linux c语言实现 tar

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

#define BLOCK_SIZE 512

typedef struct {
    char filename[100];
    char filemode[8];
    char userid[8];
    char groupid[8];
    char filesize[12];
    char mtime[12];
    char checksum[8];
    char type;
    char linkname[100];
    char magic[6];
    char version[2];
    char uname[32];
    char gname[32];
    char devmajor[8];
    char devminor[8];
    char prefix[155];
    char pad[12];
} TarHeader;

void write_header(FILE *tar, const char *filename) {
    TarHeader header;
    struct stat st;
    memset(&header, 0, sizeof(header));
    strncpy(header.filename, filename, sizeof(header.filename));
    stat(filename, &st);
    sprintf(header.filemode, "%07o", st.st_mode);
    sprintf(header.userid, "%07o", st.st_uid);
    sprintf(header.groupid, "%07o", st.st_gid);
    sprintf(header.filesize, "%011lo", (unsigned long)st.st_size);
    sprintf(header.mtime, "%011lo", (unsigned long)st.st_mtime);
    header.type = S_ISDIR(st.st_mode) ? '5' : '0';
    strncpy(header.magic, "ustar", 5);
    strncpy(header.version, "00", 2);
    strncpy(header.uname, getlogin(), sizeof(header.uname));
    strncpy(header.gname, getgid() == st.st_gid ? getlogin() : "", sizeof(header.gname));
    fwrite(&header, BLOCK_SIZE, 1, tar);
}

void write_data(FILE *tar, const char *filename) {
    FILE *file = fopen(filename, "rb");
    if (!file) return;
    char buffer[BLOCK_SIZE];
    size_t bytes_read;
    while ((bytes_read = fread(buffer, 1, BLOCK_SIZE, file)) > 0) {
        fwrite(buffer, 1, bytes_read, tar);
    }
    fclose(file);
}

void tar_directory(const char *dirname, const char *tarname) {
    FILE *tar = fopen(tarname, "wb");
    if (!tar) {
        perror("fopen");
        return;
    }
    DIR *dir = opendir(dirname);
    if (!dir) {
        perror("opendir");
        fclose(tar);
        return;
    }
    struct dirent *entry;
    while ((entry = readdir(dir)) != NULL) {
        char path[1024];
        snprintf(path, sizeof(path), "%s/%s", dirname, entry->d_name);
        if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0) continue;
        write_header(tar, path);
        if (entry->d_type == DT_REG) {
            write_data(tar, path);
        } else if (entry->d_type == DT_DIR) {
            tar_directory(path, tarname);
        }
    }
    closedir(dir);
    fclose(tar);
}

int main(int argc, char *argv[]) {
    if (argc != 3) {
        fprintf(stderr, "Usage: %s <directory> <tarfile>\n", argv[0]);
        return 1;
    }
    tar_directory(argv[1], argv[2]);
    return 0;
}