[FFmpeg-devel] [PATCH] avformat/rtmpcrypt: fix discarded const warning

[Ronald S. Bultje]

Hi,

On Sun, Oct 11, 2015 at 2:15 PM, Ganesh Ajjanagadde <gajjanag at mit.edu>
wrote:

> On Fri, Sep 18, 2015 at 5:02 PM, Michael Niedermayer <michaelni at gmx.at>
> wrote:
> > On Fri, Sep 18, 2015 at 09:50:29PM +0200, Nicolas George wrote:
> >> Le jour du Génie, an CCXXIII, Ganesh Ajjanagadde a écrit :
> >> > This patch silences a -Wdiscarded-qualifiers observed with GCC 5.2.
> >> >
> >> > Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> >> > ---
> >> >  libavformat/rtmpcrypt.c | 2 +-
> >> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> I am not sure this is correct: the buffer is const for a reason, the
> warning
> >> is right. An application would be completely allowed to give a buffer in
> >> read-only memory, or to reuse the contents of the buffer afterwards.
> >>
> >> Actually, I suspect this muxer, if used as first output in the tee
> muxer,
> >> would cause the next outputs to be corrupt.
> >
> > IIRC the code is safe, just ugly
> > the writing only occurs if handshaked is set, which is only set
> > by ff_rtmpe_update_keystream() which is not part of the public
> > interface and only called from libavformat/rtmpproto.c
> > i assume but did not double check that libavformat/rtmpproto.c
> > calls the functions so that writable buffers are used
> >
> >
> >>
> >> The correct fix would probably be to allocate a new buffer, probably
> keeping
> >> it in the context for performances reasons instead of allocating each
> time.
> >
> > id need to double check but i think the calling code possibly uses
> > the written buffer with the expectation that it has been updated
> >
> > if that is so then such fix would break it.
>
> Have you checked the code and confirmed that this patch is fine?


I don't think the explanation makes the patch fine, the explanation just
says that there's no actual issue being hidden behind the warning. It
sounds like this code needs some refactoring...

Ronald