freebsd-dev/lib/libarchive/README

$FreeBSD$

libarchive: a library for reading and writing streaming archives

This is all under a BSD license.  Use, enjoy, but don't blame me if it breaks!

Documentation:
 * libarchive.3 gives an overview of the library as a whole
 * archive_read.3 and archive_write.3 provide detailed calling
   sequences for the read and write APIs
 * archive_entry.3 details the "struct archive_entry" utility class
 * tar.5 documents the "tar" file formats supported by the library

You should also read the copious comments in "archive.h" and the source
code for the sample "bsdtar" program for more details.  Please let me know
about any errors or omissions you find.  (In particular, I no doubt missed
a few things when researching the tar.5 page.)

Currently, the library automatically detects and reads the following:
  * gzip compression
  * bzip2 compression
  * compress/LZW compression
  * GNU tar format (including GNU long filenames, long link names, and
    sparse files)
  * Solaris 9 extended tar format (including ACLs)
  * Old V7 tar archives
  * POSIX ustar
  * POSIX pax interchange format
  * POSIX octet-oriented cpio
  * SVR4 ASCII cpio
  * Binary cpio (big-endian or little-endian)

The library can write:
  * gzip compression
  * bzip2 compression
  * POSIX ustar
  * POSIX pax interchange format
  * "restricted" pax format, which will create ustar archives except for
    entries that require pax extensions (for long filenames, ACLs, etc).
  * POSIX octet-oriented cpio
  * shar archives

Notes:
 * This is a heavily stream-oriented system.  There is no direct
   support for in-place modification or random access and no intention
   of ever adding such support.  Adding such support would require
   sacrificing a lot of other features, so don't bother asking.

 * The library is designed to be extended with new compression and
   archive formats.  The only requirement is that the format be
   readable or writable as a stream and that each archive entry be
   independent.

 * On read, compression and format are always detected automatically.

 * I've attempted to minimize static link pollution.  If you don't
   explicitly invoke a particular feature (such as support for a
   particular compression or format), it won't get pulled in.
   In particular, if you don't explicitly enable a particular
   compression or decompression support, you won't need to link
   against the corresponding compression or decompression libraries.
   This also reduces the size of statically-linked binaries in
   environments where that matters.

 * On read, the library accepts whatever blocks you hand it.
   Your read callback is free to pass the library a byte at a time
   or mmap the entire archive and give it to the library at once.
   On write, the library always produces correctly-blocked
   output.

 * The object-style approach allows you to have multiple archive streams
   open at once.  bsdtar uses this in its "@archive" extension.

 * The archive itself is read/written using callback functions.
   You can read an archive directly from an in-memory buffer or
   write it to a socket, if you wish.  There are some utility
   functions to provide easy-to-use "open file," etc, capabilities.

 * The read/write APIs are designed to allow individual entries
   to be read or written to any data source:  You can create
   a block of data in memory and add it to a tar archive without
   first writing a temporary file.  You can also read an entry from
   an archive and write the data directly to a socket.  If you want
   to read/write entries to disk, there are convenience functions to
   make this especially easy.

 * Note: "pax interchange format" is really an extended tar format,
   despite what the name says.