POSIX mq_receive issue: Message too long

[katwalatapan]

Hello,

I am trying to implement posix message queue application. I am faced with an error on the mq_receive section. It says "Message too long". I've tried couple of small tweeks, but to no result. Please do suggest any rectificaitons.

mq_send section-works successfully

#include <mqueue.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <sys/stat.h>
#include <string.h>
#include <signal.h>

#define MSG_SIZE 16
#define MQ_NAME "/msgqueue"
int main(void)
{
      
      mqd_t    mqPXId;          
        char *msg = "test";
         
        
        if ((mqPXId = mq_open (MQ_NAME, O_RDWR | O_CREAT, S_IWUSR | S_IRUSR, NULL)) ==-1) 
            { 
            printf ("sendTask: mq_open failed: %s\n", strerror(errno)); 
            return 0; 
            }

           
        if (mq_send (mqPXId, msg, MSG_SIZE, NULL) == -1) 
            { 
            printf ("sendTask: mq_send failed\n"); 
            return 0; 
            } 
        else 
        {
            printf ("sendTask: mq_send succeeded, msg sent: %s\n",msg); 
         }
            return 0;
}

mq_receive section: error-Message too long

#include <stdio.h>
#include <mqueue.h>
#include <pthread.h>
#include <string.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <errno.h>
#define MSG_SIZE 16
#define MQ_NAME "/msgqueue"

int main(void)
{
    mqd_t    mqPXId;         /* msg queue descriptor */ 
        char     *msg;  /* msg buffer */ 
       // unsigned int      prio;           /* priority of message */

     
        /* open message queue using default attributes */ 
        if ((mqPXId = mq_open (MQ_NAME, O_RDWR , S_IWUSR | S_IRUSR, NULL))  
            ==  -1) 
            { 
            printf ("receiveTask: mq_open failed\n"); 
            return 0; 
            }

     
        /* try reading from queue */ 
        if (mq_receive (mqPXId,(char *)&msg,MSG_SIZE, NULL) == -1) 
            { 
            printf ("receiveTask: mq_receive failed: %s\n",strerror(errno)); 
            return 0; 
            } 
        else 
            { 
            printf ("receiveTask: Msg of priority received:\n\t\t%s\n", 
                    msg); 
            } 
return 0;
        }

[Rubberman]

Look at this part of the sender code:

        if (mq_send (mqPXId, msg, MSG_SIZE, NULL) == -1) 
            { 
            printf ("sendTask: mq_send failed\n"); 
            return 0; 
            }

Note that you send MSG_SIZE bytes, yet the string is only 5 bytes long (4 chars + NUL). On the send, you MUST specify the number of bytes in the message, 5 in this case.

[grego122]

Was this ever resolved. I took the suggestions above but I still receive the "Message too long" for mq_receive().

See code below:

#include <stdio.h>
#include <mqueue.h>
#include <pthread.h>
#include <string.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <errno.h>
#define MSG_SIZE 16
#define MQ_NAME "/msgqueue"

int main(void) {
mqd_t mqPXId; /* msg queue descriptor */
char buffer[MSG_SIZE];
ssize_t bytes_received;

/* open message queue using default attributes */
if ((mqPXId = mq_open (MQ_NAME, O_RDWR , S_IWUSR | S_IRUSR, NULL)) == -1) {
printf ("receiveTask: mq_open failed\n");
return 0;
}

/* try reading from queue */
if (mq_receive (mqPXId, buffer, sizeof(buffer), NULL) == -1) {
printf ("receiveTask: mq_receive failed: %s\n",strerror(errno));
return 0;
}
else {
printf ("receiveTask: Msg of priority received:\n\t\t%s\n", buffer);
}
return 0;
}

[Rubberman]

So, show us the code where you send the message.