af9413b539
What it is:
A library for reading and writing various streaming archive
formats, especially tar and cpio. Being a library, it should
be easy to incorporate into pkg_* tools, sysinstall, and any
other place that needs to read or write such archives.
Features:
* Full automatic detection of both compression and archive format.
* Extensible internal architecture to make it easy to add new formats.
* Support for "pax interchange format," a new POSIX-standard tar format
that eliminates essentially all of the restrictions of historic formats.
* BSD license
Thanks to: jkh for pushing me to start this work, gordon for
encouraging me to commit it, bde for answering endless style
questions, and many others for feedback and encouragement.
Status: Pretty good overall, though there are still a few rough edges and
the library could always use more testing. Feedback eagerly solicited.
91 lines
4.4 KiB
Plaintext
91 lines
4.4 KiB
Plaintext
$FreeBSD$
|
|
|
|
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!
|
|
|
|
As of February, 2004, the library proper is fairly complete and compiles
|
|
cleanly on FreeBSD 5-CURRENT. The API should be stable now.
|
|
|
|
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.)
|
|
|
|
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. For example, zip archives can't be written as a
|
|
stream because they require the compressed size of the data as part
|
|
of the file header. Similarly, some file attributes for zip
|
|
archives can't be extracted when streaming because those attributes
|
|
are only stored in the end-of-archive central directory and thus
|
|
aren't available when the corresponding entry is actually
|
|
extracted.
|
|
|
|
* Under certain circumstances, you can append entries to an archive
|
|
by opening the file for reading, skimming to the end of the archive,
|
|
noting the file location, then opening it for write with a custom write
|
|
callback that seeks to the appropriate position before writing. Be
|
|
sure to not enable any compression support if you do this!
|
|
|
|
* Compression and blocking are handled implicitly and, as far as
|
|
possible, transparently. All archive I/O is correctly blocked, even if
|
|
it's compressed. On read, the compression format is detected
|
|
automatically and the appropriate decompressor is invoked.
|
|
|
|
* It should be easy to implement a system that reads one
|
|
archive and writes entries to another archive, omitting
|
|
or adding entries as appropriate along the way. This permits
|
|
"re-writing" of archive streams in lieu of in-place modification.
|
|
bsdtar has some code to demonstrate this.
|
|
|
|
* 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.
|
|
|
|
* Read supports most common tar formats, including GNU tar,
|
|
POSIX-compliant "ustar interchange format", and the
|
|
shiny-and-improved POSIX "pax extended interchange format." The
|
|
pax format, in particular, eliminates most of the traditional tar
|
|
limitations in a standard way that is increasingly well supported.
|
|
(GNU tar notably does not support "pax interchange format"; the
|
|
GPL-licensed 'star' archiver does, however.) GNU format is only
|
|
incompletely supported at this time; if you really need GNU-format
|
|
sparse file support, volume headers, or GNU-format split archives,
|
|
let me know.
|
|
|
|
There's also support for a grab-bag of non-tar formats, including
|
|
POSIX cpio and shar.
|
|
|
|
* When writing tar formats, consider using "pax restricted" format
|
|
by default. This avoids the pax extensions whenever it can, enabling
|
|
them only on entries that cannot be correctly archived with ustar
|
|
format. Thus, you get the broad compatibility of ustar with the
|
|
safety of pax's support for very long filenames, etc.
|
|
|
|
* Note: "pax interchange format" is really an extended tar format,
|
|
despite what the name says.
|