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.Dd November 12, 2020
.Dt ARCHIVE_WRITE_OPEN 3
.Os
.Sh NAME
.Nm archive_write_open ,
.Nm archive_write_open2 ,
.Nm archive_write_open_fd ,
.Nm archive_write_open_FILE ,
.Nm archive_write_open_filename ,
.Nm archive_write_open_memory
.Nd functions for creating archives
.Sh LIBRARY
Streaming Archive Library (libarchive, -larchive)
.Sh SYNOPSIS
.In archive.h
.Ft int
.Fo archive_write_open
.Fa "struct archive *"
.Fa "void *client_data"
.Fa "archive_open_callback *"
.Fa "archive_write_callback *"
.Fa "archive_close_callback *"
.Fc
.Ft int
.Fo archive_write_open2
.Fa "struct archive *"
.Fa "void *client_data"
.Fa "archive_open_callback *"
.Fa "archive_write_callback *"
.Fa "archive_close_callback *"
.Fa "archive_free_callback *"
.Fc
.Ft int
.Fn archive_write_open_fd "struct archive *" "int fd"
.Ft int
.Fn archive_write_open_FILE "struct archive *" "FILE *file"
.Ft int
.Fn archive_write_open_filename "struct archive *" "const char *filename"
.Ft int
.Fo archive_write_open_memory
.Fa "struct archive *"
.Fa "void *buffer"
.Fa "size_t bufferSize"
.Fa "size_t *outUsed"
.Fc
.Sh DESCRIPTION
.Bl -tag -width indent
.It Fn archive_write_open
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 archive.
This does not alter the default archive padding.
.It Fn archive_write_open2
Same as
.Fn archive_write_open
with an additional fourth free callback. This function should be preferred to
.Fn archive_write_open .
.It Fn archive_write_open_fd
A convenience form of
.Fn archive_write_open
that accepts a file descriptor.
The
.Fn archive_write_open_fd
function is safe for use with tape drives or other
block-oriented devices.
.It Fn archive_write_open_FILE
A convenience form of
.Fn archive_write_open
that accepts a
.Ft "FILE *"
pointer.
Note that
.Fn archive_write_open_FILE
is not safe for writing to tape drives or other devices
that require correct blocking.
.It Fn archive_write_open_file
A deprecated synonym for
.Fn archive_write_open_filename .
.It Fn archive_write_open_filename
A convenience form of
.Fn archive_write_open
that accepts a filename.
A NULL argument indicates that the output should be written to standard output;
an argument of
.Dq -
will open a file with that name.
If you have not invoked
.Fn archive_write_set_bytes_in_last_block ,
then
.Fn 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
.Fn archive_write_set_bytes_in_last_block
before calling
.Fn archive_write_open2 .
The
.Fn archive_write_open_filename
function is safe for use with tape drives or other
block-oriented devices.
.It Fn archive_write_open_memory
A convenience form of
.Fn archive_write_open2
that accepts a pointer to a block of memory that will receive
the archive.
The final
.Ft "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 allocated until after the archive is
closed.
This function will disable padding unless you
have specifically set the block size.
.El
More information about the
.Va struct archive
object and the overall design of the library can be found in the
.Xr libarchive 3
overview.
.Pp
Note that the convenience forms above vary in how
they block the output.
See
.Xr archive_write_blocksize 3
if you need to control the block size used for writes
or the end-of-file padding behavior.
.\"
.Sh CLIENT CALLBACKS
To use this library, you will need to define and register
callback functions that will be invoked to write data to the
resulting archive.
These functions are registered by calling
.Fn archive_write_open2 :
.Bl -item -offset indent
.It
.Ft typedef int
.Fn archive_open_callback "struct archive *" "void *client_data"
.El
.Pp
The open callback is invoked by
.Fn archive_write_open .
It should return
.Cm ARCHIVE_OK
if the underlying file or data source is successfully
opened.
If the open fails, it should call
.Fn archive_set_error
to register an error code and message and return
.Cm ARCHIVE_FATAL .
Please note that if open fails, close is not called and resources must be
freed inside the open callback or with the free callback.
.Bl -item -offset indent
.It
.Ft typedef la_ssize_t
.Fo archive_write_callback
.Fa "struct archive *"
.Fa "void *client_data"
.Fa "const void *buffer"
.Fa "size_t length"
.Fc
.El
.Pp
The write callback is invoked whenever the library
needs to write raw bytes to the archive.
For correct blocking, each call to the write callback function
should translate into a single
.Xr 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
.Fn archive_set_error
to register an error code and message and return -1.
.Bl -item -offset indent
.It
.Ft typedef int
.Fn archive_close_callback "struct archive *" "void *client_data"
.El
.Pp
The close callback is invoked by archive_close when
the archive processing is complete. If the open callback fails, the close
callback is not invoked.
The callback should return
.Cm ARCHIVE_OK
on success.
On failure, the callback should invoke
.Fn archive_set_error
to register an error code and message and
return
.Cm ARCHIVE_FATAL .
.Bl -item -offset indent
.It
.Ft typedef int
.Fn archive_free_callback "struct archive *" "void *client_data"
.El
.Pp
The free callback is always invoked on archive_free.
The return code of this callback is not processed.
.Pp
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
.Fn archive_write_header ,
.Fn archive_write_data ,
.Fn archive_write_close ,
.Fn archive_write_finish ,
or
.Fn archive_write_free .
The client callback can call
.Fn archive_set_error
to provide values that can then be retrieved by
.Fn archive_errno
and
.Fn archive_error_string .
.\" .Sh EXAMPLE
.Sh RETURN VALUES
These functions return
.Cm ARCHIVE_OK
on success, or
.Cm ARCHIVE_FATAL .
.\"
.Sh ERRORS
Detailed error codes and textual descriptions are available from the
.Fn archive_errno
and
.Fn archive_error_string
functions.
.\"
.Sh SEE ALSO
.Xr tar 1 ,
.Xr archive_write 3 ,
.Xr archive_write_blocksize 3 ,
.Xr archive_write_filter 3 ,
.Xr archive_write_format 3 ,
.Xr archive_write_new 3 ,
.Xr archive_write_set_options 3 ,
.Xr libarchive 3 ,
.Xr cpio 5 ,
.Xr mtree 5 ,
.Xr tar 5
