#summary archive_read_disk 3 manual page
== NAME ==
*archive_read_disk_new*,
*archive_read_disk_set_symlink_logical*,
*archive_read_disk_set_symlink_physical*,
*archive_read_disk_set_symlink_hybrid*,
*archive_read_disk_entry_from_file*,
*archive_read_disk_gname*,
*archive_read_disk_uname*,
*archive_read_disk_set_uname_lookup*,
*archive_read_disk_set_gname_lookup*,
*archive_read_disk_set_standard_lookup*,
*archive_read_close*,
*archive_read_finish*
- functions for reading objects from disk
== SYNOPSIS ==
*#include <archive.h>*
<br>
*struct archive `*`*
<br>
*archive_read_disk_new*(_void_);
<br>
*int*
<br>
*archive_read_disk_set_symlink_logical*(_struct archive `*`_);
<br>
*int*
<br>
*archive_read_disk_set_symlink_physical*(_struct archive `*`_);
<br>
*int*
<br>
*archive_read_disk_set_symlink_hybrid*(_struct archive `*`_);
<br>
*int*
<br>
*archive_read_disk_gname*(_struct archive `*`_, _gid_t_);
<br>
*int*
<br>
*archive_read_disk_uname*(_struct archive `*`_, _uid_t_);
<br>
*int*
<br>
*archive_read_disk_set_gname_lookup*(_struct archive `*`_, _void `*`_, _const char `*`(`*`lookup)(void `*`, gid_t)_, _void (`*`cleanup)(void `*`)_);
<br>
*int*
<br>
*archive_read_disk_set_uname_lookup*(_struct archive `*`_, _void `*`_, _const char `*`(`*`lookup)(void `*`, uid_t)_, _void (`*`cleanup)(void `*`)_);
<br>
*int*
<br>
*archive_read_disk_set_standard_lookup*(_struct archive `*`_);
<br>
*int*
<br>
*archive_read_disk_entry_from_file*(_struct archive `*`_, _struct archive_entry `*`_, _int fd_, _const struct stat `*`_);
<br>
*int*
<br>
*archive_read_close*(_struct archive `*`_);
<br>
*int*
<br>
*archive_read_finish*(_struct archive `*`_);
== DESCRIPTION ==
These functions provide an API for reading information about
objects on disk.
In particular, they provide an interface for populating
*struct archive_entry*
objects.
<dl>
<dt>*archive_read_disk_new*()</dt><dd>
Allocates and initializes a
*struct archive*
object suitable for reading object information from disk.
</dd><dt>
*archive_read_disk_set_symlink_logical*(),
*archive_read_disk_set_symlink_physical*(),
*archive_read_disk_set_symlink_hybrid*()
</dt> <dd>
This sets the mode used for handling symbolic links.
The
"logical"
mode follows all symbolic links.
The
"physical"
mode does not follow any symbolic links.
The
"hybrid"
mode currently behaves identically to the
"logical"
mode.
</dd><dt>
*archive_read_disk_gname*(),
*archive_read_disk_uname*()
</dt> <dd>
Returns a user or group name given a gid or uid value.
By default, these always return a NULL string.
</dd><dt>
*archive_read_disk_set_gname_lookup*(),
*archive_read_disk_set_uname_lookup*()
</dt> <dd>
These allow you to override the functions used for
user and group name lookups.
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 or when new lookup functions are registered.
</dd><dt>*archive_read_disk_set_standard_lookup*()</dt><dd>
This convenience function installs a standard set of user
and group name lookup functions.
These functions use
*getpwid*(3)
and
*getgrid*(3)
to convert ids to names, defaulting to NULL if the names cannot
be looked up.
These functions also implement a simple memory cache to reduce
the number of calls to
*getpwid*(3)
and
*getgrid*(3).
</dd><dt>*archive_read_disk_entry_from_file*()</dt><dd>
Populates a
*struct archive_entry*
object with information about a particular file.
The
*archive_entry*
object must have already been created with
*archive_entry_new*(3)
and at least one of the source path or path fields must already be set.
(If both are set, the source path will be used.)

Information is read from disk using the path name from the
*struct archive_entry*
object.
If a file descriptor is provided, some information will be obtained using
that file descriptor, on platforms that support the appropriate
system calls.

If a pointer to a
*struct stat*
is provided, information from that structure will be used instead
of reading from the disk where appropriate.
This can provide performance benefits in scenarios where
*struct stat*
information has already been read from the disk as a side effect
of some other operation.
(For example, directory traversal libraries often provide this information.)

Where necessary, user and group ids are converted to user and group names
using the currently registered lookup functions above.
This affects the file ownership fields and ACL values in the
*struct archive_entry*
object.
</dd><dt>*archive_read_close*()</dt><dd>
This currently does nothing.
</dd><dt>*archive_write_finish*()</dt><dd>
Invokes
*archive_write_close*()
if it was not invoked manually, then releases all resources.
</dd></dl>
More information about the
_struct_ archive
object and the overall design of the library can be found in the
*libarchive*(3)
overview.
== EXAMPLE ==
The following illustrates basic usage of the library by
showing how to use it to copy an item on disk into an archive.
{{{
void
file_to_archive(struct archive *a, const char *name)
{
  char buff[8192];
  size_t bytes_read;
  struct archive *ard;
  struct archive_entry *entry;
  int fd;
  ard = archive_read_disk_new();
  archive_read_disk_set_standard_lookup(ard);
  entry = archive_entry_new();
  fd = open(name, O_RDONLY);
  if (fd < 0)
     return;
  archive_entry_copy_sourcepath(entry, name);
  archive_read_disk_entry_from_file(ard, entry, fd, NULL);
  archive_write_header(a, entry);
  while ((bytes_read = read(fd, buff, sizeof(buff))) > 0)
    archive_write_data(a, buff, bytes_read);
  archive_write_finish_entry(a);
  archive_read_finish(ard);
  archive_entry_free(entry);
}
}}}
== RETURN VALUES ==
Most functions return
*ARCHIVE_OK*
(zero) on success, or one of several negative
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.
The
*archive_errno*(3)
and
*archive_error_string*(3)
functions can be used to retrieve an appropriate error code and a
textual error message.
(See
*archive_util*(3)
for details.)

*archive_read_disk_new*()
returns a pointer to a newly-allocated
*struct archive*
object or NULL if the allocation failed for any reason.

*archive_read_disk_gname*()
and
*archive_read_disk_uname*()
return
*const char `*`*
pointers to the textual name or NULL if the lookup failed for any reason.
The returned pointer points to internal storage that
may be reused on the next call to either of these functions;
callers should copy the string if they need to continue accessing it.

== SEE ALSO ==
*archive_read*(3),
*archive_write*(3),
*archive_write_disk*(3),
*tar*(1),
*libarchive*(3)
== HISTORY ==
The
*libarchive*
library first appeared in
FreeBSD 5.3.
The
*archive_read_disk*
interface was added to
*libarchive* 2.6
and first appeared in
FreeBSD 8.0.
== AUTHORS ==
The
*libarchive*
library was written by
Tim Kientzle  <kientzle@freebsd.org.>
== BUGS ==
The
"standard"
user name and group name lookup functions are not the defaults because
*getgrid*(3)
and
*getpwid*(3)
are sometimes too large for particular applications.
The current design allows the application author to use a more
compact implementation when appropriate.

The full list of metadata read from disk by
*archive_read_disk_entry_from_file*()
is necessarily system-dependent.

The
*archive_read_disk_entry_from_file*()
function reads as much information as it can from disk.
Some method should be provided to limit this so that clients who
do not need ACLs, for instance, can avoid the extra work needed
to look up such information.

This API should provide a set of methods for walking a directory tree.
That would make it a direct parallel of the
*archive_read*(3)
API.
When such methods are implemented, the
"hybrid"
symbolic link mode will make sense.
