backend: fix unmarshaling empty refids (#1189)

Author: gabor

backend/json.go

@@ -149,10 +149,24 @@ func readQueryDataResultsJSON(qdr *QueryDataResponse, iter *jsoniter.Iterator) {
 
 			qdr.Responses = make(Responses)
 
-			for l2Field := iter.ReadObject(); l2Field != ""; l2Field = iter.ReadObject() {
+			l2Field := iter.ReadObject()
+			for {
+				// the response may have an empty-string refId. this is not allowed,
+				// but it may happen, and we want to be able to handle the case.
+				// jsonIter uses empty-string to signalize both of these cases:
+				// - end of object
+				// - key found with the value empty-string
+				// to be able to differentiate between these two cases, we use the `WhatIsNext()`
+				// function, that tells us what is coming next, but does not consume content.
+				if (l2Field == "") && (iter.WhatIsNext() != jsoniter.ObjectValue) {
+					break
+				}
+
 				dr := DataResponse{}
 				readDataResponseJSON(&dr, iter)
 				qdr.Responses[l2Field] = dr
+
+				l2Field = iter.ReadObject()
 			}
 
 		default:

backend/json_test.go

@@ -143,3 +143,39 @@ func TestQueryDataResponseOrdering(t *testing.T) {
 
 	require.JSONEq(t, expected, string(b))
 }
+
+func testQueryDataResponseRoundtrip(t *testing.T, qdr *backend.QueryDataResponse) {
+	t.Helper()
+	// to json
+	b, err := json.Marshal(qdr)
+	require.NoError(t, err)
+
+	// from json
+	qdr2 := &backend.QueryDataResponse{}
+	err = json.Unmarshal(b, qdr2)
+	require.NoError(t, err)
+
+	// to json again, to compare
+	b2, err := json.Marshal(qdr2)
+	require.NoError(t, err)
+	require.Equal(t, b2, b)
+}
+
+func TestQueryDataWithoutRefID(t *testing.T) {
+	qdr := backend.NewQueryDataResponse()
+	qdr.Responses[""] = testDataResponse()
+
+	testQueryDataResponseRoundtrip(t, qdr)
+}
+
+func TestQueryDataWithtRefID(t *testing.T) {
+	qdr := backend.NewQueryDataResponse()
+	qdr.Responses["A"] = testDataResponse()
+
+	testQueryDataResponseRoundtrip(t, qdr)
+}
+
+func TestQueryDataWithoutResponses(t *testing.T) {
+	qdr := backend.NewQueryDataResponse()
+	testQueryDataResponseRoundtrip(t, qdr)
+}