net/http: make DefaultTransport's Dialer enable DualStack ("Happy Eyeballs")

As @pmarks-net said in the bug, this is something of a prisoner's
dilemma, but it does help people who occasionally report problems.

This is temporary. IPv6 is happening regardless of our decision here,
so we'll do this for now.

Fixes #15324

Change-Id: I8cc29c6efa56222970996c71182fc9ee89d78539
Reviewed-on: https://go-review.googlesource.com/28077
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

diff --git a/src/net/http/transport.go b/src/net/http/transport.go
index b239a1d8eef6ff59986a015e558f7d25a59ea5b5..65465e25c1cb6628c28b067fe1e5d0dafd20eaf4 100644 (file)
--- a/src/net/http/transport.go
+++ b/src/net/http/transport.go
@@ -40,6 +40,7 @@ var DefaultTransport RoundTripper = &Transport{
        DialContext: (&net.Dialer{
                Timeout:   30 * time.Second,
                KeepAlive: 30 * time.Second,
+               DualStack: true,
        }).DialContext,
        MaxIdleConns:          100,
        IdleConnTimeout:       90 * time.Second,