MQTT——编写连接报文

笔者在上一章对连接报文进行了相关的讲解。这一章笔者想写一个连接报文的例子来加深理解。本来这一章也应该在上一章出现的。可是笔者怕太长了。不好方便阅。所以决定分俩章来。正如笔者上一章所讲的。笔者会用Netty通信框架进行编写。主要因为Netty已经为我们集成了相关MQTT功能。

开发环境

开发工具：intellij idea.(以前我一直在eclipse。最近新版的老报错。所以就放弃了)

Netty包：netty-all-4.1.16.Final.jar。下载网站：http://netty.io/downloads.html

JDK：JAVA 8

第三包：commons-lang3-3.6.jar。下载网站：http://commons.apache.org/proper/commons-lang/download_lang.cgi

MQTT编写

在这里笔者并不打包把客户端的代码一起编写出。事实上关于客户端的开源的代码是非常多的。笔者这里只会略微的编写一下服务端的代码。当然这里代码只是为方更了解MQTT协议。并非企业级的编蜜枣这一点希望读者见谅。为了实现连接报文。笔者定义了三个类。

Main类：用于启动服务。

BrokerHandler类：处理接受来的信息。

BrokerSessionHelper：用于发送信息给客户。

Main类的源码

 public static void main(String[] args) throws Exception  {
         EventLoopGroup bossGroup = new NioEventLoopGroup();
         EventLoopGroup workerGroup = new NioEventLoopGroup();

         Runtime.getRuntime().addShutdownHook(new Thread() {
             public void run() {
                 workerGroup.shutdownGracefully();
                 bossGroup.shutdownGracefully();
             }
         });

         ServerBootstrap b = new ServerBootstrap();
         b.group(bossGroup, workerGroup)
                 .channel(NioServerSocketChannel.class)
                 .handler(new LoggingHandler(LogLevel.INFO))
17                 .childHandler(new ChannelInitializer<SocketChannel>() {
18                     @Override
19                     public void initChannel(SocketChannel ch) throws Exception {
20
21                         ChannelPipeline p = ch.pipeline();
22
23                         p.addFirst("idleHandler", new IdleStateHandler(0, 0, 120));
24                         p.addLast("encoder", MqttEncoder.INSTANCE);
25                         p.addLast("decoder", new MqttDecoder());
26                         p.addLast("logicHandler", new BrokerHandler(65535));
27
28                     }
                 })
                 .option(ChannelOption.SO_BACKLOG, 511)
                 .childOption(ChannelOption.SO_KEEPALIVE, true);

         ChannelFuture f = b.bind("0.0.0.0", 1883).sync();

         f.channel().closeFuture().sync();
     }

上面的1、2俩行表是Netty里面俩个线程组。事实上也就是Reactor线程组。bossGroup 用于处理接受来自客户端的连接。workerGroup 用于处理接受客户端的读取信息。13行的ServerBootstrap可以理解为启动服务的一个引导类。主要关键是他的group方法。这样子就可以把俩个线程组关系在一起了。重点就在17行这里。childHandler用于处理IO事件。比如读取客户端进行。然后自己编码。你们可以看到24行的MqttEncoder.INSTANCE和25行的MqttDecoder吧。他们就是用于处理MQTT协议传来的信息进行处理。而26行BrokerHandler类就是笔者来处理每一个报文对应的响应。笔者就不在过多的说了。如果你们不懂的话，可以去看一下Netty框架的知识在过看的话会比较好。

BrokerHandler类的源码

 public class BrokerHandler extends SimpleChannelInboundHandler<MqttMessage> {
     private MqttVersion version;
     private String clientId;
     private String userName;
     private String brokerId;
     private boolean connected;
     private boolean cleanSession;
     private int keepAlive;
     private int keepAliveMax;
     private MqttPublishMessage willMessage;

     public BrokerHandler(int keepAliveMax) {

         this.keepAliveMax = keepAliveMax;
     }

     @Override
     @SuppressWarnings("ThrowableResultOfMethodCallIgnored")
     protected void channelRead0(ChannelHandlerContext ctx, MqttMessage msg) throws Exception {

         if (msg.decoderResult().isFailure()) {

             Throwable cause = msg.decoderResult().cause();

             if (cause instanceof MqttUnacceptableProtocolVersionException) {

                 BrokerSessionHelper.sendMessage(
                         ctx,
                         MqttMessageFactory.newMessage(
                                 new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0),
                                 new MqttConnAckVariableHeader(MqttConnectReturnCode.CONNECTION_REFUSED_UNACCEPTABLE_PROTOCOL_VERSION, false),
                                 null),
                         "INVALID",
                         null,
                         true);

             } else if (cause instanceof MqttIdentifierRejectedException) {

                 BrokerSessionHelper.sendMessage(
                         ctx,
                         MqttMessageFactory.newMessage(
                                 new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0),
                                 new MqttConnAckVariableHeader(MqttConnectReturnCode.CONNECTION_REFUSED_IDENTIFIER_REJECTED, false),
                                 null),
                         "INVALID",
                         null,
                         true);
             }

             ctx.close();

             return;
         }

         switch (msg.fixedHeader().messageType()) {
             case CONNECT:
                 onConnect(ctx, (MqttConnectMessage) msg);
                 break;
             case PUBLISH:
                 onPublish(ctx, (MqttPublishMessage) msg);
                 break;
             case PUBACK:
                 onPubAck(ctx, msg);
                 break;
             case PUBREC:
                 onPubRec(ctx, msg);
                 break;
             case PUBREL:
                 onPubRel(ctx, msg);
                 break;
             case PUBCOMP:
                 onPubComp(ctx, msg);
                 break;
             case SUBSCRIBE:
                 onSubscribe(ctx, (MqttSubscribeMessage) msg);
                 break;
             case UNSUBSCRIBE:
                 onUnsubscribe(ctx, (MqttUnsubscribeMessage) msg);
                 break;
             case PINGREQ:
                 onPingReq(ctx);
                 break;
             case DISCONNECT:
                 onDisconnect(ctx);
                 break;
         }

     }

     private void onConnect(ChannelHandlerContext ctx, MqttConnectMessage msg) {

         this.version = MqttVersion.fromProtocolNameAndLevel(msg.variableHeader().name(), (byte) msg.variableHeader().version());
         this.clientId = msg.payload().clientIdentifier();
         this.cleanSession = msg.variableHeader().isCleanSession();

         if (msg.variableHeader().keepAliveTimeSeconds() > 0 && msg.variableHeader().keepAliveTimeSeconds() <= this.keepAliveMax) {
             this.keepAlive = msg.variableHeader().keepAliveTimeSeconds();
         }

         //MQTT 3.1之后可能存在为空的客户ID。所以要进行处理。如果客户ID是空，而且还在保存处理相关的信息。这样子是不行。
         //必须有客户ID我们才能存保相关信息。
         if (StringUtils.isBlank(this.clientId)) {
             if (!this.cleanSession) {

                 BrokerSessionHelper.sendMessage(
                         ctx,
                         MqttMessageFactory.newMessage(
                                 new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0),
                                 new MqttConnAckVariableHeader(MqttConnectReturnCode.CONNECTION_REFUSED_IDENTIFIER_REJECTED, false),
                                 null),
                         "INVALID",
                         null,
                         true);

                 ctx.close();

                 return;

             } else {
                 this.clientId =  java.util.UUID.randomUUID().toString();
             }
         }

         //有可能发送俩次的连接包。如果已经存在连接就是关闭当前的连接。
         if (this.connected) {
             ctx.close();
             return;
         }

         boolean userNameFlag = msg.variableHeader().hasUserName();
         boolean passwordFlag = msg.variableHeader().hasPassword();
         this.userName = msg.payload().userName();

         String password = "" ;
         if( msg.payload().passwordInBytes() != null  && msg.payload().passwordInBytes().length > 0)
             password =   new String(msg.payload().passwordInBytes());

         boolean mistake = false;

         //如果有用户名标示，那么就必须有密码标示。
         //当有用户名标的时候，用户不能为空。
         //当有密码标示的时候，密码不能为空。
         if (userNameFlag) {
             if (StringUtils.isBlank(this.userName))
                 mistake = true;
         } else {
             if (StringUtils.isNotBlank(this.userName) || passwordFlag) mistake = true;
         }

         if (passwordFlag) {

             if (StringUtils.isBlank(password)) mistake = true;
         } else {
             if (StringUtils.isNotBlank(password)) mistake = true;
         }

         if (mistake) {
             BrokerSessionHelper.sendMessage(
                     ctx,
                     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),
                     this.clientId,
                     null,
                     true);
             ctx.close();
             return;
         }

         BrokerSessionHelper.sendMessage(
                 ctx,
                 MqttMessageFactory.newMessage(
                         new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0),
                         new MqttConnAckVariableHeader(MqttConnectReturnCode.CONNECTION_ACCEPTED, !this.cleanSession),
                         null),
                 this.clientId,
                 null,
                 true);

         ChannelHandlerContext lastSession = BrokerSessionHelper.removeSession(this.clientId);
         if (lastSession != null) {
             lastSession.close();
         }

         String willTopic = msg.payload().willTopic();
         String willMessage = "";
         if(msg.payload().willMessageInBytes() != null && msg.payload().willMessageInBytes().length > 0)
             willMessage =  new String(msg.payload().willMessageInBytes());

         if (msg.variableHeader().isWillFlag() && StringUtils.isNotEmpty(willTopic) && StringUtils.isNotEmpty(willMessage)) {

             this.willMessage = (MqttPublishMessage) MqttMessageFactory.newMessage(
                     new MqttFixedHeader(MqttMessageType.PUBLISH, false, MqttQoS.valueOf(msg.variableHeader().willQos()), msg.variableHeader().isWillRetain(), 0),
                     new MqttPublishVariableHeader(willTopic, 0),
                     Unpooled.wrappedBuffer(willMessage.getBytes())
             );
         }

         this.connected = true;
         BrokerSessionHelper.saveSession(this.clientId, ctx);
     }

     private void onSubscribe(ChannelHandlerContext ctx, MqttSubscribeMessage msg) {
     }

     private void onUnsubscribe(ChannelHandlerContext ctx, MqttUnsubscribeMessage msg) {
     }

     private void onPingReq(ChannelHandlerContext ctx) {
     }

     private void onDisconnect(ChannelHandlerContext ctx) {

         if (!this.connected) {
             ctx.close();
             return;
         }

         BrokerSessionHelper.removeSession(this.clientId, ctx);

         this.willMessage = null;

         this.connected = false;

         ctx.close();

     }

     private void onPubComp(ChannelHandlerContext ctx, MqttMessage msg) {

     }

     private void onPubRel(ChannelHandlerContext ctx, MqttMessage msg) {
     }

     private void onPubRec(ChannelHandlerContext ctx, MqttMessage msg) {
     }

     private void onPubAck(ChannelHandlerContext ctx, MqttMessage msg) {
     }

     private void onPublish(ChannelHandlerContext ctx, MqttPublishMessage msg) {
     }
 }

BrokerHandler类

19 行中的channelRead0方法中有俩个参数。一个为ChannelHandlerContext（通首的上下文）。一个是MqttMessage（客户端来的MQTT报文）。我们接下来动作都是跟MqttMessage来做相关的逻辑处理。这一点从55行就可以看出来。我们可以判断他是什么类型的报文。笔者这里只实现连接报文的处理。21行的代码msg.decoderResult().isFailure()是用来判断传过来的报文是不是正确的。事实上是Netty框架帮我们做了第一层的验证。23行就是获得发生的异常。

从第99行onConnect方法开始就是处理连接报文的处理。笔者这里只做下面相关的处理。

1.验证保持连接(Keep Alive)的有效性。代码如下

      if (msg.variableHeader().keepAliveTimeSeconds() > 0 && msg.variableHeader().keepAliveTimeSeconds() <= this.keepAliveMax) {
             this.keepAlive = msg.variableHeader().keepAliveTimeSeconds();
         }

2.验证客户ID为空的时候，还要求保存会话状。这是不合理的。因为我的会话状态是跟根客户ID来保存。否则的话，随更给一个。反正后面还是清除会话状态。那么为什么会有空的呢？主要是在MQTT 3.1.1里面指出客户ID可以为空了。

  if (StringUtils.isBlank(this.clientId)) {
             if (!this.cleanSession) {

                 BrokerSessionHelper.sendMessage(
                         ctx,
                         MqttMessageFactory.newMessage(
                                 new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0),
                                 new MqttConnAckVariableHeader(MqttConnectReturnCode.CONNECTION_REFUSED_IDENTIFIER_REJECTED, false),
                                 null),
                         "INVALID",
                         null,
                         true);

                 ctx.close();

                 return;

             } else {
                 this.clientId =  java.util.UUID.randomUUID().toString();
             }
         }

3.判断是否是第二次连接报文。如果是的话，就要断开了。

  if (this.connected) {
             ctx.close();
             return;
         }

4.判断用户和密码是否合法性。比如上一章出讲到的只有在用户名标志为1的时候，密码才可以出现。

   boolean userNameFlag = msg.variableHeader().hasUserName();
        boolean passwordFlag = msg.variableHeader().hasPassword();
        this.userName = msg.payload().userName();

        String password = "" ;
        if( msg.payload().passwordInBytes() != null  && msg.payload().passwordInBytes().length > 0)
            password =   new String(msg.payload().passwordInBytes());

        boolean mistake = false;

        //如果有用户名标示，那么就必须有密码标示。
        //当有用户名标的时候，用户不能为空。
        //当有密码标示的时候，密码不能为空。
        if (userNameFlag) {
            if (StringUtils.isBlank(this.userName))
                mistake = true;
        } else {
            if (StringUtils.isNotBlank(this.userName) || passwordFlag) mistake = true;
        }

        if (passwordFlag) {

            if (StringUtils.isBlank(password)) mistake = true;
        } else {
            if (StringUtils.isNotBlank(password)) mistake = true;
        }

        if (mistake) {
            BrokerSessionHelper.sendMessage(
                    ctx,
                    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),
                    this.clientId,
                    null,
                    true);
            ctx.close();
            return;
        }

6.接受客户端了。事实上笔者还有很多没有做的事情。比如保存会状态的处理。因为主要是为学习所以就没有讲出来。在加上会话状态存保就要思考保存在哪里。同时还有一个就是用户的合法性验证没有处理。

   BrokerSessionHelper.sendMessage(
                 ctx,
                 MqttMessageFactory.newMessage(
                         new MqttFixedHeader(MqttMessageType.CONNACK, false, MqttQoS.AT_MOST_ONCE, false, 0),
                         new MqttConnAckVariableHeader(MqttConnectReturnCode.CONNECTION_ACCEPTED, !this.cleanSession),
                         null),
                 this.clientId,
                 null,
                 true);

7.处理当前报文的遗嘱。

    String willTopic = msg.payload().willTopic();
         String willMessage = "";
         if(msg.payload().willMessageInBytes() != null && msg.payload().willMessageInBytes().length > 0)
             willMessage =  new String(msg.payload().willMessageInBytes());

         if (msg.variableHeader().isWillFlag() && StringUtils.isNotEmpty(willTopic) && StringUtils.isNotEmpty(willMessage)) {

             this.willMessage = (MqttPublishMessage) MqttMessageFactory.newMessage(
                     new MqttFixedHeader(MqttMessageType.PUBLISH, false, MqttQoS.valueOf(msg.variableHeader().willQos()), msg.variableHeader().isWillRetain(), 0),
                     new MqttPublishVariableHeader(willTopic, 0),
                     Unpooled.wrappedBuffer(willMessage.getBytes())
             );
         }

如果你看到这个类的最后代码的时候，会发现笔者也写了相关的ACNNACK响应。他的内容比较简单。大家看代码吧。

 private void onDisconnect(ChannelHandlerContext ctx) {

         if (!this.connected) {
             ctx.close();
             return;
         }

         BrokerSessionHelper.removeSession(this.clientId, ctx);

         this.willMessage = null;

         this.connected = false;

         ctx.close();

     }

BrokerSessionHelper类的源码

public class BrokerSessionHelper {

    private static final Map<String, ChannelHandlerContext> sessionRepository = new ConcurrentHashMap<>();

    public static void saveSession(String clientId, ChannelHandlerContext session) {
        sessionRepository.put(clientId, session);
    }

    public static ChannelHandlerContext getSession(String clientId) {

        return sessionRepository.get(clientId);
    }

    public static ChannelHandlerContext removeSession(String clientId) {

        return sessionRepository.remove(clientId);
    }

    public  static boolean removeSession(String clientId, ChannelHandlerContext session) {
        return sessionRepository.remove(clientId, session);
    }

    /**
     * 发送信息
     *
     * @param msg
     * @param clientId
     * @param packetId
     * @param flush
     */
    public static void sendMessage(MqttMessage msg, String clientId, Integer packetId, boolean flush) {
        ChannelHandlerContext ctx = getSession(clientId);
        if (ctx == null) {
            String pid = packetId == null || packetId <= 0 ? "" : String.valueOf(packetId);
            return;
        }
        sendMessage(ctx, msg, clientId, packetId, flush);
    }

    /**
     * 发送信息
     *
     * @param ctx
     * @param msg
     * @param clientId
     * @param packetId
     * @param flush
     */
    public static void sendMessage(ChannelHandlerContext ctx, MqttMessage msg, String clientId, Integer packetId, boolean flush) {
        String pid = packetId == null || packetId <= 0 ? "" : String.valueOf(packetId);
        ChannelFuture future = flush ? ctx.writeAndFlush(msg) : ctx.write(msg);
        future.addListener(f -> {
            if (f.isSuccess()) {

            } else {

            }
        });
    }
}

BrokerSessionHelper类就是用于存放当前服务器上相关通道信息。同时用于发送返回的相关报文。读者们可以进行看代码吧。

这个时候就你们只按照以前面讲的去做。就可以抓到报文了。客户端的话。笔者只用前面说的MQTTLens来测试。