Find cpio archive

find_cpio.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
//http://people.freebsd.org/~kientzle/libarchive/man/cpio.5.txt
struct cpio_newc_header {
    char    c_magic[6];// "070701"
    char    c_ino[8];  // 
    char    c_mode[8];
    char    c_uid[8];
    char    c_gid[8];
    char    c_nlink[8];
    char    c_mtime[8];
    char    c_filesize[8];
    char    c_devmajor[8];
    char    c_devminor[8];
    char    c_rdevmajor[8];
    char    c_rdevminor[8];
    char    c_namesize[8];
    char    c_check[8];    // always 0
};

#define CPIO_MAGIC "070701\0"
#define CPIO_MAGIC_SIZE strlen(CPIO_MAGIC)

static struct stat g_stat;
static struct cpio_newc_header g_cpio_header;

void usage(char *progname) {
    fprintf(stderr, "usage: %s <file>\n", progname);
}

int main(int argc, char* argv[]) {
    if (argc < 2) {
        usage(argv[0]);
        exit(0);
    }

    int fd = open(argv[1], O_RDONLY);
    if (fd < 0) {
        perror("open");
        exit(1);
    }

    // save the data about original file
    fstat(fd, &g_stat);
    fprintf(stdout, "original size: %tu\n", g_stat.st_size);

    off_t offset = 0;
    char cursor[7]= "\0\0\0\0\0\0\0";


    while (offset < (g_stat.st_size - CPIO_MAGIC_SIZE)) {
        offset = lseek(fd, offset, SEEK_SET);
        if (offset < 0) {
            perror("seek");
            exit(2);
        }

        ssize_t count = read(fd, cursor, CPIO_MAGIC_SIZE);
        if (count == 0) {// EOF
            break;
        } else if (count < CPIO_MAGIC_SIZE) {
            perror("read");
            exit(3);
        }

        if (strcmp(CPIO_MAGIC, cursor) == 0) {
            char filename[1024];
            // came back to the start of the finding
            lseek(fd, offset, SEEK_SET);

            // read the header
            read(fd, &g_cpio_header, sizeof(g_cpio_header));

            // find the size of the filename
            unsigned int header_filename_size;
            char* namesize = strdup(g_cpio_header.c_namesize);
            namesize[9] = '\0';
            if (sscanf(namesize, "%x", &header_filename_size) == 1) {

                read(fd, filename, header_filename_size);

                filename[header_filename_size] = '\0';

                printf("offset: %tu filename: %s size: %zu\n", offset, filename, (size_t)g_cpio_header.c_filesize);
            }

            lseek(fd, offset, SEEK_SET);
        }
        offset++;
        fprintf(stdout, "%tu\r", offset);
    }

    return 0;
}