProcessorConfig; private final PulsarAdmin pulsarAdmin; private final PulsarClient pulsarClient; public PulsarProcessor(MqttAuth mqttAuth, PulsarProcessorConfig pulsarProcessorConfig) { super(mqttAuth); ReentrantReadWriteLock lock = new ReentrantReadWriteLock(); rLock = lock.readLock(); wLock = lock.writeLock(); this.sessionProducerMap = new HashMap<>(); this.sessionConsumerMap = new HashMap<>(); this.producerMap = new HashMap<>(); this.consumerMap = new HashMap<>(); this.pulsarProcessorConfig = pulsarProcessorConfig; try { this.pulsarAdmin = PulsarAdmin.builder() .serviceHttpUrl(pulsarProcessorConfig.getHttpUrl()) .build(); this.pulsarClient = PulsarClient.builder() .serviceUrl(pulsarProcessorConfig.getServiceUrl()) .build(); } catch (Exception e) { throw new IllegalStateException("Failed to create pulsar client", e); } }处理publish消息
@Override protected void onPublish(ChannelHandlerContext ctx, MqttSessionKey mqttSessionKey, MqttPublishMessage msg) throws Exception { String topic = msg.variableHeader().topicName(); Producer<byte[]> producer = getOrCreateProducer(mqttSessionKey, topic); int len = msg.payload().readableBytes(); byte[] messageBytes = new byte[len]; msg.payload().getBytes(msg.payload().readerIndex(), messageBytes); switch (msg.fixedHeader().qosLevel()) { case AT_MOST_ONCE -> producer.sendAsync(messageBytes). thenAccept(messageId -> log.info("clientId [{}]," + " username [{}]. send message to pulsar success messageId: {}", mqttSessionKey.getClientId(), mqttSessionKey.getUsername(), messageId)) .exceptionally((e) -> { log.error("clientId [{}], username [{}]. send message to pulsar fail: ", mqttSessionKey.getClientId(), mqttSessionKey.getUsername(), e); return null; }); case AT_LEAST_ONCE -> { try { MessageId messageId = producer.send(messageBytes); MqttFixedHeader fixedHeader = new MqttFixedHeader(MqttMessageType.PUBACK, false, MqttQoS.AT_MOST_ONCE, false, 0); MqttPubAckMessage pubAckMessage = (MqttPubAckMessage) MqttMessageFactory.newMessage(fixedHeader, MqttMessageIdVariableHeader.from(msg.variableHeader().packetId()), null); log.info("clientId [{}], username [{}]. send pulsar success. messageId: {}", mqttSessionKey.getClientId(), mqttSessionKey.getUsername(), messageId); ctx.writeAndFlush(pubAckMessage); } catch (PulsarClientException e) { log.error("clientId [{}], username [{}]. send pulsar error: {}", mqttSessionKey.getClientId(), mqttSessionKey.getUsername(), e.getMessage()); } } case EXACTLY_ONCE, FAILURE -> throw new IllegalStateException( String.format("mqttSessionKey %s can not reach here", mqttSessionKey)); } } private Producer<byte[]> getOrCreateProducer(MqttSessionKey mqttSessionKey, String topic) throws Exception { MqttTopicKey mqttTopicKey = new MqttTopicKey(); mqttTopicKey.setTopic(topic); mqttTopicKey.setMqttSessionKey(mqttSessionKey); rLock.lock(); try { Producer<byte[]> producer = producerMap.get(mqttTopicKey); if (producer != null) { return producer; } } finally { rLock.unlock(); } wLock.lock(); try { Producer<byte[]> producer = producerMap.get(mqttTopicKey); if (producer == null) { producer = createProducer(topic); sessionProducerMap.compute(mqttSessionKey, (mqttSessionKey1, mqttTopicKeys) -> { if (mqttTopicKeys == null) { mqttTopicKeys = new ArrayList<>(); } mqttTopicKeys.add(mqttTopicKey); return mqttTopicKeys; }); producerMap.put(mqttTopicKey, producer); } return producer; } finally { wLock.unlock(); } } protected Producer<byte[]> createProducer(String topic) throws Exception { return pulsarClient.newProducer(Schema.BYTES).topic(topic).create(); }处理subscribe消息
@Override protected void onSubscribe(ChannelHandlerContext ctx, MqttSessionKey mqttSessionKey, MqttSubscribePayload subscribePayload) throws Exception { for (MqttTopicSubscription topicSubscription : subscribePayload.topicSubscriptions()) { subscribe(ctx, mqttSessionKey, topicSubscription.topicName()); } } protected void subscribe(ChannelHandlerContext ctx, MqttSessionKey mqttSessionKey, String topic) throws Exception { MqttTopicKey mqttTopicKey = new MqttTopicKey(); mqttTopicKey.setTopic(topic); mqttTopicKey.setMqttSessionKey(mqttSessionKey); wLock.lock(); try { Consumer<byte[]> consumer = consumerMap.get(mqttTopicKey); if (consumer == null) { consumer = createConsumer(ctx, mqttSessionKey.getUsername(), topic); sessionConsumerMap.compute(mqttSessionKey, (mqttSessionKey1, mqttTopicKeys) -> { if (mqttTopicKeys == null) { mqttTopicKeys = new ArrayList<>(); } mqttTopicKeys.add(mqttTopicKey); return mqttTopicKeys; }); consumerMap.put(mqttTopicKey, consumer); } } finally { wLock.unlock(); } } protected Consumer<byte[]> createConsumer(ChannelHandlerContext ctx, String username, String topic) throws Exception { BoundInt boundInt = new BoundInt(65535); try { PartitionedTopicStats partitionedStats = pulsarAdmin.topics().getPartitionedStats(topic, false); log.info("topic {} partitioned stats {}", topic, partitionedStats); } catch (PulsarAdminException.NotFoundException nfe) { log.info("topic {} not found", topic); pulsarAdmin.topics().createPartitionedTopic(topic, 1); } return pulsarClient.newConsumer(Schema.BYTES).topic(topic) .messageListener((consumer, msg) -> { log.info("receive message from pulsar, topic {}, message {}", topic, msg.getMessageId()); MqttPublishMessage mqttPublishMessage = MqttMessageUtil.publishMessage( MqttQoS.AT_LEAST_ONCE, topic, boundInt.nextVal(), msg.getData()); ctx.writeAndFlush(mqttPublishMessage); }) .subscriptionName(username).subscribe(); }测试用例鲁邦的软件应该有相应的测试用例，这里简单写了两个基础的pubsub用例，实际的production ready的项目，测试用例会更加复杂，涵盖各种异常的场景。有句话说的很好 ”单元测试是对开发人员的即时激励“，我也很认同这句话
kafka启动kafka测试broker
我们可以通过embedded-kafka-java这个项目来启动用做单元测试的kafka broker。通过如下的group引入依赖
<dependency> <groupId>io.github.embedded-middleware</groupId> <artifactId>embedded-kafka-core</artifactId> <version>0.0.2</version> <scope>test</scope> </dependency>
我们就可以通过如下的代码启动基于kafka的mqtt broker
@Slf4jpublic class MqttKafkaTestUtil { public static MqttServer setupMqttKafka() throws Exception { EmbeddedKafkaServer embeddedKafkaServer = new EmbeddedKafkaServer(); new Thread(() -> { try { embeddedKafkaServer.start(); } catch (Exception e) { log.error("kafka broker started exception ", e); } }).start(); Thread.sleep(5_000); MqttServerConfig mqttServerConfig = new MqttServerConfig(); mqttServerConfig.setPort(0); mqttServerConfig.setProcessorType(ProcessorType.KAFKA); KafkaProcessorConfig kafkaProcessorConfig = new KafkaProcessorConfig(); kafkaProcessorConfig.setBootstrapServers(String.format("localhost:%d", embeddedKafkaServer.getKafkaPort())); mqttServerConfig.setKafkaProcessorConfig(kafkaProcessorConfig); MqttServer mqttServer = new MqttServer(mqttServerConfig); new Thread(() -> { try { mqttServer.start(); } catch (Exception e) { log.error("mqsar broker started exception ", e); } }).start(); Thread.sleep(5000L); return mqttServer; }}kafka端到端测试用例，比较简单，通过mqtt client publish一条消息，然后消费出来
@Log4j2public class MqttKafkaPubSubTest { @Test public void pubSubTest() throws Exception { MqttServer mqttServer = MqttKafkaTestUtil.setupMqttKafka(); String topic = UUID.randomUUID().toString(); String content = "test-msg"; String broker = String.format("tcp://localhost:%d", mqttServer.getPort()); String clientId = UUID.randomUUID().toString(); MemoryPersistence persistence = new MemoryPersistence(); MqttClient sampleClient = new MqttClient(broker, clientId, persistence); MqttConnectOptions connOpts = new MqttConnectOptions(); connOpts.setUserName(UUID.randomUUID().toString()); connOpts.setPassword(UUID.randomUUID().toString().toCharArray()); connOpts.setCleanSession(true); log.info("Mqtt connecting to broker"); sampleClient.connect(connOpts); CompletableFuture<String> future = new CompletableFuture<>(); log.info("Mqtt subscribing"); sampleClient.subscribe(topic, (s, mqttMessage) -> { log.info("messageArrived"); future.complete(mqttMessage.toString()); }); log.info("Mqtt subscribed"); MqttMessage message = new MqttMessage(content.getBytes()); message.setQos(1); log.info("Mqtt message publishing"); sampleClient.publish(topic, message); log.info("Mqtt message published"); TimeUnit.SECONDS.sleep(3); sampleClient.disconnect(); String msg = future.get(5, TimeUnit.SECONDS); Assertions.assertEquals(content, msg); }}pulsar我们可以通过embedded-pulsar-java这个项目来启动用做单元测试的pulsar broker。通过如下的group引入依赖
<dependency> <groupId>io.github.embedded-middleware</groupId> <artifactId>embedded-pulsar-core</artifactId> <version>0.0.2</version> <scope>test</scope> </dependency>
我们就可以通过如下的代码启动基于pulsar的mqtt broker
@Slf4jpublic class MqttPulsarTestUtil { public static MqttServer setupMqttPulsar() throws Exception { EmbeddedPulsarServer embeddedPulsarServer = new EmbeddedPulsarServer(); embeddedPulsarServer.start(); MqttServerConfig mqttServerConfig = new MqttServerConfig(); mqttServerConfig.setPort(0); mqttServerConfig.setProcessorType(ProcessorType.PULSAR); PulsarProcessorConfig pulsarProcessorConfig = new PulsarProcessorConfig(); pulsarProcessorConfig.setHttpUrl(String.format(";, embeddedPulsarServer.getWebPort())); pulsarProcessorConfig.setServiceUrl(String.format("pulsar://localhost:%d", embeddedPulsarServer.getTcpPort())); mqttServerConfig.setPulsarProcessorConfig(pulsarProcessorConfig); MqttServer mqttServer = new MqttServer(mqttServerConfig); new Thread(() -> { try { mqttServer.start(); } catch (Exception e) { log.error("mqsar broker started exception ", e); } }).start(); Thread.sleep(5000L); return mqttServer; }}pulsar端到端测试用例，比较简单，通过mqtt client publish一条消息，然后消费出来
@Log4j2public class MqttPulsarPubSubTest { @Test public void pubSubTest() throws Exception { MqttServer mqttServer = MqttPulsarTestUtil.setupMqttPulsar(); String topic = UUID.randomUUID().toString(); String content = "test-msg"; String broker = String.format("tcp://localhost:%d", mqttServer.getPort()); String clientId = UUID.randomUUID().toString(); MemoryPersistence persistence = new MemoryPersistence(); MqttClient sampleClient = new MqttClient(broker, clientId, persistence); MqttConnectOptions connOpts = new MqttConnectOptions(); connOpts.setUserName(UUID.randomUUID().toString()); connOpts.setPassword(UUID.randomUUID().toString().toCharArray()); connOpts.setCleanSession(true); log.info("Mqtt connecting to broker"); sampleClient.connect(connOpts); CompletableFuture<String> future = new CompletableFuture<>(); log.info("Mqtt subscribing"); sampleClient.subscribe(topic, (s, mqttMessage) -> { log.info("messageArrived"); future.complete(mqttMessage.toString()); }); log.info("Mqtt subscribed"); MqttMessage message = new MqttMessage(content.getBytes()); message.setQos(1); log.info("Mqtt message publishing"); sampleClient.publish(topic, message); log.info("Mqtt message published"); TimeUnit.SECONDS.sleep(3); sampleClient.disconnect(); String msg = future.get(5, TimeUnit.SECONDS); Assertions.assertEquals(content, msg); }}性能优化这里我们简单描述几个性能优化点，像一些调整线程数、buffer大小这类的参数调整就不在这里赘述了，这些需要具体的性能压测来决定参数的设置。
在linux上使用Epoll网络模型
public class EventLoopUtil { /** * @return an EventLoopGroup suitable for the current platform */ public static EventLoopGroup newEventLoopGroup(int nThreads, ThreadFactory threadFactory) { if (Epoll.isAvailable()) { return new EpollEventLoopGroup(nThreads, threadFactory); } else { return new NioEventLoopGroup(nThreads, threadFactory); } } public static Class<? extends ServerSocketChannel> getServerSocketChannelClass(EventLoopGroup eventLoopGroup) { if (eventLoopGroup instanceof EpollEventLoopGroup) { return EpollServerSocketChannel.class; } else { return NioServerSocketChannel.class; } }}通过Epollo.isAvailable，以及在指定channel类型的时候通过判断group的类型选择对应的channel类型
EventLoopGroup acceptorGroup = EventLoopUtil.newEventLoopGroup(1, new DefaultThreadFactory("mqtt-acceptor")); EventLoopGroup workerGroup = EventLoopUtil.newEventLoopGroup(1, new DefaultThreadFactory("mqtt-worker")); b.group(acceptorGroup, workerGroup) // key point .channel(EventLoopUtil.getServerSocketChannelClass(workerGroup)) .option(ChannelOption.SO_BACKLOG, 100) .handler(new LoggingHandler(LogLevel.INFO)) .childHandler(new ChannelInitializer<SocketChannel>() { @Override public void initChannel(SocketChannel ch) throws Exception { ChannelPipeline p = ch.pipeline(); // decoder p.addLast(new MqttDecoder()); p.addLast(MqttEncoder.INSTANCE); p.addLast(new MqttHandler(processor(mqttServerConfig))); } });关闭tcp keepalive由于mqtt协议本身就有心跳机制，所以可以关闭tcp的keepalive，依赖mqtt协议层的心跳即可，节约海量连接下的性能。配置ChannelOption.SO_KEEPALIVE为false即可
.option(ChannelOption.SO_KEEPALIVE, false)超时时间调短
默认情况下，无论是单元测试中mqtt，还是pulsar producer和kafka producer的生产超时时间，都相对较长（一般为30s），如果在内网环境部署，可以将超时时间调整到5s。来避免无意义的超时等待
使用多个KafkaProducer来优化性能
单个KafkaProducer会达到tcp链路带宽的瓶颈，当有海量请求，而延时在kafka生产比较突出的情况下，可以考虑启动多个KafkaProducer。并根据mqtt协议的特点（链路多，单个链路上qps不高），用mqttSessionKey的哈希值来决定使用那个KafkaProducer发送消息
在KafkaProcessorConfig中添加如下配置，生产者个数，默认为1
private int producerNum = 1;
在初始化的时候，初始化Producer数组，而不是单个Producer
this.producerArray = new KafkaProducer[kafkaProcessorConfig.getProducerNum()]; for (int i = 0; i < kafkaProcessorConfig.getProducerNum(); i++) { producerArray[i] = createProducer(); }封装一个方法来获取producer
private Producer<String, ByteBuffer> getProducer(MqttSessionKey mqttSessionKey) { return producerArray[Math.abs(mqttSessionKey.hashCode() % kafkaProcessorConfig.getProducerNum())]; }结语本文的代码均已上传到github。我们这里仅仅只实现了基础的mqtt 连接、发布、订阅功能，甚至不支持暂停、取消订阅。想要实现一个成熟商用的mqtt网关，我们还需要用户隔离、对协议的更多支持、可靠性、可运维、流控、安全等能力。如有商用生产级别的mqtt需求，又无法快速构筑成熟的mqtt网关的，可以选择华为云IoTDA服务，提供稳定可靠的mqtt服务，支持海量设备连接上云、设备和云端消息双向通信能力。
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