DragonFly On-Line Manual Pages
ARCHIVE_READ(3) DragonFly 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
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_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.
EXAMPLES
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), archive_read_data(3), archive_read_extract(3),
archive_read_filter(3), archive_read_format(3), archive_read_header(3),
archive_read_new(3), archive_read_open(3), archive_read_set_options(3),
archive_util(3), libarchive(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.
DragonFly 5.9-DEVELOPMENT February 2, 2012 DragonFly 5.9-DEVELOPMENT