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
java
<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。
java
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
java
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
java
@Setter
@Getter
public class KafkaProcessorConfig {
private String bootstrapServers = "localhost:9092";
public KafkaProcessorConfig() {
}
}
java
@Setter
@Getter
public class PulsarProcessorConfig {
private String httpUrl = "http://localhost:8080";
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
java
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;
@Slf4j
public 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
java
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
java
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;
@Log4j2
public 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
java
package com.github.shoothzj.mqtt;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import lombok.extern.slf4j.Slf4j;
@Slf4j
public 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
java
@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
java
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;
@Slf4j
public 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
java
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
java
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
java
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;
@Slf4j
public 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:
java
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
java
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、qos1
- topicName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
java
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
java
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;
@Slf4j
public 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();
}
}
java
@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
java
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
java
@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
java
@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
@Slf4j
public 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
java
@Log4j2
public 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
java
<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
java
@Slf4j
public 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("http://localhost:%d", 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
java
@Log4j2
public 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
java
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
java
EventLoopGroup acceptorGroup = EventLoopUtil.newEventLoopGroup(1,
new DefaultThreadFactory("mqtt-acceptor"));
EventLoopGroup workerGroup = EventLoopUtil.newEventLoopGroup(1,
new DefaultThreadFactory("mqtt-worker"));
java
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
java
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。