在linux下使用c语言实现MQTT通信(二.编程实现)
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
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
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
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：
#include2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 }
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 }
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 }
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 }
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
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 }
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 }
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 }
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 }
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
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
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
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。