doc/wiki/ManPageArchiveWriteDisk3.wiki

ARCHIVE_WRITE_DISK(3) manual page
== NAME ==
'''archive_write_disk_new''',
'''archive_write_disk_set_options''',
'''archive_write_disk_set_skip_file''',
'''archive_write_disk_set_group_lookup''',
'''archive_write_disk_set_standard_lookup''',
'''archive_write_disk_set_user_lookup'''
- functions for creating objects on disk
== LIBRARY ==
Streaming Archive Library (libarchive, -larchive)
== SYNOPSIS ==
'''<nowiki>#include <archive.h></nowiki>'''
<br>
''struct archive *''
<br>
'''archive_write_disk_new'''(''void'');
<br>
''int''
<br>
'''archive_write_disk_set_options'''(''struct archive *'', ''int flags'');
<br>
''int''
<br>
'''archive_write_disk_set_skip_file'''(''struct archive *'', ''dev_t'', ''ino_t'');
<br>
''int''
<br>
'''archive_write_disk_set_group_lookup'''(''struct archive *'', ''void *'', ''gid_t (*)(void *, const char *gname, gid_t gid)'', ''void (*cleanup)(void *)'');
<br>
''int''
<br>
'''archive_write_disk_set_standard_lookup'''(''struct archive *'');
<br>
''int''
<br>
'''archive_write_disk_set_user_lookup'''(''struct archive *'', ''void *'', ''uid_t (*)(void *, const char *uname, uid_t uid)'', ''void (*cleanup)(void *)'');
== DESCRIPTION ==
These functions provide a complete API for creating objects on
disk from
'''struct archive_entry'''
descriptions.
They are most naturally used when extracting objects from an archive
using the
'''archive_read'''()
interface.
The general process is to read
'''struct archive_entry'''
objects from an archive, then write those objects to a
'''struct archive'''
object created using the
'''archive_write_disk'''()
family functions.
This interface is deliberately very similar to the
'''archive_write'''()
interface used to write objects to a streaming archive.
<dl>
<dt>'''archive_write_disk_new'''()</dt><dd>
Allocates and initializes a
'''struct archive'''
object suitable for writing objects to disk.
</dd><dt>'''archive_write_disk_set_skip_file'''()</dt><dd>
Records the device and inode numbers of a file that should not be
overwritten.
This is typically used to ensure that an extraction process does not
overwrite the archive from which objects are being read.
This capability is technically unnecessary but can be a significant
performance optimization in practice.
</dd><dt>'''archive_write_disk_set_options'''()</dt><dd>
The options field consists of a bitwise OR of one or more of the
following values:
<dl>
<dt>'''ARCHIVE_EXTRACT_ACL'''</dt><dd>
Attempt to restore Access Control Lists.
By default, extended ACLs are ignored.
</dd><dt>'''ARCHIVE_EXTRACT_CLEAR_NOCHANGE_FFLAGS'''</dt><dd>
Before removing a file system object prior to replacing it, clear
platform-specific file flags which might prevent its removal.
</dd><dt>'''ARCHIVE_EXTRACT_FFLAGS'''</dt><dd>
Attempt to restore file attributes (file flags).
By default, file attributes are ignored.
See
[[chattr(1)|http://www.freebsd.org/cgi/man.cgi?query=chattr&sektion=1]]
(Linux)
or
[[chflags(1)|http://www.freebsd.org/cgi/man.cgi?query=chflags&sektion=1]]
(FreeBSD, Mac OS X)
for more information on file attributes.
</dd><dt>'''ARCHIVE_EXTRACT_MAC_METADATA'''</dt><dd>
Mac OS X specific.
Restore metadata using
[[copyfile(3)|http://www.freebsd.org/cgi/man.cgi?query=copyfile&sektion=3]].
By default,
[[copyfile(3)|http://www.freebsd.org/cgi/man.cgi?query=copyfile&sektion=3]]
metadata is ignored.
</dd><dt>'''ARCHIVE_EXTRACT_NO_OVERWRITE'''</dt><dd>
Existing files on disk will not be overwritten.
By default, existing regular files are truncated and overwritten;
existing directories will have their permissions updated;
other pre-existing objects are unlinked and recreated from scratch.
</dd><dt>'''ARCHIVE_EXTRACT_OWNER'''</dt><dd>
The user and group IDs should be set on the restored file.
By default, the user and group IDs are not restored.
</dd><dt>'''ARCHIVE_EXTRACT_PERM'''</dt><dd>
Full permissions (including SGID, SUID, and sticky bits) should
be restored exactly as specified, without obeying the
current umask.
Note that SUID and SGID bits can only be restored if the
user and group ID of the object on disk are correct.
If
'''ARCHIVE_EXTRACT_OWNER'''
is not specified, then SUID and SGID bits will only be restored
if the default user and group IDs of newly-created objects on disk
happen to match those specified in the archive entry.
By default, only basic permissions are restored, and umask is obeyed.
</dd><dt>'''ARCHIVE_EXTRACT_SAFE_WRITES'''</dt><dd>
Extract files atomically, by first creating a unique temporary file and then
renaming it to its required destination name.
This avoids a race where an application might see a partial file (or no
file) during extraction.
</dd><dt>'''ARCHIVE_EXTRACT_SECURE_NOABSOLUTEPATHS'''</dt><dd>
Refuse to extract an absolute path.
The default is to not refuse such paths.
</dd><dt>'''ARCHIVE_EXTRACT_SECURE_NODOTDOT'''</dt><dd>
Refuse to extract a path that contains a
''..''
element anywhere within it.
The default is to not refuse such paths.
Note that paths ending in
''..''
always cause an error, regardless of this flag.
</dd><dt>'''ARCHIVE_EXTRACT_SECURE_SYMLINKS'''</dt><dd>
Refuse to extract any object whose final location would be altered
by a symlink on disk.
This is intended to help guard against a variety of mischief
caused by archives that (deliberately or otherwise) extract
files outside of the current directory.
The default is not to perform this check.
If
</dd><dt>'''ARCHIVE_EXTRACT_SPARSE'''</dt><dd>
Scan data for blocks of NUL bytes and try to recreate them with holes.
This results in sparse files, independent of whether the archive format
supports or uses them.
'''ARCHIVE_EXTRACT_UNLINK'''
is specified together with this option, the library will
remove any intermediate symlinks it finds and return an
error only if such symlink could not be removed.
</dd><dt>'''ARCHIVE_EXTRACT_TIME'''</dt><dd>
The timestamps (mtime, ctime, and atime) should be restored.
By default, they are ignored.
Note that restoring of atime is not currently supported.
</dd><dt>'''ARCHIVE_EXTRACT_UNLINK'''</dt><dd>
Existing files on disk will be unlinked before any attempt to
create them.
In some cases, this can prove to be a significant performance improvement.
By default, existing files are truncated and rewritten, but
the file is not recreated.
In particular, the default behavior does not break existing hard links.
</dd><dt>'''ARCHIVE_EXTRACT_XATTR'''</dt><dd>
Attempt to restore extended file attributes.
By default, they are ignored.
See
[[xattr(7)|http://www.freebsd.org/cgi/man.cgi?query=xattr&sektion=7]]
(Linux,)
[[xattr(2)|http://www.freebsd.org/cgi/man.cgi?query=xattr&sektion=2]]
(Mac OS X,)
or
[[getextattr(8)|http://www.freebsd.org/cgi/man.cgi?query=getextattr&sektion=8]]
(FreeBSD)
for more information on extended file attributes.
</dd></dl>
</dd><dt>
'''archive_write_disk_set_group_lookup'''(),
'''archive_write_disk_set_user_lookup'''()
</dt> <dd>
The
'''struct archive_entry'''
objects contain both names and ids that can be used to identify users
and groups.
These names and ids describe the ownership of the file itself and
also appear in ACL lists.
By default, the library uses the ids and ignores the names, but
this can be overridden by registering user and group lookup functions.
To register, you must provide a lookup function which
accepts both a name and id and returns a suitable id.
You may also provide a
'''void *'''
pointer to a private data structure and a cleanup function for
that data.
The cleanup function will be invoked when the
'''struct archive'''
object is destroyed.
</dd><dt>'''archive_write_disk_set_standard_lookup'''()</dt><dd>
This convenience function installs a standard set of user
and group lookup functions.
These functions use
[[getpwnam(3)|http://www.freebsd.org/cgi/man.cgi?query=getpwnam&sektion=3]]
and
[[getgrnam(3)|http://www.freebsd.org/cgi/man.cgi?query=getgrnam&sektion=3]]
to convert names to ids, defaulting to the ids if the names cannot
be looked up.
These functions also implement a simple memory cache to reduce
the number of calls to
[[getpwnam(3)|http://www.freebsd.org/cgi/man.cgi?query=getpwnam&sektion=3]]
and
[[getgrnam(3)|http://www.freebsd.org/cgi/man.cgi?query=getgrnam&sektion=3]].
</dd></dl>
More information about the
''struct'' archive
object and the overall design of the library can be found in the
[[ManPageLibarchive3]]
overview.
Many of these functions are also documented under
[[ManPageArchiveWrite3]].
== RETURN VALUES ==
Most functions return
'''ARCHIVE_OK'''
(zero) on success, or one of several non-zero
error codes for errors.
Specific error codes include:
'''ARCHIVE_RETRY'''
for operations that might succeed if retried,
'''ARCHIVE_WARN'''
for unusual conditions that do not prevent further operations, and
'''ARCHIVE_FATAL'''
for serious errors that make remaining operations impossible.

'''archive_write_disk_new'''()
returns a pointer to a newly-allocated
'''struct archive'''
object.

'''archive_write_data'''()
returns a count of the number of bytes actually written,
or
```text
-1
```
on error.
== ERRORS ==
Detailed error codes and textual descriptions are available from the
'''archive_errno'''()
and
'''archive_error_string'''()
functions.
== SEE ALSO ==
[[ManPageBsdtar1]],
[[ManPageArchiveRead3]],
[[ManPageArchiveWrite3]],
[[ManPageLibarchive3]]
== HISTORY ==
The
'''libarchive'''
library first appeared in
FreeBSD 5.3.
The
'''archive_write_disk'''
interface was added to
'''libarchive''' 2.0
and first appeared in
FreeBSD 6.3.
== AUTHORS ==
The
'''libarchive'''
library was written by
Tim Kientzle  &lt;kientzle@acm.org.&gt;
== BUGS ==
Directories are actually extracted in two distinct phases.
Directories are created during
'''archive_write_header'''(),
but final permissions are not set until
'''archive_write_close'''().
This separation is necessary to correctly handle borderline
cases such as a non-writable directory containing
files, but can cause unexpected results.
In particular, directory permissions are not fully
restored until the archive is closed.
If you use
[[chdir(2)|http://www.freebsd.org/cgi/man.cgi?query=chdir&sektion=2]]
to change the current directory between calls to
'''archive_read_extract'''()
or before calling
'''archive_read_close'''(),
you may confuse the permission-setting logic with
the result that directory permissions are restored
incorrectly.

The library attempts to create objects with filenames longer than
'''PATH_MAX'''
by creating prefixes of the full path and changing the current directory.
Currently, this logic is limited in scope; the fixup pass does
not work correctly for such objects and the symlink security check
option disables the support for very long pathnames.

Restoring the path
''aa/../bb''
does create each intermediate directory.
In particular, the directory
''aa''
is created as well as the final object
''bb''.
In theory, this can be exploited to create an entire directory hierarchy
with a single request.
Of course, this does not work if the
'''ARCHIVE_EXTRACT_NODOTDOT'''
option is specified.

Implicit directories are always created obeying the current umask.
Explicit objects are created obeying the current umask unless
'''ARCHIVE_EXTRACT_PERM'''
is specified, in which case they current umask is ignored.

SGID and SUID bits are restored only if the correct user and
group could be set.
If
'''ARCHIVE_EXTRACT_OWNER'''
is not specified, then no attempt is made to set the ownership.
In this case, SGID and SUID bits are restored only if the
user and group of the final object happen to match those specified
in the entry.

The
"standard"
user-id and group-id lookup functions are not the defaults because
[[getgrnam(3)|http://www.freebsd.org/cgi/man.cgi?query=getgrnam&sektion=3]]
and
[[getpwnam(3)|http://www.freebsd.org/cgi/man.cgi?query=getpwnam&sektion=3]]
are sometimes too large for particular applications.
The current design allows the application author to use a more
compact implementation when appropriate.

There should be a corresponding
'''archive_read_disk'''
interface that walks a directory hierarchy and returns archive
entry objects.