Add admin server that supports web socket API.

sdk/lib/_internal/pub/lib/src/barback/admin_server.dart

Index: sdk/lib/_internal/pub/lib/src/barback/admin_server.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/admin_server.dart b/sdk/lib/_internal/pub/lib/src/barback/admin_server.dart
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+// 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 pub.barback.admin_server;
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:stack_trace/stack_trace.dart';
+
+import '../log.dart' as log;
+import 'base_server.dart';
+import 'build_environment.dart';
+import 'web_socket_api.dart';
+
+/// The web admin interface to pub serve.
+// TODO(rnystrom): Currently this just provides access to the Web Socket API.
+// See #16954.
+class AdminServer extends BaseServer {
+  /// All currently open [WebSocket] connections.
+  final _webSockets = new Set<WebSocket>();
+
+  /// Creates a new server and binds it to [port] of [host].
+  static Future<AdminServer> bind(BuildEnvironment environment,
+      String host, int port) {
+    return Chain.track(HttpServer.bind(host, port)).then((server) {
+      log.fine('Bound admin server to $host:$port.');
+      return new AdminServer._(environment, server);
+    });
+  }
+
+  AdminServer._(BuildEnvironment environment, HttpServer server)
+      : super(environment, server);
+
+  /// Closes the server and all Web Socket connections.
+  Future close() {
+    var futures = [super.close()];
+    futures.addAll(_webSockets.map((socket) => socket.close()));
+    return Future.wait(futures);
+  }
+
+  /// Handles an HTTP request.
+  void handleRequest(HttpRequest request) {
+    if (WebSocketTransformer.isUpgradeRequest(request)) {
+      _handleWebSocket(request);
+      return;
+    }
+
+    // TODO(rnystrom): Actually respond to requests once there is an admin
+    // interface. See #16954.
+    logRequest(request, "501 Not Implemented");
+    request.response.headers.contentType =
+        ContentType.parse("text/plain; charset=utf-8");
+
+    request.response.statusCode = 501;
+    request.response.reasonPhrase = "Not Implemented";
+    request.response.write(
+        "Currently this server only accepts Web Socket connections.");
+    request.response.close();
+  }
+
+  /// Creates a web socket for [request] which should be an upgrade request.
+  void _handleWebSocket(HttpRequest request) {
+    Chain.track(WebSocketTransformer.upgrade(request)).then((socket) {
+      _webSockets.add(socket);
+      var api = new WebSocketApi(socket, environment);
+
+      return api.listen().whenComplete(() => _webSockets.remove(api));
+    }).catchError(addError);
+  }
+}