Improve stack traces for error responses.

lib/src/client.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 json_rpc_2.client;
 
 import 'dart:async';
 
 import 'package:stack_trace/stack_trace.dart';
 
@@ skipping 10 matching lines @@
   final TwoWayStream _streams;
 
   /// The next request id.
   var _id = 0;
 
   /// The current batch of requests to be sent together.
   ///
   /// Each element is a JSON-serializable object.
   List _batch;
 
-  /// The map of request ids for pending requests to [Completer]s that will be
-  /// completed with those requests' responses.
-  final _pendingRequests = new Map<int, Completer>();
+  /// The map of request ids to pending requests.
+  final _pendingRequests = new Map<int, _Request>();
 
   /// Returns a [Future] that completes when the connection is closed.
   ///
   /// This is the same future that's returned by [listen].
   Future get done => _streams.done;
 
   /// Creates a [Client] that writes requests to [requests] and reads responses
   /// from [responses].
   ///
   /// If [responses] is a [StreamSink] as well as a [Stream] (for example, a
@@ skipping 43 matching lines @@
   /// JSON-serializable.
   ///
   /// If the request succeeds, this returns the response result as a decoded
   /// JSON-serializable object. If it fails, it throws an [RpcException]
   /// describing the failure.
   Future sendRequest(String method, [parameters]) {
     var id = _id++;
     _send(method, parameters, id);
 
     var completer = new Completer.sync();
-    _pendingRequests[id] = completer;
+    _pendingRequests[id] = new _Request(completer, new Chain.current());
     return completer.future;
   }
 
   /// Sends a JSON-RPC 2 request to invoke the given [method] without expecting
   /// a response.
   ///
   /// If passed, [parameters] is the parameters for the method. This must be
   /// either an [Iterable] (to pass parameters by position) or a [Map] with
   /// [String] keys (to pass parameters by name). Either way, it must be
   /// JSON-serializable.
@@ skipping 56 matching lines @@
       response.forEach(_handleSingleResponse);
     } else {
       _handleSingleResponse(response);
     }
   }
 
   /// Handles a decoded response from the server after batches have been
   /// resolved.
   void _handleSingleResponse(response) {
     if (!_isResponseValid(response)) return;
-    var completer = _pendingRequests.remove(response["id"]);
+    var request = _pendingRequests.remove(response["id"]);
     if (response.containsKey("result")) {
-      completer.complete(response["result"]);
+      request.completer.complete(response["result"]);
     } else {
-      completer.completeError(new RpcException(
+      request.completer.completeError(new RpcException(
             response["error"]["code"],
             response["error"]["message"],
             data: response["error"]["data"]),
-          new Chain.current());
+          request.chain);
     }
   }
 
   /// Determines whether the server's response is valid per the spec.
   bool _isResponseValid(response) {
     if (response is! Map) return false;
     if (response["jsonrpc"] != "2.0") return false;
     if (!_pendingRequests.containsKey(response["id"])) return false;
     if (response.containsKey("result")) return true;
 
     if (!response.containsKey("error")) return false;
     var error = response["error"];
     if (error is! Map) return false;
     if (error["code"] is! int) return false;
     if (error["message"] is! String) return false;
     return true;
   }
 }
+
+/// A pending request to the server.
+class _Request {
+  /// The completer to use to complete the response future.
+  final Completer completer;
+
+  /// The stack chain from where the request was made.
+  final Chain chain;
+
+  _Request(this.completer, this.chain);
+}