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在linux下使用c语言实现MQTT通信(二.编程实现)_paho-mqtt3as

作者：Monodyee | 2024-03-06 18:31:42

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paho-mqtt3as

我是用的secureCRT登录的树莓派，要实现MQTT通信，就需要用到许多关于MQTT的函数，这里我用的是Paho.c库，所以首先下载库：
在git下下载paho C库git clone https://github.com/eclipse/paho.mqtt.c.git

cd paho.mqtt.c
make//编译
sudo make install//安装


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执行make之后我们在build/output/下能看到以下动态库：

iot@Public_RPi:~/caiwentao/team_lihaojie/caiwentao/mqtt/mqtt_publish/paho.mqtt/build/output $ ls
libpaho-mqtt3a.so      libpaho-mqtt3as.so      libpaho-mqtt3c.so      libpaho-mqtt3cs.so      paho_c_version
libpaho-mqtt3a.so.1    libpaho-mqtt3as.so.1    libpaho-mqtt3c.so.1    libpaho-mqtt3cs.so.1    samples
libpaho-mqtt3a.so.1.0  libpaho-mqtt3as.so.1.0  libpaho-mqtt3c.so.1.0  libpaho-mqtt3cs.so.1.0  test

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在这里说一下这里面的各个动态库的作用：
paho-mqtt3a ： 一般实际开发中就是使用这个，a表示的是异步消息推送（asynchronous）。
paho-mqtt3as ： as表示的是 异步+加密（asynchronous+OpenSSL）。
paho-mqtt3c ： c 表示的应该是同步（Synchronize），一般性能较差，是发送+等待模式。
paho-mqtt3cs ： cs表示的是同步+加密（asynchronous+OpenSSL）。
一丶发布端程序

get_temperature.c  get_temperature.h  get_time.c  get_time.h  opt_init.c  opt_init.h  publish.c  set_signal.c  set_signal.h

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下面解释一下这些c代码：
1丶get_temperature.c就是发布端发布的消息，其内容是实验室树莓派获取的实时温度，其代码如下：

#include<stdio.h>
#include<unistd.h>
#include<dirent.h>
#include<string.h>
#include<sys/types.h>
#include<errno.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<stdlib.h>
#include"get_temperature.h"
int  get_temperature(float *temper)
{
        char    path[128]="/sys/bus/w1/devices/";
        char    path_s[32];
        char    buf[128];
        char    *ptr;
        DIR     *dirp;
        int     a=0;
        int     fd; 
        struct dirent *direntp;
        if((dirp=opendir(path))==NULL)
        {   
                printf("Open %s failure:%s\n",path,strerror(errno));
                return -1; 
        }   
        while((direntp=readdir(dirp))!=NULL)
        {   
                if(strstr(direntp->d_name,"28-"))
                {   
                        strcpy(path_s,direntp->d_name);
                        a=1;
                }   
        }   
        if(a==0)
        {   
                printf("Can not find ds18b20 in %s\n",path);
                return -1; 
        }   
        strncat(path,path_s,sizeof(path));
        strncat(path,"/w1_slave",sizeof(path));
        if((fd=open(path,O_RDONLY))<0)
        {   
                printf("Open %s failure:%s\n",path,strerror(errno));
                return -1;
        }
        if(read(fd,buf,sizeof(buf))<0)
        {
                printf("read data from %s failure:%s\n",path,strerror(errno));
                return -1;
        }
        ptr=strstr(buf,"t=");

        ptr+=2;

        if(!ptr)
        {
                printf("ERROR:%s\n",strerror(errno));
                return 1000;
        }
        *temper=atof(ptr)/1000;
        return 0;
}

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2丶get_time.c:获取当前时间，网上有很多，我的示例代码如下：

1 #include<time.h>
  2 #include<stdio.h>
  3 #include<string.h>
  4 #include"get_time.h"
  5 int get_time(char time_s[24])
  6 {
  7         time_t   timec;
  8         char *str;
  9         time(&timec);
 10         str=ctime(&timec);
 11         char *chr=strchr(str,'\n');
 12         *chr='\0';
 13         strcpy(time_s,str);
 14         return 0;
 15 
 16 }

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3丶opt_init.c:参数初始化函数。示例代码如下：

  1 #include<stdio.h>
  2 #include<getopt.h>
  3 #include<unistd.h>
  4 #include<string.h>
  5 #include<stdlib.h>
  6 #include"opt_init.h"
  7 void usage(char *arg)
  8 {
  9         printf("%s usage:\n",arg);
 10         puts("-p (--port)get the port");
 11         puts("-d (--daemon)run back");
 12         puts("-a (-address)the publish address");
 13         puts("-h (--help)get the help message");
 14         puts("-i (--id) get the publish id");
 15         puts("-t (--topic)the publish topic");
 16         return ;
 17 }
 18 
 19 int opt_init(int *port,char name[],char sub_id[],char topic[],int argc,char **argv)
 20 {
 21         struct option opts[]=
 22         {
 23                 {"port",required_argument,NULL,'p'},
 24                 {"daemon",no_argument,NULL,'d'},
 25                 {"topic",required_argument,NULL,'t'},
 26                 {"sub_id",required_argument,NULL,'i'},
 27                 {"address",required_argument,NULL,'a'},
 28                 {"help",no_argument,NULL,'h'},
 29                 {NULL,0,NULL,0}
 30         };
 31         int       rv; 32         while((rv=getopt_long(argc,argv,"d:p:a:i:t:h",opts,NULL))!=-1)
 33         {
 34                 switch(rv)
 35                 {
 36                     case 'd':
 37                     if(daemon(0,0)<0)
 38                 {
 39                     printf("daemon error\n");
 40                     return 0;
 41                 }
 42                     case 'p':
 43                         *port=atoi(optarg);
 44                         break;
 45                     case 'a':
 46                         strcpy(name,optarg);
 47                         break;
 48                     case 'i':
 49                         strcpy(sub_id,optarg);
 50                         break;
 51                     case 't':
 52                         strcpy(topic,optarg);
 53                         break;
 54                     case 'h':
 55                         usage(argv[0]);
 56                         return 0;
 57                         default:
 58                         break;
 59                 }
 60         }
 61         if(!*port||!name)
 62         {
 63                 usage(argv[0]);
 64                 return -1;
 65         }
 66 }

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4丶set_signal.c:设置信号函数，示例代码如下：

 1 #include<signal.h>
  2 #include<stdio.h>
  3 #include<stdlib.h>
  4 #include"set_signal.h"
  5 
  6 
  7 int g_stop=0;
  8 void signal_action(int signum)
  9 {
 10         if(signum==SIGKILL)
 11         {
 12                 g_stop=1;
 13                 printf("kill signal makes program ended\n");
 14         }
 15         else if(signum==SIGINT)
 16         {
 17                 g_stop=1;
 18                 printf("Ctrl+C signal makes program ended\n");
 19         }
 20         exit(0);
 21 }
 22 
 23 int set_signal(void)
 24 {
 25         struct sigaction        sigact;
 26         sigemptyset(&sigact.sa_mask);
 27         sigact.sa_flags=0;
 28         sigact.sa_handler=signal_action;
 29 
 30         sigaction(SIGKILL,&sigact,0);
 31         sigaction(SIGINT,&sigact,0);
 32         return 0;
 33 }

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5丶publish.c:发布端函数，示例代码如下：

 1 #include<stdio.h>
  2 #include<string.h>
  3 #include<stdlib.h>
  4 #include<errno.h>
  5 #include<unistd.h>
  6 #include"MQTTClient.h"
  7 #include"set_signal.h"
  8 #include"get_time.h"
  9 #include"get_temperature.h"
 10 #include"opt_init.h"
 11 //此发布端不使用回调函数
 12 int main(int argc,char **argv)
 13 {
 14     char                      address[128];
 15     int                       port=0;
 16     char                      topic[128];
 17     char                      pub_id[128];
 18     char                      buf[128]={'\0'};
 19     char                      date[128];
 20     char                      address_s[128];
 21     float                     temper;
 22     int                       rv;
 23     const int                 qos=1;
 24     const long                timeout=10000L;
 25     if(set_signal()<0)
 26     {
 27         printf("set_signal error:%s\n",strerror(errno));
 28         return -1;
 29     }
 30     if(opt_init(&port,address,pub_id,topic,argc,argv)<0)
 31     {
 32         printf("opt_init failure:%s\n",strerror(errno));
 33         return -1;
 34     }
 35     snprintf(address_s,sizeof(address_s),"tcp://%s:%d",address,port);
 36     MQTTClient client;
 37     MQTTClient_connectOptions conn_opts=MQTTClient_connectOptions_initializer;
 38     MQTTClient_message publish_msg=MQTTClient_message_initializer;
 39     MQTTClient_deliveryToken token;
 40     conn_opts.keepAliveInterval=60;
 41     conn_opts.cleansession=1;
 42     MQTTClient_create(&client,address_s,pub_id,MQTTCLIENT_PERSISTENCE_NONE,NULL);
  43     if((rv=MQTTClient_connect(client,&conn_opts))!=MQTTCLIENT_SUCCESS)
 44     {
 45         printf("MQTTClient_connect error:%s\n",strerror(errno));
 46         return -1;
 47     }
 48     publish_msg.qos=qos;
 49     publish_msg.retained=0;
 50     while(!g_stop)
 51     {
 52         if(get_time(date)<0)
 53         {
 54             printf("get_time error:%s\n",strerror(errno));
 55             return -1;
 56         }
 57         if(get_temperature(&temper)<0)
 58         {
 59             printf("get_temperature error:%s\n",strerror(errno));
 60             return -1;
 61         }
 62         snprintf(buf,sizeof(buf),"RPI0001/%s/%f",date,temper);
 63         publish_msg.payload=(void *)buf;
 64         publish_msg.payloadlen=strlen(buf);
 65         MQTTClient_publishMessage(client,topic,&publish_msg,&token);
 66         printf("Waiting for %d seconds for publication of---- %s---- on topic %s for subscriber with id:%s\n",timeout/1000,buf,topic,pub_id);
 67         rv=MQTTClient_waitForCompletion(client,token,timeout);
 68         printf("Message with delivery token %d delivered\n",rv);
 69         sleep(30);
 70     }
 71 }

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二丶订阅端程序：

 db_init.h    insert_db.h      opt_init.c  set_signal.c   string_break.c   subscribe.c
 db_init.c    insert_db.c      opt_init.h  set_signal.h   string_break.h

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1丶db_init.c:数据库初始化函数，示例代码如下：

 13 #include<stdio.h>
 14 #include<sqlite3.h>
 15 #include"db_init.h"
 16 #include<stdlib.h>
 17 int callback(void *Notused,int argc,char **argv,char **azColName)
 18 {
 19     int i=0;
 20     for(i=0;i<argc;i++)
 21     {
 22         printf("%s=%s\n",azColName[i],argv[i]?argv[i]:"NULL");
 23     }
 24     printf("\n");
 25     return 0;
 26 }
 27 
 28 int db_init(char *db_name,char *file_name)
 29 {
 30     sqlite3     *db;
 31     char        *zErrMsg=0;
 32     int         rc;
 33     char        sql[256];
 34     rc = sqlite3_open(db_name,&db);
 35     if(rc!=0)
 36     {
 37         fprintf(stderr,"can't open database:%s\n",sqlite3_errmsg(db));
 38         return -1;
 39     }
 40     else
 41     {
 42         fprintf(stdout,"open database ok\n");
 43     }
 44      snprintf(sql,256,"CREATE TABLE IF NOT EXISTS %s("
 45         "I INTEGER   PRIMARY KEY AUTOINCREMENT ,"
 46         "ID CHAR(32)                NOT NULL,"
 47         "DATE          CHAR(48)     NOT NULL,"
 48         "TEMPERATURE   CHAR(32)     NOT NULL);",file_name);
 49      rc = sqlite3_exec(db,sql,callback,0,&zErrMsg); 
 50      if(rc!=SQLITE_OK)
 51      {
 52         fprintf(stderr,"SQL error:%s\n",zErrMsg);
 53         sqlite3_free(zErrMsg);
 54         return -1;
 55      }
 56      else
 57      {
 58         fprintf(stdout,"table create ok\n");
 59      }
 60      sqlite3_close(db);
 61      return 0;
 62 }

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2丶insert_db.c:插入数据库。示例代码如下：

 13 #include<stdio.h>
 14 #include<stdlib.h>
 15 #include<sqlite3.h>
 16 #include"insert_db.h"
 17 int call_back(void *NotUsed,int argc , char **argv,char **azColName)
 18 {
 19     int i=0;
 20     for(i=0;i<argc;i++)
 21     {
 22         printf("%s=%s\n",azColName[i],argv[i]?argv[i]:"NULL");
 23     }
 24     printf("\n");
 25     return 0;
 26 }
 27 int insert_db(char *db_name,char *file_name,char *id,char *date,char *temper)
 28 {
 29     sqlite3     *db;
 30     char        *zErrMsg=0;
 31     int         rc ;
 32     char        sql[256];
 33     rc=sqlite3_open(db_name,&db);
 34     if(rc!=0)
 35     {
 36         fprintf(stderr,"can't open database:%s\n",sqlite3_errmsg(db));
 37         return -1;
 38     }
 39     else
 40     {
 41         fprintf(stderr,"open database ok\n");
 42     }
 43     snprintf(sql,256,"INSERT INTO %s(I,ID,DATE,TEMPERATURE)VALUES (NULL,'%s','%s','%s'); ",file_name,id,date,temper);
 44     rc=sqlite3_exec(db,sql,call_back,0,&zErrMsg);
  45     if(rc!=SQLITE_OK)
 46     {
 47         fprintf(stderr,"SQL error:%s\n",zErrMsg);
 48         sqlite3_free(zErrMsg);
 49         return -1;
 50     }
 51     else
 52     {
 53         fprintf(stdout,"records careated ok\n");
 54     }
 55     sqlite3_close(db);
 56     return 0;
 57 }

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3丶string_break.c:字符串分割，示例代码如下：

  1 #include "Rectemper_server.h"
  2 
  3 int string_break(char *buf, char *sn, char *time, char *temper)
  4 {
  5     char            *p_head, *p_end ;
  6 
  7     p_end = strstr(buf, "/") ;
  8     strncpy(sn , buf, (p_end - buf)) ;
  9     printf("sn: %s\n", sn) ;
 10 
 11     p_head = p_end + 1 ;        // p_head = "2019-1-23  14:17:27/15.375000C"
 12     p_end = strstr( (p_end + 1), "/") ; // p_end= "/15.375000C"
 13     strncpy(time, p_head, (p_end-p_head));
 14     printf("time: %s\n", time) ;
 15 
 16     p_head = p_end + 1 ; // p_head ="15.375000C"
 17     p_end = strstr(p_end, "C") ;
 18     strncpy(temper, p_head, (p_end - p_head)) ;
 19     printf("Temperature: %s\n", temper) ;
 20 
 21 }

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4丶subscribe.c:订阅端程序，示例代码如下：

 1 #include<stdio.h>
  2 #include<stdlib.h>
  3 #include<string.h>
  4 #include<errno.h>
  5 #include"MQTTClient.h"
  6 #include<unistd.h>
  7 #include"set_signal.h"
  8 #include"opt_init.h"
  9 #include"db_init.h"
 10 #include"insert_db.h"
 11 #include"string_break.h"
 12 volatile MQTTClient_deliveryToken deliveredtoken;
 13 
 14 void delivered(void *context,MQTTClient_deliveryToken dt)
 15 {
 16     printf("Message with token value %d delivery confirmed\n",dt);
 17     deliveredtoken=dt;
 18 }
 19 
 20 int msgarrvd(void *context,char *topicName,int topicLen,MQTTClient_message *message)
 21 {
 22     int i;
 23     char buf[128]={'\0'};
 24     char id[128];
 25     char date[128];
 26     char temper[128];
 27     char *payloadptr;
 28     payloadptr=message->payload;
 29     printf("Message arrived \n");
 30     printf("topic:%s\n",topicName);
 31     printf("Message:%s\n",message->payload);
 32     printf("message:");
 33     for(i=0;i<message->payloadlen;i++)
 34     {
 35         buf[i]=*payloadptr;
 36         putchar(*payloadptr++);
 37     }
 38     printf("%s\n",buf);
 39     putchar('\n');
  40     if(string_break(id,date,temper,buf)<0)
 41     {
 42         printf("string_break failure:%s\n",strerror(errno));
 43         return -1;
 44     }
 45     if(db_init("Messages","message")<0)
 46     {
 47         printf("db_init failure:%s\n",strerror(errno));
 48         return -1;
 49     }
 50     if(insert_db("Messages","message",id,date,temper)<0)
 51     {
 52         printf("insert_db failure:%s\n",strerror(errno));
 53         return -1;
 54     }
 55     MQTTClient_freeMessage(&message);
 56     MQTTClient_free(topicName);
 57     return 1;
 58 }
 59 
 60 void connlost(void *context,char *cause)
 61 {
 62     printf("Connection lost\n");
 63     printf("cause %s\n",cause);
 64 }
 65 
 66 
 67 int main(int argc,char **argv)
 68 {
 69     MQTTClient client;
 70     const int qos=1;
 71         const long timeout=10000L;
 72     char buf[128];
  73     int port=0;
 74     char address[128];
 75     char sub_id[128];
 76     char topic[128];
 77     MQTTClient_connectOptions conn_opts=MQTTClient_connectOptions_initializer;
 78     int rc,ch;
 79     if(set_signal()<0)
 80     {
 81         printf("set_signal failure:%s\n",strerror(errno));
 82         return -1;
 83     }
 84     if(opt_init(&port,address,sub_id,topic,argc,argv)<0)
 85     {
 86         printf("opt_init failure:%s\n",strerror(errno));
 87         return 1;
 88     }
 89     snprintf(buf,sizeof(buf),"tcp://%s:%d",address,port);
 90     MQTTClient_create(&client,buf,sub_id,MQTTCLIENT_PERSISTENCE_NONE,NULL);
 91     conn_opts.keepAliveInterval=20;
 92     conn_opts.cleansession=1;
 93     MQTTClient_setCallbacks(client,NULL,connlost,msgarrvd,delivered);
 94 
 95     if((rc=MQTTClient_connect(client,&conn_opts))!=MQTTCLIENT_SUCCESS)
 96     {
 97         printf("MQTTClient_connect failure:%s\n",strerror(errno));
 98         return -1;
 99     }
100     printf("Subscribe to topic %s for client %s using QOS %d\n",topic,sub_id,qos);
101     MQTTClient_subscribe(client,topic,qos);
102     do
103     {
104         ch=getchar();
105     }while(ch!='q'&&ch!='Q');
106     MQTTClient_disconnect(client,10000);
107     MQTTClient_destroy(&client);
108     return rc;
109 }

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set_signal.c与opt_init.c与publish端代码一样。
三丶发布端与订阅端实现通信
下面是发布端发布时间和温度：

iot@Public_RPi:~/caiwentao/team_lihaojie/caiwentao/mqtt/mqtt_publish $ ./a.out -p 1883 -a 127.0.0.1 -i 100 -t cwt 
Waiting for 10 seconds for publication of---- RPI0001/Mon Jul 22 16:36:48 2019/25.937000---- on topic cwt for subscriber with id:100
Message with delivery token 0 delivered
Waiting for 10 seconds for publication of---- RPI0001/Mon Jul 22 16:37:19 2019/26.000000---- on topic cwt for subscriber with id:100
Message with delivery token 0 delivered

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下面是订阅端收到时间和温度：

iot@Public_RPi:~/caiwentao/team_lihaojie/caiwentao/mqtt/mqtt_subscribe $ ./a.out -p 1883 -a 127.0.0.1  -t cwt                 
Subscribe to topic cwt for client   using QOS 1
Message arrived 
topic:cwt
Message:RPI0001/Mon Jul 22 16:36:48 2019/25.937000
message:RPI0001/Mon Jul 22 16:36:48 2019/25.937000RPI0001/Mon Jul 22 16:36:48 2019/25.937000
open database ok
table create ok
open database ok
records careated ok
Message arrived 
topic:cwt
Message:RPI0001/Mon Jul 22 16:37:19 2019/26.000000
message:RPI0001/Mon Jul 22 16:37:19 2019/26.000000RPI0001/Mon Jul 22 16:37:19 2019/26.000000
open database ok
table create ok
open database ok
records careated ok

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检查是否存入数据库中：

iot@Public_RPi:~/caiwentao/team_lihaojie/caiwentao/mqtt/mqtt_subscribe $ sqlite3 
SQLite version 3.16.2 2017-01-06 16:32:41
Enter ".help" for usage hints.
Connected to a transient in-memory database.
Use ".open FILENAME" to reopen on a persistent database.
sqlite> .open Messages 
sqlite> .table
message
sqlite> select * from message;
1|RPI0001|Mon Jul 22 16:36:48 20195.937000
2|RPI0001|Mon Jul 22 16:37:19 20196.000000

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上图显示数据已经存入数据库中，可能由于显示问题后面的时间与温度数字出现重合，正确时间是2019年，温度是25.937000。
如上，成功实现MQTT通信。

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