libarchive

Libarchive is a programming library that can create and read several different streaming archive formats, including most popular tar variants and several cpio formats. It can also write shar archives and read ISO-9660 CDROM images. The bsdtar program is an implementation of tar(1) that is built on top of libarchive. It started as a test harness, but has grown and is now the standard system tar for FreeBSD 5 and 6. The libarchive library offers a number of features that make it both very flexible and very powerful. - Automatic format detection: libarchive can automatically determine both the compression and the archive format, regardless of the data source. Most tar implementations do not automatically detect the compression format, few implementation that can correctly do this when reading from stdin or a socket. (The tar program included with Gunnar Ritter's heirloom collection also does full automatic format detection.) - Writes POSIX formats: libarchive writes POSIX-standard formats, including "ustar," "pax interchange format," and the POSIX "cpio" format. - Supports pax interchange format: Pax interchange format (which, despite the name, is really an extended tar format) eliminates almost all limitations of historic tar formats and provides a standard method for incorporating vendor-specific extensions. libarchive exploits this extension mechanism to support ACLs and file flags, for example. (Joerg Schilling's star archiver is another open-source tar program that supports pax interchange format.) - Reads popular formats: libarchive can read GNU tar, ustar, pax interchange format, cpio, and older tar variants. The internal architecture is easily extensible. The only requirement for support is that it be possible to read the format without seeking in the file. (For example, a format that includes a compressed size field before the data cannot be correctly written without seeking.) - High-Level API: the libarchive API makes it fairly simple to build an archive from a list of filenames or to extract the entries from an archive. However, the API also provides extreme flexibility with regards to data sources. For example, there are generic hooks that allow you to write an archive to a socket or read data from an archive entry into a memory buffer. - Extensible. The internal design uses generic interfaces for compression, archive format detection and decoding, and archive data I/O. It should be very easy to add new formats, new compression methods, or new ways of reading/writing archives.