NAME¶
archive_write —
functions for creating
archives
LIBRARY¶
Streaming Archive Library (libarchive, -larchive)
SYNOPSIS¶
#include <archive.h>
DESCRIPTION¶
These functions provide a complete API for creating streaming archive files. The
general process is to first create the struct archive object, set any desired
options, initialize the archive, append entries, then close the archive and
release all resources.
Create archive object¶
See
archive_write_new(3).
To write an archive, you must first obtain an initialized struct archive object
from
archive_write_new().
See
archive_write_filter(3),
archive_write_format(3) and
archive_write_blocksize(3).
You can then modify this object for the desired operations with the various
archive_write_set_XXX() functions. In particular, you will
need to invoke appropriate
archive_write_add_XXX() and
archive_write_set_XXX() functions to enable the
corresponding compression and format support.
Set options¶
See
archive_read_set_options(3).
Open archive¶
See
archive_write_open(3).
Once you have prepared the struct archive object, you call
archive_write_open() to actually open the archive and
prepare it for writing. 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 write the archive data.
Produce archive¶
See
archive_write_header(3) and
archive_write_data(3).
Individual archive entries are written in a three-step process: You first
initialize a struct archive_entry structure with information about the new
entry. At a minimum, you should set the pathname of the entry and provide a
struct stat with a valid
st_mode
field, which specifies the type of object and
st_size
field, which specifies the size of the data portion of the object.
Release resources¶
See
archive_write_free(3).
After all entries have been written, use the
archive_write_free() function to release all resources.
EXAMPLE¶
The following sketch illustrates basic usage of the library. In this example,
the callback functions are simply wrappers around the standard
open(2),
write(2), and
close(2) system calls.
#ifdef __linux__
#define _FILE_OFFSET_BITS 64
#endif
#include <sys/stat.h>
#include <archive.h>
#include <archive_entry.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
struct mydata {
const char *name;
int fd;
};
int
myopen(struct archive *a, void *client_data)
{
struct mydata *mydata = client_data;
mydata->fd = open(mydata->name, O_WRONLY | O_CREAT, 0644);
if (mydata->fd >= 0)
return (ARCHIVE_OK);
else
return (ARCHIVE_FATAL);
}
ssize_t
mywrite(struct archive *a, void *client_data, const void *buff, size_t n)
{
struct mydata *mydata = client_data;
return (write(mydata->fd, buff, n));
}
int
myclose(struct archive *a, void *client_data)
{
struct mydata *mydata = client_data;
if (mydata->fd > 0)
close(mydata->fd);
return (0);
}
void
write_archive(const char *outname, const char **filename)
{
struct mydata *mydata = malloc(sizeof(struct mydata));
struct archive *a;
struct archive_entry *entry;
struct stat st;
char buff[8192];
int len;
int fd;
a = archive_write_new();
mydata->name = outname;
archive_write_add_filter_gzip(a);
archive_write_set_format_ustar(a);
archive_write_open(a, mydata, myopen, mywrite, myclose);
while (*filename) {
stat(*filename, &st);
entry = archive_entry_new();
archive_entry_copy_stat(entry, &st);
archive_entry_set_pathname(entry, *filename);
archive_write_header(a, entry);
if ((fd = open(*filename, O_RDONLY)) != -1) {
len = read(fd, buff, sizeof(buff));
while ( len > 0 ) {
archive_write_data(a, buff, len);
len = read(fd, buff, sizeof(buff));
}
close(fd);
}
archive_entry_free(entry);
filename++;
}
archive_write_free(a);
}
int main(int argc, const char **argv)
{
const char *outname;
argv++;
outname = argv++;
write_archive(outname, argv);
return 0;
}
SEE ALSO¶
tar(1),
libarchive(3),
archive_write_set_options(3),
cpio(5),
mtree(5),
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¶
There are many peculiar bugs in historic tar implementations that may cause
certain programs to reject archives written by this library. For example,
several historic implementations calculated header checksums incorrectly and
will thus reject valid archives; GNU tar does not fully support pax
interchange format; some old tar implementations required specific field
terminations.
The default pax interchange format eliminates most of the historic tar
limitations and provides a generic key/value attribute facility for
vendor-defined extensions. One oversight in POSIX is the failure to provide a
standard attribute for large device numbers. This library uses
“SCHILY.devminor” and “SCHILY.devmajor” for device
numbers that exceed the range supported by the backwards-compatible ustar
header. These keys are compatible with Joerg Schilling's
star archiver. Other implementations may not recognize these
keys and will thus be unable to correctly restore device nodes with large
device numbers from archives created by this library.