Improve Real-time response Handling for Remote Config (#15031)

Co-authored-by: Nick Cooke <36927374+ncooke3@users.noreply.github.com>

Author: 2 people

FirebaseRemoteConfig/CHANGELOG.md

@@ -1,3 +1,9 @@
+# Unreleased
+- [added] Improved how the SDK handles real-time requests when a Firebase
+  project has exceeded its available quota for real-time services.
+  Released in anticipation of future quota enforcement, this change is
+  designed to fetch the latest template even when the quota is exhausted.
+
 # 11.14.0
 - [fixed] Fix build warning from comparison of different enumeration types.
 

FirebaseRemoteConfig/Sources/Private/RCNConfigSettings.h

@@ -135,6 +135,10 @@
 /// indicates a server issue.
 - (void)updateRealtimeExponentialBackoffTime;
 
+/// Increases the throttling time for Realtime. Should only be called if we receive a Realtime
+/// retry interval in the response.
+- (void)updateRealtimeBackoffTimeWithInterval:(NSTimeInterval)realtimeRetryInterval;
+
 /// Update last active template version from last fetched template version.
 - (void)updateLastActiveTemplateVersion;
 

FirebaseRemoteConfig/Sources/RCNConfigRealtime.m

@@ -59,6 +59,7 @@
 /// Invalidation message field names.
 static NSString *const kTemplateVersionNumberKey = @"latestTemplateVersionNumber";
 static NSString *const kIsFeatureDisabled = @"featureDisabled";
+static NSString *const kRealtime_Retry_Interval = @"retryIntervalSeconds";
 
 static NSTimeInterval gTimeoutSeconds = 330;
 static NSInteger const gFetchAttempts = 3;
@@ -521,13 +522,17 @@ - (void)autoFetch:(NSInteger)remainingAttempts targetVersion:(NSInteger)targetVe
 
 - (void)evaluateStreamResponse:(NSDictionary *)response error:(NSError *)dataError {
   NSInteger updateTemplateVersion = 1;
+  NSTimeInterval realtimeRetryInterval = 0;
   if (dataError == nil) {
     if ([response objectForKey:kTemplateVersionNumberKey]) {
       updateTemplateVersion = [[response objectForKey:kTemplateVersionNumberKey] integerValue];
     }
     if ([response objectForKey:kIsFeatureDisabled]) {
       self->_isRealtimeDisabled = [response objectForKey:kIsFeatureDisabled];
     }
+    if ([response objectForKey:kRealtime_Retry_Interval]) {
+      realtimeRetryInterval = [[response objectForKey:kRealtime_Retry_Interval] integerValue];
+    }
 
     if (self->_isRealtimeDisabled) {
       [self pauseRealtimeStream];
@@ -544,6 +549,14 @@ - (void)evaluateStreamResponse:(NSDictionary *)response error:(NSError *)dataErr
       if (updateTemplateVersion > clientTemplateVersion) {
         [self autoFetch:gFetchAttempts targetVersion:updateTemplateVersion];
       }
+
+      /// This field in the response indicates that the realtime request should retry after the
+      /// specified interval to establish a long-lived connection. This interval extends the backoff
+      /// duration without affecting the number of retries, so it will not enter an exponential
+      /// backoff state.
+      if (realtimeRetryInterval > 0) {
+        [self->_settings updateRealtimeBackoffTimeWithInterval:realtimeRetryInterval];
+      }
     }
   } else {
     NSError *error =

FirebaseRemoteConfig/Sources/RCNConfigSettings.m

@@ -234,6 +234,16 @@ - (void)updateRealtimeExponentialBackoffTime {
       setCurrentRealtimeThrottlingRetryIntervalSeconds:_realtimeExponentialBackoffRetryInterval];
 }
 
+/// Increase the real-time stream's backoff period from the current time plus the retry interval.
+/// Any subsequent Realtime requests will be checked and allowed only if past this throttle end
+/// time.
+- (void)updateRealtimeBackoffTimeWithInterval:(NSTimeInterval)realtimeRetryInterval {
+  _realtimeExponentialBackoffThrottleEndTime =
+      [[NSDate date] timeIntervalSince1970] + realtimeRetryInterval;
+
+  [_userDefaultsManager setRealtimeThrottleEndTime:_realtimeExponentialBackoffThrottleEndTime];
+}
+
 - (void)setRealtimeRetryCount:(int)realtimeRetryCount {
   _realtimeRetryCount = realtimeRetryCount;
   [_userDefaultsManager setRealtimeRetryCount:_realtimeRetryCount];

FirebaseRemoteConfig/Tests/Unit/RCNRemoteConfigTest.m

@@ -1785,6 +1785,37 @@ - (void)testRealtimeDisabled {
   }
 }
 
+- (void)testRealtimeUpdatesBackoffMetadataWhenRetryIntervalIsProvided {
+  NSMutableArray<XCTestExpectation *> *expectations =
+      [[NSMutableArray alloc] initWithCapacity:RCNTestRCNumTotalInstances];
+  for (int i = 0; i < RCNTestRCNumTotalInstances; i++) {
+    expectations[i] =
+        [self expectationWithDescription:
+                  [NSString stringWithFormat:@"Test backoff metadata updates with a provided retry "
+                                             @"interval in the stream response - instance %d",
+                                             i]];
+    NSTimeInterval realtimeRetryInterval = 240;
+    NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];
+    [dictionary setValue:@"1" forKey:@"latestTemplateVersionNumber"];
+    [dictionary setValue:@(realtimeRetryInterval) forKey:@"retryIntervalSeconds"];
+
+    NSTimeInterval expectedThrottleEndTime =
+        [[NSDate date] timeIntervalSince1970] + realtimeRetryInterval;
+
+    [_configRealtime[i] evaluateStreamResponse:dictionary error:nil];
+    dispatch_after(
+        dispatch_time(DISPATCH_TIME_NOW, (int64_t)(_checkCompletionTimeout * NSEC_PER_SEC)),
+        dispatch_get_main_queue(), ^{
+          NSTimeInterval retrievedThrottleEndTime =
+              self->_configInstances[i].settings.realtimeExponentialBackoffThrottleEndTime;
+          XCTAssertEqualWithAccuracy(retrievedThrottleEndTime, expectedThrottleEndTime, 1.0);
+          [expectations[i] fulfill];
+        });
+
+    [self waitForExpectationsWithTimeout:_expectationTimeout handler:nil];
+  }
+}
+
 - (void)testRealtimeStreamRequestBody {
   XCTestExpectation *requestBodyExpectation = [self expectationWithDescription:@"requestBody"];
   __block NSData *requestBody;