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ARCHIVE_READ(3)            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
     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
     various 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
     compression 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
     reading.  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
     information 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
     provides 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), 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)

     The libarchive library first appeared in FreeBSD 5.3.

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

     Many traditional archiver programs treat empty files as valid empty
     archives.  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.

NetBSD 10.99                   February 2, 2012                   NetBSD 10.99