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 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_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() function to release all resources.

EXAMPLES

     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), archive_write_set_options(3), libarchive(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.