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archive_read(3)	       FreeBSD Library Functions Manual	       archive_read(3)

NAME
     archive_read_new, archive_read_set_bytes_per_block,
     archive_read_support_compression_all,
     archive_read_support_compression_bzip2,
     archive_read_support_compression_compress,
     archive_read_support_compression_gzip,
     archive_read_support_compression_none, archive_read_support_format_tar,
     archive_read_support_format_cpio, archive_read_support_format_all,
     archive_read_open,	archive_read_open_fd, archive_read_open_file,
     archive_read_next_header, archive_read_data, archive_read_data_block,
     archive_read_data_skip, archive_read_data_into_buffer,
     archive_read_data_into_fd,	archive_read_extract,
     archive_read_extract_set_progress_callback, archive_read_close
     archive_read_finish -- functions for reading tar archives

SYNOPSIS
     #include <archive.h>

     struct archive *
     archive_read_new(void);

     int
     archive_read_set_bytes_per_block(struct archive *,	int);

     int
     archive_read_support_compression_all(struct archive *);

     int
     archive_read_support_compression_bzip2(struct archive *);

     int
     archive_read_support_compression_compress(struct archive *);

     int
     archive_read_support_compression_gzip(struct archive *);

     int
     archive_read_support_compression_none(struct archive *);

     int
     archive_read_support_format_tar(struct archive *);

     int
     archive_read_support_format_cpio(struct archive *);

     int
     archive_read_support_format_all(struct archive *);

     int
     archive_read_open(struct archive *, void *client_data,
	 archive_read_archive_callback *, archive_open_archive_callback	*,
	 archive_close_archive_callback	*);

     int
     archive_read_open_fd(struct archive *, int	fd);

     int
     archive_read_open_file(struct archive *, const char *filename);

     int
     archive_read_next_header(struct archive *,	struct archive_entry **);

     ssize_t
     archive_read_data(struct archive *, void *buff, size_t len);

     int
     archive_read_data_block(struct archive *, const void **buff, size_t *len,
	 off_t *offset);

     int
     archive_read_data_skip(struct archive *);

     int
     archive_read_data_into_buffer(struct archive *, void *);

     int
     archive_read_data_into_fd(struct archive *, int fd);

     int
     archive_read_extract(struct archive *, int	flags);

     void
     archive_read_extract_set_progress_callback(struct archive *,
	 void (*func)(void *), void *user_data);

     int
     archive_read_close(struct archive *);

     void
     archive_read_finish(struct	archive	*);

DESCRIPTION
     These functions provide a complete	API for	reading	streaming archives.
     The general process is to first create the	struct archive object, set
     options, initialize the reader, iterate over the archive headers and
     associated	data, then close the archive and release all resources.	 The
     following summary describes the functions in approximately	the order they
     would be used:
     archive_read_new()
	     Allocates and initializes a struct	archive	object suitable	for
	     reading from an archive.
     archive_read_set_bytes_per_block()
	     Sets the block size used for reading the archive data.  This con-
	     trols the size that will be used when invoking the	read callback
	     function.	The default is 20 records or 10240 bytes for tar for-
	     mats.
     archive_read_support_compression_XXX()
	     Enables auto-detection code and decompression support for the
	     specified compression.  Note that ``none''	is always enabled by
	     default.  For convenience,	archive_read_support_compression_all()
	     enables all available decompression code.
     archive_read_support_format_XXX()
	     Enables support---including auto-detection	code---for the speci-
	     fied archive format.  In particular,
	     archive_read_support_format_tar() enables support for a variety
	     of	standard tar formats, old-style	tar, ustar, pax	interchange
	     format, and many common variants.	For convenience,
	     archive_read_support_format_all() enables support for all avail-
	     able formats.  Note that there is no default.
     archive_read_open()
	     Freeze the	settings, open the archive, and	prepare	for reading
	     entries.  This is the most	generic	version	of this	call, which
	     accepts three callback functions.	The library invokes these
	     client-provided functions to obtain raw bytes from	the archive.
	     Note: The API permits a decompression method to fork and invoke
	     the callbacks from	another	process.  Although none	of the current
	     decompression methods use this technique, future decompression
	     methods may utilize this technique.  If the decompressor forks,
	     it	will ensure that the open and close callbacks are invoked
	     within the	same process as	the read callback.  In particular,
	     clients should not	attempt	to use shared variables	to communicate
	     between the open/read/close callbacks and the mainline code.
     archive_read_open_fd()
	     Like archive_read_open(), except that it accepts a	file descrip-
	     tor rather	than a trio of function	pointers.  Note	that the file
	     descriptor	will not be automatically closed at end-of-archive.
     archive_read_open_file()
	     Like archive_read_open(), except that it accepts a	simple file-
	     name.  A NULL filename represents standard	input.
     archive_read_next_header()
	     Read the header for the next entry	and return a pointer to	a
	     struct archive_entry.
     archive_read_data()
	     Read data associated with the header just read.  Internally, this
	     is	a convenience function that calls archive_read_data_block()
	     and fills any gaps	with nulls so that callers see a single	con-
	     tinuous stream of data.
     archive_read_data_block()
	     Return the	next available block of	data for this entry.  Unlike
	     archive_read_data(), the archive_read_data_block()	function
	     avoids copying data and allows you	to correctly handle sparse
	     files, as supported by some archive formats.  The library gauran-
	     tees that offsets will increase and that blocks will not overlap.
     archive_read_data_skip()
	     A convenience function that repeatedly calls
	     archive_read_data_block() to skip all of the data for this	ar-
	     chive entry.
     archive_read_data_into_buffer()
	     A convenience function that repeatedly calls
	     archive_read_data_block() to copy the entire entry	into the
	     client-supplied buffer.  Note that	the client is responsible for
	     sizing the	buffer appropriately.
     archive_read_data_into_fd()
	     A convenience function that repeatedly calls
	     archive_read_data_block() to copy the entire entry	to the pro-
	     vided file	descriptor.
     archive_read_extract()
	     A convenience function that recreates the specified object	on
	     disk and reads the	entry data into	that object.  The flags	argu-
	     ment modifies how the object is recreated.	 It consists of	a bit-
	     wise OR of	one or more of the following values:
	     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
		     The permissions (mode bits) should	be restored for	all
		     objects.  By default, permissions are only	restored for
		     regular files.
	     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_NO_OVERWRITE
		     Existing files on disk will not be	overwritten.  By
		     default, existing files are unlinked before the new entry
		     is	written.
	     ARCHIVE_EXTRACT_UNLINK
		     Existing files on disk will be unlinked and recreated
		     from scratch.  By default,	existing files are truncated
		     and rewritten, but	the file is not	recreated.  In partic-
		     ular, the default behavior	does not break existing	hard
		     links.
     archive_read_extract_set_progress_callback()
	     Sets a pointer to a user-defined callback that can	be used	for
	     updating progress displays	during extraction.  The	progress func-
	     tion will be invoked during the extraction	of large regular
	     files.  The progress function will	be invoked with	the pointer
	     provided to this call.  Generally,	the data pointed to should
	     include a reference to the	archive	object and the archive_entry
	     object so that various statistics can be retrieved	for the
	     progress display.
     archive_read_close()
	     Complete the archive and invoke the close callback.
     archive_read_finish()
	     Invokes archive_read_close() if it	wasn't invoked maually,	then
	     release all resources.

     Note that the library determines most of the relevant information about
     the archive by inspection.	 In particular,	it automatically detects
     gzip(1) or	bzip2(1) compression and transparently performs	the appropri-
     ate decompression.	 It also automatically detects the archive format.

     The callback functions must match the following prototypes:

	   typedef ssize_t archive_read_callback(struct	archive	*, void
	   *client_data, const void **buffer)

	   typedef int archive_open_callback(struct archive *, void
	   *client_data)

	   typedef int archive_close_callback(struct archive *,	void
	   *client_data)
     These callback functions are called whenever the library requires raw
     bytes from	the archive.  Note that	it is the client's responsibility to
     correctly block the input.

     A complete	description of the struct archive and struct archive_entry
     objects can be found in the overview manual page for libarchive(3).

EXAMPLE
     The following illustrates basic usage of the library.  In this example,
     the callback functions are	simply wrappers	around the standard open(2),
     read(2), and close(2) system calls.

	   void
	   list_archive(const char *name)
	   {
	     struct mydata *mydata;
	     struct archive *a;
	     struct archive_entry *entry;

	     mydata = malloc(sizeof(struct mydata));
	     a = archive_read_new();
	     mydata->name = name;
	     archive_read_support_compression_all(a);
	     archive_read_support_format_all(a);
	     archive_read_open(a, mydata, myopen, myread, myclose);
	     while (archive_read_next_header(a,	&entry)	== ARCHIVE_OK) {
	       printf("%s\n",archive_entry_pathname(entry));
	       archive_read_data_skip(a);
	     }
	     archive_read_finish(a);
	     free(mydata);
	   }

	   ssize_t
	   myread(struct archive *a, void *client_data,	const void **buff)
	   {
	     struct mydata *mydata = client_data;

	     *buff = mydata->buff;
	     return (read(mydata->fd, mydata->buff, 10240));
	   }

	   int
	   myopen(struct archive *a, void *client_data)
	   {
	     struct mydata *mydata = client_data;

	     mydata->fd	= open(mydata->name, O_RDONLY);
	     return (mydata->fd	>= 0);
	   }

	   int
	   myclose(struct archive *a, void *client_data)
	   {
	     struct mydata *mydata = client_data;

	     if	(mydata->fd > 0)
	       close(mydata->fd);
	     return (0);
	   }

RETURN VALUES
     Most functions return zero	on success, non-zero on	error.	The possible
     return codes include: ARCHIVE_OK (the operation succeeded)	ARCHIVE_WARN
     (the operation succeeded but a non-critical error was encountered)
     ARCHIVE_EOF (end-of-archive was encountered), ARCHIVE_RETRY (the opera-
     tion failed but can be retried), and ARCHIVE_FATAL	(there was a fatal
     error; the	archive	should be closed immediately).	Detailed error codes
     and textual descriptions are available from the archive_errno() and
     archive_error_string() functions.

     archive_read_new()	returns	a pointer to a freshly allocated struct
     archive object.  It returns NULL on error.

     archive_read_data() returns a count of bytes actually read	or zero	at the
     end of the	entry.	On error, a value of ARCHIVE_FATAL, ARCHIVE_WARN, or
     ARCHIVE_RETRY is returned and an error code and textual description can
     be	retrieved from the archive_errno() and archive_error_string() func-
     tions.

     The library expects the client callbacks to behave	similarly.  If there
     is	an error, you can use archive_set_error() to set an appropriate	error
     code and description, then	return one of the non-zero values above.
     (Note that	the value eventually returned to the client may	not be the
     same; many	errors that are	not critical at	the level of basic I/O can
     prevent the archive from being properly read, thus	most I/O errors	even-
     tually cause ARCHIVE_FATAL	to be returned.)

SEE ALSO
     tar(1), archive(3), tar(5)

HISTORY
     The libarchive library first appeared in FreeBSD 5.3.

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

BUGS
FreeBSD	9.2			October	1, 2003			   FreeBSD 9.2

NAME | SYNOPSIS | DESCRIPTION | EXAMPLE | RETURN VALUES | SEE ALSO | HISTORY | AUTHORS | BUGS

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