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GSeekable: document seek-past-end semantics

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Introduce the concept of "fixed" vs. "resizable" streams and document
how g_seekable_seek() works for each case.

We don't include g_seekable_is_fixed_size() at this point because we
don't know if anyone would require it.  This may appear in the future if
someone asks for it, however.

https://bugzilla.gnome.org/show_bug.cgi?id=684842
This commit is contained in:
Ryan Lortie 2013-10-22 15:01:16 -04:00
parent 3b28df1e00
commit 38ef509cf3
1 changed files with 26 additions and 6 deletions
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20
gio/gseekable.c
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@ -34,6 +34,17 @@
* #GSeekable is implemented by streams (implementations of * #GSeekable is implemented by streams (implementations of
* #GInputStream or #GOutputStream) that support seeking. * #GInputStream or #GOutputStream) that support seeking.
* *
* Seekable streams largely fall into two categories: resizable and
* fixed-size.
*
* #GSeekable on fixed-sized streams is approximately the same as POSIX
* lseek() on a block device (for example: attmepting to seek past the
* end of the device is an error). Fixed streams typically cannot be
* truncated.
*
* #GSeekable on resizable streams is approximately the same as POSIX
* lseek() on a normal file. Seeking past the end and writing data will
* usually cause the stream to resize by introducing zero bytes.
**/ **/
typedef GSeekableIface GSeekableInterface; typedef GSeekableIface GSeekableInterface;
@ -95,6 +106,15 @@ g_seekable_can_seek (GSeekable *seekable)
* *
* Seeks in the stream by the given @offset, modified by @type. * Seeks in the stream by the given @offset, modified by @type.
* *
* Attempting to seek past the end of the stream will have different
* results depending on if the stream is fixed-sized or resizable. If
* the stream is resizable then seeking past the end and then writing
* will result in zeros filling the empty space. Seeking past the end
* of a resizable stream and reading will result in EOF. Seeking past
* the end of a fixed-sized stream will fail.
*
* Any operation that would result in a negative offset will fail.
*
* If @cancellable is not %NULL, then the operation can be cancelled by * If @cancellable is not %NULL, then the operation can be cancelled by
* triggering the cancellable object from another thread. If the operation * triggering the cancellable object from another thread. If the operation
* was cancelled, the error %G_IO_ERROR_CANCELLED will be returned. * was cancelled, the error %G_IO_ERROR_CANCELLED will be returned.