
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_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() 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);
	   }

	   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 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
