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.Dd February 2, 2012

.Dt ARCHIVE_WRITE_OPEN 3

.Os

.Sh NAME

.Nm archive_write_open ,

.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

.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_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_open .

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_open

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_open :

.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 .

.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.

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.

.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 libarchive 3 ,

.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 cpio 5 ,

.Xr mtree 5 ,

.Xr tar 5