x/net/ipv[46]: ControlMessage unimplemented on Windows

[tmm1]

Both x/net/ipv4 and x/net/ipv6 return EWINDOWS and have "TODO: implement this" comments:

https://github.com/golang/net/blob/master/ipv4/control_windows.go
https://github.com/golang/net/blob/master/ipv6/control_windows.go

It appears that Windows has a WSARecvMsg which provides access to the underlying control messages:

For datagrams received by the WSARecvMsg function over IPv4, the Control member of the WSAMSG structure received will contain a WSABUF structure that contains a WSACMSGHDR structure. The cmsg_level member of this WSACMSGHDR structure would contain IPPROTO_IP, the cmsg_type member of this structure would contain IP_PKTINFO, and the cmsg_data member would contain an in_pktinfo structure used to store received IPv4 packet address information. The IPv4 address in the in_pktinfo structure is the IPv4 address from which the packet was received.

I couldn't find any mentions of WSARecvMsg in the golang source. Indeed, it appears that netFD.readMsg is unimplemented as-well on windows:

go/src/net/fd_windows.go

Line 233 in 12c286c

return 0, 0, 0, nil, syscall.EWINDOWS

So I guess the first step would be to add a syscall wrapper for WSARecvMsg and then implement netFD.readMsg on top of it?

cc @mikioh

[mikioh]

Sure, #9252, then #7174 and #7175.

[alexbrainman]

@tmm1 feel free to send me CLs for review.
I will help in whatever way I can.

Alex

[mikioh]

I'll merge this issue into #7175.