Issue #215: Re-enable HTTP/2 support

This patch re-enables the HTTP/2 support
for go1.7 and beyond by setting the NextProto
field in the custom TLSConfig.

See golang/go#15908

cert/source.go

@@ -87,6 +87,7 @@ func TLSConfig(src Source, strictMatch bool) (*tls.Config, error) {
 
 	store := NewStore()
 	x := &tls.Config{
+		NextProtos: []string{"h2"},
 		GetCertificate: func(clientHello *tls.ClientHelloInfo) (cert *tls.Certificate, err error) {
 			return getCertificate(store.certstore(), clientHello, strictMatch)
 		},

cert/source_test.go

@@ -21,6 +21,8 @@ import (
 	"testing"
 	"time"
 
+	"golang.org/x/net/http2"
+
 	"github.com/eBay/fabio/config"
 	consulapi "github.com/hashicorp/consul/api"
 	vaultapi "github.com/hashicorp/vault/api"
@@ -388,22 +390,22 @@ func testSource(t *testing.T, source Source, rootCAs *x509.CertPool, sleep time.
 	// create the https server and start it
 	// it will be listening on 127.0.0.1
 	srv := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		fmt.Fprint(w, "OK")
+		fmt.Fprint(w, "OK ", r.Proto)
 	}))
 	srv.TLS = srvConfig
 	srv.StartTLS()
 	defer srv.Close()
 
-	// create an http client that will accept the root CAs
+	// create an HTTP/2 client that will accept the root CAs
 	// otherwise the HTTPS client will not verify the
 	// certificate presented by the server.
-	client := http.Client{
-		Transport: &http.Transport{
-			TLSClientConfig: &tls.Config{
-				RootCAs: rootCAs,
-			},
+	clientTransport := &http.Transport{
+		TLSClientConfig: &tls.Config{
+			RootCAs: rootCAs,
 		},
 	}
+	http2.ConfigureTransport(clientTransport)
+	client := http.Client{Transport: clientTransport}
 
 	call := func(host string) (statusCode int, body string, err error) {
 		// for the certificate validation to work we need to use a hostname
@@ -444,7 +446,7 @@ func testSource(t *testing.T, source Source, rootCAs *x509.CertPool, sleep time.
 	if got, want := statusCode, 200; got != want {
 		t.Fatalf("got %v want %v", got, want)
 	}
-	if got, want := body, "OK"; got != want {
+	if got, want := body, "OK HTTP/2.0"; got != want {
 		t.Fatalf("got %v want %v", got, want)
 	}
 }