Add AsyncStream support for Remote Config

FirebaseRemoteConfig/CHANGELOG.md

@@ -1,3 +1,9 @@
+# Unreleased
+- [added] Introduced a new `updates` property to `RemoteConfig` that
+  provides an `AsyncThrowingStream` for consuming real-time config updates.
+  This offers a modern, Swift Concurrency-native alternative to the existing
+  closure-based listener.
+
 # 12.3.0
 - [fixed] Add missing GoogleUtilities dependency to fix SwiftPM builds when
   building dynamically linked libraries. (#15276)

FirebaseRemoteConfig/Swift/RemoteConfig+Async.swift

@@ -0,0 +1,72 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import Foundation
+
+@available(iOS 13.0.0, macOS 10.15.0, macCatalyst 13.0.0, tvOS 13.0.0, watchOS 7.0.0, *)
+public extension RemoteConfig {
+  /// Returns an `AsyncThrowingStream` that provides real-time updates to the configuration.
+  ///
+  /// You can listen for updates by iterating over the stream using a `for try await` loop.
+  /// The stream will yield a `RemoteConfigUpdate` whenever a change is pushed from the
+  /// Remote Config backend. After receiving an update, you must call `activate()` to make the
+  /// new configuration available to your app.
+  ///
+  /// The underlying listener is automatically added when you begin iterating and is removed when
+  /// the iteration is cancelled or finishes.
+  ///
+  /// - Throws: `RemoteConfigUpdateError` if the listener encounters a server-side error or another
+  ///           issue, causing the stream to terminate.
+  ///
+  /// ### Example Usage
+  ///
+  /// ```swift
+  /// func listenForRealtimeUpdates() {
+  ///   Task {
+  ///     do {
+  ///       for try await configUpdate in remoteConfig.configUpdates {
+  ///         print("Updated keys: \(configUpdate.updatedKeys)")
+  ///         // Activate the new config to make it available
+  ///         let status = try await remoteConfig.activate()
+  ///         print("Config activated with status: \(status)")
+  ///       }
+  ///     } catch {
+  ///       print("Error listening for remote config updates: \(error)")
+  ///     }
+  ///   }
+  /// }
+  /// ```
+  @available(iOS 18.0, *)
+  var configUpdates: some AsyncSequence<RemoteConfigUpdate, Error> {
+    AsyncThrowingStream { continuation in
+      let listener = addOnConfigUpdateListener { update, error in
+        switch (update, error) {
+        case let (update?, _):
+          // If there's an update, yield it. We prioritize the update over a potential error.
+          continuation.yield(update)
+        case let (_, error?):
+          // If there's no update but there is an error, terminate the stream with the error.
+          continuation.finish(throwing: error)
+        case (nil, nil):
+          // If both are nil (the "should not happen" case), gracefully finish the stream.
+          continuation.finish()
+        }
+      }
+
+      continuation.onTermination = { @Sendable _ in
+        listener.remove()
+      }
+    }
+  }
+}

FirebaseRemoteConfig/Tests/Swift/SwiftAPI/AsyncSequenceTests.swift

@@ -0,0 +1,241 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import FirebaseCore
+@testable import FirebaseRemoteConfig
+import XCTest
+
+#if SWIFT_PACKAGE
+  import RemoteConfigFakeConsoleObjC
+#endif
+
+// MARK: - Mock Objects for Testing
+
+/// A mock listener registration that allows tests to verify that its `remove()` method was called.
+class MockListenerRegistration: ConfigUpdateListenerRegistration, @unchecked Sendable {
+  var wasRemoveCalled = false
+  override func remove() {
+    wasRemoveCalled = true
+  }
+}
+
+/// A mock for the RCNConfigRealtime component that allows tests to control the config update
+/// listener.
+class MockRealtime: RCNConfigRealtime, @unchecked Sendable {
+  /// The listener closure captured from the `configUpdates` async stream.
+  var listener: ((RemoteConfigUpdate?, Error?) -> Void)?
+  let mockRegistration = MockListenerRegistration()
+  var listenerAttachedExpectation: XCTestExpectation?
+
+  override func addConfigUpdateListener(_ listener: @escaping (RemoteConfigUpdate?, Error?)
+    -> Void) -> ConfigUpdateListenerRegistration {
+    self.listener = listener
+    listenerAttachedExpectation?.fulfill()
+    return mockRegistration
+  }
+
+  /// Simulates the backend sending a successful configuration update.
+  func sendUpdate(keys: [String]) {
+    let update = RemoteConfigUpdate(updatedKeys: Set(keys))
+    listener?(update, nil)
+  }
+
+  /// Simulates the backend sending an error.
+  func sendError(_ error: Error) {
+    listener?(nil, error)
+  }
+
+  /// Simulates the listener completing without an update or error.
+  func sendCompletion() {
+    listener?(nil, nil)
+  }
+}
+
+// MARK: - AsyncSequenceTests
+
+@available(iOS 13, tvOS 13, macOS 10.15, macCatalyst 13, watchOS 7, *)
+class AsyncSequenceTests: XCTestCase {
+  var app: FirebaseApp!
+  var config: RemoteConfig!
+  var mockRealtime: MockRealtime!
+
+  struct TestError: Error, Equatable {}
+
+  override func setUpWithError() throws {
+    try super.setUpWithError()
+
+    // Perform one-time setup of the FirebaseApp for testing.
+    if FirebaseApp.app() == nil {
+      let options = FirebaseOptions(googleAppID: "1:123:ios:123abc",
+                                    gcmSenderID: "correct_gcm_sender_id")
+      options.apiKey = "A23456789012345678901234567890123456789"
+      options.projectID = "Fake_Project"
+      FirebaseApp.configure(options: options)
+    }
+
+    app = FirebaseApp.app()!
+    config = RemoteConfig.remoteConfig(app: app)
+
+    // Install the mock realtime service.
+    mockRealtime = MockRealtime()
+    config.configRealtime = mockRealtime
+  }
+
+  override func tearDownWithError() throws {
+    app = nil
+    config = nil
+    mockRealtime = nil
+    try super.tearDownWithError()
+  }
+
+  func testSequenceYieldsUpdate_whenUpdateIsSent() async throws {
+    let expectation = self.expectation(description: "Sequence should yield an update.")
+    let keysToUpdate = ["foo", "bar"]
+
+    let listenerAttachedExpectation = self.expectation(description: "Listener should be attached.")
+    mockRealtime.listenerAttachedExpectation = listenerAttachedExpectation
+
+    let listeningTask = Task {
+      for try await update in config.configUpdates {
+        XCTAssertEqual(update.updatedKeys, Set(keysToUpdate))
+        expectation.fulfill()
+        break // End the loop after receiving the expected update.
+      }
+    }
+
+    // Wait for the listener to be attached before sending the update.
+    await fulfillment(of: [listenerAttachedExpectation], timeout: 1.0)
+
+    mockRealtime.sendUpdate(keys: keysToUpdate)
+
+    await fulfillment(of: [expectation], timeout: 1.0)
+    listeningTask.cancel()
+  }
+
+  func testSequenceFinishes_whenErrorIsSent() async throws {
+    let expectation = self.expectation(description: "Sequence should throw an error.")
+    let testError = TestError()
+
+    let listenerAttachedExpectation = self.expectation(description: "Listener should be attached.")
+    mockRealtime.listenerAttachedExpectation = listenerAttachedExpectation
+
+    let listeningTask = Task {
+      do {
+        for try await _ in config.configUpdates {
+          XCTFail("Stream should not have yielded any updates.")
+        }
+      } catch {
+        XCTAssertEqual(error as? TestError, testError)
+        expectation.fulfill()
+      }
+    }
+
+    // Wait for the listener to be attached before sending the error.
+    await fulfillment(of: [listenerAttachedExpectation], timeout: 1.0)
+
+    mockRealtime.sendError(testError)
+
+    await fulfillment(of: [expectation], timeout: 1.0)
+    listeningTask.cancel()
+  }
+
+  func testSequenceCancellation_callsRemoveOnListener() async throws {
+    let listenerAttachedExpectation = expectation(description: "Listener should be attached.")
+    mockRealtime.listenerAttachedExpectation = listenerAttachedExpectation
+
+    let listeningTask = Task {
+      for try await _ in config.configUpdates {
+        // We will cancel the task, so it should not reach here.
+      }
+    }
+
+    // Wait for the listener to be attached.
+    await fulfillment(of: [listenerAttachedExpectation], timeout: 1.0)
+
+    // Verify the listener has not been removed yet.
+    XCTAssertFalse(mockRealtime.mockRegistration.wasRemoveCalled)
+
+    // Cancel the task, which should trigger the stream's onTermination handler.
+    listeningTask.cancel()
+
+    // Give the cancellation a moment to propagate.
+    try await Task.sleep(nanoseconds: 100_000_000) // 0.1 seconds
+
+    // Verify the listener was removed.
+    XCTAssertTrue(mockRealtime.mockRegistration.wasRemoveCalled)
+  }
+
+  func testSequenceFinishesGracefully_whenListenerSendsNil() async throws {
+    let expectation = self.expectation(description: "Sequence should finish without error.")
+
+    let listenerAttachedExpectation = self.expectation(description: "Listener should be attached.")
+    mockRealtime.listenerAttachedExpectation = listenerAttachedExpectation
+
+    let listeningTask = Task {
+      var updateCount = 0
+      do {
+        for try await _ in config.configUpdates {
+          updateCount += 1
+        }
+        // The loop finished without throwing, which is the success condition.
+        XCTAssertEqual(updateCount, 0, "No updates should have been received.")
+        expectation.fulfill()
+      } catch {
+        XCTFail("Stream should not have thrown an error, but threw \(error).")
+      }
+    }
+
+    await fulfillment(of: [listenerAttachedExpectation], timeout: 1.0)
+    mockRealtime.sendCompletion()
+
+    await fulfillment(of: [expectation], timeout: 1.0)
+    listeningTask.cancel()
+  }
+
+  func testSequenceYieldsMultipleUpdates_whenMultipleUpdatesAreSent() async throws {
+    let expectation = self.expectation(description: "Sequence should receive two updates.")
+    expectation.expectedFulfillmentCount = 2
+
+    let updatesToSend = [
+      Set(["key1", "key2"]),
+      Set(["key3"]),
+    ]
+    var receivedUpdates: [Set<String>] = []
+
+    let listenerAttachedExpectation = self.expectation(description: "Listener should be attached.")
+    mockRealtime.listenerAttachedExpectation = listenerAttachedExpectation
+
+    let listeningTask = Task {
+      for try await update in config.configUpdates {
+        receivedUpdates.append(update.updatedKeys)
+        expectation.fulfill()
+        if receivedUpdates.count == updatesToSend.count {
+          break
+        }
+      }
+      return receivedUpdates
+    }
+
+    await fulfillment(of: [listenerAttachedExpectation], timeout: 1.0)
+
+    mockRealtime.sendUpdate(keys: Array(updatesToSend[0]))
+    mockRealtime.sendUpdate(keys: Array(updatesToSend[1]))
+
+    await fulfillment(of: [expectation], timeout: 2.0)
+
+    let finalUpdates = try await listeningTask.value
+    XCTAssertEqual(finalUpdates, updatesToSend)
+    listeningTask.cancel()
+  }
+}