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_archive_callback                     *,
archive_read_archive_callback *,
        archive_close_archive_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 *);
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 re

sources. 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 da

ta. 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_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 sup

port 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 specified 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 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. Most clients will

want to use
archive_read_open_file() or archive_read_open_fd()

instead. The
library invokes the client-provided functions to ob

tain raw bytes
from the archive. Note: The API permits a decom

pression method
to fork and invoke the callbacks from another pro

cess. Although
none of the current decompression methods use this

technique,
future decompression methods may utilize this tech

nique. 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 and block size rather than a trio of function

pointers. Note
that the file descriptor will not be automatically

closed at endof-archive.

archive_read_open_file()

Like archive_read_open(), except that it accepts a

simple filename 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. In

ternally, 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 en

try. Unlike
archive_read_data(), the archive_read_data_block()

function
avoids copying data and allows you to correctly han

dle sparse
files, as supported by some archive formats. The

library guarantees 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
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 re

sponsible 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

filename,
permissions, and other critical information are tak

en 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 re

stored 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 support

ed.

ARCHIVE_EXTRACT_NO_OVERWRITE

Existing files on disk will not be overwrit

ten. By
default, existing regular files are truncat

ed and overwritten; existing directories will have

their permissions
updated; other pre-existing objects are un

linked 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 recreat

ed. In particular, the default behavior does not break

existing hard
links.

ARCHIVE_EXTRACT_ACL

Attempt to restore ACLs. By default, ex

tended 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 created 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 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 was not invoked

manually, then
release all resources.

Note that the library determines most of the relevant infor

mation 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.

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 success

fully 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 processing 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 stan

dard 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, my

close);
while (archive_read_next_header(a, &entry) ==

ARCHIVE_OK) {

printf("%s0,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_FA

TAL);

}

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 en

countered),
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

ARCHIVE_RETRY is returned and an error code and textual de

scription can
be retrieved from the archive_errno() and

archive_error_string() functions.

The library expects the client callbacks to behave similar

ly. If there
is an error, you can use archive_set_error() to set an ap

propriate 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 ba

sic 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), archive_util(3), tar(5)

HISTORY

The libarchive library first appeared in FreeBSD 5.3.

AUTHORS

The libarchive library was written by Tim Kientzle <kient

zle@acm.org>.

BUGS

Directories are actually extracted in two distinct phases.

Directories
are created during archive_read_extract(), but final permis

sions are not
set until archive_read_close(). This separation is neces

sary to correctly handle borderline cases such as a non-writable direc

tory containing 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 permissions are restored incorrectly.

BSD January 8, 2005

BSD