ARCHIVE_WRITE(3)	 BSD Library Functions Manual	      ARCHIVE_WRITE(3)

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().

   Enable filters and formats, configure block size and padding

     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 vari‐

     ous 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_write_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() func‐

     tion 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);

	   }

	   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;

	   }

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 ven‐

     dor-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 implementa‐

     tions 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.

BSD			       February 2, 2012 			   BSD