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<p valign="top">LIBARCHIVE(3) FreeBSD Library Functions
Manual LIBARCHIVE(3)</p>
<p style="margin-top: 1em" valign="top"><b>NAME</b></p>
<p style="margin-left:8%;"><b>libarchive</b> —
functions for reading and writing streaming archives</p>
<p style="margin-top: 1em" valign="top"><b>LIBRARY</b></p>
<p style="margin-left:8%;">Streaming Archive Library
(libarchive, −larchive)</p>
<p style="margin-top: 1em" valign="top"><b>OVERVIEW</b></p>
<p style="margin-left:8%;">The <b>libarchive</b> library
provides a flexible interface for reading and writing
streaming archive files such as tar and cpio. The library is
inherently stream-oriented; readers serially iterate through
the archive, writers serially add things to the archive. In
particular, note that there is no built-in support for
random access nor for in-place modification.</p>
<p style="margin-left:8%; margin-top: 1em">When reading an
archive, the library automatically detects the format and
the compression. The library currently has read support
for:</p>
<p valign="top"><b>•</b></p>
<p style="margin-left:14%;">old-style tar archives,</p>
<p valign="top"><b>•</b></p>
<p style="margin-left:14%;">most variants of the POSIX
‘‘ustar’’ format,</p>
<p valign="top"><b>•</b></p>
<p style="margin-left:14%;">the POSIX ‘‘pax
interchange’’ format,</p>
<p valign="top"><b>•</b></p>
<p style="margin-left:14%;">GNU-format tar archives,</p>
<p valign="top"><b>•</b></p>
<p style="margin-left:14%;">most common cpio archive
formats,</p>
<p valign="top"><b>•</b></p>
<p style="margin-left:14%;">ISO9660 CD images (with or
without RockRidge extensions),</p>
<p valign="top"><b>•</b></p>
<p style="margin-left:14%;">Zip archives.</p>
<p style="margin-left:8%;">The library automatically
detects archives compressed with gzip(1), bzip2(1), or
compress(1) and decompresses them transparently.</p>
<p style="margin-left:8%; margin-top: 1em">When writing an
archive, you can specify the compression to be used and the
format to use. The library can write</p>
<p valign="top"><b>•</b></p>
<p style="margin-left:14%;">POSIX-standard
‘‘ustar’’ archives,</p>
<p valign="top"><b>•</b></p>
<p style="margin-left:14%;">POSIX ‘‘pax
interchange format’’ archives,</p>
<p valign="top"><b>•</b></p>
<p style="margin-left:14%;">POSIX octet-oriented cpio
archives,</p>
<p valign="top"><b>•</b></p>
<p style="margin-left:14%;">two different variants of shar
archives.</p>
<p style="margin-left:8%;">Pax interchange format is an
extension of the tar archive format that eliminates
essentially all of the limitations of historic tar formats
in a standard fashion that is supported by POSIX-compliant
pax(1) implementations on many systems as well as several
newer implementations of tar(1). Note that the default write
format will suppress the pax extended attributes for most
entries; explicitly requesting pax format will enable those
attributes for all entries.</p>
<p style="margin-left:8%; margin-top: 1em">The read and
write APIs are accessed through the
<b>archive_read_XXX</b>() functions and the
<b>archive_write_XXX</b>() functions, respectively, and
either can be used independently of the other.</p>
<p style="margin-left:8%; margin-top: 1em">The rest of this
manual page provides an overview of the library operation.
More detailed information can be found in the individual
manual pages for each API or utility function.</p>
<p style="margin-top: 1em" valign="top"><b>READING AN
ARCHIVE</b></p>
<p style="margin-left:8%;">To read an archive, you must
first obtain an initialized struct archive object from
<b>archive_read_new</b>(). You can then modify this object
for the desired operations with the various
<b>archive_read_set_XXX</b>() and
<b>archive_read_support_XXX</b>() functions. In particular,
you will need to invoke appropriate
<b>archive_read_support_XXX</b>() functions to enable the
corresponding compression and format support. Note that
these latter functions perform two distinct operations: they
cause the corresponding support code to be linked into your
program, and they enable the corresponding auto-detect code.
Unless you have specific constraints, you will generally
want to invoke <b>archive_read_support_compression_all</b>()
and <b>archive_read_support_format_all</b>() to enable
auto-detect for all formats and compression types currently
supported by the library.</p>
<p style="margin-left:8%; margin-top: 1em">Once you have
prepared the struct archive object, you call
<b>archive_read_open</b>() to actually open the archive and
prepare it for reading. There are several variants of this
function; the most basic expects you to provide pointers to
several functions that can provide blocks of bytes from the
archive. There are convenience forms that allow you to
specify a filename, file descriptor, <i>FILE *</i> object,
or a block of memory from which to read the archive data.
Note that the core library makes no assumptions about the
size of the blocks read; callback functions are free to read
whatever block size is most appropriate for the medium.</p>
<p style="margin-left:8%; margin-top: 1em">Each archive
entry consists of a header followed by a certain amount of
data. You can obtain the next header with
<b>archive_read_next_header</b>(), which returns a pointer
to an struct archive_entry structure with information about
the current archive element. If the entry is a regular file,
then the header will be followed by the file data. You can
use <b>archive_read_data</b>() (which works much like the
read(2) system call) to read this data from the archive. You
may prefer to use the higher-level
<b>archive_read_data_skip</b>(), which reads and discards
the data for this entry,
<b>archive_read_data_to_buffer</b>(), which reads the data
into an in-memory buffer,
<b>archive_read_data_to_file</b>(), which copies the data to
the provided file descriptor, or
<b>archive_read_extract</b>(), which recreates the specified
entry on disk and copies data from the archive. In
particular, note that <b>archive_read_extract</b>() uses the
struct archive_entry structure that you provide it, which
may differ from the entry just read from the archive. In
particular, many applications will want to override the
pathname, file permissions, or ownership.</p>
<p style="margin-left:8%; margin-top: 1em">Once you have
finished reading data from the archive, you should call
<b>archive_read_close</b>() to close the archive, then call
<b>archive_read_finish</b>() to release all resources,
including all memory allocated by the library.</p>
<p style="margin-left:8%; margin-top: 1em">The
archive_read(3) manual page provides more detailed calling
information for this API.</p>
<p style="margin-top: 1em" valign="top"><b>WRITING AN
ARCHIVE</b></p>
<p style="margin-left:8%;">You use a similar process to
write an archive. The <b>archive_write_new</b>() function
creates an archive object useful for writing, the various
<b>archive_write_set_XXX</b>() functions are used to set
parameters for writing the archive, and
<b>archive_write_open</b>() completes the setup and opens
the archive for writing.</p>
<p style="margin-left:8%; margin-top: 1em">Individual
archive entries are written in a three-step process: You
first initialize a struct archive_entry structure with
information about the new entry. At a minimum, you should
set the pathname of the entry and provide a <i>struct
stat</i> with a valid <i>st_mode</i> field, which specifies
the type of object and <i>st_size</i> field, which specifies
the size of the data portion of the object. The
<b>archive_write_header</b>() function actually writes the
header data to the archive. You can then use
<b>archive_write_data</b>() to write the actual data.</p>
<p style="margin-left:8%; margin-top: 1em">After all
entries have been written, use the
<b>archive_write_finish</b>() function to release all
resources.</p>
<p style="margin-left:8%; margin-top: 1em">The
archive_write(3) manual page provides more detailed calling
information for this API.</p>
<p style="margin-top: 1em" valign="top"><b>DESCRIPTION</b></p>
<p style="margin-left:8%;">Detailed descriptions of each
function are provided by the corresponding manual pages.</p>
<p style="margin-left:8%; margin-top: 1em">All of the
functions utilize an opaque struct archive datatype that
provides access to the archive contents.</p>
<p style="margin-left:8%; margin-top: 1em">The struct
archive_entry structure contains a complete description of a
single archive entry. It uses an opaque interface that is
fully documented in archive_entry(3).</p>
<p style="margin-left:8%; margin-top: 1em">Users familiar
with historic formats should be aware that the newer
variants have eliminated most restrictions on the length of
textual fields. Clients should not assume that filenames,
link names, user names, or group names are limited in
length. In particular, pax interchange format can easily
accommodate pathnames in arbitrary character sets that
exceed <i>PATH_MAX</i>.</p>
<p style="margin-top: 1em" valign="top"><b>RETURN
VALUES</b></p>
<p style="margin-left:8%;">Most functions return zero on
success, non-zero on error. The return value indicates the
general severity of the error, ranging from
<b>ARCHIVE_WARN</b>, which indicates a minor problem that
should probably be reported to the user, to
<b>ARCHIVE_FATAL</b>, which indicates a serious problem that
will prevent any further operations on this archive. On
error, the <b>archive_errno</b>() function can be used to
retrieve a numeric error code (see errno(2)). The
<b>archive_error_string</b>() returns a textual error
message suitable for display.</p>
<p style="margin-left:8%; margin-top: 1em"><b>archive_read_new</b>()
and <b>archive_write_new</b>() return pointers to an
allocated and initialized struct archive object.</p>
<p style="margin-left:8%; margin-top: 1em"><b>archive_read_data</b>()
and <b>archive_write_data</b>() return a count of the number
of bytes actually read or written. A value of zero indicates
the end of the data for this entry. A negative value
indicates an error, in which case the <b>archive_errno</b>()
and <b>archive_error_string</b>() functions can be used to
obtain more information.</p>
<p style="margin-top: 1em" valign="top"><b>ENVIRONMENT</b></p>
<p style="margin-left:8%;">There are character set
conversions within the archive_entry(3) functions that are
impacted by the currently-selected locale.</p>
<p style="margin-top: 1em" valign="top"><b>SEE ALSO</b></p>
<p style="margin-left:8%;">tar(1), archive_entry(3),
archive_read(3), archive_util(3), archive_write(3),
tar(5)</p>
<p style="margin-top: 1em" valign="top"><b>HISTORY</b></p>
<p style="margin-left:8%;">The <b>libarchive</b> library
first appeared in FreeBSD 5.3.</p>
<p style="margin-top: 1em" valign="top"><b>AUTHORS</b></p>
<p style="margin-left:8%;">The <b>libarchive</b> library
was written by Tim Kientzle
⟨kientzle@acm.org⟩.</p>
<p style="margin-top: 1em" valign="top"><b>BUGS</b></p>
<p style="margin-left:8%;">Some archive formats support
information that is not supported by struct archive_entry.
Such information cannot be fully archived or restored using
this library. This includes, for example, comments,
character sets, or the arbitrary key/value pairs that can
appear in pax interchange format archives.</p>
<p style="margin-left:8%; margin-top: 1em">Conversely, of
course, not all of the information that can be stored in an
struct archive_entry is supported by all formats. For
example, cpio formats do not support nanosecond timestamps;
old tar formats do not support large device numbers.</p>
<p style="margin-left:8%; margin-top: 1em">FreeBSD 9.0
August 19, 2006 FreeBSD 9.0</p>
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