Create a package that implements a JSON-RPC 2.0 server.

pkg/json_rpc_2/lib/src/exception.dart

Index: pkg/json_rpc_2/lib/src/exception.dart
diff --git a/pkg/json_rpc_2/lib/src/exception.dart b/pkg/json_rpc_2/lib/src/exception.dart
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+// 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.exception;
+
+import '../error_code.dart' as error_code;
+
+/// An exception from a JSON-RPC server that can be translated into an error
+/// response.
+class RpcException implements Exception {
+  /// The error code.
+  ///
+  /// All non-negative error codes are available for use by application
+  /// developers.
+  final int code;
+
+  /// The error message.
+  ///
+  /// This should be limited to a concise single sentence. Further information
+  /// should be supplied via [data].
+  final String message;
+
+  /// Extra application-defined information about the error.
+  ///
+  /// This must be a JSON-serializable object. If it's a [Map] without a
+  /// `"request"` key, a copy of the request that caused the error will
+  /// automatically be injected.
+  final data;
+
+  RpcException(this.code, this.message, {this.data});
+
+  /// An exception indicating that the method named [methodName] was not found.
+  ///
+  /// This should usually be used only by fallback handlers.
+  RpcException.methodNotFound(String methodName)
+      : this(error_code.METHOD_NOT_FOUND, 'Unknown method "$methodName".');
+
+  /// An exception indicating that the parameters for the requested method were
+  /// invalid.
+  ///
+  /// Methods can use this to reject requests with invalid parameters.
+  RpcException.invalidParams(String message)
+      : this(error_code.INVALID_PARAMS, message);
+
+  /// Converts this exception into a JSON-serializable object that's a valid
+  /// JSON-RPC 2.0 error response.
+  serialize(request) {
+    var modifiedData;
+    if (data is Map && !data.containsKey('request')) {
+      modifiedData = new Map.from(data);
+      modifiedData['request'] = request;
+    } else if (data == null) {
+      modifiedData = {'request': request};
+    }
+
+    var id = request is Map ? request['id'] : null;
+    if (id is! String && id is! num) id = null;
+    return {
+      'jsonrpc': '2.0',
+      'error': {'code': code, 'message': message, 'data': modifiedData},
+      'id': id
+    };
+  }
+}