README for libarchive bundle.
This distribution bundle includes the following components:
* libarchive: a library for reading and writing streaming archives
* tar: the 'bsdtar' program is a full-featured 'tar'
replacement built on libarchive
* cpio: the 'bsdcpio' program is a different interface to
essentially the same functionality
* examples: Some small example programs that you may find useful.
* examples/minitar: a compact sample demonstrating use of libarchive.
I use this for testing link pollution; it should produce a very
small executable file on most systems.
* contrib: Various items sent to me by third parties;
please contact the authors with any questions.
The top-level directory contains the following information files:
* NEWS - highlights of recent changes
* COPYING - what you can do with this
* INSTALL - installation instructions
* README - this file
* configure - configuration script, see INSTALL for details.
The following files in the top-level directory are used by the
'configure' script:
* Makefile.am, aclocal.m4, configure.ac
- used to build this distribution, only needed by maintainers
* Makefile.in, config.h.in
- templates used by configure script
* config.aux/* - auxiliary scripts used by build system
Guide to Documentation installed by this system:
* bsdtar.1 explains the use of the bsdtar program
* bsdcpio.1 explains the use of the bsdcpio program
* libarchive.3 gives an overview of the library as a whole
* archive_read.3, archive_write.3, and archive_write_disk.3 provide
detailed calling sequences for the read and write APIs
* archive_entry.3 details the "struct archive_entry" utility class
* archive_internals.3 provides some insight into libarchive's
internal structure and operation.
* libarchive-formats.5 documents the file formats supported by the library
* cpio.5, mtree.5, and tar.5 provide detailed information about a
variety of different archive formats, including hard-to-find details
about modern cpio and tar variants.
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.
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)
* ISO9660 CD-ROM images (with optional Rockridge extensions)
* ZIP archives (with uncompressed or "deflate" compressed entries)
* GNU and BSD 'ar' archives
* 'mtree' format
The library can write:
* gzip compression
* bzip2 compression
* compress/LZW 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
* SVR4 "newc" cpio
* shar archives
* GNU and BSD 'ar' archives
Notes about the library architecture:
* 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[1]
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.
[1] Gzip and compress formats are identical in the first byte.
For that reason, the first block must be at least two bytes if
you have both of these formats enabled at read time. This is
currently the only restriction on block size. (This restriction
could be lifted by buffering the initial blocks prior to the
compression tasting step, but it doesn't really seem worth the
effort.)
