Added interceptors. (#86)

* Add draft implementation of interceptors.

* Fix review comment.

* Revert example files.

* Revert interop files.

* Revert interop files.

* Format.

* Fix typos.

AUTHORS

@@ -4,3 +4,4 @@
 #   Name/Organization <email address>
 
 Google Inc.
+German Saprykin <saprykin.h@gmail.com>

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.5.0 - 2018-06-29
+
+* Implemented interceptors.
+
 ## 0.4.1 - 2018-04-04
 
 * Fixes for supporting Dart 2.

lib/grpc.dart

@@ -25,6 +25,7 @@ export 'src/client/options.dart';
 
 export 'src/server/call.dart';
 export 'src/server/handler.dart';
+export 'src/server/interceptor.dart';
 export 'src/server/server.dart';
 export 'src/server/service.dart';
 

lib/src/server/handler.dart

@@ -22,12 +22,14 @@ import '../shared/streams.dart';
 import '../shared/timeout.dart';
 
 import 'call.dart';
+import 'interceptor.dart';
 import 'service.dart';
 
 /// Handles an incoming gRPC call.
 class ServerHandler extends ServiceCall {
   final ServerTransportStream _stream;
   final Service Function(String service) _serviceLookup;
+  final List<Interceptor> _interceptors;
 
   StreamSubscription<GrpcMessage> _incomingSubscription;
 
@@ -51,14 +53,19 @@ class ServerHandler extends ServiceCall {
   bool _isTimedOut = false;
   Timer _timeoutTimer;
 
-  ServerHandler(this._serviceLookup, this._stream);
+  ServerHandler(this._serviceLookup, this._stream,
+      [this._interceptors = const <Interceptor>[]]);
 
   DateTime get deadline => _deadline;
+
   bool get isCanceled => _isCanceled;
+
   bool get isTimedOut => _isTimedOut;
 
   Map<String, String> get clientMetadata => _clientMetadata;
+
   Map<String, String> get headers => _customHeaders;
+
   Map<String, String> get trailers => _customTrailers;
 
   void handle() {
@@ -103,6 +110,7 @@ class ServerHandler extends ServiceCall {
     }
     final serviceName = pathSegments[1];
     final methodName = pathSegments[2];
+
     _service = _serviceLookup(serviceName);
     _descriptor = _service?.$lookupMethod(methodName);
     if (_descriptor == null) {
@@ -110,9 +118,32 @@ class ServerHandler extends ServiceCall {
       _sinkIncoming();
       return;
     }
+
+    final error = _applyInterceptors();
+    if (error != null) {
+      _sendError(error);
+      _sinkIncoming();
+      return;
+    }
+
     _startStreamingRequest();
   }
 
+  GrpcError _applyInterceptors() {
+    try {
+      for (final interceptor in _interceptors) {
+        final error = interceptor(this, this._descriptor);
+        if (error != null) {
+          return error;
+        }
+      }
+    } catch (error) {
+      final grpcError = new GrpcError.internal(error.toString());
+      return grpcError;
+    }
+    return null;
+  }
+
   void _startStreamingRequest() {
     _incomingSubscription.pause();
     _requests = _descriptor.createRequestStream(_incomingSubscription);

lib/src/server/interceptor.dart

@@ -0,0 +1,13 @@
+import '../shared/status.dart';
+
+import 'call.dart';
+import 'service.dart';
+
+/// A gRPC Interceptor.
+///
+/// An interceptor is called before the corresponding [ServiceMethod] invocation.
+/// If the interceptor returns a [GrpcError], the error will be returned as a response and [ServiceMethod] wouldn't be called.
+/// If the interceptor throws [Exception], [GrpcError.internal] with exception.toString() will be returned.
+/// If the interceptor returns null, the corresponding [ServiceMethod] of [Service] will be called.
+typedef Interceptor = GrpcError Function(
+    ServiceCall call, ServiceMethod method);

lib/src/server/server.dart

@@ -21,6 +21,7 @@ import 'package:http2/transport.dart';
 import '../shared/security.dart';
 
 import 'handler.dart';
+import 'interceptor.dart';
 import 'service.dart';
 
 class ServerTlsCredentials {
@@ -57,13 +58,16 @@ class ServerTlsCredentials {
 /// Listens for incoming RPCs, dispatching them to the right [Service] handler.
 class Server {
   final Map<String, Service> _services = {};
+  final List<Interceptor> _interceptors;
 
   ServerSocket _insecureServer;
   SecureServerSocket _secureServer;
   final _connections = <ServerTransportConnection>[];
 
   /// Create a server for the given [services].
-  Server(List<Service> services) {
+  Server(List<Service> services,
+      [List<Interceptor> interceptors = const <Interceptor>[]])
+      : _interceptors = interceptors {
     for (final service in services) {
       _services[service.$name] = service;
     }
@@ -110,7 +114,7 @@ class Server {
   }
 
   void serveStream(ServerTransportStream stream) {
-    new ServerHandler(lookupService, stream).handle();
+    new ServerHandler(lookupService, stream, _interceptors).handle();
   }
 
   Future<Null> shutdown() async {

pubspec.yaml

@@ -1,6 +1,6 @@
 name: grpc
 description: Dart implementation of gRPC.
-version: 0.4.1
+version: 0.5.0
 author: Dart Team <misc@dartlang.org>
 homepage: https://github.com/dart-lang/grpc-dart
 

test/server_test.dart

@@ -277,4 +277,60 @@ void main() {
       ..toServer.close();
     await harness.fromServer.done;
   });
+
+  group('Server with interceptor', () {
+    test('processes calls if interceptor allows request', () async {
+      const expectedRequest = 5;
+      const expectedResponse = 7;
+      Future<int> methodHandler(ServiceCall call, Future<int> request) async {
+        expect(await request, expectedRequest);
+        return expectedResponse;
+      }
+
+      GrpcError interceptorHandler(ServiceCall call, ServiceMethod method) {
+        if (method.name == "Unary") {
+          return null;
+        }
+        return new GrpcError.unauthenticated('Request is unauthenticated');
+      }
+
+      harness
+        ..interceptor.handler = interceptorHandler
+        ..service.unaryHandler = methodHandler
+        ..runTest('/Test/Unary', [expectedRequest], [expectedResponse]);
+
+      await harness.fromServer.done;
+    });
+
+    test('returns error if interceptor blocks request', () async {
+      GrpcError interceptorHandler(ServiceCall call, ServiceMethod method) {
+        if (method.name == "Unary") {
+          return new GrpcError.unauthenticated('Request is unauthenticated');
+        }
+        return null;
+      }
+
+      harness
+        ..interceptor.handler = interceptorHandler
+        ..expectErrorResponse(
+            StatusCode.unauthenticated, 'Request is unauthenticated')
+        ..sendRequestHeader('/Test/Unary');
+
+      await harness.fromServer.done;
+    });
+
+    test('returns internal error if interceptor throws exception', () async {
+      GrpcError interceptorHandler(ServiceCall call, ServiceMethod method) {
+        throw new Exception('Reason is unknown');
+      }
+
+      harness
+        ..interceptor.handler = interceptorHandler
+        ..expectErrorResponse(
+            StatusCode.internal, 'Exception: Reason is unknown')
+        ..sendRequestHeader('/Test/Unary');
+
+      await harness.fromServer.done;
+    });
+  });
 }

test/src/server_utils.dart

@@ -78,6 +78,18 @@ class TestService extends Service {
   }
 }
 
+class TestInterceptor {
+  Interceptor handler;
+
+  GrpcError call(ServiceCall call, ServiceMethod method) {
+    if (handler == null) {
+      return null;
+    }
+
+    return handler(call, method);
+  }
+}
+
 class TestServerStream extends ServerTransportStream {
   final Stream<StreamMessage> incomingMessages;
   final StreamSink<StreamMessage> outgoingMessages;
@@ -107,10 +119,12 @@ class ServerHarness {
   final toServer = new StreamController<StreamMessage>();
   final fromServer = new StreamController<StreamMessage>();
   final service = new TestService();
+  final interceptor = new TestInterceptor();
+
   Server server;
 
   ServerHarness() {
-    server = new Server([service]);
+    server = new Server(<Service>[service], <Interceptor>[interceptor]);
   }
 
   static ServiceMethod<int, int> createMethod(String name,