NAME
archive_read_new, archive_read_set_bytes_per_block, archive_read_support_compression_all, archive_read_support_compression_bzip2, archive_read_support_compression_compress, archive_read_support_compression_gzip, archive_read_support_compression_none, archive_read_support_format_tar, archive_read_support_format_cpio, archive_read_support_format_all, archive_read_open, archive_read_open_fd, archive_read_open_file, archive_read_next_header, archive_read_data, archive_read_data_block, archive_read_data_skip, archive_read_data_into_buffer, archive_read_data_into_fd, archive_read_extract, archive_read_extract_set_progress_callback, archive_read_close archive_read_finish — functions for reading tar archives
SYNOPSIS
#include <archive.h>
struct archive *
archive_read_new(void);
int
archive_read_set_bytes_per_block(struct archive *, int);
int
archive_read_support_compression_all(struct archive *);
int
archive_read_support_compression_bzip2(struct archive *);
int
archive_read_support_compression_compress(struct archive *);
int
archive_read_support_compression_gzip(struct archive *);
int
archive_read_support_compression_none(struct archive *);
int
archive_read_support_format_tar(struct archive *);
int
archive_read_support_format_cpio(struct archive *);
int
archive_read_support_format_all(struct archive *);
int
archive_read_open(struct archive *, void *client_data, archive_read_archive_callback *, archive_open_archive_callback *, archive_close_archive_callback *);
int
archive_read_open_fd(struct archive *, int fd);
int
archive_read_open_file(struct archive *, const char *filename);
int
archive_read_next_header(struct archive *, struct archive_entry **);
ssize_t
archive_read_data(struct archive *, void *buff, size_t len);
int
archive_read_data_block(struct archive *, const void **buff, size_t *len, off_t *offset);
int
archive_read_data_skip(struct archive *);
int
archive_read_data_into_buffer(struct archive *, void *);
int
archive_read_data_into_fd(struct archive *, int fd);
int
archive_read_extract(struct archive *, int flags);
void
archive_read_extract_set_progress_callback(struct archive *, void (*func)(void *), void *user_data);
int
archive_read_close(struct archive *);
void
archive_read_finish(struct archive *);
DESCRIPTION
These functions provide a complete API for reading streaming archives. The general process is to first create the struct archive object, set options, initialize the reader, iterate over the archive headers and associated data, then close the archive and release all resources. The following summary describes the functions in approximately the order they would be used:
archive_read_new()
Allocates and initializes a struct archive object suitable for reading from an archive.
archive_read_set_bytes_per_block()
Sets the block size used for reading the archive data. This controls the size that will be used when invoking the read callback function. The default is 20 records or 10240 bytes for tar formats.
archive_read_support_compression_XXX()
Enables auto-detection code and decompression support for the specified compression. Note that ’’none’’ is always enabled by default. For convenience, archive_read_support_compression_all() enables all available decompression code.
archive_read_support_format_XXX()
Enables support---including auto-detection code---for the specified archive format. In particular, archive_read_support_format_tar() enables support for a variety of standard tar formats, old-style tar, ustar, pax interchange format, and many common variants. For convenience, archive_read_support_format_all() enables support for all available formats. Note that there is no default.
archive_read_open()
Freeze the settings, open the archive, and prepare for reading entries. This is the most generic version of this call, which accepts three callback functions. The library invokes these client-provided functions to obtain raw bytes from the archive. Note: The API permits a decompression method to fork and invoke the callbacks from another process. Although none of the current decompression methods use this technique, future decompression methods may utilize this technique. If the decompressor forks, it will ensure that the open and close callbacks are invoked within the same process as the read callback. In particular, clients should not attempt to use shared variables to communicate between the open/read/close callbacks and the mainline code.
archive_read_open_fd()
Like archive_read_open(), except that it accepts a file descriptor rather than a trio of function pointers. Note that the file descriptor will not be automatically closed at end-of-archive.
archive_read_open_file()
Like archive_read_open(), except that it accepts a simple filename. A NULL filename represents standard input.
archive_read_next_header()
Read the header for the next entry and return a pointer to a struct archive_entry.
archive_read_data()
Read data associated with the header just read. Internally, this is a convenience function that calls archive_read_data_block() and fills any gaps with nulls so that callers see a single continuous stream of data.
archive_read_data_block()
Return the next available block of data for this entry. Unlike archive_read_data(), the archive_read_data_block() function avoids copying data and allows you to correctly handle sparse files, as supported by some archive formats. The library gaurantees that offsets will increase and that blocks will not overlap.
archive_read_data_skip()
A convenience function that repeatedly calls archive_read_data_block() to skip all of the data for this archive entry.
archive_read_data_into_buffer()
A convenience function that repeatedly calls archive_read_data_block() to copy the entire entry into the client-supplied buffer. Note that the client is responsible for sizing the buffer appropriately.
archive_read_data_into_fd()
A convenience function that repeatedly calls archive_read_data_block() to copy the entire entry to the provided file descriptor.
archive_read_extract()
A convenience function that recreates the specified object on disk and reads the entry data into that object. The flags argument modifies how the object is recreated. It consists of a bitwise OR of one or more of the following values:
ARCHIVE_EXTRACT_OWNER
The user and group IDs should be set on the restored file. By default, the user and group IDs are not restored.
ARCHIVE_EXTRACT_PERM
The permissions (mode bits) should be restored for all objects. By default, permissions are only restored for regular files.
ARCHIVE_EXTRACT_TIME
The timestamps (mtime, ctime, and atime) should be restored. By default, they are ignored. Note that restoring of atime is not currently supported.
ARCHIVE_EXTRACT_NO_OVERWRITE
Existing files on disk will not be overwritten. By default, existing files are unlinked before the new entry is written.
ARCHIVE_EXTRACT_UNLINK
Existing files on disk will be unlinked and recreated from scratch. By default, existing files are truncated and rewritten, but the file is not recreated. In particular, the default behavior does not break existing hard links.
archive_read_extract_set_progress_callback()
Sets a pointer to a user-defined callback that can be used for updating progress displays during extraction. The progress function will be invoked during the extraction of large regular files. The progress function will be invoked with the pointer provided to this call. Generally, the data pointed to should include a reference to the archive object and the archive_entry object so that various statistics can be retrieved for the progress display.
archive_read_close()
Complete the archive and invoke the close callback.
archive_read_finish()
Invokes archive_read_close() if it wasn’t invoked maually, then release all resources.
Note that the library determines most of the relevant information about the archive by inspection. In particular, it automatically detects gzip(1) or bzip2(1) compression and transparently performs the appropriate decompression. It also automatically detects the archive format.
The callback functions must match the following prototypes:
typedef ssize_t archive_read_callback(struct archive *, void *client_data, const void **buffer)
typedef int archive_open_callback(struct archive *, void *client_data)
typedef int archive_close_callback(struct archive *, void *client_data)
These callback functions are called whenever the library requires raw bytes from the archive. Note that it is the client’s responsibility to correctly block the input.
A complete description of the struct archive and struct archive_entry objects can be found in the overview manual page for libarchive(3).
EXAMPLE
The following illustrates basic usage of the library. In this example, the callback functions are simply wrappers around the standard open(2), read(2), and close(2) system calls.
void
list_archive(const char *name)
{
struct mydata *mydata;
struct archive *a;
struct archive_entry *entry;
mydata =
malloc(sizeof(struct mydata));
a = archive_read_new();
mydata->name = name;
archive_read_support_compression_all(a);
archive_read_support_format_all(a);
archive_read_open(a, mydata, myopen, myread, myclose);
while (archive_read_next_header(a, &entry) ==
ARCHIVE_OK) {
printf("%s\n",archive_entry_pathname(entry));
archive_read_data_skip(a);
}
archive_read_finish(a);
free(mydata);
}
ssize_t
myread(struct archive *a, void *client_data, const void
**buff)
{
struct mydata *mydata = client_data;
*buff =
mydata->buff;
return (read(mydata->fd, mydata->buff, 10240));
}
int
myopen(struct archive *a, void *client_data)
{
struct mydata *mydata = client_data;
mydata->fd =
open(mydata->name, O_RDONLY);
return (mydata->fd >= 0);
}
int
myclose(struct archive *a, void *client_data)
{
struct mydata *mydata = client_data;
if
(mydata->fd > 0)
close(mydata->fd);
return (0);
}
RETURN VALUES
Most functions return zero on success, non-zero on error. The possible return codes include: ARCHIVE_OK (the operation succeeded) ARCHIVE_WARN (the operation succeeded but a non-critical error was encountered) ARCHIVE_EOF (end-of-archive was encountered), ARCHIVE_RETRY (the operation failed but can be retried), and ARCHIVE_FATAL (there was a fatal error; the archive should be closed immediately). Detailed error codes and textual descriptions are available from the archive_errno() and archive_error_string() functions.
archive_read_new() returns a pointer to a freshly allocated struct archive object. It returns NULL on error.
archive_read_data() returns a count of bytes actually read or zero at the end of the entry. On error, a value of ARCHIVE_FATAL, ARCHIVE_WARN, or ARCHIVE_RETRY is returned and an error code and textual description can be retrieved from the archive_errno() and archive_error_string() functions.
The library expects the client callbacks to behave similarly. If there is an error, you can use archive_set_error() to set an appropriate error code and description, then return one of the non-zero values above. (Note that the value eventually returned to the client may not be the same; many errors that are not critical at the level of basic I/O can prevent the archive from being properly read, thus most I/O errors eventually cause ARCHIVE_FATAL to be returned.)
SEE ALSO
HISTORY
The libarchive library first appeared in FreeBSD 5.3.
AUTHORS
The libarchive library was written by Tim Kientzle <kientzle [AT] acm.org>.
BUGS
BSD October 1, 2003 BSD