基于paho.mqtt库在rv1126平台实现MQTT消息的发布与订阅
1、MQTT介绍
MQTT协议就是一个通信协议，通信架构可以参考如下图片
topic可以理解为消息的中转地址，无论是订阅消息还是发布消息，都需要指定topic。发布者往指定topic发布消息，订阅者如果订阅了该topic，则可收到发布者的这一条消息。
2、paho-mqtt-embended库的介绍、编译及使用
https://www.eclipse.org/paho/index.php?page=downloads.php
用的是rv1126，属于嵌入式平台，所以选择Embedded C/C++版本，源码地址：GitHub - eclipse/paho.mqtt.embedded-c: Paho MQTT C client library for embedded systems. Paho is an Eclipse IoT project (https://iot.eclipse.org/)
首先进入paho.mqtt.embedded-c目录，修改Makefile
CC ?= arm-linux-gnueabihf-gcc接下来开始编译，在终端输入以下命令：
zwx@ubuntu:~/rv1126/mqtt/paho.mqtt.embedded-c$ make
zwx@ubuntu:~/rv1126/mqtt/paho.mqtt.embedded-c$ sudo make install编译完成如下图所示：
编译生成的库文件保存在目录paho.mqtt.embedded-c/build/output下，将这三个库文件放在RV1126的/usr/lib目录下，就可以在板子上使用mqtt了。
3、使用emqx和mqtt.fx进行订阅和发布的测试
emqx可以在本地搭建一个MQTT服务器，而mqtt.fx可以模拟一个mqtt客户端，测试思路如下：先用emqx搭建服务器，rv1126使用以太网接入电脑。mqtt.fx模拟的客户端和rv1126搭建的客户端可以通过emqx搭建的MQTT服务器进行通信。
Emqx的使用方法非常简单，解压之后打开bin文件夹，打开cmd，输入 emqx.cmd start 回车。Mqtt服务器就搭建完成了。可以在浏览器输入http://localhost:18083/ 进入服务器后台管理。
mqtt.fx的使用方法也非常简单，打开软件后点击齿轮按钮进行设置，一般来说只需要修改IP地址就可以。
设置完成后就可以点击connect按钮来进行连接了，此时mqtt.fx模拟的MQTT客户端已经连接上我们刚才使用emqx搭建的服务器了。
接下来需要在rv1126中搭建一个mqtt客户端，并向pub_test这一个topic发布消息。如果成功的话，mqtt.fx软件上将会订阅到由rv1126发布的消息内容，说明发送功能正常。再用mqtt.fx向pub_test发布消息，如果正常的话，rv1126将会订阅到这条消息。测试代码我贴上来了，代码实现了订阅和发送功能。将代码放到paho.mqtt.embedded-c/MQTTClient-C/samples/linux目录下编译，编译完之后将生成的可执行文件放到rv1126板子上运行即可。记得修改该目录下的build.sh文件哦。
#include
#include
#include "MQTTClient.h"
#include
#include
#include
volatile int toStop = 0;
void usage()
{
printf("MQTT stdout subscriber\n");
printf("Usage: stdoutsub topicname , where options are:\n");
printf(" --host (default is localhost)\n");
printf(" --port (default is 1883)\n");
printf(" --qos (default is 2)\n");
printf(" --delimiter (default is \\n)\n");
printf(" --clientid (default is hostname+timestamp)\n");
printf(" --username none\n");
printf(" --password none\n");
printf(" --showtopics (default is on if the topic has a wildcard, else off)\n");
exit(-1);
}
void cfinish(int sig)
{
signal(SIGINT, NULL);
toStop = 1;
}
struct opts_struct
{
char* clientid;
int nodelimiter;
char* delimiter;
enum QoS qos;
char* username;
char* password;
char* host;
int port;
int showtopics;
} opts =
{
(char*)"52JMT02RD002", 0, (char*)"\n", QOS1, NULL, NULL, (char*)"192.168.7.101", 1883, 1
};
void getopts(int argc, char** argv)
{
int count = 2;
while (count < argc)
{
if (strcmp(argv[count], "--qos") == 0)
{
if (++count < argc)
{
if (strcmp(argv[count], "0") == 0)
opts.qos = QOS0;
else if (strcmp(argv[count], "1") == 0)
opts.qos = QOS1;
else if (strcmp(argv[count], "2") == 0)
opts.qos = QOS2;
else
usage();
}
else
usage();
}
else if (strcmp(argv[count], "--host") == 0)
{
if (++count < argc)
opts.host = argv[count];
else
usage();
}
else if (strcmp(argv[count], "--port") == 0)
{
if (++count < argc)
opts.port = atoi(argv[count]);
else
usage();
}
else if (strcmp(argv[count], "--clientid") == 0)
{
if (++count < argc)
opts.clientid = argv[count];
else
usage();
}
else if (strcmp(argv[count], "--username") == 0)
{
if (++count < argc)
opts.username = argv[count];
else
usage();
}
else if (strcmp(argv[count], "--password") == 0)
{
if (++count < argc)
opts.password = argv[count];
else
usage();
}
else if (strcmp(argv[count], "--delimiter") == 0)
{
if (++count < argc)
opts.delimiter = argv[count];
else
opts.nodelimiter = 1;
}
else if (strcmp(argv[count], "--showtopics") == 0)
{
if (++count < argc)
{
if (strcmp(argv[count], "on") == 0)
opts.showtopics = 1;
else if (strcmp(argv[count], "off") == 0)
opts.showtopics = 0;
else
usage();
}
else
usage();
}
count++;
}
}
void messageArrived(MessageData* md)
{
// printf("messageArrived!!!!!!!!!\n");
MQTTMessage* message = md->message;
if (opts.showtopics)
printf("%.*s\t", md->topicName->lenstring.len, md->topicName->lenstring.data);
if (opts.nodelimiter)
printf("%.*s", (int)message->payloadlen, (char*)message->payload);
else
printf("%.*s%s", (int)message->payloadlen, (char*)message->payload, opts.delimiter);
//fflush(stdout);
}
int main(int argc, char** argv)
{
int rc = 0;
unsigned char buf[100];
unsigned char readbuf[100];
if (argc < 2)
usage();
char* topic = argv[1];
char* topic_sub = "/v1/devices/02_52JMT02RD002/command";
int cnt = 0;
unsigned int msgid = 0;
if (strchr(topic, '#') || strchr(topic, '+'))
opts.showtopics = 1;
if (opts.showtopics)
printf("topic is %s\n", topic);
getopts(argc, argv);
Network n;
MQTTClient c;
signal(SIGINT, cfinish);
signal(SIGTERM, cfinish);
NetworkInit(&n);
NetworkConnect(&n, opts.host, opts.port);
MQTTClientInit(&c, &n, 1000, buf, 1024, readbuf, 1024);
MQTTPacket_connectData data = MQTTPacket_connectData_initializer;
data.willFlag = 0;
data.MQTTVersion = 3;
data.clientID.cstring = opts.clientid;
data.username.cstring = opts.username;
data.password.cstring = opts.password;
data.keepAliveInterval = 10;
data.cleansession = 1;
printf("Connecting to %s %d\n", opts.host, opts.port);
rc = MQTTConnect(&c, &data);
printf("Connected %d\n", rc);
printf("Subscribing to %s\n", topic_sub);
rc = MQTTSubscribe(&c, topic_sub, opts.qos, messageArrived);
printf("Subscribed %d\n", rc);
while (!toStop)
{
MQTTYield(&c, 1000);
char msg_mqtt_uploadfile[1000] = "123123123";
MQTTMessage msg =
{
QOS1,
0,
0,
0,
(void *)msg_mqtt_uploadfile,
strlen((char *)msg_mqtt_uploadfile),
};
msg.id = ++msgid;
rc = MQTTPublish(&c, topic, &msg);
printf("MQTTPublish %d, msgid %d\n", rc, msgid);
}
printf("Stopping\n");
MQTTDisconnect(&c);
NetworkDisconnect(&n);
return 0;
} 下面是我用home/garden/fountain这一个topic的测试成功截图
至此就大功告成啦~