Parse NO_CHANGE fetch response for template version (#4177)

* Parse and store fetch response for NO_CHANGE bug as well

* Fix test

* Revert change

* Format file

* Format file

* Add comments and update tests

Author: qdpham13

firebase-config/src/main/java/com/google/firebase/remoteconfig/internal/ConfigFetchHandler.java

@@ -575,11 +575,14 @@ public static FetchResponse forBackendUpdatesFetched(
           lastFetchETag);
     }
 
-    public static FetchResponse forBackendHasNoUpdates(Date fetchTime) {
+    // Passing in param fetchedConfigs because it contains templateVersion but no other active
+    // fields.
+    public static FetchResponse forBackendHasNoUpdates(
+        Date fetchTime, ConfigContainer fetchedConfigs) {
       return new FetchResponse(
           fetchTime,
           Status.BACKEND_HAS_NO_UPDATES,
-          /*fetchedConfigs=*/ null,
+          /*fetchedConfigs=*/ fetchedConfigs,
           /*lastFetchETag=*/ null);
     }
 

firebase-config/src/main/java/com/google/firebase/remoteconfig/internal/ConfigFetchHttpClient.java

@@ -216,12 +216,12 @@ FetchResponse fetch(
       } catch (IOException e) {
       }
     }
+    ConfigContainer fetchedConfigs = extractConfigs(fetchResponse, currentTime);
 
     if (!backendHasUpdates(fetchResponse)) {
-      return FetchResponse.forBackendHasNoUpdates(currentTime);
+      return FetchResponse.forBackendHasNoUpdates(currentTime, fetchedConfigs);
     }
 
-    ConfigContainer fetchedConfigs = extractConfigs(fetchResponse, currentTime);
     return FetchResponse.forBackendUpdatesFetched(fetchedConfigs, fetchResponseETag);
   }
 

firebase-config/src/test/java/com/google/firebase/remoteconfig/internal/ConfigFetchHandlerTest.java

@@ -794,7 +794,7 @@ private void setBackendResponseToNoChange(Date date) throws Exception {
             /* customHeaders= */ any(),
             /* firstOpenTime= */ any(),
             /* currentTime= */ any()))
-        .thenReturn(FetchResponse.forBackendHasNoUpdates(date));
+        .thenReturn(FetchResponse.forBackendHasNoUpdates(date, firstFetchedContainer));
   }
 
   private void fetchCallToBackendThrowsException(int httpErrorCode) throws Exception {

firebase-config/src/test/java/com/google/firebase/remoteconfig/internal/ConfigFetchHttpClientTest.java

@@ -161,13 +161,15 @@ public void fetch_newValues_responseSet() throws Exception {
   }
 
   @Test
-  public void fetch_noChange_responseNotSet() throws Exception {
+  public void fetch_noChange_responseOnlyContainsTemplateVersion() throws Exception {
     setServerResponseTo(noChangeResponseBody, SECOND_ETAG);
 
     FetchResponse response = fetch(SECOND_ETAG);
 
     assertThat(response.getLastFetchETag()).isNull();
-    assertThat(response.getFetchedConfigs()).isNull();
+    assertThat(response.getFetchedConfigs()).isNotNull();
+    assertThat(response.getFetchedConfigs().getTemplateVersionNumber()).isNotNull();
+    assertThat(response.getFetchedConfigs().getConfigs().length()).isEqualTo(0);
   }
 
   @Test