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LIBARCHIVE(3)          FreeBSD Library Functions Manual          LIBARCHIVE(3)

NAME
     libarchive - functions for reading and writing streaming archives

LIBRARY
     Streaming Archive Library (libarchive, -larchive)

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:
     +o   old-style tar archives,
     +o   most variants of the POSIX ``ustar'' format,
     +o   the POSIX ``pax interchange'' format,
     +o   GNU-format tar archives,
     +o   most common cpio archive formats,
     +o   ISO9660 CD images (including RockRidge and Joliet extensions),
     +o   Zip archives.
     The library automatically detects archives compressed with gzip(1),
     bzip2(1), xz(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
     +o   POSIX-standard ``ustar'' archives,
     +o   POSIX ``pax interchange format'' archives,
     +o   POSIX octet-oriented cpio archives,
     +o   Zip archive,
     +o   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 supported 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 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
     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 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 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 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, 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 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
     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, or archive_read_data_block() which
     provides a slightly more efficient interface.  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_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 permissions, 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_free()
     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 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 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_free()
     function to release all resources.

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

WRITING ENTRIES TO DISK
     The archive_write_disk(3) API allows you to write archive_entry(3)
     objects to disk using the same API used by archive_write(3).  The
     archive_write_disk(3) API is used internally by archive_read_extract();
     using it directly can provide greater control over how entries get
     written to disk.  This API also makes it possible to share code between
     archive-to-archive copy and archive-to-disk extraction operations.

READING ENTRIES FROM DISK
     The archive_read_disk(3) provides some support for populating
     archive_entry(3) objects from information in the filesystem.

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 ARCHIVE_OK (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 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
     formats do not support nanosecond timestamps; old tar formats do not
     support large device numbers.

     The archive_read_disk(3) API should support iterating over filesystems;
     that would make it possible to share code among disk-to-archive, archive-
     to-archive, archive-to-disk, and disk-to-disk operations.  Currently, it
     only supports reading the information for a single file.  (Which is still
     quite useful, as it hides a lot of system-specific details.)

FreeBSD 11.0-PRERELEASE          July 17, 2010         FreeBSD 11.0-PRERELEASE

NAME | LIBRARY | OVERVIEW | READING AN ARCHIVE | WRITING AN ARCHIVE | WRITING ENTRIES TO DISK | READING ENTRIES FROM DISK | DESCRIPTION | RETURN VALUES | ENVIRONMENT | SEE ALSO | HISTORY | AUTHORS | BUGS

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