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

[Jacob Trimble]

On Mon, May 14, 2018 at 4:49 PM, Jacob Trimble <modmaker at google.com> wrote:
> On Tue, May 8, 2018 at 3:47 PM, Michael Niedermayer
> <michael at niedermayer.cc> wrote:
>> 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
>>
>
> I know it's weird, but this was the design that was decided on when
> this was added.  Are there any changes you want for this patch?
>
>>
>> [...]
>> --
>> 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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