[FFmpeg-devel] [PATCH 1/2] avio_alloc_context: Allocate a buffer if NULL is passed

[Michael Niedermayer]

On Thu, May 22, 2014 at 07:20:12PM +0200, wm4 wrote:
> On Thu, 22 May 2014 19:06:54 +0200
> Michael Niedermayer <michaelni at gmx.at> wrote:
> 
> > On Thu, May 22, 2014 at 09:17:28AM +0200, wm4 wrote:
> > > On Wed, 21 May 2014 22:18:52 +0200
> > > Michael Niedermayer <michaelni at gmx.at> wrote:
> > > 
> > > > Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
> > > > ---
> > > >  libavformat/aviobuf.c |    9 +++++++++
> > > >  1 file changed, 9 insertions(+)
> > > > 
> > > > diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
> > > > index 738459e..e60574d 100644
> > > > --- a/libavformat/aviobuf.c
> > > > +++ b/libavformat/aviobuf.c
> > > > @@ -119,6 +119,15 @@ AVIOContext *avio_alloc_context(
> > > >      AVIOContext *s = av_mallocz(sizeof(AVIOContext));
> > > >      if (!s)
> > > >          return NULL;
> > > > +    if (!buffer && !buffer_size)
> > > > +        buffer_size = IO_BUFFER_SIZE;
> > > > +    if (!buffer) {
> > > > +        buffer = av_malloc(buffer_size);
> > > > +        if (!buffer) {
> > > > +            av_free(s);
> > > > +            return NULL;
> > > > +        }
> > > > +    }
> > > >      ffio_init_context(s, buffer, buffer_size, write_flag, opaque,
> > > >                    read_packet, write_packet, seek);
> > > >      return s;
> > > 
> > > Is the buffer actually free'd?
> > 
> > if the user frees it
> > do you suggest this should be done automatically ?
> 
> How the hell should the user know that he has to free it? That's
> completely arbitrary and unexpected, at least if you see this API for
> the first time. (Although last time when I was using this API, I was
> utterly surprised that lavf wanted to realloc the buffer I passed, yet I
> had to free it myself. I'm not quite sure whether it really reallocates
> the buffer, but if so, the avio_alloc_context doxygen is both incorrect
> and incomplete.)
> 
> Unfortunately, it seems there is no API function to free an avio
> context, and the user is just expected to av_free it, so I'm not sure
> what's the best course of action. Suddenly requiring the user to call
> a newly added avio_free_context() instead of av_free doesn't sound nice.

just posted a patch that makes avio_close() useable to close it
which also frees the buffer.

Currently passing NULL as buffer is not allowed, if we do add the
possibility to pass NULL we also can add the need to call avio_close()

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No human being will ever know the Truth, for even if they happen to say it
by chance, they would not even known they had done so. -- Xenophanes
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