8233435: (dc) DatagramChannel should allow IPv6 socket join IPv4 multicast groups (macOS, win)

[Daniel Fuchs]

Hi Alan,

These changes look good to me.
I have also imported your patch and played with it extensively,
I haven't observed any regression.

One remark though:
 > SAP team - I don't have any access to AIX so
 > Net.canIPv6SocketJoinIPv4Group() will return false as it has always
 > done. If you have cycles to test this change or return value for this
 > operating system changed as part of this issue then let me know. A
 > follow-on AIX specific issue is okay too.

Your changes mean that Net.canIPv6SocketJoinIPv4Group() will now
return false for *all* platforms but __linux__ __APPLE__ and
__solaris__ - whereas it previously returned false only
for __APPLE__ and __AIX__. This means that the opt-out has
now become an opt-in - and potentially affects any other
downstream platform. I agree that opt-in is probably a better
strategy than opt-out though, so that looks good to me
nonetheless.

Thanks for the fix!

best regards,

-- daniel


On 03/11/2019 16:55, Alan Bateman wrote:
> If a DatagramChannel is created with the no-arg open method or with the 
> protocol family INET6 then the channel cannot join IPv4 multicast groups 
> on macOS and Windows (no issue on Linux or Solaris). Both macOS and 
> Windows support this now so we can remove this restriction. The 
> recommendation for IPv4 multicasting app is to create the 
> DatagramChannel with protocol family INET remains of course.
> 
> Related is that on Windows, the StandardSocketOptions.IP_TOS and 
> IP_MULTICAST_* socket options cannot be accessed when the socket is a 
> dual socket that has been bound to an IPv4 local address. The Windows 
> networking stack requires using IP_ rather than IPV6_ socket options for 
> this scenario.
> 
> The webrev with the proposed changes is here. MulticastSendReceiveTests 
> has been updated to run the IPv4 multicasting tests when the system 
> under test has both IPv4 and IPv6. SocketOptionTests has been updated to 
> exercise reading and setting socket options in additional scenarios, 
> including a dual socket bound to an IPv4 local address.
> 
> http://cr.openjdk.java.net/~alanb/8233435/webrev/
> 
> SAP team - I don't have any access to AIX so 
> Net.canIPv6SocketJoinIPv4Group() will return false as it has always 
> done. If you have cycles to test this change or return value for this 
> operating system changed as part of this issue then let me know. A 
> follow-on AIX specific issue is okay too.
> 
> -Alan
> 
> PS: The motivation for this change, and the recent change to the 
> DatagramSocket adaptor, is to get closer to the point where it will be 
> possible to re-implement legacy DatagramSocket and MulticastSocket.