Tribblix: manual page: archive

ARCHIVE_WRITE(3) Introduction to Library Functions ARCHIVE_WRITE(3)

NAME

archive_write - functions for creating archives

LIBRARY

Streaming Archive Library (libarchive, -larchive)

SYNOPSIS

#include <archive.h>

DESCRIPTION

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.

Create archive object

See archive_write_new(3).

To write an archive, you must first obtain an initialized struct
archive object from archive_write_new().

Enable filters and formats, configure block size and padding
See archive_write_filter(3), archive_write_format(3) and
archive_write_blocksize(3).

You can then modify this object for the desired operations with the
various archive_write_set_XXX() functions. In particular, you will
need to invoke appropriate archive_write_add_XXX() and
archive_write_set_XXX() functions to enable the corresponding
compression and format support.

Set options

See archive_write_set_options(3).

Open archive

See archive_write_open(3).

Once you have prepared the struct archive object, you call
archive_write_open() to actually open the archive and prepare it for
writing. There are several variants of this function; the most basic
expects you to provide pointers to several functions that can provide
blocks of bytes from the archive. There are convenience forms that
allow you to specify a filename, file descriptor, FILE * object, or a
block of memory from which to write the archive data.

Produce archive

See archive_write_header(3) and archive_write_data(3).

Individual archive entries are written in a three-step process: You
first initialize a struct archive_entry structure with information
about the new entry. At a minimum, you should set the pathname of the
entry and provide a struct stat with a valid st_mode field, which
specifies the type of object and st_size field, which specifies the
size of the data portion of the object.

Release resources

See archive_write_free(3).

After all entries have been written, use the archive_write_free()
function to release all resources.

EXAMPLES

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;
}

HISTORY

The libarchive library first appeared in FreeBSD 5.3.

AUTHORS

The libarchive library was written by Tim Kientzle <kientzle@acm.org>.

BUGS

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.

illumos February 2, 2012 illumos