MQTT

MQTT是一个基于客户端服务器的消息发布/订阅传输协议。MQTT协议是轻量、简单、开放和易于实现的，这些特点使它适用范围非常广泛。在很多情况下，包括受限的环境中，如：机器与机器（M2M）通信和物联网（IoT）。其在，通过卫星链路通信传感器、偶尔拨号的医疗设备、智能家居、及一些小型化设备中已广泛使用。

证书配置

双向认证方法:让后台生成 ca.crt 和 client.p12文件(client.p12文件由client.crt和client.key合成) 我使用的是自签证书，在本地安装好openssl环境后。

1.使用命令行把crt转化为der格式

openssl x509 -in ca.crt -out ca.der -outform der

一般情况下后台都装好openssl环境 直接转换就可以了。

2.创建MQTT

MQTTSSLSecurityPolicyTransport *transport = [[MQTTSSLSecurityPolicyTransport alloc]init];
transport.host = d[@"192.168.1.ip"];
transport.port = [d[@"port"] intValue];
transport.tls = YES;
                
NSString*  ca = [[NSBundle bundleForClass:[MQTTSession class]] pathForResource:@"ca" ofType:@"der"];
NSString*  client = [[NSBundle bundleForClass:[MQTTSession class]] pathForResource:@"certificate" ofType:@"p12"];
transport.certificates = [MQTTSSLSecurityPolicyTransport clientCertsFromP12:client passphrase:@"password"];
                
MQTTSSLSecurityPolicy *securityPolicy = [MQTTSSLSecurityPolicy policyWithPinningMode:MQTTSSLPinningModeCertificate];
securityPolicy.allowInvalidCertificates = YES;
securityPolicy.validatesDomainName = NO;
securityPolicy.validatesCertificateChain = NO;
securityPolicy.pinnedCertificates = @[[NSData dataWithContentsOfFile:ca]];
transport.securityPolicy = securityPolicy;
                
self.sessionManager = [[MQTTSessionManager alloc]init];
                
NSDictionary *dic = @{@"subject":@"disconnect"};
NSData *data = [NSJSONSerialization dataWithJSONObject:dic options:NSJSONWritingPrettyPrinted error:nil];

[self.sessionManager connectTo:d[@"192.168.1.ip"] 
                            port: [d[@"port"] intValue] 
                            tls:YES
                            keepalive:60//设置心跳间隔
                            clean:NO //clean标志位向代理服务器表明客户端是否要建立持续的会话
                            auth:YES //MQTT允许发送用户名和密码以便验证客户端的身份和进行授权
                            user:@"username" 
                            pass:@"password" 
                            will:YES //是否设遗嘱 是的话需要填写willTopic和willMsg
                            willTopic:@"/topic/lastwill" //遗嘱消息主题
                            willMsg:data //遗嘱消息设置
                            willQos:0  //MQTT设计了一套保证消息稳定传输的机制，包括消息应答、存储和重传。在这套机制下，提供了三种不同层次QoS（Quality of Service）：QoS0，At most once，至多一次；QoS1，At least once，至少一次；QoS2，Exactly once，确保只有一次。
                            willRetainFlag:NO 
                            withClientId: @"clientid" //clientId 客户端标识符
                            securityPolicy:securityPolicy 
                            certificates: 
[MQTTSSLSecurityPolicyTransport clientCertsFromP12:client passphrase:@"password"]];//配置证书的时候设置的密码

// 添加监听状态观察者
self.sessionManager.delegate = self;
[self.sessionManager addObserver:self
                                      forKeyPath:@"state"
                                         options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew
                                         context:nil];

//订阅topic         可设置多个主题@{@"topic": @2, @"topic2":@2}
self.sessionManager.subscriptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:MQTTQosLevelExactlyOnce] forKey:@"/topic/mqtt"];

3.发送和接收数据

发送消息

 [self. sessionManager sendData:[self.LocationStr dataUsingEncoding:NSUTF8StringEncoding]
                     topic:@"topic"
                       qos:2
                    retain:true];

收到消息

- (void)handleMessage:(NSData *)data onTopic:(NSString *)topic retained:(BOOL)retained {

}

MQTT状态监控

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    switch (self.manager.state) {
        case MQTTSessionManagerStateClosed:
            self.NetStatus = @"closed";
            NSLog(@"MQTT已关闭");
            break;
        case MQTTSessionManagerStateClosing:
            self.NetStatus = @"closing";
            NSLog(@"MQTT关闭中");
            break;
        case MQTTSessionManagerStateConnected:
            self.NetStatus = @"已连接";
            NSLog(@"MQTT已链接");
            break;
        case MQTTSessionManagerStateConnecting:
            self.NetStatus = @"connecting";
           NSLog(@"MQTT正在连接");
            break;
        case MQTTSessionManagerStateError:
            self.NetStatus = @"error";
            NSLog(@"MQTT错误");
            break;
        case MQTTSessionManagerStateStarting:
        default:
            self.NetStatus = @"not connected";
            NSLog(@"MQTT未链接");
            break;
    }
}