NAME¶

archive_write_open, archive_write_open2, archive_write_open_fd, archive_write_open_FILE, archive_write_open_filename, archive_write_open_memory — functions for creating archives

LIBRARY¶

Streaming Archive Library (libarchive, -larchive)

SYNOPSIS¶

#include <archive.h>

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

int
archive_write_open2(struct archive *, void *client_data, archive_open_callback *, archive_write_callback *, archive_close_callback *, archive_free_callback *);

int
archive_write_open_fd(struct archive *, int fd);

int
archive_write_open_FILE(struct archive *, FILE *file);

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

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

DESCRIPTION¶

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.

archive_write_open2()

Same as archive_write_open() with an additional fourth free callback. This function should be preferred to archive_write_open().

archive_write_open_fd()

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.

archive_write_open_FILE()

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 blocking.

archive_write_open_file()

A deprecated synonym for archive_write_open_filename().

archive_write_open_filename()

A convenience form of archive_write_open() that accepts a filename. A NULL argument indicates that the output should be written 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_open2(). The archive_write_open_filename() function is safe for use with tape drives or other block-oriented devices.

archive_write_open_memory()

A convenience form of archive_write_open2() 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 allocated until after the archive is closed. This function will disable padding unless you have specifically set the block size.

More information about the struct archive object and the overall design of the library can be found in the libarchive(3) overview.

Note that the convenience forms above vary in how they block the output. See archive_write_blocksize(3) if you need to control the block size used for writes or the end-of-file padding behavior.

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 archive_write_open2():

• typedef int archive_open_callback(struct archive *, void *client_data)

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. Please note that if open fails, close is not called and resources must be freed inside the open callback or with the free callback.

• typedef la_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 callback 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 *client_data)

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 ARCHIVE_OK on success. On failure, the callback should invoke archive_set_error() to register an error code and message and return

• typedef int archive_free_callback(struct archive *, void *client_data)

The free callback is always invoked on archive_free. The return code of this callback is not processed.

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(), archive_write_finish(), or archive_write_free(). The client callback can call archive_set_error() to provide values that can then be retrieved by archive_errno() and archive_error_string().

RETURN VALUES¶

These functions return ARCHIVE_OK on success, or ARCHIVE_FATAL.

ERRORS¶

Detailed error codes and textual descriptions are available from the archive_errno() and archive_error_string() functions.

SEE ALSO¶

tar(1), archive_write(3), archive_write_blocksize(3), archive_write_filter(3), archive_write_format(3), archive_write_new(3), archive_write_set_options(3), libarchive(3), cpio(5), mtree(5), tar(5)