Enable HTTP/2 connection health checking

This limits the effect of a connection dropout by detecting it and
reconnecting after ~30s. This is added to Kubernetes in v1.19.4, but
I think we need to switch to Go modules before updating to that.

Fixes googlecloudrobotics#64.

Change-Id: I709b6bcecc35fd28bd904e6047bf479b0609117d

WORKSPACE

@@ -882,7 +882,7 @@ go_repository(
 
 go_repository(
     name = "org_golang_x_net",
-    commit = "4cb1c02c05b0e749b0365f61ae859a8e0cfceed9",
+    commit = "5f4716e94777e714bc2fb3e3a44599cb40817aac",
     importpath = "golang.org/x/net",
 )
 

src/go/cmd/cr-syncer/BUILD.bazel

@@ -33,6 +33,7 @@ go_library(
         "@io_opencensus_go//tag:go_default_library",
         "@io_opencensus_go//zpages:go_default_library",
         "@org_golang_x_net//context:go_default_library",
+        "@org_golang_x_net//http2:go_default_library",
         "@org_golang_x_oauth2//:go_default_library",
         "@org_golang_x_oauth2//google:go_default_library",
     ],

src/go/cmd/cr-syncer/main.go

@@ -56,6 +56,7 @@ import (
 	"go.opencensus.io/tag"
 	"go.opencensus.io/zpages"
 	"golang.org/x/net/context"
+	"golang.org/x/net/http2"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google"
 	crdtypes "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1"
@@ -152,6 +153,23 @@ func (r *ctxRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
 	return r.base.RoundTrip(req.WithContext(r.ctx))
 }
 
+// Configure HTTP/2 liveness checking on the connection, so that dropouts are
+// noticed and handled appropriately. Errors are ignored, as this is not
+// essential in normal conditions.
+func configureTransport(base http.RoundTripper) {
+	t1, ok := base.(*http.Transport)
+	if !ok {
+		log.Printf("failed to configure transport: expected http.Transport, got %T", base)
+	}
+	t2, err := http2.ConfigureTransports(t1)
+	if err != nil {
+		log.Printf("failed to enable HTTP/2 on transport: %v", err)
+	}
+	t2.ReadIdleTimeout = 30 * time.Second
+	t2.PingTimeout = 15 * time.Second
+	// The transport has been modified in-place, no need to return it.
+}
+
 // restConfigForRemote assembles the K8s REST config for the remote server.
 func restConfigForRemote(ctx context.Context) (*rest.Config, error) {
 	tokenSource, err := google.DefaultTokenSource(ctx, "https://www.googleapis.com/auth/cloud-platform")
@@ -163,6 +181,10 @@ func restConfigForRemote(ctx context.Context) (*rest.Config, error) {
 		return nil, err
 	}
 	transport := func(base http.RoundTripper) (rt http.RoundTripper) {
+		// Configure the transport to better handle dropped connections.
+		// TODO(rodrigoq): remove when updating to client-go kubernetes-1.19.4
+		configureTransport(base)
+
 		rt = &oauth2.Transport{
 			Source: tokenSource,
 			Base:   base,