Add StreamQueue.fork and ForkableStream.

test/forkable_stream_test.dart

+// 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.
+
+import 'dart:async';
+
+import 'package:async/async.dart';
+import 'package:test/test.dart';
+
+import 'utils.dart';
+
+void main() {
+  var controller;
+  var stream;
+  setUp(() {
+    var cancelFuture = new Future.value(42);
+    controller = new StreamController<int>(onCancel: () => cancelFuture);
+    stream = new ForkableStream<int>(controller.stream);
+  });
+
+  group("with no forks", () {
+    test("forwards events, errors, and close", () async {
+      var queue = new StreamQueue(stream);
+
+      controller.add(1);
+      expect(await queue.next, equals(1));
+
+      controller.add(2);
+      expect(await queue.next, equals(2));
+
+      controller.addError("error");
+      expect(queue.next, throwsA("error"));
+      await flushMicrotasks();
+
+      controller.add(3);
+      expect(await queue.next, equals(3));
+
+      controller.close();
+      expect(await queue.hasNext, isFalse);
+    });
+
+    test("listens to, pauses, and cancels the controller", () {
+      expect(controller.hasListener, isFalse);
+
+      var sub = stream.listen(null);
+      expect(controller.hasListener, isTrue);
+
+      sub.pause();
+      expect(controller.isPaused, isTrue);
+
+      sub.resume();
+      expect(controller.isPaused, isFalse);
+
+      sub.cancel();
+      expect(controller.hasListener, isFalse);
+    });
+
+    test("unpauses the controller when a fork is listened", () {
+      stream.listen(null).pause();
+      expect(controller.isPaused, isTrue);
+
+      var fork = stream.fork();
+      expect(controller.isPaused, isTrue);
+
+      fork.listen(null);
+      expect(controller.isPaused, isFalse);
+    });
+  });
+
+  group("with a fork created before the stream was listened", () {
+    var fork;
+    setUp(() {
+      fork = stream.fork();
+    });
+
+    test("forwards events, errors, and close to both branches", () async {
+      var queue = new StreamQueue(stream);
+      var forkQueue = new StreamQueue(fork);
+
+      controller.add(1);
+      expect(await queue.next, equals(1));
+      expect(await forkQueue.next, equals(1));
+
+      controller.add(2);
+      expect(await queue.next, equals(2));
+      expect(await forkQueue.next, equals(2));
+
+      controller.addError("error");
+      expect(queue.next, throwsA("error"));
+      expect(forkQueue.next, throwsA("error"));
+      await flushMicrotasks();
+
+      controller.add(3);
+      expect(await queue.next, equals(3));
+      expect(await forkQueue.next, equals(3));
+
+      controller.close();
+      expect(await queue.hasNext, isFalse);
+      expect(await forkQueue.hasNext, isFalse);
+    });
+
+    test('listens to the source when the original is listened', () {
+      expect(controller.hasListener, isFalse);
+      stream.listen(null);
+      expect(controller.hasListener, isTrue);
+    });
+
+    test('listens to the source when the fork is listened', () {
+      expect(controller.hasListener, isFalse);
+      fork.listen(null);
+      expect(controller.hasListener, isTrue);
+    });
+  });
+
+  test("with a fork created after the stream emitted a few events, forwards "
+      "future events, errors, and close to both branches", () async {
+    var queue = new StreamQueue(stream);
+
+    controller.add(1);
+    expect(await queue.next, equals(1));
+
+    controller.add(2);
+    expect(await queue.next, equals(2));
+
+    var fork = stream.fork();
+    var forkQueue = new StreamQueue(fork);
+
+    controller.add(3);
+    expect(await queue.next, equals(3));
+    expect(await forkQueue.next, equals(3));
+
+    controller.addError("error");
+    expect(queue.next, throwsA("error"));
+    expect(forkQueue.next, throwsA("error"));
+    await flushMicrotasks();
+
+    controller.close();
+    expect(await queue.hasNext, isFalse);
+    expect(await forkQueue.hasNext, isFalse);
+  });
+
+  group("with multiple forks", () {
+    var fork1;
+    var fork2;
+    var fork3;
+    var fork4;
+    setUp(() {
+      fork1 = stream.fork();
+      fork2 = stream.fork();
+      fork3 = stream.fork();
+      fork4 = stream.fork();
+    });
+
+    test("forwards events, errors, and close to all branches", () async {
+      var queue1 = new StreamQueue(stream);
+      var queue2 = new StreamQueue(fork1);
+      var queue3 = new StreamQueue(fork2);
+      var queue4 = new StreamQueue(fork3);
+      var queue5 = new StreamQueue(fork4);
+
+      controller.add(1);
+      expect(await queue1.next, equals(1));
+      expect(await queue2.next, equals(1));
+      expect(await queue3.next, equals(1));
+      expect(await queue4.next, equals(1));
+      expect(await queue5.next, equals(1));
+
+      controller.add(2);
+      expect(await queue1.next, equals(2));
+      expect(await queue2.next, equals(2));
+      expect(await queue3.next, equals(2));
+      expect(await queue4.next, equals(2));
+      expect(await queue5.next, equals(2));
+
+      controller.addError("error");
+      expect(queue1.next, throwsA("error"));
+      expect(queue2.next, throwsA("error"));
+      expect(queue3.next, throwsA("error"));
+      expect(queue4.next, throwsA("error"));
+      expect(queue5.next, throwsA("error"));
+      await flushMicrotasks();
+
+      controller.add(3);
+      expect(await queue1.next, equals(3));
+      expect(await queue2.next, equals(3));
+      expect(await queue3.next, equals(3));
+      expect(await queue4.next, equals(3));
+      expect(await queue5.next, equals(3));
+
+      controller.close();
+      expect(await queue1.hasNext, isFalse);
+      expect(await queue2.hasNext, isFalse);
+      expect(await queue3.hasNext, isFalse);
+      expect(await queue4.hasNext, isFalse);
+      expect(await queue5.hasNext, isFalse);
+    });
+
+    test("forwards events in order of forking", () async {
+      var queue1 = new StreamQueue(stream);
+      var queue2 = new StreamQueue(fork1);
+      var queue3 = new StreamQueue(fork2);
+      var queue4 = new StreamQueue(fork3);
+      var queue5 = new StreamQueue(fork4);
+
+      for (var i = 0; i < 4; i++) {
+        controller.add(i);
+
+        var queue1Fired = false;
+        var queue2Fired = false;
+        var queue3Fired = false;
+        var queue4Fired = false;
+        var queue5Fired = false;
+
+        queue5.next.then(expectAsync((_) {
+          queue5Fired = true;
+          expect(queue1Fired, isTrue);
+          expect(queue2Fired, isTrue);
+          expect(queue3Fired, isTrue);
+          expect(queue4Fired, isTrue);
+        }));
+
+        queue1.next.then(expectAsync((_) {
+          queue1Fired = true;
+          expect(queue2Fired, isFalse);
+          expect(queue3Fired, isFalse);
+          expect(queue4Fired, isFalse);
+          expect(queue5Fired, isFalse);
+        }));
+
+        queue4.next.then(expectAsync((_) {
+          queue4Fired = true;
+          expect(queue1Fired, isTrue);
+          expect(queue2Fired, isTrue);
+          expect(queue3Fired, isTrue);
+          expect(queue5Fired, isFalse);
+        }));
+
+        queue2.next.then(expectAsync((_) {
+          queue2Fired = true;
+          expect(queue1Fired, isTrue);
+          expect(queue3Fired, isFalse);
+          expect(queue4Fired, isFalse);
+          expect(queue5Fired, isFalse);
+        }));
+
+        queue3.next.then(expectAsync((_) {
+          queue3Fired = true;
+          expect(queue1Fired, isTrue);
+          expect(queue2Fired, isTrue);
+          expect(queue4Fired, isFalse);
+          expect(queue5Fired, isFalse);
+        }));
+      }
+    });
+
+    test("pauses the source when all forks are paused and/or not listening",
+        () {
+      var sub1 = stream.listen(null);
+      var sub2 = fork1.listen(null);
+      expect(controller.isPaused, isFalse);
+
+      sub1.pause();
+      expect(controller.isPaused, isFalse);
+
+      sub2.pause();
+      expect(controller.isPaused, isTrue);
+
+      var sub3 = fork2.listen(null);
+      expect(controller.isPaused, isFalse);
+
+      sub3.pause();
+      expect(controller.isPaused, isTrue);
+
+      sub2.resume();
+      expect(controller.isPaused, isFalse);
+
+      sub2.cancel();
+      expect(controller.isPaused, isTrue);
+    });
+
+    test("cancels the source when all forks are canceled", () async {
+      var sub1 = stream.listen(null);
+      expect(controller.hasListener, isTrue);
+
+      var sub2 = fork1.listen(null);
+      expect(controller.hasListener, isTrue);
+
+      expect(sub1.cancel(), isNull);
+      await flushMicrotasks();
+      expect(controller.hasListener, isTrue);
+
+      expect(sub2.cancel(), isNull);
+      await flushMicrotasks();
+      expect(controller.hasListener, isTrue);
+
+      expect(fork2.listen(null).cancel(), isNull);
+      await flushMicrotasks();
+      expect(controller.hasListener, isTrue);
+
+      expect(fork3.listen(null).cancel(), isNull);
+      await flushMicrotasks();
+      expect(controller.hasListener, isTrue);
+
+      expect(fork4.listen(null).cancel(), completion(equals(42)));
+      await flushMicrotasks();
+      expect(controller.hasListener, isFalse);
+    });
+  });
+
+  group("modification during dispatch:", () {
+    test("forking during onCancel", () {
+      controller = new StreamController<int>(onCancel: expectAsync(() {
+        expect(stream.fork, throwsStateError);
+      }));
+      stream = new ForkableStream<int>(controller.stream);
+
+      stream.listen(null).cancel();
+    });
+
+    test("forking during onPause", () {
+      controller = new StreamController<int>(onPause: expectAsync(() {
+        stream.fork().listen(null);
+      }));
+      stream = new ForkableStream<int>(controller.stream);
+
+      stream.listen(null).pause();
+
+      // The fork created in onPause should have resumed the stream.
+      expect(controller.isPaused, isFalse);
+    });
+
+    test("forking during onData", () {
+      var sub;
+      sub = stream.listen(expectAsync((value1) {
+        expect(value1, equals(1));
+        stream.fork().listen(expectAsync((value2) {
+          expect(value2, equals(2));
+        }));
+        sub.cancel();
+      }));
+
+      controller.add(1);
+      controller.add(2);
+    });
+
+    test("canceling a fork during onData", () {
+      var fork = stream.fork();
+      var forkSub = fork.listen(expectAsync((_) {}, count: 0));
+
+      stream.listen(expectAsync((_) => forkSub.cancel()));
+      controller.add(null);
+    });
+
+    test("forking during onError", () {
+      var sub;
+      sub = stream.listen(null, onError: expectAsync((error1) {
+        expect(error1, equals("error 1"));
+        stream.fork().listen(null, onError: expectAsync((error2) {
+          expect(error2, equals("error 2"));
+        }));
+        sub.cancel();
+      }));
+
+      controller.addError("error 1");
+      controller.addError("error 2");
+    });
+
+    test("canceling a fork during onError", () {
+      var fork = stream.fork();
+      var forkSub = fork.listen(expectAsync((_) {}, count: 0));
+
+      stream.listen(null, onError: expectAsync((_) => forkSub.cancel()));
+      controller.addError("error");
+    });
+
+    test("forking during onDone", () {
+      stream.listen(null, onDone: expectAsync(() {
+        expect(stream.fork, throwsStateError);
+      }));
+
+      controller.close();
+    });
+
+    test("canceling a fork during onDone", () {
+      var fork = stream.fork();
+      var forkSub = fork.listen(null, onDone: expectAsync(() {}, count: 0));
+
+      stream.listen(null, onDone: expectAsync(() => forkSub.cancel()));
+      controller.close();
+    });
+  });
+
+  group("throws an error when", () {
+    test("a cancelled stream is forked", () {
+      stream.listen(null).cancel();
+      expect(stream.fork, throwsStateError);
+    });
+
+    test("a cancelled stream is forked even when other forks are alive", () {
+      stream.fork().listen(null);
+      stream.listen(null).cancel();
+
+      expect(controller.hasListener, isTrue);
+      expect(stream.fork, throwsStateError);
+    });
+
+    test("a closed stream is forked", () async {
+      controller.close();
+      await stream.listen(null).asFuture();
+      expect(stream.fork, throwsStateError);
+    });
+  });
+}