LIBARCHIVE(3)            BSD Library Functions Manual            LIBARCHIVE(3)

NAME
     libarchive - functions for reading and writing streaming
     archives

LIBRARY
     library ``libarchive''

OVERVIEW
     The libarchive 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.

     When reading an archive, the library automatically detects
     the format and the compression.  The library currently has
     read support for:
        old-style tar archives,
        most variants of the POSIX ``ustar'' format,
        the POSIX ``pax interchange'' format,
        GNU-format tar archives,
        most common cpio archive formats,
        ISO9660 CD images (with or without RockRidge exten-
         sions),
        Zip 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 eliminates essentially all of the limitations
     of historic tar formats in a standard fashion that is sup-
     ported by POSIX-compliant pax(1) implementations on many
     systems as well as several newer implementations of
     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.

     The read and write APIs are accessed through the
     archive_read_XXX() functions and the archive_write_XXX()
     functions, respectively, and either can be used indepen-
     dently 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 object from archive_read_new().  You can
     then modify this object for the desired operations with
     the various archive_read_set_XXX() and
     archive_read_support_XXX() functions.  In particular, you
     will need to invoke appropriate archive_read_support_XXX()
     functions to enable the corresponding compression and for-
     mat 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
     archive_read_support_compression_all() and
     archive_read_support_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 pre-
     pare 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, 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.

     Each archive entry consists of a header followed by a cer-
     tain 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 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 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_close() to close the archive,
     then call archive_read_finish() to release all resources,
     including all memory allocated 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 min-
     imum, 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.  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() function 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 provides 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 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 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_WARN, 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 display.

     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 cur-
     rently-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 sup-
     ported 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 inter-
     change 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 formats do not support
     nanosecond timestamps; old tar formats do not support
     large device numbers.

BSD                             August 19, 2006                            BSD
