pass map representation of proto duration for patch of delete_version…

…_after (#62)

path_metadata.go

@@ -333,7 +333,17 @@ func metadataPatchPreprocessor() framework.PatchPreprocessorFunc {
 		for _, k := range patchableKeys {
 			if v, ok := input[k]; ok {
 				if k == "delete_version_after" {
-					patchData[k] = ptypes.DurationProto(time.Duration(v.(int)) * time.Second)
+					d := ptypes.DurationProto(time.Duration(v.(int)) * time.Second)
+
+					// underlying Seconds and Nanos fields in durationpb.Duration
+					// use omitempty json tags. Providing "0s" will result in an
+					// empty map after JSON marshaling which will act as a noop
+					// come JSON merge patch time. Instead, we pass in a
+					// map-representation of the data to enable patching with "0s"
+					patchData[k] = map[string]interface{}{
+						"seconds": d.Seconds,
+						"nanos": d.Nanos,
+					}
 				} else {
 					patchData[k] = v
 				}

path_metadata_test.go

@@ -1189,10 +1189,10 @@ func TestVersionedKV_Metadata_Patch_Success(t *testing.T) {
 			map[string]interface{}{
 				"cas_required":         true,
 				"max_versions":         uint32(15),
-				"delete_version_after": nil,
+				"delete_version_after": "0s",
 				"updated_time":         ignoreVal,
 			},
-			2,
+			3,
 		},
 	}
 
@@ -1207,6 +1207,7 @@ func TestVersionedKV_Metadata_Patch_Success(t *testing.T) {
 				Storage:   storage,
 				Data: map[string]interface{}{
 					"max_versions": uint32(10),
+					"delete_version_after": "10s",
 				},
 			}