Add an exitOnClose function to the "pub serve" WebSocket API.

sdk/lib/_internal/pub/lib/src/barback/web_socket_api.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 pub.barback.web_socket_api;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:http_parser/http_parser.dart';
 import 'package:path/path.dart' as path;
 import 'package:json_rpc_2/json_rpc_2.dart' as json_rpc;
 
+import '../exit_codes.dart' as exit_codes;
+import '../io.dart';
+import '../log.dart' as log;
 import '../utils.dart';
 import 'asset_environment.dart';
 
 /// Implements the [WebSocket] API for communicating with a running pub serve
 /// process, mainly for use by the Editor.
 ///
 /// This is a [JSON-RPC 2.0](http://www.jsonrpc.org/specification) server. Its
 /// methods are described in the method-level documentation below.
 class WebSocketApi {
   final CompatibleWebSocket _socket;
   final AssetEnvironment _environment;
   final _server = new json_rpc.Server();
 
+  /// Whether the application should exit when this connection closes.
+  bool _exitOnClose = false;
+
   WebSocketApi(this._socket, this._environment) {
     _server.registerMethod("urlToAssetId", _urlToAssetId);
     _server.registerMethod("pathToUrls", _pathToUrls);
     _server.registerMethod("serveDirectory", _serveDirectory);
     _server.registerMethod("unserveDirectory", _unserveDirectory);
+
+    /// Tells the server to exit as soon as this WebSocket connection is closed.
+    ///
+    /// This takes no arguments and returns no results. It can safely be called
+    /// as a JSON-RPC notification.
+    _server.registerMethod("exitOnClose", () => _exitOnClose = true);
   }
 
   /// Listens on the socket.
   ///
   /// Returns a future that completes when the socket has closed. It will
   /// complete with an error if the socket had an error, otherwise it will
   /// complete to `null`.
   Future listen() {
     return _socket.listen((request) {
       _server.parseRequest(request).then((response) {
         if (response != null) _socket.add(response);
       });
-    }, cancelOnError: true).asFuture();
+    }, cancelOnError: true).asFuture().then((_) {
+      if (!_exitOnClose) return;
+      log.message("WebSocket connection closed, terminating.");
+      flushThenExit(exit_codes.SUCCESS);
+    });
   }
 
   /// Given a URL to an asset that is served by pub, returns the ID of the
   /// asset that would be accessed by that URL.
   ///
   /// The method name is "urlToAssetId" and it takes a "url" parameter for the
   /// URL being mapped:
   ///
   ///     "params": {
   ///       "url": "http://localhost:8080/index.html"
@@ skipping 232 matching lines @@
 
 
 /// The pub-specific JSON RPC error codes.
 class _Error {
   /// The specified directory is not being served.
   static const NOT_SERVED = 1;
 
   /// The specified directory overlaps one or more ones already being served.
   static const OVERLAPPING = 2;
 }