[FFmpeg-devel] [PATCH] Fix setsockopt IP_MULTICAST_TTL on OpenBSD

[Chad Fraleigh]

On 1/26/2022 12:50 PM, Marton Balint wrote:
> 
> 
> On Wed, 26 Jan 2022, Brad Smith wrote:
> 
>> On Wed, Jan 12, 2022 at 12:13:14AM -0500, Brad Smith wrote:
>>> Fix setsockopt() usage on OpenBSD with IP_MULTICAST_TTL. The field
>>> type should be an unsigned char on anything but Linux.
>>
>> Based on feedback so far. Here is a much simpler approach to this issue..
> 
> Win32 needs DWORD unfortunately. I missed it earlier, sorry.
> 
> https://docs.microsoft.com/en-us/windows/win32/winsock/ipproto-ip-socket-options

It gets worse from there. Since I can't look at the real Win32 source to see if it handles it both way, I had to go with Wine and ReactOS..

In Wine, the tests seem to use just an 'int' (which is probably always the same as 'DWORD'). But then, it proceeds to check it using a 1, 2, 3, and 4 byte optlen. In the implementation, it appears to just pass the values as-is to the underlying OS, rather than explicitly translate it to the appropriate type.

For ReactOS, it blindly treats it as an unsigned char (regardless of optlen, as long as it at least 1) when setting/getting the value. But then in a debug line just below that, it treats optval as an 'int *'.

Maybe some tests need to be done on Win32 to see if it works with either size (i.e. set as uchar, get as DWORD, then in reverse and make sure the input/output match in all cases).

I didn't check to see what msys/mingw* does, if anything.

> 
> Regards,
> Marton
> 
>>
>>
>> diff --git a/libavformat/udp.c b/libavformat/udp.c
>> index 83c042d079..da1b98890b 100644
>> --- a/libavformat/udp.c
>> +++ b/libavformat/udp.c
>> @@ -164,7 +164,9 @@ static int udp_set_multicast_ttl(int sockfd, int mcastTTL,
>> {
>> #ifdef IP_MULTICAST_TTL
>>     if (addr->sa_family == AF_INET) {
>> -        if (setsockopt(sockfd, IPPROTO_IP, IP_MULTICAST_TTL, &mcastTTL, sizeof(mcastTTL)) < 0) {
>> +        unsigned char ttl = mcastTTL;  /* ignore the outdated Linux documentation */
>> +
>> +        if (setsockopt(sockfd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl)) < 0) {
>>             ff_log_net_error(logctx, AV_LOG_ERROR, "setsockopt(IP_MULTICAST_TTL)");
>>             return ff_neterrno();
>>         }
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