Re: [FFmpeg-devel] [PATCH 1/2] avformat/demux: use io_close2 when closing avfromat

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Michael Niedermayer:
> On Sat, May 17, 2025 at 03:03:19PM +0200, Andreas Rheinhardt wrote:
>> Andreas Rheinhardt:
>>> Kacper Michajłow:
>>>> It's not valid to call avio_close() on context that has not been open
>>>> with avio_open().
>>>>
>>>> This fixes use of custom IO. (io_open / io_close2 callbacks)
>>>>
>>>> Note that by default io_close2 is set to io_close2_default() which calls
>>>> avio_close(), so default case will work the same as before.
>>>>
>>>> Signed-off-by: Kacper Michajłow <kasper93@gmail.com>
>>>> ---
>>>>  libavformat/demux.c | 3 +--
>>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>>>
>>>> diff --git a/libavformat/demux.c b/libavformat/demux.c
>>>> index 2795863567..ecd4f40da9 100644
>>>> --- a/libavformat/demux.c
>>>> +++ b/libavformat/demux.c
>>>> @@ -383,11 +383,10 @@ void avformat_close_input(AVFormatContext **ps)
>>>>          if (ffifmt(s->iformat)->read_close)
>>>>              ffifmt(s->iformat)->read_close(s);
>>>>  
>>>> +    ff_format_io_close(s, &pb);
>>>>      avformat_free_context(s);
>>>>  
>>>>      *ps = NULL;
>>>> -
>>>> -    avio_close(pb);
>>>>  }
>>>>  
>>>>  static void force_codec_ids(AVFormatContext *s, AVStream *st)
>>>
>>> avformat_open_input() sets AVFMT_FLAG_CUSTOM_IO when using custom IO and
>>> avformat_close_input() checks for this and does not free the
>>> AVFormatContext's AVIOContext in this case (but does avio_close(NULL) in
>>> this case).
>>> Your patch furthermore presumes that the custom IO context is compatible
>>> with io_close2, which need not be true at all (one can use custom IO
>>> without ever touching io_open/io_close2 pointers; I expect users that
>>> use custom IO, but not formats that open new AVIOContexts to do so).
>>
>> On reading a bit further, init_input() uses io_open to open the
>> AVIOContext in case no AVIOContext was supplied (and one is needed).
>> This means that the AVFMT_FLAG_CUSTOM_IO flag is misleading, as it is
>> possible to use custom IO even with this flag unset.
> 
>> It also means that
>> your patch is likely correct.
> 
> does any reason remain against applying it ?
> 

I don't see any.

- Andreas

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