guard against invalid request id / method

pkg/analysis_server/lib/src/protocol.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 protocol;
 
 import 'dart:convert' show JsonDecoder;
 
 /**
  * Instances of the class [Request] represent a request that was received.
@@ skipping 55 matching lines @@
    *
    * where the parameters are optional and can contain any number of name/value
    * pairs.
    */
   factory Request.fromString(String data) {
     try {
       var result = DECODER.convert(data);
       if (result is! Map) {
         return null;
       }
-      String id = result[Request.ID];
-      String method = result[Request.METHOD];
+      var id = result[Request.ID];
+      var method = result[Request.METHOD];
+      if (id is! String || method is! String) {
+        return null;
+      }
       var params = result[Request.PARAMS];
       Request request = new Request(id, method);
       if (params is Map) {
         params.forEach((String key, Object value) {
           request.setParameter(key, value);
         });
+      } else if (params != null) {
+        return null;
       }
       return request;
     } catch (exception) {
       return null;
     }
   }
 
   /**
    * Return the value of the parameter with the given [name], or `null` if there
    * is no such parameter associated with this request.
@@ skipping 480 matching lines @@
   /**
    * The response to be returned as a result of the failure.
    */
   final Response response;
 
   /**
    * Initialize a newly created exception to return the given reponse.
    */
   RequestFailure(this.response);
 }