Fix race condition with "server already started" error.

pkg/analysis_server/lib/http_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 http.server;
 
 import 'dart:io';
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/channel.dart';
 import 'package:analysis_server/src/domain_context.dart';
 import 'package:analysis_server/src/domain_server.dart';
 import 'package:analysis_server/src/get_handler.dart';
 import 'package:args/args.dart';
+import 'package:analysis_server/src/protocol.dart';

[Brian Wilkerson, 2014/04/14 21:25:43]

nit: I believe that we're generally keeping the imports in alphabetic order.

 
 /**
  * Instances of the class [HttpServer] implement a simple HTTP server. The
  * primary responsibility of this server is to listen for an UPGRADE request and
  * to start an analysis server.
  */
 class HttpAnalysisServer {
   /**
    * The name of the application that is used to start a server.
    */
@@ skipping 66 matching lines @@
     }
   }
 
   /**
    * Attach a listener to a newly created HTTP server.
    */
   void _handleServer(HttpServer httServer) {
     httServer.listen((HttpRequest request) {
       List<String> updateValues = request.headers[HttpHeaders.UPGRADE];
       if (updateValues != null && updateValues.indexOf('websocket') >= 0) {
-        if (analysisServer != null) {
-          _returnServerAlreadyStarted(request);
-          return;
-        }
         WebSocketTransformer.upgrade(request).then((WebSocket websocket) {
           _handleWebSocket(websocket);
         });
       } else if (request.method == 'GET') {
         _handleGetRequest(request);
       } else {
         _returnUnknownRequest(request);
       }
     });
   }
 
   /**
    * Handle a GET request received by the HTTP server.
    */
   void _handleGetRequest(HttpRequest request) {
     if (getHandler == null) {
       getHandler = new GetHandler();
       getHandler.server = analysisServer;
     }
     getHandler.handleGetRequest(request);
   }
 
   /**
    * Handle an UPGRADE request received by the HTTP server by creating and
    * running an analysis server on a [WebSocket]-based communication channel.
    */
   void _handleWebSocket(WebSocket socket) {
+    ServerCommunicationChannel serverChannel = new WebSocketServerChannel(socket);
+    if (analysisServer != null) {
+      // TODO(paulberry): add a message to the protocol so that the server can
+      // inform the client of a successful connection.
+      var error = new RequestError.serverAlreadyStarted();
+      serverChannel.sendResponse(new Response('', error));
+      serverChannel.listen((Request request) {
+        serverChannel.sendResponse(new Response(request.id, error));
+      });
+      return;
+    }
     analysisServer = new AnalysisServer(new WebSocketServerChannel(socket));
     _initializeHandlers(analysisServer);
     if (getHandler != null) {
       getHandler.server = analysisServer;
     }
     analysisServer.run();
   }
 
   /**
    * Initialize the handlers to be used by the given [server].
    */
   void _initializeHandlers(AnalysisServer server) {
     server.handlers = [
         new ServerDomainHandler(server),
         new ContextDomainHandler(server),
     ];
   }
 
   /**
    * Print information about how to use the server.
    */
   void _printUsage(ArgParser parser) {
     print('Usage: $BINARY_NAME [flags]');
     print('');
     print('Supported flags are:');
     print(parser.getUsage());
   }
 
   /**
-   * Return an error in response to an UPGRADE request received after the server
-   * has already been started by a previous UPGRADE request.
-   */
-  void _returnServerAlreadyStarted(HttpRequest request) {
-    HttpResponse response = request.response;
-    response.statusCode = HttpStatus.SERVICE_UNAVAILABLE;
-    response.headers.add(HttpHeaders.CONTENT_TYPE, "text/plain");
-    response.write('The server has already been started');
-    response.close();
-  }
-
-  /**
    * Return an error in response to an unrecognized request received by the HTTP
    * server.
    */
   void _returnUnknownRequest(HttpRequest request) {
     HttpResponse response = request.response;
     response.statusCode = HttpStatus.NOT_FOUND;
     response.headers.add(HttpHeaders.CONTENT_TYPE, "text/plain");
     response.write('Not found');
     response.close();
   }
 }