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 .\" Copyright (c) 2003-2007 Tim Kientzle
 .\" All rights reserved.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
 .\" are met:
 .\" 1. Redistributions of source code must retain the above copyright
 .\"    notice, this list of conditions and the following disclaimer.
 .\" 2. Redistributions in binary form must reproduce the above copyright
 .\"    notice, this list of conditions and the following disclaimer in the
 .\"    documentation and/or other materials provided with the distribution.
 .\"
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 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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 .\" $FreeBSD: src/lib/libarchive/libarchive.3,v 1.11 2007/01/09 08:05:56 kientzle Exp $
 .\"
 .Dd August 19, 2006
 .Dt LIBARCHIVE 3
 .Os
 .Sh NAME
 .Nm libarchive
 .Nd functions for reading and writing streaming archives
 .Sh LIBRARY
 .Lb libarchive
 .Sh OVERVIEW
 The
 .Nm
 library provides a flexible interface for reading and writing
 streaming archive files such as tar and cpio.
 The library is inherently stream-oriented; readers serially iterate through
 the archive, writers serially add things to the archive.
 In particular, note that there is no built-in support for
 random access nor for in-place modification.
 .Pp
 When reading an archive, the library automatically detects the
 format and the compression.
 The library currently has read support for:
 .Bl -bullet -compact
 .It
 old-style tar archives,
 .It
 most variants of the POSIX
 .Dq ustar
 format,
 .It
 the POSIX
 .Dq pax interchange
 format,
 .It
 GNU-format tar archives,
 .It
 most common cpio archive formats,
 .It
 ISO9660 CD images (with or without RockRidge extensions),
 .It
 Zip archives.
 .El
 The library automatically detects archives compressed with
 .Xr gzip 1 ,
 .Xr bzip2 1 ,
 or
 .Xr compress 1
 and decompresses them transparently.
 .Pp
 When writing an archive, you can specify the compression
 to be used and the format to use.
 The library can write
 .Bl -bullet -compact
 .It
 POSIX-standard
 .Dq ustar
 archives,
 .It
 POSIX
 .Dq pax interchange format
 archives,
 .It
 POSIX octet-oriented cpio archives,
 .It
 two different variants of shar archives.
 .El
 Pax interchange format is an extension of the tar archive format that
 eliminates essentially all of the limitations of historic tar formats
 in a standard fashion that is supported
 by POSIX-compliant
 .Xr pax 1
 implementations on many systems as well as several newer implementations of
 .Xr tar 1 .
 Note that the default write format will suppress the pax extended
 attributes for most entries; explicitly requesting pax format will
 enable those attributes for all entries.
 .Pp
 The read and write APIs are accessed through the
 .Fn archive_read_XXX
 functions and the
 .Fn archive_write_XXX
 functions, respectively, and either can be used independently
 of the other.
 .Pp
 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.
 .Sh READING AN ARCHIVE
 To read an archive, you must first obtain an initialized
 .Tn struct archive
 object from
 .Fn archive_read_new .
 You can then modify this object for the desired operations with the
 various
 .Fn archive_read_set_XXX
 and
 .Fn archive_read_support_XXX
 functions.
 In particular, you will need to invoke appropriate
 .Fn archive_read_support_XXX
 functions to enable the corresponding 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-detect code.
 Unless you have specific constraints, you will generally want
 to invoke
 .Fn archive_read_support_compression_all
 and
 .Fn archive_read_support_format_all
 to enable auto-detect for all formats and compression types
 currently supported by the library.
 .Pp
 Once you have prepared the
 .Tn struct archive
 object, you call
 .Fn archive_read_open
 to actually open the archive and prepare it for reading.
 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 read the archive data.
 Note that the core library makes no assumptions about the
 size of the blocks read;
 callback functions are free to read whatever block size is
 most appropriate for the medium.
 .Pp
 Each archive entry consists of a header followed by a certain
 amount of data.
 You can obtain the next header with
 .Fn archive_read_next_header ,
 which returns a pointer to an
 .Tn struct archive_entry
 structure with information 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
 .Fn archive_read_data
 (which works much like the
 .Xr read 2
 system call)
 to read this data from the archive.
 You may prefer to use the higher-level
 .Fn archive_read_data_skip ,
 which reads and discards the data for this entry,
 .Fn archive_read_data_to_buffer ,
 which reads the data into an in-memory buffer,
 .Fn archive_read_data_to_file ,
 which copies the data to the provided file descriptor, or
 .Fn archive_read_extract ,
 which recreates the specified entry on disk and copies data
 from the archive.
 In particular, note that
 .Fn archive_read_extract
 uses the
 .Tn 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 permissions, or ownership.
 .Pp
 Once you have finished reading data from the archive, you
 should call
 .Fn archive_read_close
 to close the archive, then call
 .Fn archive_read_finish
 to release all resources, including all memory allocated by the library.
 .Pp
 The
 .Xr archive_read 3
 manual page provides more detailed calling information for this API.
 .Sh WRITING AN ARCHIVE
 You use a similar process to write an archive.
 The
 .Fn archive_write_new
 function creates an archive object useful for writing,
 the various
 .Fn archive_write_set_XXX
 functions are used to set parameters for writing the archive, and
 .Fn archive_write_open
 completes the setup and opens the archive for writing.
 .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.
 The
 .Fn archive_write_header
 function actually writes the header data to the archive.
 You can then use
 .Fn archive_write_data
 to write the actual data.
 .Pp
 After all entries have been written, use the
 .Fn archive_write_finish
 function to release all resources.
 .Pp
 The
 .Xr archive_write 3
 manual page provides more detailed calling information for this API.
 .Sh DESCRIPTION
 Detailed descriptions of each function are provided by the
 corresponding manual pages.
 .Pp
 All of the functions utilize an opaque
 .Tn struct archive
 datatype that provides access to the archive contents.
 .Pp
 The
 .Tn struct archive_entry
 structure contains a complete description of a single archive
 entry.
 It uses an opaque interface that is fully documented in
 .Xr archive_entry 3 .
 .Pp
 Users familiar with historic formats should be aware that the newer
 variants 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 accommodate pathnames
 in arbitrary character sets that exceed
 .Va PATH_MAX .
 .Sh RETURN VALUES
 Most functions return zero on success, non-zero on error.
 The return value indicates the general severity of the error, ranging
 from
 .Cm ARCHIVE_WARN ,
 which indicates a minor problem that should probably be reported
 to the user, to
 .Cm ARCHIVE_FATAL ,
 which indicates a serious problem that will prevent any further
 operations on this archive.
 On error, the
 .Fn archive_errno
 function can be used to retrieve a numeric error code (see
 .Xr errno 2 ) .
 The
 .Fn archive_error_string
 returns a textual error message suitable for display.
 .Pp
 .Fn archive_read_new
 and
 .Fn archive_write_new
 return pointers to an allocated and initialized
 .Tn struct archive
 object.
 .Pp
 .Fn archive_read_data
 and
 .Fn 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
 .Fn archive_errno
 and
 .Fn archive_error_string
 functions can be used to obtain more information.
 .Sh ENVIRONMENT
 There are character set conversions within the
 .Xr archive_entry 3
 functions that are impacted by the currently-selected locale.
 .Sh SEE ALSO
 .Xr tar 1 ,
 .Xr archive_entry 3 ,
 .Xr archive_read 3 ,
 .Xr archive_util 3 ,
 .Xr archive_write 3 ,
 .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
 Some archive formats support information that is not supported by
 .Tn 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.
 .Pp
 Conversely, of course, not all of the information that can be
 stored in an
 .Tn struct archive_entry
 is supported by all formats.
 For example, cpio formats do not support nanosecond timestamps;
 old tar formats do not support large device numbers.
	.\" Copyright (c) 2003-2007 Tim Kientzle
	.\" All rights reserved.
	.\"
	.\" Redistribution and use in source and binary forms, with or without
	.\" modification, are permitted provided that the following conditions
	.\" are met:
	.\" 1. Redistributions of source code must retain the above copyright
	.\" notice, this list of conditions and the following disclaimer.
	.\" 2. Redistributions in binary form must reproduce the above copyright
	.\" notice, this list of conditions and the following disclaimer in the
	.\" documentation and/or other materials provided with the distribution.
	.\"
	.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	.\" SUCH DAMAGE.
	.\"
	.\" $FreeBSD: src/lib/libarchive/libarchive.3,v 1.11 2007/01/09 08:05:56 kientzle Exp $
	.\"
	.Dd August 19, 2006
	.Dt LIBARCHIVE 3
	.Os
	.Sh NAME
	.Nm libarchive
	.Nd functions for reading and writing streaming archives
	.Sh LIBRARY
	.Lb libarchive
	.Sh OVERVIEW
	The
	.Nm
	library provides a flexible interface for reading and writing
	streaming archive files such as tar and cpio.
	The library is inherently stream-oriented; readers serially iterate through
	the archive, writers serially add things to the archive.
	In particular, note that there is no built-in support for
	random access nor for in-place modification.
	.Pp
	When reading an archive, the library automatically detects the
	format and the compression.
	The library currently has read support for:
	.Bl -bullet -compact
	.It
	old-style tar archives,
	.It
	most variants of the POSIX
	.Dq ustar
	format,
	.It
	the POSIX
	.Dq pax interchange
	format,
	.It
	GNU-format tar archives,
	.It
	most common cpio archive formats,
	.It
	ISO9660 CD images (with or without RockRidge extensions),
	.It
	Zip archives.
	.El
	The library automatically detects archives compressed with
	.Xr gzip 1 ,
	.Xr bzip2 1 ,
	or
	.Xr compress 1
	and decompresses them transparently.
	.Pp
	When writing an archive, you can specify the compression
	to be used and the format to use.
	The library can write
	.Bl -bullet -compact
	.It
	POSIX-standard
	.Dq ustar
	archives,
	.It
	POSIX
	.Dq pax interchange format
	archives,
	.It
	POSIX octet-oriented cpio archives,
	.It
	two different variants of shar archives.
	.El
	Pax interchange format is an extension of the tar archive format that
	eliminates essentially all of the limitations of historic tar formats
	in a standard fashion that is supported
	by POSIX-compliant
	.Xr pax 1
	implementations on many systems as well as several newer implementations of
	.Xr tar 1 .
	Note that the default write format will suppress the pax extended
	attributes for most entries; explicitly requesting pax format will
	enable those attributes for all entries.
	.Pp
	The read and write APIs are accessed through the
	.Fn archive_read_XXX
	functions and the
	.Fn archive_write_XXX
	functions, respectively, and either can be used independently
	of the other.
	.Pp
	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.
	.Sh READING AN ARCHIVE
	To read an archive, you must first obtain an initialized
	.Tn struct archive
	object from
	.Fn archive_read_new .
	You can then modify this object for the desired operations with the
	various
	.Fn archive_read_set_XXX
	and
	.Fn archive_read_support_XXX
	functions.
	In particular, you will need to invoke appropriate
	.Fn archive_read_support_XXX
	functions to enable the corresponding 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-detect code.
	Unless you have specific constraints, you will generally want
	to invoke
	.Fn archive_read_support_compression_all
	and
	.Fn archive_read_support_format_all
	to enable auto-detect for all formats and compression types
	currently supported by the library.
	.Pp
	Once you have prepared the
	.Tn struct archive
	object, you call
	.Fn archive_read_open
	to actually open the archive and prepare it for reading.
	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 read the archive data.
	Note that the core library makes no assumptions about the
	size of the blocks read;
	callback functions are free to read whatever block size is
	most appropriate for the medium.
	.Pp
	Each archive entry consists of a header followed by a certain
	amount of data.
	You can obtain the next header with
	.Fn archive_read_next_header ,
	which returns a pointer to an
	.Tn struct archive_entry
	structure with information 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
	.Fn archive_read_data
	(which works much like the
	.Xr read 2
	system call)
	to read this data from the archive.
	You may prefer to use the higher-level
	.Fn archive_read_data_skip ,
	which reads and discards the data for this entry,
	.Fn archive_read_data_to_buffer ,
	which reads the data into an in-memory buffer,
	.Fn archive_read_data_to_file ,
	which copies the data to the provided file descriptor, or
	.Fn archive_read_extract ,
	which recreates the specified entry on disk and copies data
	from the archive.
	In particular, note that
	.Fn archive_read_extract
	uses the
	.Tn 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 permissions, or ownership.
	.Pp
	Once you have finished reading data from the archive, you
	should call
	.Fn archive_read_close
	to close the archive, then call
	.Fn archive_read_finish
	to release all resources, including all memory allocated by the library.
	.Pp
	The
	.Xr archive_read 3
	manual page provides more detailed calling information for this API.
	.Sh WRITING AN ARCHIVE
	You use a similar process to write an archive.
	The
	.Fn archive_write_new
	function creates an archive object useful for writing,
	the various
	.Fn archive_write_set_XXX
	functions are used to set parameters for writing the archive, and
	.Fn archive_write_open
	completes the setup and opens the archive for writing.
	.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.
	The
	.Fn archive_write_header
	function actually writes the header data to the archive.
	You can then use
	.Fn archive_write_data
	to write the actual data.
	.Pp
	After all entries have been written, use the
	.Fn archive_write_finish
	function to release all resources.
	.Pp
	The
	.Xr archive_write 3
	manual page provides more detailed calling information for this API.
	.Sh DESCRIPTION
	Detailed descriptions of each function are provided by the
	corresponding manual pages.
	.Pp
	All of the functions utilize an opaque
	.Tn struct archive
	datatype that provides access to the archive contents.
	.Pp
	The
	.Tn struct archive_entry
	structure contains a complete description of a single archive
	entry.
	It uses an opaque interface that is fully documented in
	.Xr archive_entry 3 .
	.Pp
	Users familiar with historic formats should be aware that the newer
	variants 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 accommodate pathnames
	in arbitrary character sets that exceed
	.Va PATH_MAX .
	.Sh RETURN VALUES
	Most functions return zero on success, non-zero on error.
	The return value indicates the general severity of the error, ranging
	from
	.Cm ARCHIVE_WARN ,
	which indicates a minor problem that should probably be reported
	to the user, to
	.Cm ARCHIVE_FATAL ,
	which indicates a serious problem that will prevent any further
	operations on this archive.
	On error, the
	.Fn archive_errno
	function can be used to retrieve a numeric error code (see
	.Xr errno 2 ) .
	The
	.Fn archive_error_string
	returns a textual error message suitable for display.
	.Pp
	.Fn archive_read_new
	and
	.Fn archive_write_new
	return pointers to an allocated and initialized
	.Tn struct archive
	object.
	.Pp
	.Fn archive_read_data
	and
	.Fn 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
	.Fn archive_errno
	and
	.Fn archive_error_string
	functions can be used to obtain more information.
	.Sh ENVIRONMENT
	There are character set conversions within the
	.Xr archive_entry 3
	functions that are impacted by the currently-selected locale.
	.Sh SEE ALSO
	.Xr tar 1 ,
	.Xr archive_entry 3 ,
	.Xr archive_read 3 ,
	.Xr archive_util 3 ,
	.Xr archive_write 3 ,
	.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
	Some archive formats support information that is not supported by
	.Tn 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.
	.Pp
	Conversely, of course, not all of the information that can be
	stored in an
	.Tn struct archive_entry
	is supported by all formats.
	For example, cpio formats do not support nanosecond timestamps;
	old tar formats do not support large device numbers.