ARCHIVE_WRITE(3) | Library Functions Manual | ARCHIVE_WRITE(3) |
archive_write
—
functions for creating archives
Streaming Archive Library (libarchive, -larchive)
#include
<archive.h>
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.
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.
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.
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.
After all entries have been written, use
the
archive_write_free
()
function to release all resources.
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); } la_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; /* Set archive format and filter according to output file extension. * If it fails, set default format. Platform depended function. * See supported formats in archive_write_set_format_filter_by_ext.c */ if (archive_write_set_format_filter_by_ext(a, outname) != ARCHIVE_OK) { 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; }
tar(1), archive_write_set_options(3), libarchive(3), cpio(5), mtree(5), tar(5)
The libarchive
library first appeared in
FreeBSD 5.3.
The libarchive
library was written by
Tim Kientzle ⟨kientzle@acm.org⟩.
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.
February 2, 2012 | macOS 14.6 |