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_to_file(), 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.

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_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);
           }

           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), 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)

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.