archive_read(3)          BSD Library Functions Manual          archive_read(3)

NAME
     archive_read_new, archive_read_support_compression_all,
     archive_read_support_compression_bzip2,
     archive_read_support_compression_compress,
     archive_read_support_compression_gzip,
     archive_read_support_compression_none,
     archive_read_support_compression_program,
     archive_read_support_format_all,
     archive_read_support_format_cpio,
     archive_read_support_format_empty,
     archive_read_support_format_iso9660,
     archive_read_support_format_tar,
     archive_read_support_format_zip, archive_read_open,
     archive_read_open2, archive_read_open_fd,
     archive_read_open_FILE, archive_read_open_filename,
     archive_read_open_memory, archive_read_next_header,
     archive_read_data, archive_read_data_block,
     archive_read_data_skip, archive_read_data_into_buffer,
     archive_read_data_into_fd, archive_read_extract,
     archive_read_extract_set_progress_callback,
     archive_read_close, archive_read_finish - functions for
     reading streaming archives

SYNOPSIS
     #include <archive.h>

     struct archive *
     archive_read_new(void);

     int
     archive_read_support_compression_all(struct archive *);

     int
     archive_read_support_compression_bzip2(struct archive *);

     int
     archive_read_support_compression_compress(struct archive *);

     int
     archive_read_support_compression_gzip(struct archive *);

     int
     archive_read_support_compression_none(struct archive *);

     int
     archive_read_support_compression_program(struct archive *,
             const char *cmd);

     int
     archive_read_support_format_all(struct archive *);

     int
     archive_read_support_format_cpio(struct archive *);

     int
     archive_read_support_format_empty(struct archive *);

     int
     archive_read_support_format_iso9660(struct archive *);

     int
     archive_read_support_format_tar(struct archive *);

     int
     archive_read_support_format_zip(struct archive *);

     int
     archive_read_open(struct archive *, void *client_data,
             archive_open_callback *, archive_read_callback *,
             archive_close_callback *);

     int
     archive_read_open2(struct archive *, void *client_data,
             archive_open_callback *, archive_read_callback *,
             archive_skip_callback *,
             archive_close_callback *);

     int
     archive_read_open_FILE(struct archive *, FILE *file);

     int
     archive_read_open_fd(struct archive *, int fd,
             size_t block_size);

     int
     archive_read_open_filename(struct archive *,
             const char *filename, size_t block_size);

     int
     archive_read_open_memory(struct archive *, void *buff,
             size_t size);

     int
     archive_read_next_header(struct archive *,
             struct archive_entry **);

     ssize_t
     archive_read_data(struct archive *, void *buff,
             size_t len);

     int
     archive_read_data_block(struct archive *,
             const void **buff, size_t *len, off_t *offset);

     int
     archive_read_data_skip(struct archive *);

     int
     archive_read_data_into_buffer(struct archive *, void *,
             ssize_t len);

     int
     archive_read_data_into_fd(struct archive *, int fd);

     int
     archive_read_extract(struct archive *,
             struct archive_entry *, int flags);

     void
     archive_read_extract_set_progress_callback(struct archive *,
             void (*func)(void *), void *user_data);

     int
     archive_read_close(struct archive *);

     int
     archive_read_finish(struct archive *);

DESCRIPTION
     These functions provide a complete API for reading stream-
     ing 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.  The follow-
     ing summary describes the functions in approximately the
     order they would be used:
     archive_read_new()
             Allocates and initializes a struct archive object
             suitable for reading from an archive.
     archive_read_support_compression_all(),
             archive_read_support_compression_bzip2(),
             archive_read_support_compression_compress(),
             archive_read_support_compression_gzip(),
             archive_read_support_compression_none()
             Enables auto-detection code and decompression sup-
             port for the specified compression.  Note that
             ``none'' is always enabled by default.  For conve-
             nience, archive_read_support_compression_all()
             enables all available decompression code.
     archive_read_support_compression_program()
             Data is fed through the specified external program
             before being dearchived.  Note that this disables
             automatic detection of the compression format, so
             it makes no sense to specify this in conjunction
             with any other decompression option.
     archive_read_support_format_all(),
             archive_read_support_format_cpio(),
             archive_read_support_format_empty(),
             archive_read_support_format_iso9660(),
             archive_read_support_format_tar,()
             archive_read_support_format_zip()
             Enables support---including auto-detection
             code---for the specified archive format.  For
             example, archive_read_support_format_tar() enables
             support for a variety of standard tar formats,
             old-style tar, ustar, pax interchange format, and
             many common variants.  For convenience,
             archive_read_support_format_all() enables support
             for all available formats.  Only empty archives
             are supported by default.
     archive_read_open()
             The same as archive_read_open2(), except that the
             skip callback is assumed to be NULL.
     archive_read_open2()
             Freeze the settings, open the archive, and prepare
             for reading entries.  This is the most generic
             version of this call, which accepts four callback
             functions.  Most clients will want to use
             archive_read_open_filename(),
             archive_read_open_FILE(), archive_read_open_fd(),
             or archive_read_open_memory() instead.  The
             library invokes the client-provided functions to
             obtain raw bytes from the archive.
     archive_read_open_FILE()
             Like archive_read_open(), except that it accepts a
             FILE * pointer.  This function should not be used
             with tape drives or other devices that require
             strict I/O blocking.
     archive_read_open_fd()
             Like archive_read_open(), except that it accepts a
             file descriptor and block size rather than a set
             of function pointers.  Note that the file descrip-
             tor will not be automatically closed at end-of-
             archive.  This function is safe for use with tape
             drives or other blocked devices.
     archive_read_open_file()
             This is a deprecated synonym for
             archive_read_open_filename().
     archive_read_open_filename()
             Like archive_read_open(), except that it accepts a
             simple filename and a block size.  A NULL filename
             represents standard input.  This function is safe
             for use with tape drives or other blocked devices.
     archive_read_open_memory()
             Like archive_read_open(), except that it accepts a
             pointer and size of a block of memory containing
             the archive data.
     archive_read_next_header()
             Read the header for the next entry and return a
             pointer to a struct archive_entry.
     archive_read_data()
             Read data associated with the header just read.
             Internally, this is a convenience function that
             calls archive_read_data_block() and fills any gaps
             with nulls so that callers see a single continuous
             stream of data.
     archive_read_data_block()
             Return the next available block of data for this
             entry.  Unlike archive_read_data(), the
             archive_read_data_block() function avoids copying
             data and allows you to correctly handle sparse
             files, as supported by some archive formats.  The
             library guarantees that offsets will increase and
             that blocks will not overlap.  Note that the
             blocks returned from this function can be much
             larger than the block size read from disk, due to
             compression and internal buffer optimizations.
     archive_read_data_skip()
             A convenience function that repeatedly calls
             archive_read_data_block() to skip all of the data
             for this archive entry.
     archive_read_data_into_buffer()
             This function is deprecated and will be removed.
             Use archive_read_data() instead.
     archive_read_data_into_fd()
             A convenience function that repeatedly calls
             archive_read_data_block() to copy the entire entry
             to the provided file descriptor.
     archive_read_extract(),
             archive_read_extract_set_skip_file()
             A convenience function that wraps the correspond-
             ing archive_write_disk(3) interfaces.  The first
             call to archive_read_extract() creates a restore
             object using archive_write_disk_new(3) and
             archive_write_disk_set_standard_lookup(3), then
             transparently invokes
             archive_write_disk_set_options(3),
             archive_write_header(3), archive_write_data(3),
             and archive_write_finish_entry(3) to create the
             entry on disk and copy data into it.  The flags
             argument is passed unmodified to
             archive_write_disk_set_options(3).
     archive_read_extract_set_progress_callback()
             Sets a pointer to a user-defined callback that can
             be used for updating progress displays during
             extraction.  The progress function will be invoked
             during the extraction of large regular files.  The
             progress function will be invoked with the pointer
             provided to this call.  Generally, the data
             pointed to should include a reference to the
             archive object and the archive_entry object so
             that various statistics can be retrieved for the
             progress display.
     archive_read_close()
             Complete the archive and invoke the close call-
             back.
     archive_read_finish()
             Invokes archive_read_close() if it was not invoked
             manually, then release all resources.  Note: In
             libarchive 1.x, this function was declared to
             return void, which made it impossible to detect
             certain errors when archive_read_close() was
             invoked implicitly from this function.  The decla-
             ration is corrected beginning with libarchive 2.0.

     Note that the library determines most of the relevant
     information about the archive by inspection.  In particu-
     lar, it automatically detects gzip(1) or bzip2(1) compres-
     sion and transparently performs the appropriate decompres-
     sion.  It also automatically detects the archive format.

     A complete description of the struct archive and struct
     archive_entry objects can be found in the overview manual
     page for libarchive(3).

CLIENT CALLBACKS
     The callback functions must match the following proto-
     types:

           typedef ssize_t archive_read_callback(struct archive
           *, void *client_data, const void **buffer)

           typedef int archive_skip_callback(struct archive *,
           void *client_data, size_t request)

           typedef int archive_open_callback(struct archive *,
           void *client_data)

           typedef int archive_close_callback(struct archive *,
           void *client_data)

     The open callback is invoked by archive_open().  It should
     return ARCHIVE_OK if the underlying file or data source is
     successfully opened.  If the open fails, it should call
     archive_set_error() to register an error code and message
     and return ARCHIVE_FATAL.

     The read callback is invoked whenever the library requires
     raw bytes from the archive.  The read callback should read
     data into a buffer, set the const void **buffer argument
     to point to the available data, and return a count of the
     number of bytes available.  The library will invoke the
     read callback again only after it has consumed this data.
     The library imposes no constraints on the size of the data
     blocks returned.  On end-of-file, the read callback should
     return zero.  On error, the read callback should invoke
     archive_set_error() to register an error code and message
     and return -1.

     The skip callback is invoked when the library wants to
     ignore a block of data.  The return value is the number of
     bytes actually skipped, which may differ from the request.
     If the callback cannot skip data, it should return zero.
     If the skip callback is not provided (the function pointer
     is NULL ), the library will invoke the read function
     instead and simply discard the result.  A skip callback
     can provide significant performance gains when reading
     uncompressed archives from slow disk drives or other media
     that can skip quickly.

     The close callback is invoked by archive_close when the
     archive processing is complete.  The callback should
     return ARCHIVE_OK on success.  On failure, the callback
     should invoke archive_set_error() to register an error
     code and message and return ARCHIVE_FATAL.

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_compression_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_finish(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);
           }

RETURN VALUES
     Most functions return zero on success, non-zero on error.
     The possible return codes include: ARCHIVE_OK (the opera-
     tion succeeded), ARCHIVE_WARN (the operation succeeded but
     a non-critical error was encountered), ARCHIVE_EOF (end-
     of-archive was encountered), ARCHIVE_RETRY (the operation
     failed but can be retried), and ARCHIVE_FATAL (there was a
     fatal error; the archive should be closed immediately).
     Detailed error codes and textual descriptions are avail-
     able from the archive_errno() and archive_error_string()
     functions.

     archive_read_new() returns a pointer to a freshly allo-
     cated struct archive object.  It returns NULL on error.

     archive_read_data() returns a count of bytes actually read
     or zero at the end of the entry.  On error, a value of
     ARCHIVE_FATAL, ARCHIVE_WARN, or ARCHIVE_RETRY is returned
     and an error code and textual description can be retrieved
     from the archive_errno() and archive_error_string() func-
     tions.

     The library expects the client callbacks to behave simi-
     larly.  If there is an error, you can use
     archive_set_error() to set an appropriate error code and
     description, then return one of the non-zero values above.
     (Note that the value eventually returned to the client may
     not be the same; many errors that are not critical at the
     level of basic I/O can prevent the archive from being
     properly read, thus most I/O errors eventually cause
     ARCHIVE_FATAL to be returned.)

SEE ALSO
     tar(1), archive(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 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.

BSD                             August 19, 2006                            BSD
