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.\" Copyright (c) 2003-2007 Tim Kientzle
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.\" All rights reserved.
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" $FreeBSD: src/lib/libarchive/libarchive.3,v 1.11 2007/01/09 08:05:56 kientzle Exp $
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.Nd functions for reading and writing streaming archives
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library provides a flexible interface for reading and writing
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streaming archive files such as tar and cpio.
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The library is inherently stream-oriented; readers serially iterate through
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the archive, writers serially add things to the archive.
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In particular, note that there is no built-in support for
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random access nor for in-place modification.
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When reading an archive, the library automatically detects the
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format and the compression.
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The library currently has read support for:
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old-style tar archives,
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most variants of the POSIX
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GNU-format tar archives,
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most common cpio archive formats,
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ISO9660 CD images (with or without RockRidge extensions),
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The library automatically detects archives compressed with
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and decompresses them transparently.
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When writing an archive, you can specify the compression
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to be used and the format to use.
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.Dq pax interchange format
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POSIX octet-oriented cpio archives,
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two different variants of shar archives.
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Pax interchange format is an extension of the tar archive format that
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eliminates essentially all of the limitations of historic tar formats
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in a standard fashion that is supported
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implementations on many systems as well as several newer implementations of
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Note that the default write format will suppress the pax extended
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attributes for most entries; explicitly requesting pax format will
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enable those attributes for all entries.
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The read and write APIs are accessed through the
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.Fn archive_write_XXX
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functions, respectively, and either can be used independently
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The rest of this manual page provides an overview of the library
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More detailed information can be found in the individual manual
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pages for each API or utility function.
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.Sh READING AN ARCHIVE
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To read an archive, you must first obtain an initialized
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.Fn archive_read_new .
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You can then modify this object for the desired operations with the
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.Fn archive_read_set_XXX
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.Fn archive_read_support_XXX
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In particular, you will need to invoke appropriate
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.Fn archive_read_support_XXX
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functions to enable the corresponding compression and format
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Note that these latter functions perform two distinct operations:
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they cause the corresponding support code to be linked into your
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program, and they enable the corresponding auto-detect code.
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Unless you have specific constraints, you will generally want
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.Fn archive_read_support_compression_all
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.Fn archive_read_support_format_all
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to enable auto-detect for all formats and compression types
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currently supported by the library.
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Once you have prepared the
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.Fn archive_read_open
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to actually open the archive and prepare it for reading.
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There are several variants of this function;
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the most basic expects you to provide pointers to several
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functions that can provide blocks of bytes from the archive.
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There are convenience forms that allow you to
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specify a filename, file descriptor,
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object, or a block of memory from which to read the archive data.
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Note that the core library makes no assumptions about the
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size of the blocks read;
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callback functions are free to read whatever block size is
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most appropriate for the medium.
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Each archive entry consists of a header followed by a certain
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You can obtain the next header with
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.Fn archive_read_next_header ,
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which returns a pointer to an
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.Tn struct archive_entry
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structure with information about the current archive element.
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If the entry is a regular file, then the header will be followed
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.Fn archive_read_data
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(which works much like the
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to read this data from the archive.
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You may prefer to use the higher-level
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.Fn archive_read_data_skip ,
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which reads and discards the data for this entry,
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.Fn archive_read_data_to_buffer ,
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which reads the data into an in-memory buffer,
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.Fn archive_read_data_to_file ,
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which copies the data to the provided file descriptor, or
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.Fn archive_read_extract ,
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which recreates the specified entry on disk and copies data
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In particular, note that
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.Fn archive_read_extract
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.Tn struct archive_entry
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structure that you provide it, which may differ from the
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entry just read from the archive.
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In particular, many applications will want to override the
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pathname, file permissions, or ownership.
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Once you have finished reading data from the archive, you
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.Fn archive_read_close
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to close the archive, then call
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.Fn archive_read_finish
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to release all resources, including all memory allocated by the library.
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manual page provides more detailed calling information for this API.
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.Sh WRITING AN ARCHIVE
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You use a similar process to write an archive.
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.Fn archive_write_new
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function creates an archive object useful for writing,
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.Fn archive_write_set_XXX
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functions are used to set parameters for writing the archive, and
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.Fn archive_write_open
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completes the setup and opens the archive for writing.
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Individual archive entries are written in a three-step
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You first initialize a
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.Tn struct archive_entry
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structure with information about the new entry.
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At a minimum, you should set the pathname of the
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field, which specifies the type of object and
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field, which specifies the size of the data portion of the object.
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.Fn archive_write_header
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function actually writes the header data to the archive.
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.Fn archive_write_data
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to write the actual data.
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After all entries have been written, use the
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.Fn archive_write_finish
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function to release all resources.
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manual page provides more detailed calling information for this API.
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Detailed descriptions of each function are provided by the
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corresponding manual pages.
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All of the functions utilize an opaque
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datatype that provides access to the archive contents.
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.Tn struct archive_entry
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structure contains a complete description of a single archive
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It uses an opaque interface that is fully documented in
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.Xr archive_entry 3 .
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Users familiar with historic formats should be aware that the newer
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variants have eliminated most restrictions on the length of textual fields.
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Clients should not assume that filenames, link names, user names, or
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group names are limited in length.
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In particular, pax interchange format can easily accommodate pathnames
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in arbitrary character sets that exceed
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Most functions return zero on success, non-zero on error.
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The return value indicates the general severity of the error, ranging
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which indicates a minor problem that should probably be reported
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which indicates a serious problem that will prevent any further
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operations on this archive.
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function can be used to retrieve a numeric error code (see
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.Fn archive_error_string
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returns a textual error message suitable for display.
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.Fn archive_write_new
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return pointers to an allocated and initialized
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.Fn archive_read_data
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.Fn archive_write_data
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return a count of the number of bytes actually read or written.
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A value of zero indicates the end of the data for this entry.
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A negative value indicates an error, in which case the
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.Fn archive_error_string
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functions can be used to obtain more information.
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There are character set conversions within the
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functions that are impacted by the currently-selected locale.
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.Xr archive_entry 3 ,
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.Xr archive_write 3 ,
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library first appeared in
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library was written by
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.An Tim Kientzle Aq kientzle@acm.org .
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Some archive formats support information that is not supported by
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.Tn struct archive_entry .
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Such information cannot be fully archived or restored using this library.
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This includes, for example, comments, character sets,
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or the arbitrary key/value pairs that can appear in
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pax interchange format archives.
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Conversely, of course, not all of the information that can be
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.Tn struct archive_entry
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is supported by all formats.
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For example, cpio formats do not support nanosecond timestamps;
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old tar formats do not support large device numbers.
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src/libarchive/libarchive/libarchive.3
