net/http/httptest: httptest on Windows is IPv4-specific

[ItsMattL]

What version of Go are you using (go version)?

go version go1.11.1 windows/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

windows/amd64

What did you do?

Run a test leveraging net/http/httptest on a host with IPv6 but without IPv4.

To reproduce:

1. As administrator, run

   netsh interface ipv4 uninstall

2. Reboot
3. Execute an httptest as in https://play.golang.org/p/xlMUEEhgj5s

What did you expect to see?

Test would pass, since the client and server code were both valid, and pass when IPv4 is available.

What did you see instead?

2019/01/15 17:26:59 Get http://[::1]:49679: dial tcp [::1]:49679: failed to find ConnectEx: An address incompatible with the requested protocol was used.

[gopherbot]

Change https://golang.org/cl/241137 mentions this issue: net/http/httptest: use IPv6 when IPv4 is unavailable

[linsite]

I've confirmed that the following code is the reason.

func LoadConnectEx() error {
	connectExFunc.once.Do(func() {
		var s Handle
		s, connectExFunc.err = Socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) // here, always try to new a IPv4 socket
		if connectExFunc.err != nil {
			return
		}
     ...

go/src/syscall/syscall_windows.go

Line 1101 in a909306

s, connectExFunc.err = Socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)

I'd like to give it a try. But I don't know if adding a Socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP) retry is a good idea or not.

Calling for help. cc @qmuntal

[gopherbot]

Change https://go.dev/cl/726101 mentions this issue: syscall: make LoadConnectEx not IPv4-specific on Windows