如何用C语言实现支持TLS加密的MQTT客户端程序（进阶篇）

本人转载。

mosquitto_pub&mosquitto_sub

在实现MQTT client之前&＃xff0c;我们可以先使用mosquitto_pub和mosquitto_sub模拟&＃xff0c;MQTT的发布和订阅

fflush( stdout );

mbedtls_entropy_init( &entropy );

if( ( ret &＃61; mbedtls_ctr_drbg_seed( &ctr_drbg, mbedtls_entropy_func, &entropy,

(const unsigned char *) pers,

strlen( pers ) ) ) !&＃61; 0 )

{

mbedtls_printf( " failed\n ! mbedtls_ctr_drbg_seed returned %d\n", ret );

goto exit;

}

mbedtls_printf( " ok\n" );

加载证书

ret &＃61; mbedtls_x509_crt_parse_file( &cacert, "./cacert.pem");

if( ret <0 )

{

mbedtls_printf( " failed\n ! mbedtls_x509_crt_parse returned -0x%x\n\n", -ret );

goto exit;

}

mbedtls_printf( " ok (%d skipped)\n", ret );

ret &＃61; mbedtls_x509_crt_parse_file( &clicert, "./client.crt");

if( ret !&＃61; 0 )

{

mbedtls_printf( " failed\n ! mbedtls_x509_crt_parse returned %d\n\n", ret );

goto exit;

}

ret &＃61; mbedtls_pk_parse_keyfile( &pkey, "./client.key", "123456");

if( ret !&＃61; 0 )

{

mbedtls_printf( " failed\n ! mbedtls_pk_parse_key returned %d\n\n", ret );

goto exit;

}

mbedtls_pk_parse_keyfile 第三个参数是生成客户端证书&＃xff0c;自己输入的密钥

建立TCP连接

/*

* 1. Start the connection

*/

mbedtls_printf( " . Connecting to tcp/%s/%s...", SERVER_NAME, SERVER_PORT );

fflush( stdout );

if( ( ret &＃61; mbedtls_net_connect( &server_fd, SERVER_NAME,

SERVER_PORT, MBEDTLS_NET_PROTO_TCP ) ) !&＃61; 0 )

{

mbedtls_printf( " failed\n ! mbedtls_net_connect returned %d\n\n", ret );

goto exit;

}

TLS握手

/*

* 4. Handshake

*/

mbedtls_printf( " . Performing the SSL/TLS handshake..." );

fflush( stdout );

while( ( ret &＃61; mbedtls_ssl_handshake( &ssl ) ) !&＃61; 0 )

{

if( ret !&＃61; MBEDTLS_ERR_SSL_WANT_READ && ret !&＃61; MBEDTLS_ERR_SSL_WANT_WRITE )

{

mbedtls_printf( " failed\n ! mbedtls_ssl_handshake returned -0x%x\n\n", -ret );

goto exit;

}

}

mbedtls_printf( " ok\n" );

握手阶段结束&＃xff0c;就完成了TLS连接&＃xff0c;开始加密通讯&＃xff0c;下面就是应用层MQTT的连接

MQTT连接

mbedtls_printf(" \n.....................mqtttenter.....................\n" );

PTmqtttenter();

mqtt_connect((mqtt_broker_handle_t *)PTMqttGetBroker());

mbedtls_printf( "\n....................mqtt_connect.....................\n" );

mqtt_subscribe((mqtt_broker_handle_t *)PTMqttGetBroker(), MQTTSUBTOPIC, 0);

mqtt_publish((mqtt_broker_handle_t *)PTMqttGetBroker(), MQTTPUBTOPIC, test, strlen(test), 0);

这样就完成MQTT的连接&＃xff0c;我们来看下实际效果

如上图&＃xff0c;我发送的MQTT消息&＃xff0c;主题为mtopic 消息为test_cfd

订阅的终端&＃xff0c;可以成功收到消息。

注意&＃xff1a;程序运行加载的证书是在工程目录下&＃xff0c;并且需要各位根据自己生成的客户端证书进行相应的替换。