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<p>ARCHIVE_READ(3) BSD Library Functions Manual
ARCHIVE_READ(3)</p>
<p style="margin-top: 1em"><b>NAME</b></p>
<p style="margin-left:6%;"><b>archive_read</b> —
functions for reading streaming archives</p>
<p style="margin-top: 1em"><b>LIBRARY</b></p>
<p style="margin-left:6%;">Streaming Archive Library
(libarchive, -larchive)</p>
<p style="margin-top: 1em"><b>SYNOPSIS</b></p>
<p style="margin-left:6%;"><b>#include
<archive.h></b></p>
<p style="margin-top: 1em"><b>DESCRIPTION</b></p>
<p style="margin-left:6%;">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.</p>
<p style="margin-left:6%; margin-top: 1em"><b>Create
archive object</b> <br>
See archive_read_new(3).</p>
<p style="margin-left:6%; margin-top: 1em">To read an
archive, you must first obtain an initialized struct archive
object from <b>archive_read_new</b>().</p>
<p style="margin-left:6%; margin-top: 1em"><b>Enable
filters and formats</b> <br>
See archive_read_filter(3) and archive_read_format(3).</p>
<p style="margin-left:6%; margin-top: 1em">You can then
modify this object for the desired operations with the
various <b>archive_read_set_XXX</b>() and
<b>archive_read_support_XXX</b>() functions. In particular,
you will need to invoke appropriate
<b>archive_read_support_XXX</b>() 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 <b>archive_read_support_filter_all</b>() and
<b>archive_read_support_format_all</b>() to enable
auto-detect for all formats and compression types currently
supported by the library.</p>
<p style="margin-left:6%; margin-top: 1em"><b>Set
options</b> <br>
See archive_read_set_options(3).</p>
<p style="margin-left:6%; margin-top: 1em"><b>Open
archive</b> <br>
See archive_read_open(3).</p>
<p style="margin-left:6%; margin-top: 1em">Once you have
prepared the struct archive object, you call
<b>archive_read_open</b>() 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, <i>FILE *</i> 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.</p>
<p style="margin-left:6%; margin-top: 1em"><b>Consume
archive</b> <br>
See archive_read_header(3), archive_read_data(3) and
archive_read_extract(3).</p>
<p style="margin-left:6%; margin-top: 1em">Each archive
entry consists of a header followed by a certain amount of
data. You can obtain the next header with
<b>archive_read_next_header</b>(), 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 <b>archive_read_data</b>() (which works much like the
read(2) system call) to read this data from the archive, or
<b>archive_read_data_block</b>() which provides a slightly
more efficient interface. You may prefer to use the
higher-level <b>archive_read_data_skip</b>(), which reads
and discards the data for this entry,
<b>archive_read_data_into_fd</b>(), which copies the data to
the provided file descriptor, or
<b>archive_read_extract</b>(), which recreates the specified
entry on disk and copies data from the archive. In
particular, note that <b>archive_read_extract</b>() 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.</p>
<p style="margin-left:6%; margin-top: 1em"><b>Release
resources</b> <br>
See archive_read_free(3).</p>
<p style="margin-left:6%; margin-top: 1em">Once you have
finished reading data from the archive, you should call
<b>archive_read_close</b>() to close the archive, then call
<b>archive_read_free</b>() to release all resources,
including all memory allocated by the library.</p>
<p style="margin-top: 1em"><b>EXAMPLE</b></p>
<p style="margin-left:6%;">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.</p>
<p style="margin-left:14%; margin-top: 1em">void <br>
list_archive(const char *name) <br>
{ <br>
struct mydata *mydata; <br>
struct archive *a; <br>
struct archive_entry *entry;</p>
<p style="margin-left:14%; margin-top: 1em">mydata =
malloc(sizeof(struct mydata)); <br>
a = archive_read_new(); <br>
mydata->name = name; <br>
archive_read_support_filter_all(a); <br>
archive_read_support_format_all(a); <br>
archive_read_open(a, mydata, myopen, myread, myclose); <br>
while (archive_read_next_header(a, &entry) ==
ARCHIVE_OK) { <br>
printf("%s\n",archive_entry_pathname(entry)); <br>
archive_read_data_skip(a); <br>
} <br>
archive_read_free(a); <br>
free(mydata); <br>
}</p>
<p style="margin-left:14%; margin-top: 1em">la_ssize_t <br>
myread(struct archive *a, void *client_data, const void
**buff) <br>
{ <br>
struct mydata *mydata = client_data;</p>
<p style="margin-left:14%; margin-top: 1em">*buff =
mydata->buff; <br>
return (read(mydata->fd, mydata->buff, 10240)); <br>
}</p>
<p style="margin-left:14%; margin-top: 1em">int <br>
myopen(struct archive *a, void *client_data) <br>
{ <br>
struct mydata *mydata = client_data;</p>
<p style="margin-left:14%; margin-top: 1em">mydata->fd =
open(mydata->name, O_RDONLY); <br>
return (mydata->fd >= 0 ? ARCHIVE_OK : ARCHIVE_FATAL);
<br>
}</p>
<p style="margin-left:14%; margin-top: 1em">int <br>
myclose(struct archive *a, void *client_data) <br>
{ <br>
struct mydata *mydata = client_data;</p>
<p style="margin-left:14%; margin-top: 1em">if
(mydata->fd > 0) <br>
close(mydata->fd); <br>
return (ARCHIVE_OK); <br>
}</p>
<p style="margin-top: 1em"><b>SEE ALSO</b></p>
<p style="margin-left:6%;">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)</p>
<p style="margin-top: 1em"><b>HISTORY</b></p>
<p style="margin-left:6%;">The <b>libarchive</b> library
first appeared in FreeBSD 5.3.</p>
<p style="margin-top: 1em"><b>AUTHORS</b></p>
<p style="margin-left:6%;">The <b>libarchive</b> library
was written by Tim Kientzle <kientzle@acm.org>.</p>
<p style="margin-top: 1em"><b>BUGS</b></p>
<p style="margin-left:6%;">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.</p>
<p style="margin-left:6%; margin-top: 1em">BSD
February 2, 2012 BSD</p>
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