archive_write - Man Page

Streaming Archive Library (libarchive, -larchive)

#include <archive.h>

These functions provide a complete API for creating streaming archive files. The general process is to first create the struct archive object, set any desired options, initialize the archive, append entries, then close the archive and release all resources.

The following sketch illustrates basic usage of the library. In this example, the callback functions are simply wrappers around the standard open(2), write(2), and close(2) system calls.

#ifdef __linux__
#define	_FILE_OFFSET_BITS 64
#endif
#include <sys/stat.h>
#include <archive.h>
#include <archive_entry.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>

struct mydata {
  const char *name;
  int fd;
};

int
myopen(struct archive *a, void *client_data)
{
  struct mydata *mydata = client_data;

  mydata->fd = open(mydata->name, O_WRONLY | O_CREAT, 0644);
  if (mydata->fd >= 0)
    return (ARCHIVE_OK);
  else
    return (ARCHIVE_FATAL);
}

la_ssize_t
mywrite(struct archive *a, void *client_data, const void *buff, size_t n)
{
  struct mydata *mydata = client_data;

  return (write(mydata->fd, buff, n));
}

int
myclose(struct archive *a, void *client_data)
{
  struct mydata *mydata = client_data;

  if (mydata->fd > 0)
    close(mydata->fd);
  return (0);
}

void
write_archive(const char *outname, const char **filename)
{
  struct mydata *mydata = malloc(sizeof(struct mydata));
  struct archive *a;
  struct archive_entry *entry;
  struct stat st;
  char buff[8192];
  int len;
  int fd;

  a = archive_write_new();
  mydata->name = outname;
  /* Set archive format and filter according to output file extension.
   * If it fails, set default format. Platform depended function.
   * See supported formats in archive_write_set_format_filter_by_ext.c */
  if (archive_write_set_format_filter_by_ext(a, outname) != ARCHIVE_OK)  {
    archive_write_add_filter_gzip(a);
    archive_write_set_format_ustar(a);
  }
  archive_write_open(a, mydata, myopen, mywrite, myclose);
  while (*filename) {
    stat(*filename, &st);
    entry = archive_entry_new();
    archive_entry_copy_stat(entry, &st);
    archive_entry_set_pathname(entry, *filename);
    archive_write_header(a, entry);
    if ((fd = open(*filename, O_RDONLY)) != -1) {
      len = read(fd, buff, sizeof(buff));
      while (len > 0) {
        archive_write_data(a, buff, len);
        len = read(fd, buff, sizeof(buff));
      }
      close(fd);
    }
    archive_entry_free(entry);
    filename++;
  }
  archive_write_free(a);
}

int main(int argc, const char **argv)
{
  const char *outname;
  argv++;
  outname = *argv++;
  write_archive(outname, argv);
  return 0;
}

tar(1), archive_write_set_options(3), libarchive(3), cpio(5), mtree(5), tar(5)

The libarchive library first appeared in FreeBSD 5.3.

The libarchive library was written by Tim Kientzle ⟨kientzle@acm.org⟩.

There are many peculiar bugs in historic tar implementations that may cause certain programs to reject archives written by this library. For example, several historic implementations calculated header checksums incorrectly and will thus reject valid archives; GNU tar does not fully support pax interchange format; some old tar implementations required specific field terminations.

The default pax interchange format eliminates most of the historic tar limitations and provides a generic key/value attribute facility for vendor-defined extensions. One oversight in POSIX is the failure to provide a standard attribute for large device numbers. This library uses “SCHILY.devminor” and “SCHILY.devmajor” for device numbers that exceed the range supported by the backwards-compatible ustar header. These keys are compatible with Joerg Schilling's star archiver. Other implementations may not recognize these keys and will thus be unable to correctly restore device nodes with large device numbers from archives created by this library.

archive_read_disk(3), archive_util(3), archive_write_disk(3), archive_write_filter(3), archive_write_format(3), archive_write_new(3), archive_write_open(3), archive_write_set_options(3), archive_write_set_passphrase(3), bsdtar(1), libarchive(3), libarchive_changes(3), libarchive_internals(3).