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为什么使用paho.mqtt.c发送此消息，导致分割故障



我正在尝试使用MQTT协议发送特定的消息类型。我正在使用paho.mqtt.c库，我的经纪人是兔子3.6.12，运行erlang 20.0。我正在处理运行CentOS 6.9的虚拟机。我首先尝试通过为我的特定消息类型创建结构来进行操作，然后在提出此问题之前，我还尝试使用JSON创建我的特定消息类型。我安装了CJSON（从这里）。

这是我使用CJSON的整个代码：

pubframe.c：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"
#include "../tools.c"
#include <cjson/cJSON.h>
#define ADDRESS      "tcp://localhost:1883"
#define CLIENTID     "MY_PUB"
#define TOPIC        "MQTT/Test"
int main(int argc, char* argv[])
{   
        frame1 test = {42,"test"};
        cJSON* frm = NULL;
        frm = cJSON_CreateObject();
        cJSON_AddNumberToObject(frm,"entier",test.E);
        cJSON_AddStringToObject(frm,"string",test.S);
        print_frame1(frm);
        int i = cJSON_GetArraySize(frm);
        printf("number of items in frame : %dn",i);
        cJSON* entier = NULL;
        entier = cJSON_GetObjectItem(frm,"entier");
        char* pt = cJSON_Print(entier);
        printf("entier : %sn",pt);
        cJSON* str = NULL;
        str = cJSON_GetObjectItem(frm,"string");
        char* st = cJSON_Print(str);
        printf("string : %sn",st);
        printf("size of message : %dn",sizeof(cJSON));
        MQTTClient publisher;
        MQTTClient_connectOptions connexion = MQTTClient_connectOptions_initializer;
        MQTTClient_message msg = msg_creation(frm,sizeof(cJSON),0,0);
    MQTTClient_deliveryToken token;
        int rc;
        MQTTClient_create(&publisher, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);
    connexion.cleansession = 1;
        MQTTClient_setCallbacks(publisher, NULL, connlost, frame_json_arrvd, NULL);
        if ((rc = MQTTClient_connect(publisher,&connexion)) != MQTTCLIENT_SUCCESS)
        {
            printf("Failed to connect, return code %dn", rc);
        }
        MQTTClient_publishMessage(publisher, TOPIC,&msg,NULL);
        printf("Message sent!n");
        cJSON_Delete(frm);
        MQTTClient_disconnect(publisher,10000);
        MQTTClient_destroy(&publisher);
        return rc;
}

副帧：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"
#include "../tools.c"
#include <cjson/cJSON.h>

#define ADDRESS     "tcp://localhost:1883"
#define CLIENTID    "ClientID"
#define TOPIC       "MQTT/Test"
#define QOS         0
#define TIMEOUT     10000L
int main(int argc, char* argv[])
{
    MQTTClient client;
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    int rc;
    int ch;
    MQTTClient_create(&client, ADDRESS, CLIENTID,
        MQTTCLIENT_PERSISTENCE_NONE, NULL);
    conn_opts.keepAliveInterval = 20;
    conn_opts.cleansession = 1;
    MQTTClient_setCallbacks(client, NULL, connlost, frame_json_arrvd, NULL);
    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to connect, return code %dn", rc);
        exit(EXIT_FAILURE);
    }
    printf("Subscribing to topic %snfor client %s using QoS%dnn"
           "Press Q<Enter> to quitnn", TOPIC, CLIENTID, QOS);
    MQTTClient_subscribe(client, TOPIC, QOS);
    do
    {
        ch = getchar();
    } while(ch!='Q' && ch != 'q');
    MQTTClient_disconnect(client, 10000);
    MQTTClient_destroy(&client);
    return rc;
}

tools.c：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <sys/time.h>
#include <cjson/cJSON.h>
#include "MQTTClient.h"
int compteur;
// message frames
typedef struct frame1
{
    int E;
    char* S;
} frame1;
void print_frame1bis(frame1* F)
{
        printf("     %sn",F->S);
        printf("     %dn",F->E);
}
void print_frame1(cJSON* frame1)
{
    char * str = cJSON_Print(frame1);
    printf("%sn",str);
}
int frame_json_arrvd(void* context, char* topicName, int topicLen, MQTTClient_message* msg)
{
        cJSON* payload_ptr = NULL;
        printf("size of message : %dn",sizeof(msg->payload));
        int j = cJSON_GetArraySize(msg->payload);
        printf("okn");
        printf("number of items in frame : %dn",j);
        payload_ptr = cJSON_CreateObject();
        payload_ptr = msg->payload;
        int i = cJSON_GetArraySize(payload_ptr);
        printf("number of items in frame : %dn",i);
        print_frame1(payload_ptr);
        cJSON_Delete(payload_ptr);
        MQTTClient_freeMessage(&msg);
        MQTTClient_free(topicName);
        return 1;
}
// in case connexion is lost
void connlost(void *context, char *cause)
{
    printf("nConnection lostn");
    printf("     cause: %sn", cause);
}

// create message
MQTTClient_message msg_creation(void* payload, int length, int qos, int retained)
{
    MQTTClient_message pubmsg = MQTTClient_message_initializer;
    pubmsg.payload = payload;
    pubmsg.payloadlen = length;
    pubmsg.qos = qos;
    pubmsg.retained = retained;
    return pubmsg;
}

订阅者的支出为

Subscribing to topic MQTT/Test
for client ClientID using QoS0
Press Q<Enter> to quit
size of message : 8
Segmentation fault (core dumped)

因此，由于订户尝试获取项目数，似乎没有正确收到消息。

这是我运行GDB时得到的，不确定是否有帮助。

Program terminated with signal 11, Segmentation fault.
#0  0x00007f4e49a8b63e in cJSON_GetArraySize () from /usr/lib64/libcjson.so.1
(gdb) bt
#0  0x00007f4e49a8b63e in cJSON_GetArraySize () from /usr/lib64/libcjson.so.1
#1  0x00000000004010c9 in frame_json_arrvd (context=0x0,
    topicName=0x7f4e440009e4 "MQTT/Test", topicLen=0, msg=0x7f4e44000bb4)
    at ../tools.c:110
#2  0x00007f4e49c962a5 in MQTTClient_run (n=<value optimized out>)
    at src/MQTTClient.c:604
#3  0x000000378b807aa1 in start_thread (arg=0x7f4e49a83700) at pthread_create.c:301
#4  0x000000378b4e8bcd in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:115

发布者的输出是

{
        "entier":       42,
        "string":       "test"
}
number of items in frame : 2
entier : 42
string : "test"
size of message : 64
Message sent!

因此，该消息看起来正确创建了。

我最近刚刚调查了CJSON，因此，如果我使用错误的话，我将继续进行调查，但是任何帮助都将不胜感激。我试图按照评论中的建议将其缩小范围，但是我看不到我能做什么，因为它试图访问消息的有效载荷时就会崩溃。

请记住，我只是一个在计算机科学方面拥有一年经验的学生。另外，英语不是我的母语，我希望我对自己的解释足够清楚。

解决问题（Kinda）

我只是将整个消息框架发送为字符串，然后在msgarrvd函数中解析它：

pubframe.c：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"
#include "../tools.c"
#include <cjson/cJSON.h>
#define ADDRESS      "tcp://localhost:1883"
#define CLIENTID     "MY_PUB"
#define TOPIC        "MQTT/Test"
volatile MQTTClient_deliveryToken deliveredtoken;
void delivered(void *context, MQTTClient_deliveryToken dt)
{
    printf("Message with token value %d delivery confirmedn", dt);
    deliveredtoken = dt;
}
int main(int argc, char* argv[])
{   
    char* test = "{"string" : "whatever", "entier" : 42}";
    MQTTClient publisher;
    MQTTClient_connectOptions connexion = MQTTClient_connectOptions_initializer;
    MQTTClient_message msg = msg_creation(test,strlen(test),0,0);
    int rc;
    MQTTClient_create(&publisher, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);
    connexion.cleansession = 1;
    MQTTClient_setCallbacks(publisher, NULL, connlost, frame_test_arrvd, NULL);
    if ((rc = MQTTClient_connect(publisher,&connexion)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to connect, return code %dn", rc);
    }
    MQTTClient_publishMessage(publisher, TOPIC,&msg,&token);
    printf("Message sent!n");
    cJSON_Delete(frm);
    MQTTClient_disconnect(publisher,10000);
    MQTTClient_destroy(&publisher);
    return rc;
}

tools.c：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <sys/time.h>
#include <cjson/cJSON.h>
#include "MQTTClient.h"
// message frames
void print_frame1(cJSON* frame1)
{
    char * str = cJSON_Print(frame1);
    printf("%sn",str);
}
int frame_test_arrvd(void* context, char* topicName, int topicLen, MQTTClient_message* msg)
{
    printf("message original : %sn",msg->payload);
    cJSON* payload_ptr = cJSON_Parse(msg->payload);
    print_frame1(payload_ptr);
    int i = cJSON_GetArraySize(payload_ptr);
    printf("number of items in frame : %dn",i);
    cJSON* entier = NULL;
    entier = cJSON_GetObjectItem(payload_ptr,"entier");
    char* pt = cJSON_Print(entier);
    printf("entier : %sn",pt);
    cJSON* str = NULL;
    str = cJSON_GetObjectItem(payload_ptr,"string");
    char* st = cJSON_Print(str);
    printf("string : %sn",st);
    cJSON_Delete(payload_ptr);
    MQTTClient_freeMessage(&msg);
    MQTTClient_free(topicName);
    return 1;
}
// in case connexion is lost
void connlost(void *context, char *cause)
{
    printf("nConnection lostn");
    printf("     cause: %sn", cause);
}

// create message
MQTTClient_message msg_creation(void* payload, int length, int qos, int retained)
{
    MQTTClient_message pubmsg = MQTTClient_message_initializer;
    pubmsg.payload = payload;
    pubmsg.payloadlen = length;
    pubmsg.qos = qos;
    pubmsg.retained = retained;
    return pubmsg;
}

副帧：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"
#include "../tools.c"
#include <cjson/cJSON.h>

#define ADDRESS     "tcp://localhost:1883"
#define CLIENTID    "ClientID"
#define TOPIC       "MQTT/Test"
#define QOS         0
#define TIMEOUT     10000L
int main(int argc, char* argv[])
{
    MQTTClient client;
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    int rc;
    int ch;
    MQTTClient_create(&client, ADDRESS, CLIENTID,
        MQTTCLIENT_PERSISTENCE_NONE, NULL);
    conn_opts.keepAliveInterval = 20;
    conn_opts.cleansession = 1;
    MQTTClient_setCallbacks(client, NULL, connlost, frame_test_arrvd, NULL);
    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to connect, return code %dn", rc);
        exit(EXIT_FAILURE);
    }
    printf("Subscribing to topic %snfor client %s using QoS%dnn"
           "Press Q<Enter> to quitnn", TOPIC, CLIENTID, QOS);
    MQTTClient_subscribe(client, TOPIC, QOS);
    do
    {
        ch = getchar();
    } while(ch!='Q' && ch != 'q');
    MQTTClient_disconnect(client, 10000);
    MQTTClient_destroy(&client);
    return rc;
}

我仍然想创建特定类型的消息，这不是理想的，我还没有找到导致分割错误的是什么，但是它以这种方式工作得很好。

update

我找到了一种创建特定类型的消息的方法，并仍将它们作为字符串发送以在MSGARRVD函数中解析它们，我刚刚创建了一个函数CJSON_TOSTRING将CJSON*对象转换为字符串，以便我可以创建CJOSN从我想要的任何结构中，然后将其转换为字符串发送。

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