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archive_write(3)	 BSD Library Functions Manual	      archive_write(3)

     archive_write_new, archive_write_set_format_cpio,
     archive_write_set_format_pax, archive_write_set_format_pax_restricted,
     archive_write_set_format_shar, archive_write_set_format_shar_binary,
     archive_write_set_format_ustar, archive_write_get_bytes_per_block,
     archive_write_set_bytes_per_block, archive_write_set_bytes_in_last_block,
     archive_write_set_compression_gzip, archive_write_set_compression_none,
     archive_write_set_compressor_options, archive_write_set_format_options,
     archive_write_set_options, archive_write_open, archive_write_open_fd,
     archive_write_open_FILE, archive_write_open_filename,
     archive_write_open_memory, archive_write_header, archive_write_data,
     archive_write_finish_entry, archive_write_close, archive_write_finish —
     functions for creating archives

     #include <archive.h>

     struct archive *

     archive_write_get_bytes_per_block(struct archive *);

     archive_write_set_bytes_per_block(struct archive *, int bytes_per_block);

     archive_write_set_bytes_in_last_block(struct archive *, int);

     archive_write_set_compression_bzip2(struct archive *);

     archive_write_set_compression_compress(struct archive *);

     archive_write_set_compression_gzip(struct archive *);

     archive_write_set_compression_none(struct archive *);

     archive_write_set_compression_program(struct archive *,
	 const char * cmd);

     archive_write_set_format_cpio(struct archive *);

     archive_write_set_format_pax(struct archive *);

     archive_write_set_format_pax_restricted(struct archive *);

     archive_write_set_format_shar(struct archive *);

     archive_write_set_format_shar_binary(struct archive *);

     archive_write_set_format_ustar(struct archive *);

     archive_write_set_format_options(struct archive *, const char *);

     archive_write_set_compressor_options(struct archive *, const char *);

     archive_write_set_options(struct archive *, const char *);

     archive_write_open(struct archive *, void *client_data,
	 archive_open_callback *, archive_write_callback *,
	 archive_close_callback *);

     archive_write_open_fd(struct archive *, int fd);

     archive_write_open_FILE(struct archive *, FILE *file);

     archive_write_open_filename(struct archive *, const char *filename);

     archive_write_open_memory(struct archive *, void *buffer,
	 size_t bufferSize, size_t *outUsed);

     archive_write_header(struct archive *, struct archive_entry *);

     archive_write_data(struct archive *, const void *, size_t);

     archive_write_finish_entry(struct archive *);

     archive_write_close(struct archive *);

     archive_write_finish(struct archive *);

     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.  The following summary
     describes the functions in approximately the order they are ordinarily

	     Allocates and initializes a struct archive object suitable for
	     writing a tar archive.

	     Sets the block size used for writing the archive data.  Every
	     call to the write callback function, except possibly the last
	     one, will use this value for the length.  The third parameter is
	     a boolean that specifies whether or not the final block written
	     will be padded to the full block size.  If it is zero, the last
	     block will not be padded.	If it is non-zero, padding will be
	     added both before and after compression.  The default is to use a
	     block size of 10240 bytes and to pad the last block.  Note that a
	     block size of zero will suppress internal blocking and cause
	     writes to be sent directly to the write callback as they occur.

	     Retrieve the block size to be used for writing.  A value of -1
	     here indicates that the library should use default values.	 A
	     value of zero indicates that internal blocking is suppressed.

	     Sets the block size used for writing the last block.  If this
	     value is zero, the last block will be padded to the same size as
	     the other blocks.	Otherwise, the final block will be padded to a
	     multiple of this size.  In particular, setting it to 1 will cause
	     the final block to not be padded.	For compressed output, any
	     padding generated by this option is applied only after the com‐
	     pression.	The uncompressed data is always unpadded.  The default
	     is to pad the last block to the full block size (note that
	     archive_write_open_filename() will set this based on the file
	     type).  Unlike the other “set” functions, this function can be
	     called after the archive is opened.

	     Retrieve the currently-set value for last block size.  A value of
	     -1 here indicates that the library should use default values.

     archive_write_set_format_cpio(), archive_write_set_format_pax(),
	     Sets the format that will be used for the archive.	 The library
	     can write POSIX octet-oriented cpio format archives, POSIX-stan‐
	     dard “pax interchange” format archives, traditional “shar” ar‐
	     chives, enhanced “binary” shar archives that store a variety of
	     file attributes and handle binary files, and POSIX-standard
	     “ustar” archives.	The pax interchange format is a backwards-com‐
	     patible tar format that adds key/value attributes to each entry
	     and supports arbitrary filenames, linknames, uids, sizes, etc.
	     “Restricted pax interchange format” is the library default; this
	     is the same as pax format, but suppresses the pax extended header
	     for most normal files.  In most cases, this will result in ordi‐
	     nary ustar archives.

	     The resulting archive will be compressed as specified.  Note that
	     the compressed output is always properly blocked.

	     The archive will be fed into the specified compression program.
	     The output of that program is blocked and written to the client
	     write callbacks.

	     archive_write_set_format_options(), archive_write_set_options()
	     Specifies options that will be passed to the currently-enabled
	     compressor and/or format writer.  The argument is a comma-sepa‐
	     rated list of individual options.	Individual options have one of
	     the following forms:
		     The option/value pair will be provided to every module.
		     Modules that do not accept an option with this name will
		     ignore it.
	     option  The option will be provided to every module with a value
		     of “1”.
		     The option will be provided to every module with a NULL
	     module:option=value, module:option, module:!option
		     As above, but the corresponding option and value will be
		     provided only to modules whose name matches module.
	     The return value will be ARCHIVE_OK if any module accepts the
	     option, or ARCHIVE_WARN if no module accepted the option, or
	     ARCHIVE_FATAL if there was a fatal error while attempting to
	     process the option.

	     The currently supported options are:
	     Compressor gzip
			     The value is interpreted as a decimal integer
			     specifying the gzip compression level.
	     Compressor xz
			     The value is interpreted as a decimal integer
			     specifying the compression level.
	     Format mtree
		     cksum, device, flags, gid, gname, indent, link, md5,
			     mode, nlink, rmd160, sha1, sha256, sha384,
			     sha512, size, time, uid, uname
			     Enable a particular keyword in the mtree output.
			     Prefix with an exclamation mark to disable the
			     corresponding keyword.  The default is equivalent
			     to “device, flags, gid, gname, link, mode, nlink,
			     size, time, type, uid, uname”.
		     all     Enables all of the above keywords.
			     Enables generation of /set lines that specify
			     default values for the following files and/or
		     indent  XXX needs explanation XXX

	     Freeze the settings, open the archive, and prepare for writing
	     entries.  This is the most generic form of this function, which
	     accepts pointers to three callback functions which will be
	     invoked by the compression layer to write the constructed ar‐

	     A convenience form of archive_write_open() that accepts a file
	     descriptor.  The archive_write_open_fd() function is safe for use
	     with tape drives or other block-oriented devices.

	     A convenience form of archive_write_open() that accepts a FILE *
	     pointer.  Note that archive_write_open_FILE() is not safe for
	     writing to tape drives or other devices that require correct

	     A deprecated synonym for archive_write_open_filename().

	     A convenience form of archive_write_open() that accepts a file‐
	     name.  A NULL argument indicates that the output should be writ‐
	     ten to standard output; an argument of “-” will open a file with
	     that name.	 If you have not invoked
	     archive_write_set_bytes_in_last_block(), then
	     archive_write_open_filename() will adjust the last-block padding
	     depending on the file: it will enable padding when writing to
	     standard output or to a character or block device node, it will
	     disable padding otherwise.	 You can override this by manually
	     invoking archive_write_set_bytes_in_last_block() before calling
	     archive_write_open().  The archive_write_open_filename() function
	     is safe for use with tape drives or other block-oriented devices.

	     A convenience form of archive_write_open() that accepts a pointer
	     to a block of memory that will receive the archive.  The final
	     size_t * argument points to a variable that will be updated after
	     each write to reflect how much of the buffer is currently in use.
	     You should be careful to ensure that this variable remains allo‐
	     cated until after the archive is closed.

	     Build and write a header using the data in the provided struct
	     archive_entry structure.  See archive_entry(3) for information on
	     creating and populating struct archive_entry objects.

	     Write data corresponding to the header just written.  Returns
	     number of bytes written or -1 on error.

	     Close out the entry just written.	In particular, this writes out
	     the final padding required by some formats.  Ordinarily, clients
	     never need to call this, as it is called automatically by
	     archive_write_next_header() and archive_write_close() as needed.

	     Complete the archive and invoke the close callback.

	     Invokes archive_write_close() if it was not invoked manually,
	     then releases all resources.  Note that this function was
	     declared to return void in libarchive 1.x, which made it impossi‐
	     ble to detect errors when archive_write_close() was invoked
	     implicitly from this function.  This is corrected beginning with
	     libarchive 2.0.
     More information about the struct archive object and the overall design
     of the library can be found in the libarchive(3) overview.

     Compression support is built-in to libarchive, which uses zlib and bzlib
     to handle gzip and bzip2 compression, respectively.

     To use this library, you will need to define and register callback func‐
     tions that will be invoked to write data to the resulting archive.	 These
     functions are registered by calling archive_write_open():

	   typedef int archive_open_callback(struct archive *, void

     The open callback is invoked by archive_write_open().  It should return
     ARCHIVE_OK if the underlying file or data source is successfully opened.
     If the open fails, it should call archive_set_error() to register an
     error code and message and return ARCHIVE_FATAL.

	   typedef ssize_t archive_write_callback(struct archive *,
	   void *client_data, const void *buffer, size_t length)

     The write callback is invoked whenever the library needs to write raw
     bytes to the archive.  For correct blocking, each call to the write call‐
     back function should translate into a single write(2) system call.	 This
     is especially critical when writing archives to tape drives.  On success,
     the write callback should return the number of bytes actually written.
     On error, the callback should invoke archive_set_error() to register an
     error code and message and return -1.

	   typedef int archive_close_callback(struct archive *, void

     The close callback is invoked by archive_close when the archive process‐
     ing is complete.  The callback should return ARCHIVE_OK on success.  On
     failure, the callback should invoke archive_set_error() to register an
     error code and message and return ARCHIVE_FATAL.

     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
	   #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;

	   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);
	       return (ARCHIVE_FATAL);

	   mywrite(struct archive *a, void *client_data, const void *buff, size_t n)
	     struct mydata *mydata = client_data;

	     return (write(mydata->fd, buff, n));

	   myclose(struct archive *a, void *client_data)
	     struct mydata *mydata = client_data;

	     if (mydata->fd > 0)
	     return (0);

	   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_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);
	       fd = open(*filename, O_RDONLY);
	       len = read(fd, buff, sizeof(buff));
	       while ( len > 0 ) {
		   archive_write_data(a, buff, len);
		   len = read(fd, buff, sizeof(buff));

	   int main(int argc, const char **argv)
		   const char *outname;
		   outname = argv++;
		   write_archive(outname, argv);
		   return 0;

     Most functions return ARCHIVE_OK (zero) on success, or one of several
     non-zero error codes for errors.  Specific error codes include:
     ARCHIVE_RETRY for operations that might succeed if retried, ARCHIVE_WARN
     for unusual conditions that do not prevent further operations, and
     ARCHIVE_FATAL for serious errors that make remaining operations impossi‐
     ble.  The archive_errno() and archive_error_string() functions can be
     used to retrieve an appropriate error code and a textual error message.

     archive_write_new() returns a pointer to a newly-allocated struct archive

     archive_write_data() returns a count of the number of bytes actually
     written.  On error, -1 is returned and the archive_errno() and
     archive_error_string() functions will return appropriate values.  Note
     that if the client-provided write callback function returns a non-zero
     value, that error will be propagated back to the caller through whatever
     API function resulted in that call, which may include
     archive_write_header(), archive_write_data(), archive_write_close(), or
     archive_write_finish().  The client callback can call archive_set_error()
     to provide values that can then be retrieved by archive_errno() and

     tar(1), libarchive(3), tar(5)

     The libarchive library first appeared in FreeBSD 5.3.

     The libarchive library was written by Tim Kientzle ⟨⟩.

     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				 May 11, 2008				   BSD

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