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.Dd February 2, 2012

.Dt ARCHIVE_WRITE 3

.Os

.Sh NAME

.Nm archive_write

.Nd functions for creating archives

.Sh LIBRARY

Streaming Archive Library (libarchive, -larchive)

.Sh SYNOPSIS

.In archive.h

.Sh DESCRIPTION

These functions provide a complete API for creating streaming

archive files.

The general process is to first create the

.Tn struct archive

object, set any desired options, initialize the archive, append entries, then

close the archive and release all resources.

.\"

.Ss Create archive object

See

.Xr archive_write_new 3 .

.Pp

To write an archive, you must first obtain an initialized

.Tn struct archive

object from

.Fn archive_write_new .

.\"

.Ss Enable filters and formats, configure block size and padding

See

.Xr archive_write_filter 3 ,

.Xr archive_write_format 3

and

.Xr archive_write_blocksize 3 .

.Pp

You can then modify this object for the desired operations with the

various

.Fn archive_write_set_XXX

functions.

In particular, you will need to invoke appropriate

.Fn archive_write_add_XXX

and

.Fn archive_write_set_XXX

functions to enable the corresponding compression and format

support.

.\"

.Ss Set options

See

.Xr archive_read_set_options 3 .

.\"

.Ss Open archive

See

.Xr archive_write_open 3 .

.Pp

Once you have prepared the

.Tn struct archive

object, you call

.Fn 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,

.Ft "FILE *"

object, or a block of memory from which to write the archive data.

.\"

.Ss Produce archive

See

.Xr archive_write_header 3

and

.Xr archive_write_data 3 .

.Pp

Individual archive entries are written in a three-step

process:

You first initialize a

.Tn struct archive_entry

structure with information about the new entry.

At a minimum, you should set the pathname of the

entry and provide a

.Va struct stat

with a valid

.Va st_mode

field, which specifies the type of object and

.Va st_size

field, which specifies the size of the data portion of the object.

.\"

.Ss Release resources

See

.Xr archive_write_free 3 .

.Pp

After all entries have been written, use the

.Fn archive_write_free

function to release all resources.

.\"

.Sh EXAMPLE

The following sketch illustrates basic usage of the library.

In this example,

the callback functions are simply wrappers around the standard

.Xr open 2 ,

.Xr write 2 ,

and

.Xr close 2

system calls.

.Bd -literal -offset indent

#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;

}

.Ed

.Sh SEE ALSO

.Xr tar 1 ,

.Xr libarchive 3 ,

.Xr archive_write_set_options 3 ,

.Xr cpio 5 ,

.Xr mtree 5 ,

.Xr tar 5

.Sh HISTORY

The

.Nm libarchive

library first appeared in

.Fx 5.3 .

.Sh AUTHORS

.An -nosplit

The

.Nm libarchive

library was written by

.An Tim Kientzle Aq kientzle@acm.org .

.Sh 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.

.Pp

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

.Dq SCHILY.devminor

and

.Dq SCHILY.devmajor

for device numbers that exceed the range supported by the backwards-compatible

ustar header.

These keys are compatible with Joerg Schilling's

.Nm 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.