Read farbfeld image into header array and body buffer

ff3.c

#include <err.h>
#include <inttypes.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

int
main(int argc, char **argv)
{
    struct stat s;
    uint32_t header[4];
    unsigned char *img;
    size_t img_size;
    FILE *f;

    if (argc != 2)
        errx(EXIT_FAILURE, "Usage: ff <file>");
    if (stat(argv[1], &s) != 0)
        err(EXIT_FAILURE, "Cannot stat %s", argv[1]);
    if ((size_t)s.st_size < sizeof(header))
        errx(EXIT_FAILURE, "%s is too small", argv[1]);

    img_size = s.st_size - sizeof(header);

    if ((img = malloc(img_size)) == NULL)
        err(EXIT_FAILURE, "Cannot allocate memory for reading %s", argv[1]);
    if ((f = fopen(argv[1], "r")) == NULL)
        err(EXIT_FAILURE, "Cannot open %s", argv[1]);
    if (fread(header, 1, sizeof(header), f) != sizeof(header))
        err(EXIT_FAILURE, "Cannot read header of %s", argv[1]);
    if (fread(img, 1, img_size, f) != img_size)
        err(EXIT_FAILURE, "Cannot read image data of %s", argv[1]);
    if (fclose(f) != 0)
        err(EXIT_FAILURE, "Cannot close %s", argv[1]);
    if (memcmp(header, "farbfeld", sizeof("farbfeld") - 1) != 0)
        errx(EXIT_FAILURE, "%s is not a farbfeld image", argv[1]);

    (void)printf("W: %"PRIu32"\n", ntohl(header[2]));
    (void)printf("H: %"PRIu32"\n", ntohl(header[3]));

    free(img);
    return 0;
}