Thread: information about file - stat sys call

I want to implemment ipc as is described in the comments. I'am having trouble with the stat sys call. After receiving file name in server if i write

Code:

 printf("%ld\n", st.st_size);

i get 1 when the file has 5M... Then it gives error in the perror when it tries to write. What it wrong?
server: write error
: Bad address

Code:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <string.h>

#define BUFSIZE 1024

int main()
{
    int fd1[2], fd2[2], pid;
    size_t n;
    char buf[BUFSIZE];
    struct stat st;
    pipe(fd1);
    pipe(fd2);
    if ((pid = fork()) == 0)
    {
        close(fd1[0]);
        close(fd2[1]);
        n = read(STDIN_FILENO, buf, BUFSIZE - 1); // 1. client(child) reads file name from stdin
        buf[n] = '\0';
        write(fd1[1], buf, n); // 2. client sends file name over pipe to server
        while ((n = read(fd2[0], buf, BUFSIZE)) > 0)
        {
            if ((write (STDOUT_FILENO, buf, n)) != n) // 6. client reads file info from pipe and outputs to stdout
            {
                perror("client: write error\n");
            }
        }
    }
    else
    {
        close(fd1[1]);
        close(fd2[0]);
        read(fd1[0], buf, BUFSIZE); // 3. server (parent) reads file name from pipe
        stat(buf, &st); // 4. server obtains information about the file (stat sys call)
        if (write(fd2[1], (void *)st.st_size, sizeof(st.st_size)) != sizeof(st.st_size)) // 5. server sends file information over pipe to client
        {
            perror("server: write error\n");
        } 
        if (write(fd2[1], (void *)st.st_atime, sizeof(st.st_atime)) != sizeof (st.st_atime))
        {
            perror("server: write error\n");
        }
    }
    return 0;
}

You forgot to zero-terminate the filename that the server reads (which should be limited to BUFSIZE-1). Ditto for the read in the client.

You're sending the newline as part of the filename.

read and write return an ssize_t (a signed value), not a size_t (an unsigned value).

Writing the raw binary of the returned value to stdout is not going to be very useful. Why not use printf?

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>

#define BUFSIZE 1024
enum {IN, OUT};

int main() {
    int CtoS[2], StoC[2], pid;
    ssize_t n;
    char buf[BUFSIZE];

    pipe(CtoS);
    pipe(StoC);
    pid = fork();
    if (pid == -1) {
        perror("fork error");
        exit(1);
    }

    if (pid == 0) {
        close(CtoS[IN]);
        close(StoC[OUT]);

        printf("Enter filename: ");
        fflush(stdout);
        fgets(buf, BUFSIZE, stdin);
        n = strlen(buf);
        if (buf[n - 1] == '\n')
            buf[--n] = '\0';

        write(CtoS[OUT], buf, n);

        ssize_t pos = 0;
        while ((n = read(StoC[IN], buf + pos, BUFSIZE - 1 - pos)) > 0)
            pos += n;
        buf[pos] = '\0';

        printf("size :[%ld]\n", (long)*(off_t*)buf);
        printf("atime:[%ld]\n", (long)*(time_t*)(buf + sizeof(off_t)));
    }

    else {
        struct stat st;

        close(CtoS[OUT]);
        close(StoC[IN]);

        n = read(CtoS[IN], buf, BUFSIZE - 1);
        buf[n] = '\0';

        if (stat(buf, &st) != 0) {
            perror("server: stat error");
            exit(1);
        }

        if (write(StoC[OUT], &st.st_size, sizeof(st.st_size)) != sizeof(st.st_size)) {
            perror("server: write error 1");
            exit(1);
        } 

        if (write(StoC[OUT], &st.st_atime, sizeof(st.st_atime)) != sizeof (st.st_atime)) {
            perror("server: write error 2");
            exit(1);
        }
    }

    return 0;
}