[FFmpeg-devel] [PATCH] avformat: enable UDP IPv6 multicast interface selection

[Ignjatović, Lazar (RS)]

This message has been marked as Public on 03/19/2024 09:40Z.
On Friday, March 15, 2024 5:27 PM Rémi Denis-Courmont wrote:

>>
>> localaddr option now properly works with IPv6 addresses. Properly
>> resolved interface index in places where default 0 interface index is
>> used (marked with TODO: within udp.c). Added SO_BINDTODEVICE for mcast
>> sockets that are used for reading from the network.
>
> AFAIK, that is privileged, and is not intended for the purpose of scoping multicast.Where the need arises to specify an interface for multicast, there is typically a dedicated ioctl or field of an ioctl.

I agree, although it gets the job done, in this case it is more acceptable to modify `sin6_scope_id` field to point to the desired interface.
Will change within V2 of the patch.

>> +    /* Special case for link-local addresses, relevant interface is
>> + stored
>> in sin6_scope_id */ +#if HAVE_STRUCT_SOCKADDR_IN6 &&
>> defined(IN6_IS_ADDR_LINKLOCAL)
>> +    if (local_addr->ss_family == AF_INET6 &&
>> IN6_IS_ADDR_LINKLOCAL(&((struct sockaddr_in6*)local_addr)->sin6_addr))
>> {
>
> Invalid cast, breaks aliasing, AFAICT.

AFAIK the primary purpose of `sockaddr_storage` is to store sockaddr regardles of address family. In this case it is used to store local addr, wether it is V4 or V6.
With checking that the `ss_family` is in fact `AF_INET6`, `sockaddr_storage` can be safely cast into `sockaddr_in6`.

Maybe I'm missing something here. Would you mind further elaborating your comment?

Thank you for your time!

Sincirely,
Lazar Ignjatović
Associate Software Engineer

Cubic Defense
cubic.com