net: TestInterfaces failing on windows

[bradfitz]

I rebuilt the Windows image (the same as normal, following the checklist in x/build/env), but now TestInterfaces is failing for some reason:

--- FAIL: TestInterfaces (0.01s)
    interface_test.go:71: "Local Area Connection": flags "up|broadcast|multicast", ifindex 12, mtu 1430
    interface_test.go:72: hardware address "42:01:0a:f0:24:ca:00:00"
    interface_test.go:169: interface address "10.240.36.202/16"
    interface_test.go:190: joined group address "224.0.0.1"
    interface_test.go:190: joined group address "224.0.0.252"
    interface_test.go:90: got 0; want more than or equal to one
    interface_test.go:102: got 0; want more than or equal to one
FAIL
FAIL    net 4.015s

e.g. http://build.golang.org/log/abdd7adc73e7a65beec1773f5a04b3ed7065d3a6

/cc @alexbrainman @mikioh

[bradfitz]

I'll also note that this is a bad error message:

got 0; want more than or equal to one

Zero whats?

[alexbrainman]

I will see what the problem is tomorrow. Thank you for getting builders up again @bradfitz .

Alex

[bradfitz]

From a quick read, it seems that the Windows builder appears to pass the supportsIPv6 test, and has one non-loopback interface ("Local Area Connection") but no interface (0 out of 1) has an IPv6 address.

From https://cloud.google.com/compute/docs/networking#networks :

All Compute Engine networks use the IPv4 protocol. Compute Engine currently does not support IPv6. However, Google is a major advocate of IPv6 and it is an important future direction.

I'm not sure what TestInterfaces is trying to test. The probeIPv6Stack function just tries to make & bind some syscall.AF_INET6 sockets, which works. So I guess the assumption is that there should be some interface with an IPv6 address to which they must be bound?

I'll also note that when I rebuilt this Windows image, Google has in the meantime also updated the base layer Windows image (it's now 30GB instead of 100GB, and has some new GCE-specific tweaks I think), so it's not identical to what it was before, even though I followed the same setup procedures.

To be clear, I'm not working on this bug. Help wanted.

[bradfitz]

@mikioh has a pending CL at https://go-review.googlesource.com/#/c/7924/