rpc example for directory file listing

runtime/bin/directory_exp.dart

+// Copyright (c) 2011, 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.
+
+/**
+ * EXPERIMENTAL.
+ *
+ * (NOTE - DO NOT USE.   This is just an example to illustrate
+ * how to use the RPC system and isolates to provide an asynchronous API
+ * on top of a system service that is synchronous.)
+ *
+ * Provides a synchronous API to list the files in a directory.
+ */
+class DirectorySync {
+  final String _path;
+
+  DirectorySync(this._path);
+
+  bool isDirectory() {
+    // this returns an error message string if there was a file system error
+    var isDir = _isDirectory(_path);
+    if (isDir is bool) {
+      return isDir;
+    }
+    String message = isDir;
+    throw new DirectorySyncException(message);
+  }
+
+  List<String> list() {
+    if (!isDirectory()) {
+      return null;
+    }
+    return _list(_path);
+  }
+
+  static List<String> _list(String path) native "FilePath_List";
+  static Object _isDirectory(String path) native "FilePath_IsDirectory";
+}
+
+/**
+ * Thrown if any of the native calls return an error message.  This will
+ * propagate back through the RPC system to the calling isolate.
+ */
+class DirectorySyncException implements Exception {
+  final String message;
+  DirectorySyncException(this.message);
+  String toString() => "DirectorySyncException: $message";
+}
+
+/**
+ * Provides an asynchronous API on top of the synchronous DirectorySync class.
+ * (See RpcProxy for more details.)
+ */
+class DirectoryProxy extends RpcProxy {
+  final String path;
+  DirectoryProxy(this.path, Future<SendPort> futurePort) : super(futurePort) {
+    sendCommand("init", [path]);
+  }
+
+  Future<List<String>> list() {
+    return sendCommand("list", null);
+  }
+
+  Future<bool> isDirectory() {
+    return sendCommand("isDirectory", null);
+  }
+
+  static DirectoryProxy create(String path) {
+    return new DirectoryProxy(path, new DirectoryIsolate().spawn());
+  }
+
+  String toString() {
+    return path;
+  }
+}
+
+/**
+ * Wraps the DirectorySync target object.
+ */
+class DirectoryReceiver extends RpcReceiver {
+  DirectorySync directorySync;
+  DirectoryReceiver(ReceivePort receivePort) : super(receivePort);
+
+  Object receiveCommand(String command, List args) {
+    switch(command) {
+        case "init":
+          String path = args[0];
+          directorySync = new DirectorySync(path);
+          return;
+        case "list":
+          return directorySync.list();
+        case "isDirectory":
+          return directorySync.isDirectory();
+    }
+  }
+}
+
+/**
+ * Used to spawn the directory service isolate.
+ */
+class DirectoryIsolate extends Isolate {

[Siggi Cherem (dart-lang), 2011/11/11 23:41:51]

what about have RpcReceiver extend from isolate instead?

[Ben Laurie (Google), 2011/11/11 23:45:38]

That's not a good idea: you control who can send by who has the RpcProxy
corresponding to your RpcReceiver, which means you need more than one per
isolate.

[Siggi Cherem (dart-lang), 2011/11/11 23:54:08]

makes sense - I guess in this example it was clear that the proxy-user created
an isolate just for this purpose, but more generally there is an isolate running
and you want to connect to a service it provides (rpcreceiver).

+  main() {
+    new DirectoryReceiver(port);
+  }
+}