refactoring http_server example to use async/await

R=lrn@google.com

Review URL: https://codereview.chromium.org//1033843002

example/http_server.dart

@@ -15,25 +15,24 @@ import "package:isolate/runner.dart";
 typedef Future RemoteStop();
 
 Future<RemoteStop> runHttpServer(
-    Runner runner, ServerSocket socket, HttpListener listener) {
-  return runner.run(_startHttpServer, new List(2)..[0] = socket.reference
-                                                 ..[1] = listener)
-               .then((SendPort stopPort) => () => _sendStop(stopPort));
-}
+    Runner runner, int port, HttpListener listener) async {
+  var stopPort = await runner.run(_startHttpServer, [port, listener]);
 
-Future _sendStop(SendPort stopPort) {
-  return singleResponseFuture(stopPort.send);
+  return () => _sendStop(stopPort);
 }
 
-Future<SendPort> _startHttpServer(List args) {
-  ServerSocketReference ref = args[0];
+Future _sendStop(SendPort stopPort) => singleResponseFuture(stopPort.send);
+
+Future<SendPort> _startHttpServer(List args) async {
+  int port = args[0];
   HttpListener listener = args[1];
-  return ref.create().then((socket) {
-    return listener.start(new HttpServer.listenOn(socket));
-  }).then((_) {
-    return singleCallbackPort((SendPort resultPort) {
-      sendFutureResult(new Future.sync(listener.stop), resultPort);
-    });
+
+  var server =
+      await HttpServer.bind(InternetAddress.ANY_IP_V6, port, shared: true);
+  await listener.start(server);
+
+  return singleCallbackPort((SendPort resultPort) {
+    sendFutureResult(new Future.sync(listener.stop), resultPort);
   });
 }
 
@@ -52,65 +51,79 @@ abstract class HttpListener {
 /// Returns the message content plus an ID describing the isolate that
 /// handled the request.
 class EchoHttpListener implements HttpListener {
+  static const _delay = const Duration(seconds: 2);
+  static final _id = Isolate.current.hashCode;
+  final SendPort _counter;
+
   StreamSubscription _subscription;
-  static int _id = new Object().hashCode;
-  SendPort _counter;
 
   EchoHttpListener(this._counter);
 
-  start(HttpServer server) {
+  Future start(HttpServer server) async {
     print("Starting isolate $_id");
-    _subscription = server.listen((HttpRequest request) {
-      request.response.addStream(request).then((_) {
-        _counter.send(null);
-        print("Request to $_id");
-        request.response.write("#$_id\n");
-        var t0 = new DateTime.now().add(new Duration(seconds: 2));
-        while (new DateTime.now().isBefore(t0));
-        print("Response from $_id");
-        request.response.close();
-      });
+    _subscription = server.listen((HttpRequest request) async {
+      await request.response.addStream(request);
+      print("Request to $hashCode");
+      request.response.write("#$_id\n");
+      var watch = new Stopwatch()..start();
+      while (watch.elapsed < _delay);
+      print("Response from $_id");
+      await request.response.close();
+      _counter.send(null);
     });
   }
 
-  stop() {
+  Future stop() async {
     print("Stopping isolate $_id");
-    _subscription.cancel();
+    await _subscription.cancel();
     _subscription = null;
   }
 }
 
-main(args) {
+main(List<String> args) async {
   int port = 0;
   if (args.length > 0) {
     port = int.parse(args[0]);
   }
-  RawReceivePort counter = new RawReceivePort();
+
+  var counter = new ReceivePort();
   HttpListener listener = new EchoHttpListener(counter.sendPort);
-  ServerSocket
-    .bind(InternetAddress.ANY_IP_V6, port)
-    .then((ServerSocket socket) {
-      port = socket.port;
-      return Future.wait(new Iterable.generate(5, (_) => IsolateRunner.spawn()),
-                         cleanUp: (isolate) { isolate.close(); })
-                   .then((List<IsolateRunner> isolates) {
-                     return Future.wait(isolates.map((IsolateRunner isolate) {
-                       return runHttpServer(isolate, socket, listener);
-                     }), cleanUp: (server) { server.stop(); });
-                   })
-                   .then((stoppers) {
-                     socket.close();
-                     int count = 25;
-                     counter.handler = (_) {
-                       count--;
-                       if (count == 0) {
-                         stoppers.forEach((f) => f());
-                         counter.close();
-                       }
-                     };
-                     print("Server listening on port $port for 25 requests");
-                     print("Test with:");
-                     print("  ab -c10 -n 25  http://localhost:$port/");
-                   });
+
+  // Used to ensure the requested port is available or to find an available
+  // port if `0` is provided.
+  ServerSocket socket =
+      await ServerSocket.bind(InternetAddress.ANY_IP_V6, port, shared: true);
+
+  port = socket.port;
+  var isolates = await Future.wait(
+      new Iterable.generate(5, (_) => IsolateRunner.spawn()),
+      cleanUp: (isolate) {
+    isolate.close();
+  });
+
+  List<RemoteStop> stoppers = await Future.wait(isolates
+      .map((IsolateRunner isolate) {
+    return runHttpServer(isolate, socket.port, listener);
+  }), cleanUp: (server) {
+    server.stop();
   });
+
+  await socket.close();
+  int count = 25;
+
+  print("Server listening on port $port for $count requests");
+  print("Test with:");
+  print("  ab -l -c10 -n $count http://localhost:$port/");
+
+  await for (var event in counter) {
+    count--;
+    if (count == 0) {
+      print('Shutting down');
+      for (var stopper in stoppers) {
+        await stopper();
+      }
+      counter.close();
+    }
+  }
+  print('Finished');
 }