rpc example for directory file listing

tests/isolate/src/MintMakerRpcTest.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.
+
+/***
+ * Background:
+ *
+ * There are two "target" classes here that are the actual implementation
+ * of some service that performs some function.  These "target" classes
+ * do not know about ports, isolates or rpc.  They expose a local (usually
+ * synchronous) interface to perform some task.  In this example, the "target"
+ * classes are very simple:
+ *
+ *    Mint - creates new Purse objects with an initial amount of money
+ *    Purse - holds an amount of money, and supports making deposits
+ *        by taking money out of another purse.
+ *
+ * The point of this example is to show how to create a new Dart isolate
+ * and run Mint and Purse objects in that isolate, and communicate with
+ * these objects with a SendPort/ReceivePort message/reply conversation,
+ * where command arguments are marshalled and unmarshalled by RpcProxy and
+ * RpcReceiver objects.
+ *
+ * This example also shows:
+ *     1. how the messages in the conversation can refer to target
+ *          objects besides the direct recipient of the message
+ *     2. how target objects can throw exceptions and these are propagated back
+ *          through the SendPort/ReceivePort channel and back to the Future
+ *          object that is waiting for the reply.
+ *
+ * Classes:
+ *
+ *    Mint - used to create Purse objects
+ *    Purse - holds a bank balance, supports depositing money from another Purse
+ *    MintReceiver - listens on a ReceivePort and forwards commands to Mint
+ *    PurseReceiver - listens on a ReceivePort and forwards commands to Purse
+ *    MintProxy - sends commands to a SendPort (which is connected to a
+ *        MintReceiver)
+ *    PurseProxy - sends commands to a SendPort (which is connected to a
+ *        PurseReceiver)
+ *    MintIsolate - used to spawn a new Isolate and return the initial MintProxy
+ *
+ * Base classes used: (these are defined in proxy.dart)
+ *    RpcReceiver - MintReceiver and PurseReceiver derive from RpcReceiver to
+ *         get behavior common to all Receivers.
+ *    RpcProxy - MintProxy and PurseProxy derive from RpcProxy to get behavior
+ *         common to all proxies
+ *
+ * Explanation:
+ *
+ * We make a "receiver" object (MintReceiver and PurseReceiver) for each
+ * target object that is being exposed.  Each "receiver" object gets
+ * its own ReceivePort, where it listen for messages that it interprets
+ * as commands for its target object.
+ *
+ * When a command is received by a receiver, the receiver calls the appropriate
+ * method on the the target object.  The receiver object runs in the same
+ * isolate as its target object.  This isolate is called the "service" isolate.
+ *
+ * RpcProxy objects run in the "client" isolate.  Each proxy object has a
+ * SendPort which is connected to the ReceivePort of a corresponding receiver
+ * object.
+ *
+ * So, a MintProxy object (running in the "client" isolate) is connected
+ * to a MintReceiver object (running in the "service" isolate) which is
+ * connected to a Mint target object (also running in the "service" isolate).
+ *
+ * Startup/Shutdown:
+ *
+ * The MintIsolate has a method open that spawns a new isolate and returns
+ * a MintProxy object.
+ *
+ * To shut down the MintIsolate, call 'close' on the MintProxy object.  This
+ * will close all receive ports of all receivers in the isolate, which will
+ * cause the mint isolate to shutdown.
+ */
+
+class Mint {
+  Mint();
+  Purse createPurse(int initialBalance) {
+    return new Purse(initialBalance);
+  }
+}
+
+class Purse {
+  int _balance;
+
+  Purse(this._balance) {}
+
+  int queryBalance() {
+    return _balance;
+  }
+
+  int deposit(int amount, Purse source) {
+    if (source._balance < amount) {
+      throw "OverdraftException";
+    }
+    source._balance -= amount;
+    _balance += amount;
+    return _balance;
+  }
+}
+
+
+class MintProxy extends RpcProxy {
+  MintProxy(Future<SendPort> sendPort) : super(sendPort) { }
+  Future<PurseProxy> createPurse(int initialBalance) {
+    return sendCommand("createPurse", [initialBalance], (sendPort) {
+      Completer<SendPort> completer = new Completer();
+      completer.complete(sendPort);
+      return new PurseProxy(completer.future);
+    });
+  }
+  Future<String> close() {
+    return sendCommand("close", null, null);
+  }
+}
+
+class MintReceiver extends RpcReceiver<Mint> {
+  MintReceiver(ReceivePort receivePort) : super(new Mint(), receivePort) {}
+  Object receiveCommand(String command, List args) {
+    switch(command) {
+      case "createPurse":
+        int balance = args[0];
+        Purse purse = target.createPurse(balance);
+        return new PurseReceiver(purse, new ReceivePort());
+      case "close":
+        RpcReceiver.closeAll();
+        return "close command processed";
+      default:
+          throw "MintReceiver unrecognized command";
+      }
+  }
+}
+
+class PurseProxy extends RpcProxy {
+  PurseProxy(Future<SendPort> sendPort) : super(sendPort) { }
+  Future<int> queryBalance() {
+    return sendCommand("queryBalance", null, null);
+  }
+  Future<int> deposit(int amount, PurseProxy from) {
+    return sendCommand("deposit", [amount, from], null);
+  }
+}
+
+class PurseReceiver extends RpcReceiver<Purse> {
+
+  PurseReceiver(Purse purse, ReceivePort receivePort) : super(purse, receivePort) {}
+
+  Object receiveCommand(String command, List args) {
+    switch(command) {
+      case "queryBalance":
+        return target.queryBalance();
+      case "deposit":
+        int amount = args[0];
+        Purse fromPurse = args[1];
+        return target.deposit(amount, fromPurse);
+      default:
+        throw "PurseReceiver unrecognized command";
+    }
+  }
+}
+
+class MintIsolate extends Isolate {
+  MintIsolate() : super.light() {}
+
+  MintProxy open() {
+    return new MintProxy(spawn());
+  }
+
+  void main() {
+    ReceivePort receivePort = port;
+    new MintReceiver(receivePort);
+  }
+}
+
+class MintTest {
+  static void testMain() {
+    print("starting test");
+    MintProxy mint = new MintIsolate().open();
+    mint.createPurse(100).then((PurseProxy purse1) {
+      purse1.queryBalance().then((int balance) {
+        Expect.equals(100, balance);
+        mint.createPurse(0).then((PurseProxy purse2) {
+          purse2.queryBalance().then((int balance) {
+            Expect.equals(0, balance);
+            purse2.deposit(5, purse1).then((int newBalance) {
+              Expect.equals(0 + 5, newBalance);
+              purse1.queryBalance().then((int balance) {
+                Expect.equals(100 - 5, balance);
+              });
+              purse2.deposit(42, purse1).then((int newBalance) {
+                int balance2 = newBalance;
+                Expect.equals(0 + 5 + 42, balance2);
+                purse1.queryBalance().then((int balance) {
+                  int balance1 = balance;
+                  Expect.equals(100 - 5 - 42, balance);
+                  // Now try to deposit more money into purse1 than
+                  // is currently in purse2.  Make sure we get an exception
+                  // doing this.
+                  Future<int> badBalance = purse1.deposit(1000, purse2);
+                  badBalance.then((int newBalance) {
+                    // Should never arrive here because there are
+                    // insufficient funds to actually do the deposit
+                    Expect.fail("did not detect overdraft");
+                  });
+                  badBalance.handleException((Object exception) {
+                    if (exception.toString().contains(
+                        "OverdraftException", 0)) {
+                      print("Correctly detected overdraft.");
+                      // Check that the balance in each purse is unchanged from
+                      // before we attempted to do the overdraft.
+                      purse1.queryBalance().then((int balance) {
+                        Expect.equals(balance, balance1);
+                        purse2.queryBalance().then((int balance) {
+                          Expect.equals(balance, balance2);
+                          // OK, we're all done now, close down the mint isolate
+                          mint.close().then((reply) {
+                            print(reply);
+                          });
+                        });
+                      });
+                      return true;
+                    } else {
+                      return false;
+                    }
+                  });
+                });
+              });
+            });
+          });
+        });
+      });
+    });
+    print ("exit main");
+  }
+}
+
+main() {
+  MintTest.testMain();
+}