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archive_read(3)        FreeBSD Library Functions Manual        archive_read(3)

NAME
     archive_read_new, archive_read_set_bytes_per_block,
     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_format_all,
     archive_read_support_format_cpio, archive_read_support_format_iso9660,
     archive_read_support_format_tar, archive_read_support_format_zip,
     archive_read_open, archive_read_open_fd, archive_read_open_file,
     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_set_bytes_per_block(struct archive *, int);

     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_format_all(struct archive *);

     int
     archive_read_support_format_cpio(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_open_fd(struct archive *, int fd, size_t block_size);

     int
     archive_read_open_file(struct archive *, const char *filename,
         size_t block_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 *);

     void
     archive_read_finish(struct archive *);

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.  The
     following 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_set_bytes_per_block()
             Sets the block size used for reading the archive data.  This con-
             trols the size that will be used when invoking the read callback
             function.  The default is 20 records or 10240 bytes for tar for-
             mats.
     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 support for the
             specified compression.  Note that ``none'' is always enabled by
             default.  For convenience, archive_read_support_compression_all()
             enables all available decompression code.
     archive_read_support_format_all(), archive_read_support_format_cpio(),
             archive_read_support_format_iso9660(),
             archive_read_support_format_tar,()
             archive_read_support_format_zip()
             Enables support---including auto-detection code---for the speci-
             fied 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 avail-
             able formats.  Note that there is no default.
     archive_read_open()
             Freeze the settings, open the archive, and prepare for reading
             entries.  This is the most generic version of this call, which
             accepts three callback functions.  Most clients will want to use
             archive_read_open_file() or archive_read_open_fd() instead.  The
             library invokes the client-provided functions to obtain raw bytes
             from the archive.  Note: The API permits a decompression method
             to fork and invoke the callbacks from another process.  Although
             none of the current decompression methods use this technique,
             future decompression methods may utilize this technique.  If the
             decompressor forks, it will ensure that the open and close call-
             backs are invoked within the same process as the read callback.
             In particular, clients should not attempt to use shared variables
             to communicate between the open/read/close callbacks and the
             mainline code.
     archive_read_open_fd()
             Like archive_read_open(), except that it accepts a file descrip-
             tor and block size rather than a trio of function pointers.  Note
             that the file descriptor will not be automatically closed at end-
             of-archive.
     archive_read_open_file()
             Like archive_read_open(), except that it accepts a simple file-
             name and a block size.  A NULL filename represents standard
             input.
     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 con-
             tinuous 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 guaran-
             tees 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 ar-
             chive entry.
     archive_read_data_into_buffer()
             A convenience function that repeatedly calls
             archive_read_data_block() to copy the entire entry into the
             client-supplied buffer.  Note that the client is responsible for
             sizing the buffer appropriately.
     archive_read_data_into_fd()
             A convenience function that repeatedly calls
             archive_read_data_block() to copy the entire entry to the pro-
             vided file descriptor.
     archive_read_extract()
             A convenience function that recreates the specified object on
             disk and reads the entry data into that object.  The filename,
             permissions, and other critical information are taken from the
             provided archive_entry object.  The flags argument modifies how
             the object is recreated.  It consists of a bitwise OR of one or
             more of the following values:
             ARCHIVE_EXTRACT_OWNER
                     The user and group IDs should be set on the restored
                     file.  By default, the user and group IDs are not
                     restored.
             ARCHIVE_EXTRACT_PERM
                     The permissions (mode bits) should be restored for all
                     objects.  By default, permissions are only restored for
                     regular files.
             ARCHIVE_EXTRACT_TIME
                     The timestamps (mtime, ctime, and atime) should be
                     restored.  By default, they are ignored.  Note that
                     restoring of atime is not currently supported.
             ARCHIVE_EXTRACT_NO_OVERWRITE
                     Existing files on disk will not be overwritten.  By
                     default, existing regular files are truncated and over-
                     written; existing directories will have their permissions
                     updated; other pre-existing objects are unlinked and
                     recreated from scratch.
             ARCHIVE_EXTRACT_UNLINK
                     Existing files on disk will be unlinked and recreated
                     from scratch.  By default, existing files are truncated
                     and rewritten, but the file is not recreated.  In partic-
                     ular, the default behavior does not break existing hard
                     links.
             ARCHIVE_EXTRACT_ACL
                     Attempt to restore ACLs.  By default, extended ACLs are
                     ignored.
             ARCHIVE_EXTRACT_FFLAGS
                     Attempt to restore extended file flags.  By default, file
                     flags are ignored.
             Note that not all attributes are set immediately; some attributes
             are cached in memory and written to disk only when the archive is
             closed.  (For example, read-only directories are initially cre-
             ated writable so that files within those directories can be
             restored.  The final permissions are set when the archive is
             closed.)
     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 func-
             tion 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 callback.
     archive_read_finish()
             Invokes archive_read_close() if it was not invoked manually, then
             release all resources.

     Note that the library determines most of the relevant information about
     the archive by inspection.  In particular, it automatically detects
     gzip(1) or bzip2(1) compression and transparently performs the appropri-
     ate decompression.  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 prototypes:

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

           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 close callback is invoked by archive_close when the archive process-
     ing 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 operation succeeded), ARCHIVE_WARN
     (the operation succeeded but a non-critical error was encountered),
     ARCHIVE_EOF (end-of-archive was encountered), ARCHIVE_RETRY (the opera-
     tion 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 available from the archive_errno() and
     archive_error_string() functions.

     archive_read_new() returns a pointer to a freshly allocated 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 similarly.  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 even-
     tually 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
     Directories are actually extracted in two distinct phases.  Directories
     are created during archive_read_extract(), but final permissions are not
     set until archive_read_close().  This separation is necessary to cor-
     rectly handle borderline cases such as a non-writable directory contain-
     ing files, but can cause unexpected results.  In particular, directory
     permissions are not fully restored until the archive is closed.  If you
     use chdir(2) to change the current directory between calls to
     archive_read_extract() or before calling archive_read_close(), you may
     confuse the permission-setting logic with the result that directory per-
     missions are restored incorrectly.

FreeBSD 6.2                     January 8, 2005                    FreeBSD 6.2

NAME | SYNOPSIS | DESCRIPTION | CLIENT CALLBACKS | EXAMPLE | RETURN VALUES | SEE ALSO | HISTORY | AUTHORS | BUGS

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