Thread: Client to Server Communication using a Message Queue

So here's my issue. I enable the server first and then enable the client to send the message over to server, where the server does a simple lowercase to uppercase transformation on the message sent from the client, and then the server sends it back to the client with all uppercase letters. However, during the process of communication on the server side after receiving the client's message, I'm receiving a Segmentation Fault and I can't track down why. Any idea of why this is happening?


Here is the client side's code:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <string.h>
#include <ctype.h>
#include <fcntl.h>

#define SERVER 1L
typedef struct {
    long    msg_to;
    long    msg_fm;
    char    buffer[BUFSIZ];
} MESSAGE;

int mid;
key_t key;
struct msqid_ds buf;
MESSAGE msg;
FILE *inFile;

int main(int argc, char** argv) {

    //Aquiring Message Queue ID
    key = ftok(".", 'z');
    mid = msgget(key, 0);

    //Display Message Queue and Client ID
    printf("Message Queue ID: %d\n", mid);
    printf("Client ID: %ld\n", (long)getpid());

    //Opeining input file, throw an error if invalid file
    inFile = fopen(argv[1], "r");
    if(inFile == NULL){
        printf("Unable to open File = %s\n", argv[1]);
        return 1;
    }

    //Copy input characters into msg.buffer, loops breaks when EOF is reached
    int i = 0;
    while(1){
        msg.buffer[i] = fgetc(inFile);
        if(msg.buffer[i]==EOF){
            msg.buffer[i] = '\0';
            break;
        }
        i++;
    }

    //Displaying message before conversion of server
    printf("Message before conversion:\n");
    printf("%s\n", msg.buffer);

    //Getting Client PID and preparing message to message queue
    long iD = (long)getpid();
    msg.msg_to = SERVER;
    msg.msg_fm = (long)getpid();

    //Send message to Message Queue for Server, throws and error for invalid input
    if(msgsnd(mid, &msg, sizeof(msg.buffer), 0)==-1){
        perror("msgsnd");
        exit(-1);
    }

    //Client waits for response from Server, throws an error if invalid input
    if(msgrcv(mid, &msg, sizeof(msg), iD, 0)<0){
        perror("msgrcv");
        exit(-1);
    }

    //Display new converting message.
    printf("Message after conversion\n");
    printf("%s\n", msg.buffer);

    //Removing message queue
    msgctl(mid, IPC_RMID, (struct msqid_ds *) 0);

    //Client exits
    return (EXIT_SUCCESS);
}

And here is the server side's code

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <string.h>
#include <ctype.h>
#include <fcntl.h>

#define SERVER 1L
typedef struct {
    long    msg_to;
    long    msg_fm;
    char    buffer[BUFSIZ];
} MESSAGE;

int mid;
key_t key;
struct msqid_ds buf;
MESSAGE msg;

int main(int argc, char** argv) {

    //Creating a message queue
    key = ftok(".", 'z');
    if((mid = msgget(key, IPC_CREAT | 0660))<0){
        printf("Error Creating Message Queue\n");
        exit(-1);
    }

    //Display Message Queue and Server ID
    printf("Message Queue ID: %d\n", mid);
    printf("Server ID: %ld\n", (long)getpid());    

    //Receiving message from client, throws and error if input is invalid
    if(msgrcv(mid, &msg, sizeof(msg.buffer), SERVER, 0)<0){
        perror("msgrcv");
        exit(-1);
    }

    //Server displays received message
    printf("SERVER receives:\n");
    printf("%s\n", msg.buffer);

    //Aquiring Cliend PID to message return
    long client = msg.msg_fm;

    //convert all lowercase characters to uppercase
    int i;
    while(msg.buffer[i] != '\0'){
        msg.buffer[i] = toupper(msg.buffer[i]);
        i++;
    }

    //prep return message
    msg.msg_fm = SERVER;
    msg.msg_to = client;

    //send converting message back to client, throws and error if input is invalid
    if(msgsnd(mid, (struct MESSAGE*)&msg, sizeof(msg.buffer), 0)==-1){
        perror("msgsnd");
        exit(-1);
    }

    //server exits
    return (EXIT_SUCCESS);
}

Much love Salem, thanks for the quick fix. Now my expected output is my actual output .