use incremental API for envoy xDS (#1732)

* use incremental API

* add test

* use backoff v4

* remove panic, add comment to exponential try, add test for HashProto

* merge master

* fix missing import

pkg/cryptutil/hash_test.go

@@ -8,6 +8,9 @@ import (
 	"io/ioutil"
 	"os"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"google.golang.org/protobuf/types/known/structpb"
 )
 
 func TestPasswordHashing(t *testing.T) {
@@ -79,3 +82,25 @@ func ExampleHash() {
 	fmt.Println(hex.EncodeToString(digest))
 	// Output: 9f4c795d8ae5c207f19184ccebee6a606c1fdfe509c793614066d613580f03e1
 }
+
+func TestHashProto(t *testing.T) {
+	// This test will hash a protobuf message that has a map 1000 times
+	// each attempt should result in the same hash if the output is
+	// deterministic.
+	var cur []byte
+	for i := 0; i < 1000; i++ {
+		s, err := structpb.NewStruct(map[string]interface{}{
+			"1": "a", "2": "b", "3": "c", "4": "d",
+			"5": "e", "6": "f", "7": "g", "8": "h",
+		})
+		assert.NoError(t, err)
+		if i == 0 {
+			cur = HashProto(s)
+		} else {
+			nxt := HashProto(s)
+			if !assert.Equal(t, cur, nxt) {
+				return
+			}
+		}
+	}
+}