diff --git a/example/googleapis/pubspec.yaml b/example/googleapis/pubspec.yaml
index b62fef2..f40d296 100644
--- a/example/googleapis/pubspec.yaml
+++ b/example/googleapis/pubspec.yaml
@@ -7,7 +7,7 @@ environment:
   sdk: '>=1.24.3 <2.0.0'
 
 dependencies:
-  async: ^1.13.3
+  async: '>=1.13.3 <3.0.0'
   grpc:
     path: ../../
   protobuf: ^0.7.0
diff --git a/example/helloworld/pubspec.yaml b/example/helloworld/pubspec.yaml
index e8e2044..764e574 100644
--- a/example/helloworld/pubspec.yaml
+++ b/example/helloworld/pubspec.yaml
@@ -7,7 +7,7 @@ environment:
   sdk: '>=1.24.3 <2.0.0'
 
 dependencies:
-  async: ^1.13.3
+  async: '>=1.13.3 <3.0.0'
   grpc:
     path: ../../
   protobuf: ^0.7.0
diff --git a/example/metadata/pubspec.yaml b/example/metadata/pubspec.yaml
index be2e439..ad2ee4d 100644
--- a/example/metadata/pubspec.yaml
+++ b/example/metadata/pubspec.yaml
@@ -7,7 +7,7 @@ environment:
   sdk: '>=1.24.3 <2.0.0'
 
 dependencies:
-  async: ^1.13.3
+  async: '>=1.13.3 <3.0.0'
   grpc:
     path: ../../
   protobuf: ^0.7.0
diff --git a/example/route_guide/lib/src/common.dart b/example/route_guide/lib/src/common.dart
index c9a0437..f8e5500 100644
--- a/example/route_guide/lib/src/common.dart
+++ b/example/route_guide/lib/src/common.dart
@@ -24,7 +24,7 @@ final List<Feature> featuresDb = _readDatabase();
 
 List<Feature> _readDatabase() {
   final dbData = new File('data/route_guide_db.json').readAsStringSync();
-  final List<Map<String, dynamic>> db = JSON.decode(dbData);
+  final List db = JSON.decode(dbData);
   return db.map((entry) {
     final location = new Point()
       ..latitude = entry['location']['latitude']
diff --git a/example/route_guide/pubspec.yaml b/example/route_guide/pubspec.yaml
index da8edc7..dc661a5 100644
--- a/example/route_guide/pubspec.yaml
+++ b/example/route_guide/pubspec.yaml
@@ -7,7 +7,7 @@ environment:
   sdk: '>=1.24.3 <2.0.0'
 
 dependencies:
-  async: ^1.13.3
+  async: '>=1.13.3 <3.0.0'
   grpc:
     path: ../../
   protobuf: ^0.7.0
diff --git a/interop/bin/server.dart b/interop/bin/server.dart
index f26f6be..b722f77 100644
--- a/interop/bin/server.dart
+++ b/interop/bin/server.dart
@@ -136,6 +136,7 @@ Future<Null> main(List<String> args) async {
     tlsCredentials = new ServerTlsCredentials(
         certificate: await certificate, privateKey: await privateKey);
   }
-  await server.serve(port: port, security: tlsCredentials);
+  await server.serve(
+      address: 'localhost', port: port, security: tlsCredentials);
   print('Server listening on port ${server.port}...');
 }
diff --git a/interop/pubspec.yaml b/interop/pubspec.yaml
index bf2bc2a..37b3472 100644
--- a/interop/pubspec.yaml
+++ b/interop/pubspec.yaml
@@ -8,7 +8,7 @@ environment:
 
 dependencies:
   args: ^0.13.0
-  async: ^1.13.3
+  async: '>=1.13.3 <3.0.0'
   collection: ^1.14.2
   grpc:
     path: ../
diff --git a/lib/src/auth/auth.dart b/lib/src/auth/auth.dart
index fa53ac5..bfb4a34 100644
--- a/lib/src/auth/auth.dart
+++ b/lib/src/auth/auth.dart
@@ -29,7 +29,7 @@ abstract class BaseAuthenticator {
   auth.AccessToken _accessToken;
   String _lastUri;
 
-  Future authenticate(Map<String, String> metadata, String uri) async {
+  Future<Null> authenticate(Map<String, String> metadata, String uri) async {
     if (uri == null) {
       throw new GrpcError.unauthenticated(
           'Credentials require secure transport.');
@@ -54,13 +54,13 @@ abstract class BaseAuthenticator {
 
   CallOptions get toCallOptions => new CallOptions(providers: [authenticate]);
 
-  Future obtainAccessCredentials(String uri);
+  Future<Null> obtainAccessCredentials(String uri);
 }
 
 abstract class HttpBasedAuthenticator extends BaseAuthenticator {
-  Future _call;
+  Future<Null> _call;
 
-  Future obtainAccessCredentials(String uri) {
+  Future<Null> obtainAccessCredentials(String uri) {
     if (_call == null) {
       final authClient = new http.Client();
       _call = obtainCredentialsWithClient(authClient, uri).then((credentials) {
@@ -72,11 +72,13 @@ abstract class HttpBasedAuthenticator extends BaseAuthenticator {
     return _call;
   }
 
-  Future obtainCredentialsWithClient(http.Client client, String uri);
+  Future<auth.AccessCredentials> obtainCredentialsWithClient(
+      http.Client client, String uri);
 }
 
 class ComputeEngineAuthenticator extends HttpBasedAuthenticator {
-  Future obtainCredentialsWithClient(http.Client client, String uri) =>
+  Future<auth.AccessCredentials> obtainCredentialsWithClient(
+          http.Client client, String uri) =>
       auth.obtainAccessCredentialsViaMetadataServer(client);
 }
 
@@ -94,7 +96,8 @@ class ServiceAccountAuthenticator extends HttpBasedAuthenticator {
 
   String get projectId => _projectId;
 
-  Future obtainCredentialsWithClient(http.Client client, String uri) =>
+  Future<auth.AccessCredentials> obtainCredentialsWithClient(
+          http.Client client, String uri) =>
       auth.obtainAccessCredentialsViaServiceAccount(
           _serviceAccountCredentials, _scopes, client);
 }
@@ -114,7 +117,7 @@ class JwtServiceAccountAuthenticator extends BaseAuthenticator {
 
   String get projectId => _projectId;
 
-  Future obtainAccessCredentials(String uri) async {
+  Future<Null> obtainAccessCredentials(String uri) async {
     _accessToken = _jwtTokenFor(_serviceAccountCredentials, _keyId, uri);
   }
 }
diff --git a/lib/src/client/call.dart b/lib/src/client/call.dart
index 8832734..f60132c 100644
--- a/lib/src/client/call.dart
+++ b/lib/src/client/call.dart
@@ -91,7 +91,7 @@ class ClientCall<Q, R> implements Response {
     if (options.metadataProviders.isEmpty) {
       _sendRequest(connection, _sanitizeMetadata(options.metadata));
     } else {
-      final metadata = new Map.from(options.metadata);
+      final metadata = new Map<String, String>.from(options.metadata);
       String audience;
       if (connection.options.credentials.isSecure) {
         final port = connection.port != 443 ? ':${connection.port}' : '';
diff --git a/lib/src/server/handler.dart b/lib/src/server/handler.dart
index 86fb0e6..ef813b9 100644
--- a/lib/src/server/handler.dart
+++ b/lib/src/server/handler.dart
@@ -113,53 +113,13 @@ class ServerHandler extends ServiceCall {
     _startStreamingRequest();
   }
 
-  Future<T> _toSingleFuture<T>(Stream<T> stream) {
-    T _ensureOnlyOneRequest(T previous, T element) {
-      if (previous != null) {
-        throw new GrpcError.unimplemented('More than one request received');
-      }
-      return element;
-    }
-
-    T _ensureOneRequest(T value) {
-      if (value == null)
-        throw new GrpcError.unimplemented('No requests received');
-      return value;
-    }
-
-    final future =
-        stream.fold(null, _ensureOnlyOneRequest).then(_ensureOneRequest);
-    // Make sure errors on the future aren't unhandled, but return the original
-    // future so the request handler can also get the error.
-    future.catchError((_) {});
-    return future;
-  }
-
   void _startStreamingRequest() {
     _incomingSubscription.pause();
-    _requests = new StreamController(
-        onListen: _incomingSubscription.resume,
-        onPause: _incomingSubscription.pause,
-        onResume: _incomingSubscription.resume);
+    _requests = _descriptor.createRequestStream(_incomingSubscription);
     _incomingSubscription.onData(_onDataActive);
 
     _service.$onMetadata(this);
-    if (_descriptor.streamingResponse) {
-      if (_descriptor.streamingRequest) {
-        _responses = _descriptor.handler(this, _requests.stream);
-      } else {
-        _responses =
-            _descriptor.handler(this, _toSingleFuture(_requests.stream));
-      }
-    } else {
-      Future response;
-      if (_descriptor.streamingRequest) {
-        response = _descriptor.handler(this, _requests.stream);
-      } else {
-        response = _descriptor.handler(this, _toSingleFuture(_requests.stream));
-      }
-      _responses = response.asStream();
-    }
+    _responses = _descriptor.handle(this, _requests.stream);
 
     _responseSubscription = _responses.listen(_onResponse,
         onError: _onResponseError,
@@ -213,7 +173,7 @@ class ServerHandler extends ServiceCall {
     final data = message as GrpcData;
     var request;
     try {
-      request = _descriptor.requestDeserializer(data.data);
+      request = _descriptor.deserialize(data.data);
     } catch (error) {
       final grpcError =
           new GrpcError.internal('Error deserializing request: $error');
@@ -231,7 +191,7 @@ class ServerHandler extends ServiceCall {
 
   void _onResponse(response) {
     try {
-      final bytes = _descriptor.responseSerializer(response);
+      final bytes = _descriptor.serialize(response);
       if (!_headersSent) {
         sendHeaders();
       }
diff --git a/lib/src/server/service.dart b/lib/src/server/service.dart
index 5630686..26d869c 100644
--- a/lib/src/server/service.dart
+++ b/lib/src/server/service.dart
@@ -13,6 +13,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+import 'dart:async';
+
+import '../shared/status.dart';
 import 'call.dart';
 
 /// Definition of a gRPC service method.
@@ -34,6 +37,56 @@ class ServiceMethod<Q, R> {
       this.streamingResponse,
       this.requestDeserializer,
       this.responseSerializer);
+
+  StreamController<Q> createRequestStream(StreamSubscription incoming) =>
+      new StreamController<Q>(
+          onListen: incoming.resume,
+          onPause: incoming.pause,
+          onResume: incoming.resume);
+
+  Q deserialize(List<int> data) => requestDeserializer(data);
+
+  List<int> serialize(dynamic response) => responseSerializer(response as R);
+
+  Stream<R> handle(ServiceCall call, Stream<Q> requests) {
+    if (streamingResponse) {
+      if (streamingRequest) {
+        return handler(call, requests);
+      } else {
+        return handler(call, _toSingleFuture(requests));
+      }
+    } else {
+      Future<R> response;
+      if (streamingRequest) {
+        response = handler(call, requests);
+      } else {
+        response = handler(call, _toSingleFuture(requests));
+      }
+      return response.asStream();
+    }
+  }
+
+  Future<Q> _toSingleFuture(Stream<Q> stream) {
+    Q _ensureOnlyOneRequest(Q previous, Q element) {
+      if (previous != null) {
+        throw new GrpcError.unimplemented('More than one request received');
+      }
+      return element;
+    }
+
+    Q _ensureOneRequest(Q value) {
+      if (value == null)
+        throw new GrpcError.unimplemented('No requests received');
+      return value;
+    }
+
+    final future =
+        stream.fold(null, _ensureOnlyOneRequest).then(_ensureOneRequest);
+    // Make sure errors on the future aren't unhandled, but return the original
+    // future so the request handler can also get the error.
+    future.catchError((_) {});
+    return future;
+  }
 }
 
 /// Definition of a gRPC service.