[FFmpeg-devel] libavutil/encryption_info: Allow multiple init info.

[Michael Niedermayer]

On Mon, May 07, 2018 at 04:59:33PM -0700, Jacob Trimble wrote:
> On Mon, May 7, 2018 at 3:18 PM, Michael Niedermayer
> <michael at niedermayer.cc> wrote:
> > On Mon, Apr 23, 2018 at 11:03:57AM -0700, Jacob Trimble wrote:
> >> While integrating my encryption info changes, I noticed a problem with
> >> the init info structs.  I implemented them as side-data on the Stream.
> >> But this means there can only be one per stream.  However, there can
> >> be multiple 'pssh' atoms in a single stream (e.g. for key rotation or
> >> multiple key systems). (sorry for not noticing sooner)
> >>
> >> Attached is a patch to fix this by making the init info a
> >> singly-linked-list.  It is ABI compatible and is still easy to use and
> >> understand.  The alternative would be to break ABI and have the
> >> side-data methods return an array of pointers.  I could do that
> >> instead if that is preferable.
> >
> >>  encryption_info.c |  154 +++++++++++++++++++++++++++++++++++-------------------
> >>  encryption_info.h |    5 +
> >>  2 files changed, 106 insertions(+), 53 deletions(-)
> >> e5eecc73a6997bbd11541771372d38ea9c3972a7  0001-libavutil-encryption_info-Allow-multiple-init-info.patch
> >> From bb941a77e882e93629d63d63059d0063b9519e29 Mon Sep 17 00:00:00 2001
> >> From: Jacob Trimble <modmaker at google.com>
> >> Date: Mon, 23 Apr 2018 10:33:58 -0700
> >> Subject: [PATCH] libavutil/encryption_info: Allow multiple init info.
> >>
> >> It is possible for there to be multiple encryption init info structure.
> >> For example, to support multiple key systems or in key rotation.  This
> >> changes the AVEncryptionInitInfo struct to be a linked list so there
> >> can be multiple structs without breaking ABI.
> >>
> >> Signed-off-by: Jacob Trimble <modmaker at google.com>
> >> ---
> >>  libavutil/encryption_info.c | 154 +++++++++++++++++++++++-------------
> >>  libavutil/encryption_info.h |   5 ++
> >>  2 files changed, 106 insertions(+), 53 deletions(-)
> >>
> >> diff --git a/libavutil/encryption_info.c b/libavutil/encryption_info.c
> >> index 20a752d6b4..9935c10d74 100644
> >> --- a/libavutil/encryption_info.c
> >> +++ b/libavutil/encryption_info.c
> >> @@ -160,13 +160,16 @@ uint8_t *av_encryption_info_add_side_data(const AVEncryptionInfo *info, size_t *
> >>  }
> >>
> >>  // The format of the AVEncryptionInitInfo side data:
> >> -// u32be system_id_size
> >> -// u32be num_key_ids
> >> -// u32be key_id_size
> >> -// u32be data_size
> >> -// u8[system_id_size] system_id
> >> -// u8[key_id_size][num_key_id] key_ids
> >> -// u8[data_size] data
> >> +// u32be init_info_count
> >> +// {
> >> +//   u32be system_id_size
> >> +//   u32be num_key_ids
> >> +//   u32be key_id_size
> >> +//   u32be data_size
> >> +//   u8[system_id_size] system_id
> >> +//   u8[key_id_size][num_key_id] key_ids
> >> +//   u8[data_size] data
> >> +// }[init_info_count]
> >>
> >>  #define FF_ENCRYPTION_INIT_INFO_EXTRA 16
> >>
> >> @@ -215,6 +218,7 @@ void av_encryption_init_info_free(AVEncryptionInitInfo *info)
> >>          for (i = 0; i < info->num_key_ids; i++) {
> >>              av_free(info->key_ids[i]);
> >>          }
> >> +        av_encryption_init_info_free(info->next);
> >>          av_free(info->system_id);
> >>          av_free(info->key_ids);
> >>          av_free(info->data);
> >> @@ -225,71 +229,115 @@ void av_encryption_init_info_free(AVEncryptionInitInfo *info)
> >>  AVEncryptionInitInfo *av_encryption_init_info_get_side_data(
> >>      const uint8_t *side_data, size_t side_data_size)
> >>  {
> >> -    AVEncryptionInitInfo *info;
> >> +    AVEncryptionInitInfo *ret = NULL, *info;
> >>      uint64_t system_id_size, num_key_ids, key_id_size, data_size, i;
> >> +    uint64_t init_info_count;
> >>
> >> -    if (!side_data || side_data_size < FF_ENCRYPTION_INIT_INFO_EXTRA)
> >> -        return NULL;
> >> -
> >> -    system_id_size = AV_RB32(side_data);
> > [...]
> >> +    init_info_count = AV_RB32(side_data);
> >
> > i may be missing something but this looks like the meaning of the first
> > field changes, this thus doesnt look compatible to me
> 
> It changes the binary format of the side-data, but that was explicitly
> not part of ABI.  The fields in the structs are unchanged.  This would
> only cause a problem if the side data bytes were stored out-of-band
> from a different version of FFmpeg.

yes, right.
its side data that is neighter a C struct nor a well defined byte stream
its a opaque block that can only be passed to libavutil which then translates
it into a C struct.
its not new but it still feels clumsy to use this as means to pass data around


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

If you think the mosad wants you dead since a long time then you are either
wrong or dead since a long time.
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