Allow Dart code to register service protocol handlers

sdk/lib/developer/extension.dart

Index: sdk/lib/developer/extension.dart
diff --git a/sdk/lib/developer/extension.dart b/sdk/lib/developer/extension.dart
new file mode 100644
index 0000000000000000000000000000000000000000..e94e748e7a1770eae0915f77111a62cf6d75768b
--- /dev/null
+++ b/sdk/lib/developer/extension.dart
@@ -0,0 +1,60 @@
+// 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.
+
+part of dart.developer;
+
+/// Index of [response] that the result should be stored.
+const kResultIndex = 0;
+/// Index of [response] that the error code should be stored.
+const kErrorCodeIndex = 1;
+/// Index of [response] that the error message be stored.
+const kErrorMessageIndex = 2;
+
+/// A service protocol extension handler. Registered with [registerExtension].
+///
+/// Must modify [response] according to the following contract:
+/// On success, set index 0 to a JSON encoded result
+/// OR
+/// On failure, set index 1 to an error code and index 2 to a error message.
+///
+/// [method] - the method name.
+/// [parameters] - the parameters.
+/// [response] - a list of length three that the handler must set.
+typedef void ServiceExtensionHandler(String method,
+                                     Map paremeters,
+                                     List<String> response);
+
+final _extensions = new Map<String, ServiceExtensionHandler>();
+
+/// Register a [ServiceExtensionHandler] that will be invoked in this isolate
+/// for [method].
+void registerExtension(String method, ServiceExtensionHandler handler) {
+  if (_extensions[method] != null) {
+    throw new ArgumentError('Extension already registered: $method.');
+  }
+  if (handler is! ServiceExtensionHandler) {
+    throw new ArgumentError('handler must be a ServiceExtensionHandler.');
+  }
+  _extensions[method] = handler;
+}
+
+bool _extensionExists(String method) {
+  return _extensions[method] != null;
+}
+
+bool _invokeExtension(String method,

[turnidge, 2015/08/04 18:21:27]

As discussed offline, let's make this async.

+                      List<String> parameterKeys,
+                      List<String> parameterValues,
+                      List<String> response) {
+  ServiceExtensionHandler handler = _extensions[method];
+  if (handler == null) {
+    return false;
+  }
+  var parameters = {};
+  for (var i = 0; i < parameterKeys.length; i++) {
+    parameters[parameterKeys[i]] = parameterValues[i];
+  }
+  handler(method, parameters, response);
+  return true;
+}