Provided by: libarchive-dev_3.7.2-2ubuntu0.5_amd64 bug

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 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 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
       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.

EXAMPLES

       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);
             }

SEE ALSO

       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)

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  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.

Debian                                          February 2, 2012                                 ARCHIVE_READ(3)