Reduce copying in sending service responses.

sdk/lib/vmservice/vmservice.dart

 // Copyright (c) 2015, 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 dart._vmservice;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:isolate';
@@ skipping 312 matching lines @@
 
     Isolate.spawnUri(Uri.parse(uri), args, msg).then((isolate) {
       _spawnUriNotify(isolate.controlPort, token);
     }).catchError((e) {
       _spawnUriNotify(e.toString(), token);
     });
 
     return encodeSuccess(message);
   }
 
+  static responseAsJson(portResponse) {
+    if (portResponse is String) {
+      return JSON.decode(portResponse);
+    } else {
+      var cstring = portResponse[0];
+      return JSON.fuse(UTF8).decode(cstring);
+    }
+  }
+
   // TODO(johnmccutchan): Turn this into a command line tool that uses the
   // service library.
   Future<String> _getCrashDump(Message message) async {
     var client = message.client;
     final perIsolateRequests = [
         // ?isolateId=<isolate id> will be appended to each of these requests.
         // Isolate information.
         Uri.parse('getIsolate'),
         // State of heap.
         Uri.parse('_getAllocationProfile'),
         // Call stack + local variables.
         Uri.parse('getStack?_full=true'),
     ];
 
     // Snapshot of running isolates.
     var isolates = runningIsolates.isolates.values.toList();
 
     // Collect the mapping from request uris to responses.
     var responses = {
     };
 
     // Request VM.
     var getVM = Uri.parse('getVM');
-    var getVmResponse = JSON.decode(
+    var getVmResponse = responseAsJson(
         await new Message.fromUri(client, getVM).sendToVM());
     responses[getVM.toString()] = getVmResponse['result'];
 
     // Request command line flags.
     var getFlagList = Uri.parse('getFlagList');
-    var getFlagListResponse = JSON.decode(
+    var getFlagListResponse = responseAsJson(
         await new Message.fromUri(client, getFlagList).sendToVM());
     responses[getFlagList.toString()] = getFlagListResponse['result'];
 
     // Make requests to each isolate.
     for (var isolate in isolates) {
       for (var request in perIsolateRequests) {
         var message = new Message.forIsolate(client, request, isolate);
         // Decode the JSON and and insert it into the map. The map key
         // is the request Uri.
-        var response = JSON.decode(await isolate.route(message));
+        var response = responseAsJson(await isolate.route(message));
         responses[message.toUri().toString()] = response['result'];
       }
       // Dump the object id ring requests.
       var message =
           new Message.forIsolate(client, Uri.parse('_dumpIdZone'), isolate);
-      var response = JSON.decode(await isolate.route(message));
+      var response = responseAsJson(await isolate.route(message));
       // Insert getObject requests into responses map.
       for (var object in response['result']['objects']) {
         final requestUri =
             'getObject&isolateId=${isolate.serviceId}?objectId=${object["id"]}';
         responses[requestUri] = object;
       }
     }
 
     // Encode the entire crash dump.
     return encodeResult(message, responses);
@@ skipping 49 matching lines @@
 external bool _vmListenStream(String streamId);
 
 /// Cancel a subscription to a service stream.
 external void _vmCancelStream(String streamId);
 
 /// Get the bytes to the tar archive.
 external Uint8List _requestAssets();
 
 /// Notify the vm service that an isolate has been spawned via rpc.
 external void _spawnUriNotify(obj, String token);