global header if nothing else has been written before the closing of
the archive. This will change the behaviour when creating archives
without members, i.e., instead of generating a 0-size archive file, an
archive with just the global header (8 bytes in total) will be created
and it is indeed a valid archive by the definition of libarchive, thus
subsequent operation on this archive will be accepted. This especially
solves the failure caused by following sequence: (several ports do)
% ar cru libfoo.a # without specifying obj files
% ranlib libfoo.a
Reviewed by: kientzle, jkoshy
Approved by: kientzle
Approved by: jkoshy (mentor)
Reported by: erwin
MFC after: 1 month
$FreeBSD$
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, 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
* libarchive-formats.5 documents the file formats supported by the library
* tar.5 provides some detailed information about a variety of different
"tar" formats.
You should also read the copious comments in "archive.h" and the source
code for the sample "bsdtar" and "minitar" programs 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)
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, the archive_write_disk interface
treats a directory as if it were an archive so you can copy
from archive->disk using the same code you use for archive->archive
transfers.
* Note: "pax interchange format" is really an extended tar format,
despite what the name says.
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