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。