Anton Khirnov:
> Quoting Andreas Rheinhardt (2020-03-27 03:25:14)
>> Up until now, it was completely unspecified what the content of the
>> destination packet dst was on error. Depending upon where the error
>> happened calling av_packet_unref() on dst might be dangerous.
>>
>> This commit changes this by making sure that dst is blank on error, so
>> unreferencing it again is safe (and still pointless). This behaviour is
>> documented.
>>
>> Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@gmail.com>
>> ---
>> doc/APIchanges | 4 ++++
>> libavcodec/avcodec.h | 3 ++-
>> libavcodec/avpacket.c | 7 ++++---
>> libavcodec/version.h | 2 +-
>> 4 files changed, 11 insertions(+), 5 deletions(-)
>>
>> diff --git a/doc/APIchanges b/doc/APIchanges
>> index 8eeaec2028..f2bb2d242b 100644
>> --- a/doc/APIchanges
>> +++ b/doc/APIchanges
>> @@ -15,6 +15,10 @@ libavutil: 2017-10-21
>>
>> API changes, most recent first:
>>
>> +2020-03-27 - xxxxxxxxxx - lavc 58.77.100 - avcodec.h
>> + av_packet_ref() now guarantees to return the destination packet
>> + in a blank state on error.
>> +
>> 2020-03-10 - xxxxxxxxxx - lavc 58.75.100 - avcodec.h
>> Add AV_PKT_DATA_ICC_PROFILE.
>>
>> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
>> index f918d20a61..8fc0ad92c9 100644
>> --- a/libavcodec/avcodec.h
>> +++ b/libavcodec/avcodec.h
>> @@ -4651,7 +4651,8 @@ void av_packet_free_side_data(AVPacket *pkt);
>> * @param dst Destination packet. Will be completely overwritten.
>> * @param src Source packet
>> *
>> - * @return 0 on success, a negative AVERROR on error.
>> + * @return 0 on success, a negative AVERROR on error. On error, dst
>> + * will be blank (as if returned by av_packet_alloc()).
>> */
>> int av_packet_ref(AVPacket *dst, const AVPacket *src);
>>
>> diff --git a/libavcodec/avpacket.c b/libavcodec/avpacket.c
>> index 132567bc2d..c622718a45 100644
>> --- a/libavcodec/avpacket.c
>> +++ b/libavcodec/avpacket.c
>> @@ -610,12 +610,13 @@ int av_packet_ref(AVPacket *dst, const AVPacket *src)
>> {
>> int ret;
>>
>> + dst->buf = NULL;
>> +
>
> I really think av_init_packet() would be more robust against future
> changes. But I'm not going to push for that especially strongly, so feel
> free to push whichever version you prefer.
>
Applied as is. After all, avpacket.c would be checked thoroughly in case
of a future addition to AVPacket with something that needs to be
allocated and freed (whereas lots of other places might be forgotten).
- Andreas
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