ARCHIVE_WRITE_DISK(3)	 BSD Library Functions Manual	 ARCHIVE_WRITE_DISK(3)

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
     #include <archive.h>

     struct archive *
     archive_write_disk_new(void);

     int
     archive_write_disk_set_options(struct archive *, int flags);

     int
     archive_write_disk_set_skip_file(struct archive *, dev_t, ino_t);

     int
     archive_write_disk_set_group_lookup(struct archive *, void *,
	 gid_t (*)(void *, const char *gname, gid_t gid),
	 void (*cleanup)(void *));

     int
     archive_write_disk_set_standard_lookup(struct archive *);

     int
     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 ex‐
     tracting 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.

     archive_write_disk_new()
	     Allocates and initializes a struct archive object suitable for
	     writing objects to disk.

     archive_write_disk_set_skip_file()
	     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 be‐
	     ing read.	This capability is technically unnecessary but can be
	     a significant performance optimization in practice.

     archive_write_disk_set_options()
	     The options field consists of a bitwise OR of one or more of the
	     following values:
	     ARCHIVE_EXTRACT_ACL
		     Attempt to restore Access Control Lists.  By default, ex‐
		     tended ACLs are ignored.
	     ARCHIVE_EXTRACT_CLEAR_NOCHANGE_FFLAGS
		     Before removing a file system object prior to replacing
		     it, clear platform-specific file flags which might pre‐
		     vent its removal.
	     ARCHIVE_EXTRACT_FFLAGS
		     Attempt to restore file attributes (file flags).  By de‐
		     fault, file attributes are ignored.  See chattr(1)
		     (Linux) or chflags(1) (FreeBSD, Mac OS X) for more infor‐
		     mation on file attributes.
	     ARCHIVE_EXTRACT_MAC_METADATA
		     Mac OS X specific.  Restore metadata using copyfile(3).
		     By default, copyfile(3) metadata is ignored.
	     ARCHIVE_EXTRACT_NO_OVERWRITE
		     Existing files on disk will not be overwritten.  By de‐
		     fault, existing regular files are truncated and overwrit‐
		     ten; existing directories will have their permissions up‐
		     dated; other pre-existing objects are unlinked and recre‐
		     ated from scratch.
	     ARCHIVE_EXTRACT_OWNER
		     The user and group IDs should be set on the restored
		     file.  By default, the user and group IDs are not re‐
		     stored.
	     ARCHIVE_EXTRACT_PERM
		     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 speci‐
		     fied, 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.
	     ARCHIVE_EXTRACT_SAFE_WRITES
		     Extract files atomically, by first creating a unique tem‐
		     porary file and then renaming it to its required destina‐
		     tion name.  This avoids a race where an application might
		     see a partial file (or no file) during extraction.
	     ARCHIVE_EXTRACT_SECURE_NOABSOLUTEPATHS
		     Refuse to extract an absolute path.  The default is to
		     not refuse such paths.
	     ARCHIVE_EXTRACT_SECURE_NODOTDOT
		     Refuse to extract a path that contains a .. element any‐
		     where within it.  The default is to not refuse such
		     paths.  Note that paths ending in .. always cause an er‐
		     ror, regardless of this flag.
	     ARCHIVE_EXTRACT_SECURE_SYMLINKS
		     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 ar‐
		     chives that (deliberately or otherwise) extract files
		     outside of the current directory.	The default is not to
		     perform this check.  If
	     ARCHIVE_EXTRACT_SPARSE
		     Scan data for blocks of NUL bytes and try to recreate
		     them with holes.  This results in sparse files, indepen‐
		     dent 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.
	     ARCHIVE_EXTRACT_TIME
		     The timestamps (mtime, ctime, and atime) should be re‐
		     stored.  By default, they are ignored.  Note that restor‐
		     ing of atime is not currently supported.
	     ARCHIVE_EXTRACT_UNLINK
		     Existing files on disk will be unlinked before any at‐
		     tempt 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.
	     ARCHIVE_EXTRACT_XATTR
		     Attempt to restore extended file attributes.  By default,
		     they are ignored.	See xattr(7) (Linux), xattr(2) (Mac OS
		     X), or getextattr(8) (FreeBSD) for more information on
		     extended file attributes.

     archive_write_disk_set_group_lookup(),
	     archive_write_disk_set_user_lookup()
	     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 func‐
	     tion 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.

     archive_write_disk_set_standard_lookup()
	     This convenience function installs a standard set of user and
	     group lookup functions.  These functions use getpwnam(3) and
	     getgrnam(3) to convert names to ids, defaulting to the ids if the
	     names cannot be looked up.  These functions also implement a sim‐
	     ple memory cache to reduce the number of calls to getpwnam(3) and
	     getgrnam(3).
     More information about the struct archive object and the overall design
     of the library can be found in the libarchive(3) overview.  Many of these
     functions are also documented under archive_write(3).

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 impossi‐
     ble.

     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 -1 on error.

ERRORS
     Detailed error codes and textual descriptions are available from the
     archive_errno() and archive_error_string() functions.

SEE ALSO
     tar(1), archive_read(3), archive_write(3), libarchive(3)

HISTORY
     The libarchive library first appeared in FreeBSD 5.3.  The
     archive_write_disk interface was added to libarchive 2.0 and first ap‐
     peared in FreeBSD 6.3.

AUTHORS
     The libarchive library was written by Tim Kientzle <kientzle@acm.org>.

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 cor‐
     rectly handle borderline cases such as a non-writable directory contain‐
     ing files, but can cause unexpected results.  In particular, directory
     permissions are not fully restored until the archive is closed.  If you
     use chdir(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 per‐
     missions 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.  Ex‐
     plicit 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) and getpwnam(3) are sometimes too large for particu‐
     lar 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.

BSD			       January 19, 2020 			   BSD
