Extract out a StreamManager class from json_rpc.Server.

pkg/json_rpc_2/lib/src/server.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library json_rpc_2.server;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
 
 import 'package:stack_trace/stack_trace.dart';
 
 import '../error_code.dart' as error_code;
 import 'exception.dart';
 import 'parameters.dart';
+import 'two_way_stream.dart';
 import 'utils.dart';
 
 /// A JSON-RPC 2.0 server.
 ///
 /// A server exposes methods that are called by requests, to which it provides
 /// responses. Methods can be registered using [registerMethod] and
 /// [registerFallback]. Requests can be handled using [handleRequest] and
 /// [parseRequest].
 ///
 /// Note that since requests can arrive asynchronously and methods can run
 /// asynchronously, it's possible for multiple methods to be invoked at the same
 /// time, or even for a single method to be invoked multiple times at once.
 class Server {
-  /// The stream for decoded requests.
-  final Stream _requests;
-
-  /// The subscription to the decoded request stream.
-  StreamSubscription _requestSubscription;
-
-  /// The sink for decoded responses.
-  final StreamSink _responses;
-
-  /// The completer for [listen].
-  ///
-  /// This is non-`null` after [listen] has been called.
-  Completer _listenCompleter;
+  TwoWayStream _streams;
 
   /// The methods registered for this server.
   final _methods = new Map<String, Function>();
 
   /// The fallback methods for this server.
   ///
   /// These are tried in order until one of them doesn't throw a
   /// [RpcException.methodNotFound] exception.
   final _fallbacks = new Queue<Function>();
 
   /// Creates a [Server] that reads requests from [requests] and writes
   /// responses to [responses].
   ///
   /// If [requests] is a [StreamSink] as well as a [Stream] (for example, a
   /// `WebSocket`), [responses] may be omitted.
   ///
   /// Note that the server won't begin listening to [requests] until
   /// [Server.listen] is called.
-  factory Server(Stream<String> requests, [StreamSink<String> responses]) {
-    if (responses == null) {
-      if (requests is! StreamSink) {
-        throw new ArgumentError("Either `requests` must be a StreamSink or "
-            "`responses` must be passed.");
-      }
-      responses = requests as StreamSink;
-    }
-
-    var wrappedResponses = mapStreamSink(responses, JSON.encode);
-    return new Server.withoutJson(requests.expand((request) {
-      var decodedRequest;
-      try {
-        decodedRequest = JSON.decode(request);
-      } on FormatException catch (error) {
-        wrappedResponses.add(new RpcException(error_code.PARSE_ERROR,
-            'Invalid JSON: ${error.message}').serialize(request));
-        return [];
-      }
-
-      return [decodedRequest];
-    }), wrappedResponses);
+  Server(Stream<String> requests, [StreamSink<String> responses]) {
+    _streams = new TwoWayStream("Server", requests, "requests",
+        responses, "responses", onInvalidInput: (message, error) {
+      _streams.add(new RpcException(error_code.PARSE_ERROR,
+          'Invalid JSON: ${error.message}').serialize(message));
+    });
   }
 
   /// Creates a [Server] that reads decoded requests from [requests] and writes
   /// decoded responses to [responses].
   ///
   /// Unlike [new Server], this doesn't read or write JSON strings. Instead, it
   /// reads and writes decoded maps or lists.
   ///
   /// If [requests] is a [StreamSink] as well as a [Stream], [responses] may be
   /// omitted.
   ///
   /// Note that the server won't begin listening to [requests] until
   /// [Server.listen] is called.
   Server.withoutJson(Stream requests, [StreamSink responses])
-      : _requests = requests,
-        _responses = responses == null && requests is StreamSink ?
-            requests : responses {
-    if (_responses == null) {
-      throw new ArgumentError("Either `requests` must be a StreamSink or "
-          "`responses` must be passed.");
-    }
-  }
+      : _streams = new TwoWayStream.withoutJson(
+            "Server", requests, "requests", responses, "responses");
 
   /// Starts listening to the underlying stream.
   ///
   /// Returns a [Future] that will complete when the stream is closed or when it
   /// has an error.
   ///
   /// [listen] may only be called once.
-  Future listen() {
-    if (_listenCompleter != null) {
-      throw new StateError(
-          "Can only call Server.listen once on a given server.");
-    }
-
-    _listenCompleter = new Completer();
-    _requestSubscription = _requests.listen(_handleRequest,
-        onError: (error, stackTrace) {
-      if (_listenCompleter.isCompleted) return;
-      _responses.close();
-      _listenCompleter.completeError(error, stackTrace);
-    }, onDone: () {
-      if (_listenCompleter.isCompleted) return;
-      _responses.close();
-      _listenCompleter.complete();
-    }, cancelOnError: true);
-
-    return _listenCompleter.future;
-  }
+  Future listen() => _streams.listen(_handleRequest);
 
   /// Closes the server's request subscription and response sink.
   ///
   /// Returns a [Future] that completes when all resources have been released.
   ///
   /// A server can't be closed before [listen] has been called.
-  Future close() {
-    if (_listenCompleter == null) {
-      throw new StateError("Can't call Server.close before Server.listen.");
-    }
-
-    if (!_listenCompleter.isCompleted) _listenCompleter.complete();
-
-    var subscriptionFuture = _requestSubscription.cancel();
-    // TODO(nweiz): include the response future in the return value when issue
-    // 19095 is fixed.
-    _responses.close();
-    return subscriptionFuture == null ? new Future.value() : subscriptionFuture;
-  }
+  Future close() => _streams.close();
 
   /// Registers a method named [name] on this server.
   ///
   /// [callback] can take either zero or one arguments. If it takes zero, any
   /// requests for that method that include parameters will be rejected. If it
   /// takes one, it will be passed a [Parameters] object.
   ///
   /// [callback] can return either a JSON-serializable object or a Future that
   /// completes to a JSON-serializable object. Any errors in [callback] will be
   /// reported to the client as JSON-RPC 2.0 errors.
@@ skipping 32 matching lines @@
       if (request is! List) return _handleSingleRequest(request);
       if (request.isEmpty) {
         return new RpcException(error_code.INVALID_REQUEST, 'A batch must '
             'contain at least one request.').serialize(request);
       }
 
       return Future.wait(request.map(_handleSingleRequest)).then((results) {
         var nonNull = results.where((result) => result != null);
         return nonNull.isEmpty ? null : nonNull.toList();
       });
-    }).then(_responses.add);
+    }).then(_streams.add);
   }
 
   /// Handles an individual parsed request.
   Future _handleSingleRequest(request) {
     return syncFuture(() {
       _validateRequest(request);
 
       var name = request['method'];
       var method = _methods[name];
       if (method == null) method = _tryFallbacks;
@@ skipping 88 matching lines @@
       return syncFuture(() => iterator.current(params)).catchError((error) {
         if (error is! RpcException) throw error;
         if (error.code != error_code.METHOD_NOT_FOUND) throw error;
         return _tryNext();
       });
     }
 
     return _tryNext();
   }
 }