retro-imager/dependencies/libarchive-3.5.2/doc/wiki/ManPageArchiveReadOpen3.wiki

ARCHIVE_READ_OPEN(3) manual page 
== NAME == 
'''archive_read_open''', 
'''archive_read_open2''', 
'''archive_read_open_fd''', 
'''archive_read_open_FILE''', 
'''archive_read_open_filename''', 
'''archive_read_open_memory''' 
- functions for reading streaming archives 
== LIBRARY == 
Streaming Archive Library (libarchive, -larchive) 
== SYNOPSIS == 
'''<nowiki>#include <archive.h></nowiki>''' 
<br> 
''int'' 
<br> 
'''archive_read_open'''(''struct archive *'', ''void *client_data'', ''archive_open_callback *'', ''archive_read_callback *'', ''archive_close_callback *''); 
<br> 
''int'' 
<br> 
'''archive_read_open2'''(''struct archive *'', ''void *client_data'', ''archive_open_callback *'', ''archive_read_callback *'', ''archive_skip_callback *'', ''archive_close_callback *''); 
<br> 
''int'' 
<br> 
'''archive_read_open_FILE'''(''struct archive *'', ''FILE *file''); 
<br> 
''int'' 
<br> 
'''archive_read_open_fd'''(''struct archive *'', ''int fd'', ''size_t block_size''); 
<br> 
''int'' 
<br> 
'''archive_read_open_filename'''(''struct archive *'', ''const char *filename'', ''size_t block_size''); 
<br> 
''int'' 
<br> 
'''archive_read_open_memory'''(''struct archive *'', ''const void *buff'', ''size_t size''); 
== DESCRIPTION == 
<dl> 
<dt>'''archive_read_open'''()</dt><dd> 
The same as 
'''archive_read_open2'''(), 
except that the skip callback is assumed to be 
NULL. 
</dd><dt>'''archive_read_open2'''()</dt><dd> 
Freeze the settings, open the archive, and prepare for reading entries. 
This is the most generic version of this call, which accepts 
four callback functions. 
Most clients will want to use 
'''archive_read_open_filename'''(), 
'''archive_read_open_FILE'''(), 
'''archive_read_open_fd'''(), 
or 
'''archive_read_open_memory'''() 
instead. 
The library invokes the client-provided functions to obtain 
raw bytes from the archive. 
</dd><dt>'''archive_read_open_FILE'''()</dt><dd> 
Like 
'''archive_read_open'''(), 
except that it accepts a 
''FILE *'' 
pointer. 
This function should not be used with tape drives or other devices 
that require strict I/O blocking. 
</dd><dt>'''archive_read_open_fd'''()</dt><dd> 
Like 
'''archive_read_open'''(), 
except that it accepts a file descriptor and block size rather than 
a set of function pointers. 
Note that the file descriptor will not be automatically closed at 
end-of-archive. 
This function is safe for use with tape drives or other blocked devices. 
</dd><dt>'''archive_read_open_file'''()</dt><dd> 
This is a deprecated synonym for 
'''archive_read_open_filename'''(). 
</dd><dt>'''archive_read_open_filename'''()</dt><dd> 
Like 
'''archive_read_open'''(), 
except that it accepts a simple filename and a block size. 
A NULL filename represents standard input. 
This function is safe for use with tape drives or other blocked devices. 
</dd><dt>'''archive_read_open_memory'''()</dt><dd> 
Like 
'''archive_read_open'''(), 
except that it accepts a pointer and size of a block of 
memory containing the archive data. 
</dd></dl> 

A complete description of the 
'''struct archive''' 
and 
'''struct archive_entry''' 
objects can be found in the overview manual page for 
[[ManPageLibarchive3]]. 
== CLIENT CALLBACKS == 
The callback functions must match the following prototypes: 
<ul> 
<li> 
''typedef la_ssize_t'' 
'''archive_read_callback'''(''struct archive *'', ''void *client_data'', ''const void **buffer'') 
</li><li> 
''typedef la_int64_t'' 
'''archive_skip_callback'''(''struct archive *'', ''void *client_data'', ''off_t request'') 
</li><li> 
''typedef int'' 
'''archive_open_callback'''(''struct archive *'', ''void *client_data'') 
</li><li> 
''typedef int'' 
'''archive_close_callback'''(''struct archive *'', ''void *client_data'') 
</li></ul> 

The open callback is invoked by 
'''archive_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'''. 

The read callback is invoked whenever the library 
requires raw bytes from the archive. 
The read callback should read data into a buffer, 
set the 
```text
const void **buffer 
```
argument to point to the available data, and 
return a count of the number of bytes available. 
The library will invoke the read callback again 
only after it has consumed this data. 
The library imposes no constraints on the size 
of the data blocks returned. 
On end-of-file, the read callback should 
return zero. 
On error, the read callback should invoke 
'''archive_set_error'''() 
to register an error code and message and 
return -1. 

The skip callback is invoked when the 
library wants to ignore a block of data. 
The return value is the number of bytes actually 
skipped, which may differ from the request. 
If the callback cannot skip data, it should return 
zero. 
If the skip callback is not provided (the 
function pointer is 
NULL ), 
the library will invoke the read function 
instead and simply discard the result. 
A skip callback can provide significant 
performance gains when reading uncompressed 
archives from slow disk drives or other media 
that can skip quickly. 

The close callback is invoked by archive_close when 
the archive processing 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'''. 
== 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 == 
[[ManPageBsdtar1]], 
[[ManPageArchiveRead3]], 
[[ManPageArchiveReadData3]], 
[[ManPageArchiveReadFilter3]], 
[[ManPageArchiveReadFormat3]], 
[[ManPageArchiveReadSetOptions3]], 
[[ManPageArchiveUtil3]], 
[[ManPageLibarchive3]], 
[[ManPageTar5]]