[Config] Follow-up to 'RCNRealtime' port (#14303)

Author: ncooke3

FirebaseRemoteConfig/SwiftNew/ConfigRealtime.swift

@@ -417,6 +417,7 @@ class ConfigRealtime: NSObject, URLSessionDataDelegate {
         }
         if status == .success {
           if Int(self.configFetch.templateVersionNumber) ?? 0 >= targetVersion {
+            // Only notify listeners if there is a change.
             if let update = update, !update.updatedKeys.isEmpty {
               self.realtimeLockQueue.async { [weak self] in
                 guard let self else { return }
@@ -443,15 +444,19 @@ class ConfigRealtime: NSObject, URLSessionDataDelegate {
 
   @objc(scheduleFetch:targetVersion:) public
   func scheduleFetch(remainingAttempts: Int, targetVersion: Int) {
+    // Needs fetch to occur between 0 - 3 seconds. Randomize to not cause DDoS
+    // alerts in backend.
     let delay = TimeInterval.random(in: 0 ... 3) // Random delay between 0 and 3 seconds
     realtimeLockQueue.asyncAfter(deadline: .now() + delay) {
       self.fetchLatestConfig(remainingAttempts: remainingAttempts, targetVersion: targetVersion)
     }
   }
 
+  /// Perform fetch and handle developers callbacks.
   @objc(autoFetch:targetVersion:) public
   func autoFetch(attempts: Int, targetVersion: Int) {
-    realtimeLockQueue.async {
+    realtimeLockQueue.async { [weak self] in
+      guard let self else { return }
       guard attempts > 0 else {
         let error = NSError(domain: RemoteConfigUpdateErrorDomain,
                             code: RemoteConfigUpdateError.notFetched.rawValue,
@@ -468,13 +473,13 @@ class ConfigRealtime: NSObject, URLSessionDataDelegate {
 
   // MARK: - URLSessionDataDelegate
 
+  /// Delegate to asynchronously handle every new notification that comes over
+  /// the wire. Auto-fetches and runs callback for each new notification.
   public func urlSession(_ session: URLSession, dataTask: URLSessionDataTask,
                          didReceive data: Data) {
-    if !session.isEqual(self.session) {
-      return
-    }
-
     let strData = String(data: data, encoding: .utf8) ?? ""
+    // If response data contains the API enablement link, return the entire
+    // message to the user in the form of a error.
     if strData.contains(serverForbiddenStatusCode) {
       let error = NSError(domain: RemoteConfigUpdateErrorDomain,
                           code: RemoteConfigUpdateError.streamError.rawValue,
@@ -496,7 +501,13 @@ class ConfigRealtime: NSObject, URLSessionDataDelegate {
           evaluateStreamResponse(response)
         }
       } catch {
-        propagateErrors(error)
+        let wrappedError = NSError(domain: RemoteConfigUpdateErrorDomain,
+                                   code: RemoteConfigUpdateError.messageInvalid.rawValue,
+                                   userInfo: [
+                                     NSLocalizedDescriptionKey: "Unable to parse ConfigUpdate. \(strData)",
+                                     NSUnderlyingErrorKey: error,
+                                   ])
+        propagateErrors(wrappedError)
         return
       }
     }
@@ -534,13 +545,10 @@ class ConfigRealtime: NSObject, URLSessionDataDelegate {
       statusCode == fetchResponseHTTPStatusCodeGatewayTimeout
   }
 
+  /// Delegate to handle initial reply from the server.
   public func urlSession(_ session: URLSession, dataTask: URLSessionDataTask,
                          didReceive response: URLResponse,
                          completionHandler: @escaping (URLSession.ResponseDisposition) -> Void) {
-    if !session.isEqual(self.session) {
-      completionHandler(.cancel) // Cancel if not current session
-      return
-    }
     isRequestInProgress = false
     if let httpResponse = response as? HTTPURLResponse {
       let statusCode = httpResponse.statusCode
@@ -555,8 +563,6 @@ class ConfigRealtime: NSObject, URLSessionDataDelegate {
 
         if isStatusCodeRetryable(statusCode) {
           retryHTTPConnection()
-          completionHandler(.cancel) // cancel the failing task
-
         } else {
           let error = NSError(
             domain: RemoteConfigUpdateErrorDomain,
@@ -568,16 +574,17 @@ class ConfigRealtime: NSObject, URLSessionDataDelegate {
           )
           RCLog.error("I-RCN000021", "Cannot establish connection. Error: \(error)")
           propagateErrors(error)
-          completionHandler(.cancel) // cancel the failing task
         }
       } else {
+        // On success, reset retry parameters.
         remainingRetryCount = maxRetries
         settings.realtimeRetryCount = 0
-        completionHandler(.allow)
       }
+      completionHandler(.allow)
     }
   }
 
+  /// Delegate to handle data task completion.
   public func urlSession(_ session: URLSession, task: URLSessionTask,
                          didCompleteWithError error: Error?) {
     if !session.isEqual(self.session) {
@@ -591,10 +598,8 @@ class ConfigRealtime: NSObject, URLSessionDataDelegate {
     retryHTTPConnection()
   }
 
+  /// Delegate to handle session invalidation.
   public func urlSession(_ session: URLSession, didBecomeInvalidWithError error: Error?) {
-    if !session.isEqual(self.session) {
-      return
-    }
     if !isRequestInProgress {
       if let _ = error {
         settings.updateRealtimeExponentialBackoffTime()
@@ -608,13 +613,15 @@ class ConfigRealtime: NSObject, URLSessionDataDelegate {
 
   @objc public
   func beginRealtimeStream() {
-    realtimeLockQueue.async {
+    realtimeLockQueue.async { [weak self] in
+      guard let self else { return }
+      guard self.settings.realtimeBackoffInterval() <= 0.0 else {
+        self.retryHTTPConnection()
+        return
+      }
       if self.canMakeConnection() {
-        guard self.settings.realtimeBackoffInterval() <= 0.0 else {
-          self.retryHTTPConnection()
-          return
-        }
-        self.createRequestBody { requestBody in
+        self.createRequestBody { [weak self] requestBody in
+          guard let self else { return }
           var request = self.request
           request.httpBody = requestBody
           self.isRequestInProgress = true
@@ -627,7 +634,8 @@ class ConfigRealtime: NSObject, URLSessionDataDelegate {
 
   @objc public
   func pauseRealtimeStream() {
-    realtimeLockQueue.async {
+    realtimeLockQueue.async { [weak self] in
+      guard let self else { return }
       if let task = self.dataTask {
         task.cancel()
         self.dataTask = nil
@@ -639,7 +647,8 @@ class ConfigRealtime: NSObject, URLSessionDataDelegate {
   @objc public func addConfigUpdateListener(_ listener: @Sendable @escaping (RemoteConfigUpdate?,
                                                                              Error?) -> Void)
     -> ConfigUpdateListenerRegistration {
-    realtimeLockQueue.async {
+    realtimeLockQueue.async { [weak self] in
+      guard let self else { return }
       let temp = self.listeners.mutableCopy() as! NSMutableOrderedSet
       temp.add(listener)
       self.listeners = temp
@@ -650,7 +659,8 @@ class ConfigRealtime: NSObject, URLSessionDataDelegate {
 
   @objc public func removeConfigUpdateListener(_ listener: @escaping (RemoteConfigUpdate?, Error?)
     -> Void) {
-    realtimeLockQueue.async {
+    realtimeLockQueue.async { [weak self] in
+      guard let self else { return }
       let temp: NSMutableOrderedSet = self.listeners.mutableCopy() as! NSMutableOrderedSet
       temp.remove(listener)
       self.listeners = temp