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LIBARCHIVE(3)		     Library Functions Manual		   LIBARCHIVE(3)

NAME
     libarchive -- functions for reading and writing streaming archives

LIBRARY
     Reading and Writing Streaming Archives Library (libarchive, -larchive)

OVERVIEW
     The  libarchive library provides a flexible interface for reading and writ-
     ing streaming archive files such as tar and cpio.	The  library  is  inher-
     ently  stream-oriented; readers serially iterate through the archive, writ-
     ers serially add things to the archive.  In particular, note that there  is
     no built-in support for random access nor for in-place modification.

     When  reading  an archive, the library automatically detects the format and
     the compression.  The library currently has read support for:
     *	 old-style tar
     *	 most variants of the POSIX "ustar" format,
     *	 the POSIX "pax interchange" format,
     *	 GNU-format tar archives,
     *	 POSIX octet-oriented cpio archives.
     The  library  automatically  detects  archives  compressed  with	gzip(1),
     bzip2(1), or compress(1) and decompresses them transparently.

     When writing an archive, you can specify the compression to be used and the
     format to use.  The library can write
     *	 POSIX-standard "ustar" archives,
     *	 POSIX "pax interchange format" archives,
     *	 POSIX octet-oriented cpio archives,
     *	 two different variants of shar archives.
     Pax interchange format is an extension of the tar archive format that elim-
     inates  essentially  all  of  the	limitations of historic tar formats in a
     standard fashion that is supported by  POSIX-compliant  pax(1)  implementa-
     tions  on	many systems as well as several newer implementations of tar(1).
     Note that the default write format will suppress the pax  extended  attrib-
     utes  for	most entries; explicitly requesting pax format will enable those
     attributes for all entries.

     The read and write APIs are accessed through the  archive_read_XXX()  func-
     tions  and  the archive_write_XXX() functions, respectively, and either can
     be used independently of the other.

     The rest of this manual page provides an overview of the library operation.
     More detailed information can be found in the individual manual  pages  for
     each API or utility function.

READING AN ARCHIVE
     To read an archive, you must first obtain an initialized struct archive ob-
     ject  from archive_read_new().  You can then modify this object for the de-
     sired   operations   with	 the	various    archive_read_set_XXX()    and
     archive_read_support_XXX()  functions.  In particular, you will need to in-
     voke appropriate archive_read_support_XXX() functions to enable the  corre-
     sponding  compression and format support.	Note that these latter functions
     perform two distinct operations: they cause the corresponding support  code
     to  be linked into your program, and they enable the corresponding auto-de-
     tect code.  Unless you have specific constraints, you will  generally  want
     to   invoke  archive_read_support_compression_all()  and  archive_read_sup-
     port_format_all() to enable auto-detect for  all  formats	and  compression
     types currently supported by the library.

     Once   you   have	 prepared   the   struct   archive   object,   you  call
     archive_read_open() to actually open the archive and prepare it  for  read-
     ing.

     Each  archive  entry  consists  of a header followed by a certain amount of
     data.  You can obtain  the  next  header  with  archive_read_next_header(),
     which  returns a pointer to an struct archive_entry structure with informa-
     tion about the current archive element.  If the entry is  a  regular  file,
     then  the	header	will  be  followed  by	the  file  data.   You	can  use
     archive_read_data() (which works much like the read(2) system call) to read
     this data from the  archive.   You  may  prefer  to  use  the  higher-level
     archive_read_data_skip(), which reads and discards the data for this entry,
     archive_read_data_to_buffer(),  which  reads  the	data  into  an in-memory
     buffer, archive_read_data_to_file(), which copies the data to the	provided
     file  descriptor,	or archive_read_extract(), which recreates the specified
     entry on disk and copies data from the archive.  In particular,  note  that
     archive_read_extract()  uses  the	struct	archive_entry structure that you
     provide it, which may differ from the entry just read from the archive.  In
     particular, many applications will want to override the pathname, file per-
     missions, or ownership.

     Once you have finished reading data  from	the  archive,  you  should  call
     archive_read_finish()   to   release   all   resources.	In   particular,
     archive_read_finish() closes the archive and frees any memory that was  al-
     located by the library.

     The  archive_read(3) manual page provides more detailed calling information
     for this API.

WRITING AN ARCHIVE
     You use a similar process to write  an  archive.	The  archive_write_new()
     function  creates	an  archive  object  useful  for  writing,  the  various
     archive_write_set_XXX() functions are used to set	parameters  for  writing
     the  archive,  and  archive_write_open()  completes the setup and opens the
     archive for writing.

     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 ob-
     ject and st_size field, which specifies the size of the data portion of the
     object.  The archive_write_header() function  actually  writes  the  header
     data  to  the  archive.  You can then use archive_write_data() to write the
     actual data.

     After all entries have been written, use the  archive_write_finish()  func-
     tion to release all resources.

     The archive_write(3) manual page provides more detailed calling information
     for this API.

DESCRIPTION
     Detailed  descriptions  of  each function are provided by the corresponding
     manual pages.

     All of the functions utilize an opaque struct archive  datatype  that  pro-
     vides access to the archive contents.

     The  struct  archive_entry  structure  contains a complete description of a
     single archive entry.  It uses an opaque interface that is fully documented
     in archive_entry(3).

     Users familiar with historic formats should be aware that the  newer  vari-
     ants  have  eliminated  most  restrictions on the length of textual fields.
     Clients should not assume that filenames, link names, user names, or  group
     names  are  limited  in  length.  In particular, pax interchange format can
     easily  accomodate  pathnames  in	arbitrary  character  sets  that  exceed
     PATH_MAX.

RETURN VALUES
     Most functions return zero on success, non-zero on error.	The return value
     indicates	the general severity of the error, ranging from ARCHIVE_WARNING,
     which indicates a minor problem that should probably  be  reported  to  the
     user, to ARCHIVE_FATAL, which indicates a serious problem that will prevent
     any  further  operations  on  this  archive.  On error, the archive_errno()
     function can be used to retrieve a numeric error code (see errno(2)).   The
     archive_error_string()  returns  a  textual error message suitable for dis-
     play.

     archive_read_new() and archive_write_new() return pointers to an  allocated
     and initialized struct archive object.

     archive_read_data()  and  archive_write_data() return a count of the number
     of bytes actually read or written.  A value of zero indicates  the  end  of
     the  data	for  this  entry.  A negative value indicates an error, in which
     case the archive_errno() and archive_error_string() functions can	be  used
     to obtain more information.

ENVIRONMENT
     There  are  character set conversions within the archive_entry(3) functions
     that are impacted by the currently-selected locale.

SEE ALSO
     tar(1),	  archive_entry(3),	 archive_read(3),	archive_util(3),
     archive_write(3), tar(5)

HISTORY
     The libarchive library first appeared in FreeBSD 5.3.

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

BUGS
     Some  archive  formats  support information that is not supported by struct
     archive_entry.  Such information cannot be fully archived or restored using
     this library.  This includes, for example, comments, character sets, or the
     arbitrary key/value  pairs  that  can  appear  in	pax  interchange  format
     archives.

     Conversely,  of course, not all of the information that can be stored in an
     struct archive_entry is supported by all formats.	For example,  cpio  for-
     mats  do  not support nanosecond timestamps; old tar formats do not support
     large device numbers.

FreeBSD 5.5			 January 8, 2005		   LIBARCHIVE(3)
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