chore(datastore): add subscribe() impl (#4846)

packages/amplify_datastore/ios/Classes/FlutterApiPlugin.swift

@@ -9,8 +9,19 @@ import Combine
 public class FlutterApiPlugin: APICategoryPlugin
 {
     public var key: PluginKey = "awsAPIPlugin"
-    init() {
-
+    private let apiAuthFactory: APIAuthProviderFactory
+    private let nativeApiPlugin: NativeApiPlugin
+    private let nativeSubscriptionEvents: PassthroughSubject<NativeGraphQLSubscriptionResponse, Never>
+    private var cancellables = Set<AnyCancellable>()
+
+    init(
+        apiAuthProviderFactory: APIAuthProviderFactory,
+        nativeApiPlugin: NativeApiPlugin,
+        subscriptionEventBus: PassthroughSubject<NativeGraphQLSubscriptionResponse, Never>
+    ) {
+        self.apiAuthFactory = apiAuthProviderFactory
+        self.nativeApiPlugin = nativeApiPlugin
+        self.nativeSubscriptionEvents = subscriptionEventBus
     }
 
     // TODO: Implment in Async Swift v2
@@ -23,15 +34,97 @@ public class FlutterApiPlugin: APICategoryPlugin
         preconditionFailure("method not supported")
     }
 
-    // TODO: Implment in Async Swift v2
-    public func subscribe<R>(request: GraphQLRequest<R>) -> AmplifyAsyncThrowingSequence<GraphQLSubscriptionEvent<R>> where R : Decodable {
-        preconditionFailure("method not supported")
+    public func subscribe<R: Decodable>(
+        request: GraphQLRequest<R>
+    ) -> AmplifyAsyncThrowingSequence<GraphQLSubscriptionEvent<R>> where R : Decodable {
+        var subscriptionId: String? = ""
+
+        // TODO: write a e2e test to ensure we don't go over 100 AppSync connections
+        func unsubscribe(subscriptionId: String?){
+            if let subscriptionId {
+                DispatchQueue.main.async {
+                    self.nativeApiPlugin.unsubscribe(subscriptionId: subscriptionId) {}
+                }
+            }
+        }
+
+        // TODO: shouldn't there be a timeout if there is no start_ack returned in a certain period of time
+        let (sequence, cancellable) = nativeSubscriptionEvents
+            .receive(on: DispatchQueue.global())
+            .filter { $0.subscriptionId == subscriptionId }
+            .handleEvents(receiveCompletion: {_ in
+                unsubscribe(subscriptionId: subscriptionId)
+            }, receiveCancel: {
+                unsubscribe(subscriptionId: subscriptionId)
+            })
+            .compactMap { [weak self] event -> GraphQLSubscriptionEvent<R>? in
+                switch event.type {
+                    case "connecting":
+                        return .connection(.connecting)
+                    case "start_ack":
+                        return .connection(.connected)
+                    case "complete":
+                        return .connection(.disconnected)
+                    case "data":
+                        if let responseDecoded: GraphQLResponse<R> =
+                            try? self?.decodeGraphQLPayloadJson(request: request, payload: event.payloadJson)
+                        {
+                            return .data(responseDecoded)
+                        }
+                        return nil
+                    case "error":
+                        if let payload = event.payloadJson {
+                            return .data(.fromAppSyncSubscriptionErrorResponse(string: payload))
+                        }
+                    return nil
+                    default:
+                        print("ERROR unsupported subscription event type! \(String(describing: event.type))")
+                        return nil
+                }
+            }
+            .toAmplifyAsyncThrowingSequence()
+        cancellables.insert(cancellable) // the subscription is bind with class instance lifecycle, it should be released when stream is finished or unsubscribed
+        sequence.send(.connection(.connecting))
+        DispatchQueue.main.async {
+            self.nativeApiPlugin.subscribe(request: request.toNativeGraphQLRequest()) { response in
+                subscriptionId = response.subscriptionId
+            }
+        }
+        return sequence
+    }
+
+    private func decodeGraphQLPayloadJson<R>(
+        request: GraphQLRequest<R>,
+        payload: String?
+    ) throws -> GraphQLResponse<R> {
+        guard let payload else {
+            throw DataStoreError.decodingError("Request payload could not be empty", "")
+        }
+
+        return GraphQLResponse<R>.fromAppSyncResponse(
+            string: payload,
+            decodePath: request.decodePath
+        )
+    }
+
+    private func decodeGraphQLSubscriptionPayloadJson<R>(
+        request: GraphQLRequest<R>,
+        payload: String?
+    ) throws -> GraphQLResponse<R> {
+        guard let payload else {
+            throw DataStoreError.decodingError("Request payload could not be empty", "")
+        }
+
+        return GraphQLResponse<R>.fromAppSyncSubscriptionResponse(
+            string: payload,
+            decodePath: request.decodePath
+        )
     }
 
     public func configure(using configuration: Any?) throws { }
 
     public func apiAuthProviderFactory() -> APIAuthProviderFactory {
-        preconditionFailure("method not supported")
+        return self.apiAuthFactory
     }
 
     public func add(interceptor: any URLRequestInterceptor, for apiName: String) throws {
@@ -67,7 +160,7 @@ public class FlutterApiPlugin: APICategoryPlugin
     }
 
     public func reachabilityPublisher() throws -> AnyPublisher<ReachabilityUpdate, Never>? {
-        preconditionFailure("method not supported")
+        return nil
     }
 
 

packages/amplify_datastore/ios/Classes/SwiftAmplifyDataStorePlugin.swift

@@ -14,6 +14,7 @@ public class SwiftAmplifyDataStorePlugin: NSObject, FlutterPlugin, NativeAmplify
     private let customTypeSchemaRegistry: FlutterSchemaRegistry
     private let dataStoreObserveEventStreamHandler: DataStoreObserveEventStreamHandler?
     private let dataStoreHubEventStreamHandler: DataStoreHubEventStreamHandler?
+    private let nativeSubscriptionEventBus = PassthroughSubject<NativeGraphQLSubscriptionResponse, Never>()
     private var channel: FlutterMethodChannel?
     private var observeSubscription: AnyCancellable?
     private let nativeAuthPlugin: NativeAuthPlugin
@@ -88,7 +89,14 @@ public class SwiftAmplifyDataStorePlugin: NSObject, FlutterPlugin, NativeAmplify
                 AWSAuthorizationType(rawValue: $0)
             }
             try Amplify.add(
-                plugin: FlutterApiPlugin()
+                plugin: FlutterApiPlugin(
+                    apiAuthProviderFactory: FlutterAuthProviders(
+                        authProviders: authProviders,
+                        nativeApiPlugin: nativeApiPlugin
+                    ), 
+                    nativeApiPlugin: nativeApiPlugin,
+                    subscriptionEventBus: nativeSubscriptionEventBus
+                )
             )
             return completion(.success(()))
         } catch let apiError as APIError {
@@ -608,7 +616,7 @@ public class SwiftAmplifyDataStorePlugin: NSObject, FlutterPlugin, NativeAmplify
     }
 
     func sendSubscriptionEvent(event: NativeGraphQLSubscriptionResponse, completion: @escaping (Result<Void, any Error>) -> Void) {
-        fatalError("not implemented")
+        nativeSubscriptionEventBus.send(event)
     }
 
     private func checkArguments(args: Any) throws -> [String: Any] {

packages/amplify_datastore/ios/Classes/api/GraphQLRequest+Extension.swift

@@ -0,0 +1,26 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+
+import Foundation
+import Amplify
+
+extension GraphQLRequest {
+    func toNativeGraphQLRequest() -> NativeGraphQLRequest {
+        let variablesJson = self.variables
+            .flatMap { try? JSONSerialization.data(withJSONObject: $0, options: []) }
+            .flatMap { String(data: $0, encoding: .utf8) }
+
+        return NativeGraphQLRequest(
+            document: self.document,
+            apiName: self.apiName,
+            variablesJson: variablesJson ?? "{}",
+            responseType: String(describing: self.responseType),
+            decodePath: self.decodePath
+        )
+    }
+}