From 38ef509cf3558bffb326f7c6d511bcd77e98981b Mon Sep 17 00:00:00 2001 From: Ryan Lortie Date: Tue, 22 Oct 2013 15:01:16 -0400 Subject: [PATCH] GSeekable: document seek-past-end semantics 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 --- gio/gseekable.c | 32 ++++++++++++++++++++++++++------ 1 file changed, 26 insertions(+), 6 deletions(-) diff --git a/gio/gseekable.c b/gio/gseekable.c index ac77b12..f831c5e 100644 --- a/gio/gseekable.c +++ b/gio/gseekable.c @@ -30,10 +30,21 @@ * @short_description: Stream seeking interface * @include: gio/gio.h * @see_also: #GInputStream, #GOutputStream - * - * #GSeekable is implemented by streams (implementations of + * + * #GSeekable is implemented by streams (implementations of * #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; @@ -89,12 +100,21 @@ g_seekable_can_seek (GSeekable *seekable) * @seekable: a #GSeekable. * @offset: a #goffset. * @type: a #GSeekType. - * @cancellable: (allow-none): optional #GCancellable object, %NULL to ignore. - * @error: a #GError location to store the error occurring, or %NULL to + * @cancellable: (allow-none): optional #GCancellable object, %NULL to ignore. + * @error: a #GError location to store the error occurring, or %NULL to * ignore. - * + * * 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 * triggering the cancellable object from another thread. If the operation * was cancelled, the error %G_IO_ERROR_CANCELLED will be returned. -- 2.7.4