Realtime Fetch ID (#4328)

* Create overloaded fetch method specifically for realtime and add custom headers

* Add comments for vars

* Update header name

* Change realtimeFetch name and params

* Remove fetchHandler tests and move them to seperate PR

* Remove unused vars and revert tests

* Format tests

* Add comments

* Format files

Author: qdpham13

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

@@ -40,7 +40,7 @@
 
 public class ConfigAutoFetch {
 
-  private static final int FETCH_RETRY = 3;
+  private static final int MAXIMUM_FETCH_ATTEMPTS = 3;
   private static final String TEMPLATE_VERSION_KEY = "latestTemplateVersionNumber";
   private static final String REALTIME_DISABLED_KEY = "featureDisabled";
 
@@ -155,7 +155,7 @@ private void handleNotifications(InputStream inputStream) throws IOException {
               long oldTemplateVersion = configFetchHandler.getTemplateVersionNumber();
               long targetTemplateVersion = jsonObject.getLong(TEMPLATE_VERSION_KEY);
               if (targetTemplateVersion > oldTemplateVersion) {
-                autoFetch(FETCH_RETRY, targetTemplateVersion);
+                autoFetch(MAXIMUM_FETCH_ATTEMPTS, targetTemplateVersion);
               }
             }
           } catch (JSONException ex) {
@@ -195,7 +195,13 @@ public void run() {
 
   @VisibleForTesting
   public synchronized void fetchLatestConfig(int remainingAttempts, long targetVersion) {
-    Task<ConfigFetchHandler.FetchResponse> fetchTask = configFetchHandler.fetch(0L);
+    int currentAttempts = remainingAttempts - 1;
+
+    // fetchAttemptNumber is calculated by subtracting current attempts from the max number of
+    // possible attempts.
+    Task<ConfigFetchHandler.FetchResponse> fetchTask =
+        configFetchHandler.fetchNowWithTypeAndAttemptNumber(
+            ConfigFetchHandler.FetchType.REALTIME, MAXIMUM_FETCH_ATTEMPTS - currentAttempts);
     fetchTask.onSuccessTask(
         (fetchResponse) -> {
           long newTemplateVersion = 0;
@@ -214,7 +220,7 @@ public synchronized void fetchLatestConfig(int remainingAttempts, long targetVer
                 "Fetched template version is the same as SDK's current version."
                     + " Retrying fetch.");
             // Continue fetching until template version number if greater then current.
-            autoFetch(remainingAttempts - 1, targetVersion);
+            autoFetch(currentAttempts, targetVersion);
           }
           return Tasks.forResult(null);
         });

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

@@ -85,6 +85,9 @@ public class ConfigFetchHandler {
    */
   @VisibleForTesting static final String FIRST_OPEN_TIME_KEY = "_fot";
 
+  /** Custom Http header key to identify the fetch type. */
+  private static final String X_FIREBASE_RC_FETCH_TYPE = "X-Firebase-RC-Fetch-Type";
+
   private final FirebaseInstallationsApi firebaseInstallations;
   private final Provider<AnalyticsConnector> analyticsConnector;
 
@@ -156,13 +159,66 @@ public Task<FetchResponse> fetch() {
    *     updates, the {@link FetchResponse}'s configs will be {@code null}.
    */
   public Task<FetchResponse> fetch(long minimumFetchIntervalInSeconds) {
+
+    // Make a copy to prevent any concurrency issues between Fetches.
+    Map<String, String> copyOfCustomHttpHeaders = new HashMap<>(customHttpHeaders);
+    copyOfCustomHttpHeaders.put(X_FIREBASE_RC_FETCH_TYPE, FetchType.BASE.getValue() + "/" + 1);
+
     return fetchedConfigsCache
         .get()
         .continueWithTask(
             executor,
             (cachedFetchConfigsTask) ->
                 fetchIfCacheExpiredAndNotThrottled(
-                    cachedFetchConfigsTask, minimumFetchIntervalInSeconds));
+                    cachedFetchConfigsTask,
+                    minimumFetchIntervalInSeconds,
+                    copyOfCustomHttpHeaders));
+  }
+
+  /**
+   * Starts fetching configs from the Firebase Remote Config server.
+   *
+   * <p>Guarantees consistency between memory and disk; fetched configs are saved to memory only
+   * after they have been written to disk.
+   *
+   * <p>Fetches even if the read of the fetch cache fails (assumes there are no cached fetched
+   * configs in that case).
+   *
+   * <p>If the fetch request could not be created or there was error connecting to the server, the
+   * returned Task throws a {@link FirebaseRemoteConfigClientException}.
+   *
+   * <p>If the server responds with an error, the returned Task throws a {@link
+   * FirebaseRemoteConfigServerException}.
+   *
+   * <p>If any of the following is true, then the returned Task throws a {@link
+   * FirebaseRemoteConfigFetchThrottledException}:
+   *
+   * <ul>
+   *   <li>The backoff duration from a previous throttled exception has not expired,
+   *   <li>The backend responded with a throttled error, or
+   *   <li>The backend responded with unavailable errors for the last two fetch requests.
+   * </ul>
+   *
+   * @param {@link FetchType} and fetchAttemptNumber help detail what started the fetch call.
+   * @return A {@link Task} representing an immediate fetch call that returns a {@link
+   *     FetchResponse} with the configs fetched from the backend. If the backend was not called or
+   *     the backend had no updates, the {@link FetchResponse}'s configs will be {@code null}.
+   */
+  public Task<FetchResponse> fetchNowWithTypeAndAttemptNumber(
+      FetchType fetchType, int fetchAttemptNumber) {
+
+    // Make a copy to prevent any concurrency issues between Fetches.
+    Map<String, String> copyOfCustomHttpHeaders = new HashMap<>(customHttpHeaders);
+    copyOfCustomHttpHeaders.put(
+        X_FIREBASE_RC_FETCH_TYPE, fetchType.getValue() + "/" + fetchAttemptNumber);
+
+    return fetchedConfigsCache
+        .get()
+        .continueWithTask(
+            executor,
+            (cachedFetchConfigsTask) ->
+                fetchIfCacheExpiredAndNotThrottled(
+                    cachedFetchConfigsTask, 0, copyOfCustomHttpHeaders));
   }
 
   /**
@@ -173,7 +229,9 @@ public Task<FetchResponse> fetch(long minimumFetchIntervalInSeconds) {
    * fetch time and {@link BackoffMetadata} in {@link ConfigMetadataClient}.
    */
   private Task<FetchResponse> fetchIfCacheExpiredAndNotThrottled(
-      Task<ConfigContainer> cachedFetchConfigsTask, long minimumFetchIntervalInSeconds) {
+      Task<ConfigContainer> cachedFetchConfigsTask,
+      long minimumFetchIntervalInSeconds,
+      Map<String, String> customFetchHeaders) {
     Date currentTime = new Date(clock.currentTimeMillis());
     if (cachedFetchConfigsTask.isSuccessful()
         && areCachedFetchConfigsValid(minimumFetchIntervalInSeconds, currentTime)) {
@@ -218,7 +276,7 @@ && areCachedFetchConfigsValid(minimumFetchIntervalInSeconds, currentTime)) {
                     String installationId = installationIdTask.getResult();
                     String installationToken = installationAuthTokenTask.getResult().getToken();
                     return fetchFromBackendAndCacheResponse(
-                        installationId, installationToken, currentTime);
+                        installationId, installationToken, currentTime, customFetchHeaders);
                   });
     }
 
@@ -278,9 +336,13 @@ private String createThrottledMessage(long throttledDurationInMillis) {
    * {@code fetchedConfigsCache}.
    */
   private Task<FetchResponse> fetchFromBackendAndCacheResponse(
-      String installationId, String installationToken, Date fetchTime) {
+      String installationId,
+      String installationToken,
+      Date fetchTime,
+      Map<String, String> customFetchHeaders) {
     try {
-      FetchResponse fetchResponse = fetchFromBackend(installationId, installationToken, fetchTime);
+      FetchResponse fetchResponse =
+          fetchFromBackend(installationId, installationToken, fetchTime, customFetchHeaders);
       if (fetchResponse.getStatus() != Status.BACKEND_UPDATES_FETCHED) {
         return Tasks.forResult(fetchResponse);
       }
@@ -303,7 +365,10 @@ private Task<FetchResponse> fetchFromBackendAndCacheResponse(
    */
   @WorkerThread
   private FetchResponse fetchFromBackend(
-      String installationId, String installationToken, Date currentTime)
+      String installationId,
+      String installationToken,
+      Date currentTime,
+      Map<String, String> customFetchHeaders)
       throws FirebaseRemoteConfigException {
     try {
       HttpURLConnection urlConnection = frcBackendApiClient.createHttpURLConnection();
@@ -315,7 +380,7 @@ private FetchResponse fetchFromBackend(
               installationToken,
               getUserProperties(),
               frcMetadata.getLastFetchETag(),
-              customHttpHeaders,
+              customFetchHeaders,
               getFirstOpenTime(),
               currentTime);
 
@@ -626,4 +691,19 @@ public ConfigContainer getFetchedConfigs() {
       int LOCAL_STORAGE_USED = 2;
     }
   }
+
+  public enum FetchType {
+    BASE("Base"),
+    REALTIME("Realtime");
+
+    private final String value;
+
+    FetchType(String value) {
+      this.value = value;
+    }
+
+    String getValue() {
+      return value;
+    }
+  }
 }

firebase-config/src/test/java/com/google/firebase/remoteconfig/FirebaseRemoteConfigTest.java

@@ -1156,7 +1156,9 @@ public void realtime_stream_listen_and_retry_success() throws Exception {
             new ByteArrayInputStream(
                 "{ \"latestTemplateVersionNumber\": 1 }".getBytes(StandardCharsets.UTF_8)));
     when(mockFetchHandler.getTemplateVersionNumber()).thenReturn(1L);
-    when(mockFetchHandler.fetch(0)).thenReturn(Tasks.forResult(realtimeFetchedContainerResponse));
+    when(mockFetchHandler.fetchNowWithTypeAndAttemptNumber(
+            ConfigFetchHandler.FetchType.REALTIME, 1))
+        .thenReturn(Tasks.forResult(realtimeFetchedContainerResponse));
     configAutoFetch.listenForNotifications();
 
     verify(mockRetryListener).onEvent();
@@ -1245,7 +1247,9 @@ public void realtime_stream_listen_and_failsafe_disabled() throws Exception {
                 "{ \"featureDisabled\": false,  \"latestTemplateVersionNumber\": 2 }"
                     .getBytes(StandardCharsets.UTF_8)));
     when(mockFetchHandler.getTemplateVersionNumber()).thenReturn(1L);
-    when(mockFetchHandler.fetch(0)).thenReturn(Tasks.forResult(realtimeFetchedContainerResponse));
+    when(mockFetchHandler.fetchNowWithTypeAndAttemptNumber(
+            ConfigFetchHandler.FetchType.REALTIME, 1))
+        .thenReturn(Tasks.forResult(realtimeFetchedContainerResponse));
     configAutoFetch.listenForNotifications();
 
     verify(mockUnavailableEventListener, never())
@@ -1258,7 +1262,9 @@ public void realtime_stream_listen_get_inputstream_fail() throws Exception {
     when(mockHttpURLConnection.getResponseCode()).thenReturn(200);
     when(mockHttpURLConnection.getInputStream()).thenThrow(IOException.class);
     when(mockFetchHandler.getTemplateVersionNumber()).thenReturn(1L);
-    when(mockFetchHandler.fetch(0)).thenReturn(Tasks.forResult(realtimeFetchedContainerResponse));
+    when(mockFetchHandler.fetchNowWithTypeAndAttemptNumber(
+            ConfigFetchHandler.FetchType.REALTIME, 1))
+        .thenReturn(Tasks.forResult(realtimeFetchedContainerResponse));
     configAutoFetch.listenForNotifications();
 
     verify(mockInvalidMessageEventListener).onError(any(FirebaseRemoteConfigClientException.class));
@@ -1267,16 +1273,20 @@ public void realtime_stream_listen_get_inputstream_fail() throws Exception {
   @Test
   public void realtime_stream_autofetch_success() {
     when(mockFetchHandler.getTemplateVersionNumber()).thenReturn(1L);
-    when(mockFetchHandler.fetch(0)).thenReturn(Tasks.forResult(realtimeFetchedContainerResponse));
-    configAutoFetch.fetchLatestConfig(1, 1);
+    when(mockFetchHandler.fetchNowWithTypeAndAttemptNumber(
+            ConfigFetchHandler.FetchType.REALTIME, 1))
+        .thenReturn(Tasks.forResult(realtimeFetchedContainerResponse));
+    configAutoFetch.fetchLatestConfig(3, 1);
 
     verify(mockOnEventListener).onEvent();
   }
 
   @Test
   public void realtime_stream_autofetch_failure() {
     when(mockFetchHandler.getTemplateVersionNumber()).thenReturn(1L);
-    when(mockFetchHandler.fetch(0)).thenReturn(Tasks.forResult(realtimeFetchedContainerResponse));
+    when(mockFetchHandler.fetchNowWithTypeAndAttemptNumber(
+            ConfigFetchHandler.FetchType.REALTIME, 3))
+        .thenReturn(Tasks.forResult(realtimeFetchedContainerResponse));
     configAutoFetch.fetchLatestConfig(1, 1000);
 
     verify(mockNotFetchedEventListener).onError(any(FirebaseRemoteConfigServerException.class));