Fix ctxtags TagBasedRequestFieldExtractor extracting from fields in a…

… oneof

Resolves grpc-ecosystem#326

tags/fieldextractor.go

@@ -64,7 +64,7 @@ func reflectMessageTags(msg interface{}, existingMap map[string]interface{}, tag
 		field := v.Field(i)
 		kind := field.Kind()
 		// Only recurse down direct pointers, which should only be to nested structs.
-		if kind == reflect.Ptr && field.CanInterface() {
+		if (kind == reflect.Ptr || kind == reflect.Interface) && field.CanInterface() {
 			reflectMessageTags(field.Interface(), existingMap, tagName)
 		}
 		// In case of arrays/slices (repeated fields) go down to the concrete type.

tags/fieldextractor_test.go

@@ -52,6 +52,16 @@ func TestTaggedRequestFiledExtractor_PongRequest(t *testing.T) {
 	assert.EqualValues(t, []string{"tagone", "tagtwo"}, valMap["meta_tags"])
 }
 
+func TestTaggedRequestFiledExtractor_OneOfLogField(t *testing.T) {
+	req := &pb_gogotestproto.OneOfLogField{
+		Identifier: &pb_gogotestproto.OneOfLogField_BarId{
+			BarId: "bar-log-field",
+		},
+	}
+	valMap := grpc_ctxtags.TagBasedRequestFieldExtractor("log_field")("", req)
+	assert.EqualValues(t, "bar-log-field", valMap["bar_id"])
+}
+
 // Test to ensure TagBasedRequestFieldExtractor does not panic when encountering private struct members such as
 // when using gogoproto.stdtime which results in a time.Time that has private struct members
 func TestTaggedRequestFiledExtractor_GogoTime(t *testing.T) {

testing/gogotestproto/fields.proto

@@ -30,6 +30,13 @@ message Pong {
     string id = 1 [(gogoproto.moretags) = "log_field:\"pong_id\""];
 }
 
+message OneOfLogField {
+    oneof identifier {
+        string bar_id = 1 [(gogoproto.moretags) = "log_field:\"bar_id\""];
+        string baz_id = 2 [(gogoproto.moretags) = "log_field:\"baz_id\""];
+    }
+}
+
 message PongRequest {
     Pong pong = 1;
     Metadata meta = 2;