net/http: in the IdleConnStrsForTesting_h2 helper, omit conns that cannot be reused

In #59155, we observed that the IdleConnStrsForTesting_h2 helper
function sometimes reported extra connections after a
"client conn not usable" failure and retry. It turns out that that
state corresponds exactly to the
http2clientConnIdleState.canTakeNewRequest field, so (with a bit of
extra nethttpomithttp2 plumbing) we can use that field in the helper
to filter out the unusable connections.

Fixes #59155.

Change-Id: Ief6283c9c8c5ec47dd9f378beb0ddf720832484e
Reviewed-on: https://go-review.googlesource.com/c/go/+/477856
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/src/net/http/export_test.go b/src/net/http/export_test.go
index fb5ab9396a..8a61e651dc 100644
--- a/src/net/http/export_test.go
+++ b/src/net/http/export_test.go
@@ -142,9 +142,11 @@ func (t *Transport) IdleConnStrsForTesting_h2() []string {
 	pool.mu.Lock()
 	defer pool.mu.Unlock()
 
-	for k, cc := range pool.conns {
-		for range cc {
-			ret = append(ret, k)
+	for k, ccs := range pool.conns {
+		for _, cc := range ccs {
+			if cc.idleState().canTakeNewRequest {
+				ret = append(ret, k)
+			}
 		}
 	}