[common-go] Support rate limiting by enum key (#16899)

Author: WVerlaek

components/common-go/grpc/ratelimit.go

@@ -6,6 +6,7 @@ package grpc
 
 import (
 	"context"
+	"strconv"
 	"strings"
 	"time"
 
@@ -110,12 +111,16 @@ func getFieldValue(msg protoreflect.Message, path []string) (val string, ok bool
 		return getFieldValue(child, path[1:])
 	}
 
-	if field.Kind() != protoreflect.StringKind {
-		// we only support string fields
+	switch field.Kind() {
+	case protoreflect.StringKind:
+		return msg.Get(field).String(), true
+	case protoreflect.EnumKind:
+		enumNum := msg.Get(field).Enum()
+		return strconv.Itoa(int(enumNum)), true
+	default:
+		// we only support string and enum fields
 		return "", false
 	}
-
-	return msg.Get(field).String(), true
 }
 
 // RatelimitingInterceptor limits how often a gRPC function may be called. If the limit has been

components/common-go/grpc/ratelimit_test.go

@@ -5,13 +5,15 @@
 package grpc
 
 import (
+	"strconv"
 	"strings"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
 	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/types/known/apipb"
 	"google.golang.org/protobuf/types/known/sourcecontextpb"
+	"google.golang.org/protobuf/types/known/typepb"
 )
 
 func TestGetFieldValue(t *testing.T) {
@@ -32,11 +34,23 @@ func TestGetFieldValue(t *testing.T) {
 			Expectation: Expectation{Found: true, Val: "bar"},
 		},
 		{
-			Name:        "empty field",
+			Name:        "empty string field",
 			Message:     &apipb.Api{},
 			Path:        "name",
 			Expectation: Expectation{Found: true},
 		},
+		{
+			Name:        "enum field",
+			Message:     &apipb.Api{Syntax: typepb.Syntax_SYNTAX_PROTO3},
+			Path:        "syntax",
+			Expectation: Expectation{Found: true, Val: strconv.Itoa(int(typepb.Syntax_SYNTAX_PROTO3))},
+		},
+		{
+			Name:        "empty enum field",
+			Message:     &apipb.Api{},
+			Path:        "syntax",
+			Expectation: Expectation{Found: true, Val: "0"},
+		},
 		{
 			Name:        "non-existent field",
 			Message:     &apipb.Api{},