ARCHIVE_READ(3) 	 BSD Library Functions Manual	       ARCHIVE_READ(3)

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 vari‐

     ous 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 compres‐

     sion 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 read‐

     ing.  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 infor‐

     mation 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 pro‐

     vides 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.

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);

	   }

	   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), 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 ar‐

     chives.  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			       February 2, 2012 			   BSD