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

NAME
     archive_read — functions for reading streaming archives

LIBRARY
     Streaming Archive Library (libarchive, ‐larchive)

SYNOPSIS
     #include <archive.h>

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.

   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
     archive_read_extract(3).

     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_to_file(), 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.

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_filter_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_free(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 ? ARCHIVE_OK : ARCHIVE_FATAL);
	   }

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

	     if (mydata‐>fd > 0)
	       close(mydata‐>fd);
	     return (ARCHIVE_OK);
	   }

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