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

     extracting objects from an archive using the archive_read() interface.

     The general process is to read struct archive_entry objects from an ar‐

     chive, then write those objects to a struct archive object created using

     the archive_write_disk() family functions.  This interface is deliber‐

     ately 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

	     being 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,

		     extended 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

		     default, 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

		     default, existing regular files are truncated and over‐

		     written; existing directories will have their permissions

		     updated; other pre-existing objects are unlinked and

		     recreated 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

		     restored.

	     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_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

		     error, 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

		     restored.	By default, they are ignored.  Note that

		     restoring of atime is not currently supported.

	     ARCHIVE_EXTRACT_UNLINK

		     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.

	     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

     archive_read(3), archive_write(3), tar(1), 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

     appeared 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.

     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) 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				 April 3, 2017				   BSD