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ARCHIVE_READ(3)		 BSD Library Functions Manual	       ARCHIVE_READ(3)

     archive_read -- functions for reading streaming archives

     Streaming Archive Library (libarchive, -larchive)

     #include <archive.h>

     These functions provide a complete	API for	reading	streaming archives.
     The general process is to first create the	struct archive object, set op-
     tions, initialize the reader, iterate over	the archive headers and	asso-
     ciated data, then close the archive and release all resources.

   Create archive object
     See archive_read_new(3).

     To	read an	archive, you must first	obtain an initialized struct archive
     object from archive_read_new().

   Enable filters and formats
     See archive_read_filter(3)	and archive_read_format(3).

     You can then modify this object for the desired operations	with the vari-
     ous archive_read_set_XXX()	and archive_read_support_XXX() functions.  In
     particular, you will need to invoke appropriate
     archive_read_support_XXX()	functions to enable the	corresponding compres-
     sion and format support.  Note that these latter functions	perform	two
     distinct operations: they cause the corresponding support code to be
     linked into your program, and they	enable the corresponding auto-detect
     code.  Unless you have specific constraints, you will generally want to
     invoke archive_read_support_filter_all() and
     archive_read_support_format_all() to enable auto-detect for all formats
     and compression types currently supported by the library.

   Set options
     See archive_read_set_options(3).

   Open	archive
     See archive_read_open(3).

     Once you have prepared the	struct archive object, you call
     archive_read_open() to actually open the archive and prepare it for read-
     ing.  There are several variants of this function;	the most basic expects
     you to provide pointers to	several	functions that can provide blocks of
     bytes from	the archive.  There are	convenience forms that allow you to
     specify a filename, file descriptor, FILE * object, or a block of memory
     from which	to read	the archive data.  Note	that the core library makes no
     assumptions about the size	of the blocks read; callback functions are
     free to read whatever block size is most appropriate for the medium.

   Consume archive
     See archive_read_header(3), archive_read_data(3) and

     Each archive entry	consists of a header followed by a certain amount of
     data.  You	can obtain the next header with	archive_read_next_header(),
     which returns a pointer to	an struct archive_entry	structure with infor-
     mation about the current archive element.	If the entry is	a regular
     file, then	the header will	be followed by the file	data.  You can use
     archive_read_data() (which	works much like	the read(2) system call) to
     read this data from the archive, or archive_read_data_block() which pro-
     vides a slightly more efficient interface.	 You may prefer	to use the
     higher-level archive_read_data_skip(), which reads	and discards the data
     for this entry, archive_read_data_into_fd(), which	copies the data	to the
     provided file descriptor, or archive_read_extract(), which	recreates the
     specified entry on	disk and copies	data from the archive.	In particular,
     note that archive_read_extract() uses the struct archive_entry structure
     that you provide it, which	may differ from	the entry just read from the
     archive.  In particular, many applications	will want to override the
     pathname, file permissions, or ownership.

   Release resources
     See archive_read_free(3).

     Once you have finished reading data from the archive, you should call
     archive_read_close() to close the archive,	then call archive_read_free()
     to	release	all resources, including all memory allocated by the library.

     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.

	   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_open(a, mydata, myopen, myread, myclose);
	     while (archive_read_next_header(a,	&entry)	== ARCHIVE_OK) {

	   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));

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

	     mydata->fd	= open(mydata->name, O_RDONLY);
	     return (mydata->fd	>= 0 ? ARCHIVE_OK : ARCHIVE_FATAL);

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

	     if	(mydata->fd > 0)
	     return (ARCHIVE_OK);

     tar(1), archive_read_data(3), archive_read_extract(3),
     archive_read_filter(3), archive_read_format(3), archive_read_header(3),
     archive_read_new(3), archive_read_open(3),	archive_read_set_options(3),
     archive_util(3), libarchive(3), tar(5)

     The libarchive library first appeared in FreeBSD 5.3.

     The libarchive library was	written	by Tim Kientzle	<>.

     Many traditional archiver programs	treat empty files as valid empty ar-
     chives.  For example, many	implementations	of tar(1) allow	you to append
     entries to	an empty file.	Of course, it is impossible to determine the
     format of an empty	file by	inspecting the contents, so this library
     treats empty files	as having a special "empty" format.

BSD			       February	2, 2012				   BSD


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