[FFmpeg-devel,1/7] avcodec/iff: Split extract_header into extradata and packet part

183132872a1d8bc8a32e7fd8f994fa2f1b2d6bfc made the iff demuxer
output extradata and made the decoder parse said extradata.
To make this extradata extensible, it came with its own internal
length field (containing the offset of the palette at the end
of the extradata). Furthermore, in order to support mid-stream
extradata changes, the packets returned by the demuxer also have
such a length field (containing the offset of the actual packet
data). Therefore the packet parsing the extradata accepted its
input from both AVPackets as well as from ordinary extradata.

Yet the demuxer never made use of this "feature": The packet's
length field always indicated that the packet data starts
immediately after the length field.

Later, commit cb928fc448f9566e6f6c28d53fa4c2388e732a2b stopped
appending the length field to the packets' data; of course,
it also stopped searching for extradata in this data.

Instead it added code to parse the packet's header to the function
that parses extradata. This made this function consist of two disjoint
parts, one of which is only reachable if this function is called
from init (when parsing extradata) and one of which is reachable
when parsing packet headers.

Therefore this commit splits this function into two.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
Btw: Both of these commits broke API/ABI.

 libavcodec/iff.c | 116 +++++++++++++++++++++++++----------------------
 1 file changed, 61 insertions(+), 55 deletions(-)

Andreas Rheinhardt:
> 183132872a1d8bc8a32e7fd8f994fa2f1b2d6bfc made the iff demuxer
> output extradata and made the decoder parse said extradata.
> To make this extradata extensible, it came with its own internal
> length field (containing the offset of the palette at the end
> of the extradata). Furthermore, in order to support mid-stream
> extradata changes, the packets returned by the demuxer also have
> such a length field (containing the offset of the actual packet
> data). Therefore the packet parsing the extradata accepted its
> input from both AVPackets as well as from ordinary extradata.
> 
> Yet the demuxer never made use of this "feature": The packet's
> length field always indicated that the packet data starts
> immediately after the length field.
> 
> Later, commit cb928fc448f9566e6f6c28d53fa4c2388e732a2b stopped
> appending the length field to the packets' data; of course,
> it also stopped searching for extradata in this data.
> 
> Instead it added code to parse the packet's header to the function
> that parses extradata. This made this function consist of two disjoint
> parts, one of which is only reachable if this function is called
> from init (when parsing extradata) and one of which is reachable
> when parsing packet headers.
> 
> Therefore this commit splits this function into two.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
> Btw: Both of these commits broke API/ABI.
> 
>  libavcodec/iff.c | 116 +++++++++++++++++++++++++----------------------
>  1 file changed, 61 insertions(+), 55 deletions(-)
> 
> diff --git a/libavcodec/iff.c b/libavcodec/iff.c
> index 74ebddc621..4abbed8dfb 100644
> --- a/libavcodec/iff.c
> +++ b/libavcodec/iff.c
> @@ -199,11 +199,9 @@ static int cmap_read_palette(AVCodecContext *avctx, uint32_t *pal)
>   * decoder structures.
>   *
>   * @param avctx the AVCodecContext where to extract extra context to
> - * @param avpkt the AVPacket to extract extra context from or NULL to use avctx
>   * @return >= 0 in case of success, a negative error code otherwise
>   */
> -static int extract_header(AVCodecContext *const avctx,
> -                          const AVPacket *const avpkt)
> +static int extract_header(AVCodecContext *const avctx)
>  {
>      IffContext *s = avctx->priv_data;
>      const uint8_t *buf;
> @@ -216,55 +214,6 @@ static int extract_header(AVCodecContext *const avctx,
>      }
>      palette_size = avctx->extradata_size - AV_RB16(avctx->extradata);
>  
> -    if (avpkt && avctx->codec_tag == MKTAG('A', 'N', 'I', 'M')) {
> -        uint32_t chunk_id;
> -        uint64_t data_size;
> -        GetByteContext *gb = &s->gb;
> -
> -        bytestream2_skip(gb, 4);
> -        while (bytestream2_get_bytes_left(gb) >= 1) {
> -            chunk_id  = bytestream2_get_le32(gb);
> -            data_size = bytestream2_get_be32(gb);
> -
> -            if (chunk_id == MKTAG('B', 'M', 'H', 'D')) {
> -                bytestream2_skip(gb, data_size + (data_size & 1));
> -            } else if (chunk_id == MKTAG('A', 'N', 'H', 'D')) {
> -                unsigned extra;
> -                if (data_size < 40)
> -                    return AVERROR_INVALIDDATA;
> -
> -                s->compression = (bytestream2_get_byte(gb) << 8) | (s->compression & 0xFF);
> -                bytestream2_skip(gb, 19);
> -                extra = bytestream2_get_be32(gb);
> -                s->is_short = !(extra & 1);
> -                s->is_brush = extra == 2;
> -                s->is_interlaced = !!(extra & 0x40);
> -                data_size -= 24;
> -                bytestream2_skip(gb, data_size + (data_size & 1));
> -            } else if (chunk_id == MKTAG('D', 'L', 'T', 'A') ||
> -                       chunk_id == MKTAG('B', 'O', 'D', 'Y')) {
> -                if (chunk_id == MKTAG('B','O','D','Y'))
> -                    s->compression &= 0xFF;
> -                break;
> -            } else if (chunk_id == MKTAG('C', 'M', 'A', 'P')) {
> -                int count = data_size / 3;
> -                uint32_t *pal = s->pal;
> -
> -                if (count > 256)
> -                    return AVERROR_INVALIDDATA;
> -                if (s->ham) {
> -                    for (i = 0; i < count; i++)
> -                        pal[i] = 0xFF000000 | bytestream2_get_le24(gb);
> -                } else {
> -                    for (i = 0; i < count; i++)
> -                        pal[i] = 0xFF000000 | bytestream2_get_be24(gb);
> -                }
> -                bytestream2_skip(gb, data_size & 1);
> -            } else {
> -                bytestream2_skip(gb, data_size + (data_size&1));
> -            }
> -        }
> -    } else if (!avpkt) {
>          buf = avctx->extradata;
>          buf_size = bytestream_get_be16(&buf);
>          if (buf_size <= 1 || palette_size < 0) {
> @@ -273,7 +222,6 @@ static int extract_header(AVCodecContext *const avctx,
>                     buf_size, palette_size);
>              return AVERROR_INVALIDDATA;
>          }
> -    }
>  
>      if (buf_size >= 41) {
>          s->compression  = bytestream_get_byte(&buf);
> @@ -449,7 +397,7 @@ static av_cold int decode_init(AVCodecContext *avctx)
>              return AVERROR(ENOMEM);
>      }
>  
> -    if ((err = extract_header(avctx, NULL)) < 0)
> +    if ((err = extract_header(avctx)) < 0)
>          return err;
>  
>      return 0;
> @@ -1525,6 +1473,64 @@ static int unsupported(AVCodecContext *avctx)
>      return AVERROR_INVALIDDATA;
>  }
>  
> +static int parse_packet_header(AVCodecContext *const avctx,
> +                               GetByteContext *gb)
> +{
> +    IffContext *s = avctx->priv_data;
> +    int i;
> +
> +    if (avctx->codec_tag == MKTAG('A', 'N', 'I', 'M')) {
> +        uint32_t chunk_id;
> +        uint64_t data_size;
> +
> +        bytestream2_skip(gb, 4);
> +        while (bytestream2_get_bytes_left(gb) >= 1) {
> +            chunk_id  = bytestream2_get_le32(gb);
> +            data_size = bytestream2_get_be32(gb);
> +
> +            if (chunk_id == MKTAG('B', 'M', 'H', 'D')) {
> +                bytestream2_skip(gb, data_size + (data_size & 1));
> +            } else if (chunk_id == MKTAG('A', 'N', 'H', 'D')) {
> +                unsigned extra;
> +                if (data_size < 40)
> +                    return AVERROR_INVALIDDATA;
> +
> +                s->compression = (bytestream2_get_byte(gb) << 8) | (s->compression & 0xFF);
> +                bytestream2_skip(gb, 19);
> +                extra = bytestream2_get_be32(gb);
> +                s->is_short = !(extra & 1);
> +                s->is_brush = extra == 2;
> +                s->is_interlaced = !!(extra & 0x40);
> +                data_size -= 24;
> +                bytestream2_skip(gb, data_size + (data_size & 1));
> +            } else if (chunk_id == MKTAG('D', 'L', 'T', 'A') ||
> +                       chunk_id == MKTAG('B', 'O', 'D', 'Y')) {
> +                if (chunk_id == MKTAG('B','O','D','Y'))
> +                    s->compression &= 0xFF;
> +                break;
> +            } else if (chunk_id == MKTAG('C', 'M', 'A', 'P')) {
> +                int count = data_size / 3;
> +                uint32_t *pal = s->pal;
> +
> +                if (count > 256)
> +                    return AVERROR_INVALIDDATA;
> +                if (s->ham) {
> +                    for (i = 0; i < count; i++)
> +                        pal[i] = 0xFF000000 | bytestream2_get_le24(gb);
> +                } else {
> +                    for (i = 0; i < count; i++)
> +                        pal[i] = 0xFF000000 | bytestream2_get_be24(gb);
> +                }
> +                bytestream2_skip(gb, data_size & 1);
> +            } else {
> +                bytestream2_skip(gb, data_size + (data_size&1));
> +            }
> +        }
> +    }
> +
> +    return 0;
> +}
> +
>  static int decode_frame(AVCodecContext *avctx, AVFrame *frame,
>                          int *got_frame, AVPacket *avpkt)
>  {
> @@ -1538,7 +1544,7 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *frame,
>  
>      bytestream2_init(gb, avpkt->data, avpkt->size);
>  
> -    if ((res = extract_header(avctx, avpkt)) < 0)
> +    if ((res = parse_packet_header(avctx, gb)) < 0)
>          return res;
>  
>      if ((res = ff_get_buffer(avctx, frame, 0)) < 0)

Will apply this patchset tonight unless there are objections.

- Andreas