[FFmpeg-devel] [PATCH 1/3] avcodec/avpacket: add av_packet_resize()

[Marton Balint]

On Thu, 11 Mar 2021, James Almer wrote:

> This function acts as a replacement for both av_grow_packet() and
> av_shrink_packet(), the latter which is now deprecated and will be removed as
> it does not correctly handle non-writable packets.

I don't think this is a good idea, av_shrink_packet cannot fail, 
av_grow_packet can. By using the same function you are losing the 
information if the end result should be checked or not.

Regards,
Marton

>
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
> libavcodec/avpacket.c | 19 +++++++++++++++----
> libavcodec/packet.h   | 16 ++++++++++++++++
> libavcodec/version.h  |  3 +++
> 3 files changed, 34 insertions(+), 4 deletions(-)
>
> diff --git a/libavcodec/avpacket.c b/libavcodec/avpacket.c
> index 32cb71fcf0..7d0dbadbed 100644
> --- a/libavcodec/avpacket.c
> +++ b/libavcodec/avpacket.c
> @@ -100,6 +100,7 @@ int av_new_packet(AVPacket *pkt, int size)
>     return 0;
> }
> 
> +#if FF_API_SHRINK_PACKET
> void av_shrink_packet(AVPacket *pkt, int size)
> {
>     if (pkt->size <= size)
> @@ -107,16 +108,26 @@ void av_shrink_packet(AVPacket *pkt, int size)
>     pkt->size = size;
>     memset(pkt->data + size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
> }
> +#endif
> 
> int av_grow_packet(AVPacket *pkt, int grow_by)
> {
> -    int new_size;
>     av_assert0((unsigned)pkt->size <= INT_MAX - AV_INPUT_BUFFER_PADDING_SIZE);
>     if ((unsigned)grow_by >
>         INT_MAX - (pkt->size + AV_INPUT_BUFFER_PADDING_SIZE))
>         return AVERROR(ENOMEM);
> 
> -    new_size = pkt->size + grow_by + AV_INPUT_BUFFER_PADDING_SIZE;
> +    return av_packet_resize(pkt, pkt->size + grow_by);
> +}
> +
> +int av_packet_resize(AVPacket *pkt, int size)
> +{
> +    int new_size;
> +
> +    if (size < 0 || size > INT_MAX - AV_INPUT_BUFFER_PADDING_SIZE)
> +        return AVERROR(EINVAL);
> +
> +    new_size = size + AV_INPUT_BUFFER_PADDING_SIZE;
>     if (pkt->buf) {
>         size_t data_offset;
>         uint8_t *old_data = pkt->data;
> @@ -143,10 +154,10 @@ int av_grow_packet(AVPacket *pkt, int grow_by)
>         if (!pkt->buf)
>             return AVERROR(ENOMEM);
>         if (pkt->size > 0)
> -            memcpy(pkt->buf->data, pkt->data, pkt->size);
> +            memcpy(pkt->buf->data, pkt->data, FFMIN(pkt->size, size));
>         pkt->data = pkt->buf->data;
>     }
> -    pkt->size += grow_by;
> +    pkt->size = size;
>     memset(pkt->data + pkt->size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
>
>     return 0;
> diff --git a/libavcodec/packet.h b/libavcodec/packet.h
> index 3d9013d783..1720d973f5 100644
> --- a/libavcodec/packet.h
> +++ b/libavcodec/packet.h
> @@ -484,13 +484,29 @@ void av_init_packet(AVPacket *pkt);
>  */
> int av_new_packet(AVPacket *pkt, int size);
> 
> +#if FF_API_SHRINK_PACKET
> /**
>  * Reduce packet size, correctly zeroing padding
>  *
>  * @param pkt packet
>  * @param size new size
> + *
> + * @deprecated Use av_packet_resize
>  */
> +attribute_deprecated
> void av_shrink_packet(AVPacket *pkt, int size);
> +#endif
> +
> +/**
> + * Resize the payload of a packet, correctly zeroing padding and avoiding data
> + * copy if possible.
> + *
> + * @param pkt packet
> + * @param size new size
> + *
> + * @return 0 on success, a negative AVERROR on error
> + */
> +int av_packet_resize(AVPacket *pkt, int size);
> 
> /**
>  * Increase packet size, correctly zeroing padding
> diff --git a/libavcodec/version.h b/libavcodec/version.h
> index 3124ec8061..6c362b43e2 100644
> --- a/libavcodec/version.h
> +++ b/libavcodec/version.h
> @@ -162,5 +162,8 @@
> #ifndef FF_API_GET_FRAME_CLASS
> #define FF_API_GET_FRAME_CLASS     (LIBAVCODEC_VERSION_MAJOR < 60)
> #endif
> +#ifndef FF_API_SHRINK_PACKET
> +#define FF_API_SHRINK_PACKET       (LIBAVCODEC_VERSION_MAJOR < 60)
> +#endif
> 
> #endif /* AVCODEC_VERSION_H */
> -- 
> 2.30.2
>
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