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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_tar,
     archive_read_support_format_cpio, archive_read_support_format_all,
     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 tar 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_tar(struct archive *);

     int
     archive_read_support_format_cpio(struct archive *);

     int
     archive_read_support_format_all(struct archive *);

     int
     archive_read_open(struct archive *, void *client_data,
         archive_read_archive_callback *, archive_open_archive_callback *,
         archive_close_archive_callback *);

     int
     archive_read_open_fd(struct archive *, int fd);

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

     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 *);

     int
     archive_read_data_into_fd(struct archive *, int fd);

     int
     archive_read_extract(struct archive *, 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
             controls the size that will be used when invoking the read
             callback function.  The default is 20 records or 10240 bytes for
             tar formats.
     archive_read_support_compression_XXX()
             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_XXX()
             Enables support---including auto-detection code---for the
             specified archive format.  In particular,
             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.  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.  The library invokes these
             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 callbacks 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
             descriptor 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
             filename.  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
             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
             gaurantees that offsets will increase and that blocks will not
             overlap.
     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()
             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
             provided file descriptor.
     archive_read_extract()
             A convenience function that recreates the specified object on
             disk and reads the entry data into that 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 files are unlinked before the new entry
                     is written.
             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
                     particular, the default behavior does not break existing
                     hard links.
     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 callback.
     archive_read_finish()
             Invokes archive_read_close() if it wasn't invoked maually, 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
     appropriate decompression.  It also automatically detects the archive
     format.

     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)
     These callback functions are called whenever the library requires raw
     bytes from the archive.  Note that it is the client's responsibility to
     correctly block the input.

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

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);
           }

           int
           myclose(struct archive *a, void *client_data)
           {
             struct mydata *mydata = client_data;

             if (mydata->fd > 0)
               close(mydata->fd);
             return (0);
           }

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
     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 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()
     functions.

     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
     eventually cause ARCHIVE_FATAL to be returned.)

SEE ALSO
     tar(1), archive(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

FreeBSD 11.0-PRERELEASE         October 1, 2003        FreeBSD 11.0-PRERELEASE

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

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