Reduce copying in sending service responses.

runtime/bin/vmservice/server.dart

 // Copyright (c) 2013, 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.
 
 part of vmservice_io;
 
 class WebSocketClient extends Client {
   static const int PARSE_ERROR_CODE = 4000;
   static const int BINARY_MESSAGE_ERROR_CODE = 4001;
   static const int NOT_MAP_ERROR_CODE = 4002;
@@ skipping 33 matching lines @@
       socket.close(BINARY_MESSAGE_ERROR_CODE, 'Message must be a string.');
     }
   }
 
   void post(dynamic result) {
     if (result == null) {
       // Do nothing.
       return;
     }
     try {
-      socket.add(result);
+      if (result is String || result is Uint8List) {
+        socket.add(result);  // String or binary message.
+      } else {
+        // String message as external Uint8List.
+        assert(result is List);
+        Uint8List cstring = result[0];
+        // TODO(rmacnak): cstring may be large. Add a way to pass an encoded
+        // string to a web socket that will be sent as a text message to avoid
+        // the space overhead of converting cstring to a Dart string.
+        socket.add(UTF8.decode(cstring));
+      }
     } catch (_) {
       print("Ignoring error posting over WebSocket.");
     }
   }
 
   dynamic toJson() {
     Map map = super.toJson();
     map['type'] = 'WebSocketClient';
     map['socket'] = '$socket';
     return map;
   }
 }
 
 
 class HttpRequestClient extends Client {
   static ContentType jsonContentType =
       new ContentType("application", "json", charset: "utf-8");
   final HttpRequest request;
 
   HttpRequestClient(this.request, VMService service)
       : super(service, sendEvents:false);
 
   disconnect() {
     request.response.close();
     close();
   }
 
-  void post(String result) {
+  void post(dynamic result) {
     if (result == null) {
       close();
       return;
     }
-    request.response..headers.contentType = jsonContentType
-                    ..write(result)
-                    ..close();
+    HttpResponse response = request.response;
+    response.headers.contentType = jsonContentType;
+    if (result is String) {
+      response.write(result);
+    } else {
+      assert(result is List);
+      Uint8List cstring = result[0];  // Already in UTF-8.
+      response.add(cstring);
+    }
+    response.close();
     close();
   }
 
   dynamic toJson() {
     Map map = super.toJson();
     map['type'] = 'HttpRequestClient';
     map['request'] = '$request';
     return map;
   }
 }
@@ skipping 204 matching lines @@
       _notifyServerState("", 0);
       onServerAddressChange(null);
       return this;
     });
   }
 
 }
 
 void _notifyServerState(String ip, int port)
     native "VMServiceIO_NotifyServerState";