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

1mNAME0m
     1marchive_read 22m— functions for reading streaming archives

1mLIBRARY0m
     Streaming Archive Library (libarchive, -larchive)

1mSYNOPSIS0m
     1m#include <archive.h>0m

1mDESCRIPTION0m
     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.

   1mCreate archive object0m
     See archive_read_new(3).

     To read an archive, you must first obtain an initialized struct archive
     object from 1marchive_read_new22m().

   1mEnable filters and formats0m
     See archive_read_filter(3) and archive_read_format(3).

     You can then modify this object for the desired operations with the vari‐
     ous 1marchive_read_set_XXX22m() and 1marchive_read_support_XXX22m() functions.  In
     particular, you will need to invoke appropriate
     1marchive_read_support_XXX22m() 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 1marchive_read_support_filter_all22m() and
     1marchive_read_support_format_all22m() to enable auto-detect for all formats
     and compression types currently supported by the library.

   1mSet options0m
     See archive_read_set_options(3).

   1mOpen archive0m
     See archive_read_open(3).

     Once you have prepared the struct archive object, you call
     1marchive_read_open22m() 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, 4mFILE24m 4m*24m 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.

   1mConsume archive0m
     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 1marchive_read_next_header22m(),
     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
     1marchive_read_data22m() (which works much like the read(2) system call) to
     read this data from the archive, or 1marchive_read_data_block22m() which pro‐
     vides a slightly more efficient interface.  You may prefer to use the
     higher-level 1marchive_read_data_skip22m(), which reads and discards the data
     for this entry, 1marchive_read_data_into_fd22m(), which copies the data to the
     provided file descriptor, or 1marchive_read_extract22m(), which recreates the
     specified entry on disk and copies data from the archive.	In particular,
     note that 1marchive_read_extract22m() 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.

   1mRelease resources0m
     See archive_read_free(3).

     Once you have finished reading data from the archive, you should call
     1marchive_read_close22m() to close the archive, then call 1marchive_read_free22m()
     to release all resources, including all memory allocated by the library.

1mEXAMPLE0m
     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);
	   }

	   la_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);
	   }

1mSEE ALSO0m
     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)

1mHISTORY0m
     The 1mlibarchive 22mlibrary first appeared in FreeBSD 5.3.

1mAUTHORS0m
     The 1mlibarchive 22mlibrary was written by Tim Kientzle <kientzle@acm.org>.

1mBUGS0m
     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
