Wrap Directory.watch on Mac OS for the watcher package.

pkg/watcher/lib/src/directory_watcher/mac_os.dart

Index: pkg/watcher/lib/src/directory_watcher/mac_os.dart
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+// Copyright (c) 2013, 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 watcher.directory_watcher.mac_os;
+
+import 'dart:async';
+import 'dart:io';
+
+import '../constructable_file_system_event.dart';
+import '../path_set.dart';
+import '../utils.dart';
+import '../watch_event.dart';
+import 'resubscribable.dart';
+
+import 'package:path/path.dart' as p;
+
+/// Uses the FSEvents subsystem to watch for filesystem events.
+///
+/// FSEvents has two main idiosynchrasies that this class works around. First,

[Bob Nystrom, 2013/11/09 00:42:57]

"idiosyncrasies"

[nweiz, 2013/11/09 02:19:26]

Ten Signs You've Been Writing The Word "Asynchronous" Too Often

+/// it will occasionally report events that occurred before the filesystem watch
+/// was initiated. Second, if multiple events happen to the same file in close
+/// succession, it won't report them in the order they occurred. See issue
+/// 14373.
+///
+/// This also works around issues 14793, 14806, and 14849 in the implementation
+/// of [Directory.watch].
+class MacOSDirectoryWatcher extends ResubscribableDirectoryWatcher {
+  MacOSDirectoryWatcher(String directory)
+      : super(directory, () => new _MacOSDirectoryWatcher(directory));
+}
+
+class _MacOSDirectoryWatcher implements ManuallyClosedDirectoryWatcher {
+  final String directory;
+
+  Stream<WatchEvent> get events => _eventsController.stream;
+  final _eventsController = new StreamController<WatchEvent>.broadcast();
+
+  bool get isReady => _readyCompleter.isCompleted;
+
+  Future get ready => _readyCompleter.future;
+  final _readyCompleter = new Completer();
+
+  /// The number of event batches that have been received from
+  /// [Directory.watch].
+  ///
+  /// This is used to determine if the [Directory.watch] stream was falsely
+  /// closed due to issue 14849. A close caused by events in the past will only
+  /// happen before or immediately after the first batch of events.
+  int batches = 0;
+
+  /// The set of files that are known to exist recursively within the watched
+  /// directory.
+  ///
+  /// The state of files on the filesystem is compared against this to determine
+  /// the real change that occurred when working around issue 14373. This is
+  /// also used to emit REMOVE events when subdirectories are moved out of the
+  /// watched directory.
+  final PathSet _files;
+
+  /// The subscription to the stream returned by [Directory.watch].
+  ///
+  /// This is separate from [_subscriptions] because this stream occasionally
+  /// needs to be resubscribed in order to work around issue 14849.
+  StreamSubscription<FileSystemEvent> _watchSubscription;
+
+  /// A set of subscriptions that this watcher subscribes to.
+  ///
+  /// These are gathered together so that they may all be canceled when the
+  /// watcher is closed. This does not include [_watchSubscription].
+  final _subscriptions = new Set<StreamSubscription>();
+
+  _MacOSDirectoryWatcher(String directory)
+      : directory = directory,
+        _files = new PathSet(directory) {
+    _startWatch();
+
+    _listen(new Directory(directory).list(recursive: true),
+        (entity) {
+      if (entity is! Directory) _files.add(entity.path);
+    },
+        onError: _emitError,
+        onDone: _readyCompleter.complete,
+        cancelOnError: true);
+  }
+
+  void close() {
+    for (var subscription in _subscriptions) {
+      subscription.cancel();
+    }
+    _subscriptions.clear();
+    if (_watchSubscription != null) _watchSubscription.cancel();
+    _watchSubscription = null;
+    _eventsController.close();
+  }
+
+  /// The callback that's run when [Directory.watch] emits a batch of events.
+  void _onBatch(List<FileSystemEvent> batch) {
+    batches++;
+
+    _sortEvents(batch).forEach((path, events) {
+      var canonicalEvent = _canonicalEvent(events);
+      events = canonicalEvent == null ? [] : [canonicalEvent];
+      if (events.isEmpty) events = _eventsBasedOnFileSystem(path);

[Bob Nystrom, 2013/11/09 00:42:57]

Why set to an empty list above just to change it something else here?

[nweiz, 2013/11/09 02:19:26]

Good point. Changed.

+
+      for (var event in events) {
+        if (event is FileSystemCreateEvent) {
+          if (!event.isDirectory) {
+            _emitEvent(ChangeType.ADD, path);
+            _files.add(path);
+            continue;
+          }
+
+          _listen(new Directory(path).list(recursive: true), (entity) {
+            if (entity is Directory) return;
+            _emitEvent(ChangeType.ADD, entity.path);
+            _files.add(entity.path);
+          }, onError: _emitError, cancelOnError: true);
+        } else if (event is FileSystemModifyEvent) {
+          assert(!event.isDirectory);
+          _emitEvent(ChangeType.MODIFY, path);
+        } else {
+          assert(event is FileSystemDeleteEvent);
+          for (var removedPath in _files.remove(path)) {
+            _emitEvent(ChangeType.REMOVE, removedPath);
+          }
+        }
+      }
+    });
+  }
+
+  /// Sort all the events in a batch into sets based on their path.
+  ///
+  /// A single input event may result in multiple events in the returned map;
+  /// for example, a MOVE event becomes a DELETE event for the source and a
+  /// CREATE event for the destination.
+  ///
+  /// The returned events won't contain any [FileSystemMoveEvent]s, nor will it
+  /// contain any events relating to [directory].

[Bob Nystrom, 2013/11/09 00:42:57]

"[directory]" is not a parameter here.

[nweiz, 2013/11/09 02:19:26]

It is a field on the class, though.

+  Map<String, Set<FileSystemEvent>> _sortEvents(List<FileSystemEvent> batch) {
+    var eventsForPaths = {};
+
+    // FSEvents can report past events, including events on the root directory
+    // such as it being created. We want to ignore these. If the directory is
+    // really deleted, that's handled by [_onDone].
+    batch = batch.where((event) => event.path != directory).toList();

[Bob Nystrom, 2013/11/09 00:42:57]

Is the .toList() needed here?

[nweiz, 2013/11/09 02:19:26]

Since Iterables are lazy, the [where] will be executed again and again whenever
we call any method on [batch]. Using [toList] means it's only executed once.

Also I'd have to rename the variable if I didn't make it a list, since [batch]
is typed as a List.

+
+    // Events within directories that already have events are superfluous; the
+    // directory's full contents will be examined anyway, so we ignore such
+    // events. Emitting them could cause useless or out-of-order events.
+    var directories = unionAll(batch.map((event) {
+      if (!event.isDirectory) return new Set();
+      if (event is! FileSystemMoveEvent) return new Set.from([event.path]);
+      return new Set.from([event.path, event.destination]);
+    }));
+    isInModifiedDirectory(path) =>

[Bob Nystrom, 2013/11/09 00:42:57]

Nit: blank line above this please.

[nweiz, 2013/11/09 02:19:26]

Done.

+        directories.any((dir) => path != dir && path.startsWith(dir));
+
+    addEvent(path, event) {
+      if (isInModifiedDirectory(path)) return;
+      var set = eventsForPaths.putIfAbsent(path, () => new Set());
+      set.add(event);
+    }
+
+    for (var event in batch.where((event) => event is! FileSystemMoveEvent)) {
+      addEvent(event.path, event);
+    }
+
+    // Issue 14806 means that move events can be misleading if they're in the
+    // same batch as another modification of a related file. If they are, we
+    // make the event set empty to ensure we check the state of the filesystem.
+    // Otherwise, treat them as a DELETE followed by an ADD.
+    for (var event in batch.where((event) => event is FileSystemMoveEvent)) {
+      if (eventsForPaths.containsKey(event.path) ||
+          eventsForPaths.containsKey(event.destination)) {
+
+        if (!isInModifiedDirectory(event.path)) {
+          eventsForPaths[event.path] = new Set();
+        }
+        if (!isInModifiedDirectory(event.destination)) {
+          eventsForPaths[event.destination] = new Set();
+        }
+
+        continue;
+      }
+
+      addEvent(event.path, new ConstructableFileSystemDeleteEvent(
+          event.path, event.isDirectory));
+      addEvent(event.destination, new ConstructableFileSystemCreateEvent(
+          event.path, event.isDirectory));
+    }
+
+    return eventsForPaths;
+  }
+
+  /// Returns the canonical event from a batch of events on the same path, if
+  /// one exists.
+  ///
+  /// If [batch] doesn't contain any contradictory events (e.g. DELETE and
+  /// CREATE, or events with different values for [isDirectory]), this returns a
+  /// single event that describes that happened to the path in question.

[Bob Nystrom, 2013/11/09 00:42:57]

"that happened" -> "what happened".

[nweiz, 2013/11/09 02:19:26]

Done.

+  ///
+  /// If [batch] does contain contradictory events, this returns `null` to
+  /// indicate that the state of the path on the filesystem should be checked to
+  /// determine what occurred.
+  FileSystemEvent _canonicalEvent(Set<FileSystemEvent> batch) {
+    // An empty batch indicates that we've learned earlier that the batch is
+    // contradictory (e.g. because of a move).
+    if (batch.isEmpty) return null;
+
+    var type = batch.first.type;
+    var isDir = batch.first.isDirectory;
+
+    for (var event in batch.skip(1)) {
+      // If one event reports that the file is a directory and another event
+      // doesn't, that's a contradiction so we should return null.

[Bob Nystrom, 2013/11/09 00:42:57]

Remove "so we should return null".

[nweiz, 2013/11/09 02:19:26]

Done.

[nweiz, 2013/11/09 02:19:26]

Done.

+      if (isDir != event.isDirectory) return null;
+
+      // Modify events don't contradict either CREATE or REMOVE events. We can
+      // safely assume the file was modified after a CREATE or before the
+      // REMOVE; otherwise there will also be a REMOVE or CREATE event
+      // (respectively) that will be contradictory.
+      if (event is FileSystemModifyEvent) continue;
+      assert(event is FileSystemCreateEvent || event is FileSystemDeleteEvent);
+
+      // If we previously thought this was a MODIFY, we now consider it to be a
+      // CREATE or REMOVE event. This is safe for the same reason as above.
+      if (type == FileSystemEvent.MODIFY) {
+        type = event.type;
+        continue;
+      }
+
+      // A CREATE event contradicts a REMOVE event and vice versa.
+      assert(type == FileSystemEvent.CREATE || type == FileSystemEvent.DELETE);
+      if (type != event.type) return null;
+    }
+
+    switch (type) {
+      case FileSystemEvent.CREATE:
+        // Issue 14793 means that CREATE events can actually mean DELETE, so we
+        // should always check the filesystem for them.
+        return null;
+      case FileSystemEvent.DELETE:
+        return new ConstructableFileSystemDeleteEvent(batch.first.path, isDir);
+      case FileSystemEvent.MODIFY:
+        return new ConstructableFileSystemModifyEvent(
+            batch.first.path, isDir, false);
+      default: assert(false);
+    }
+  }
+
+  /// Returns one or more events that describe the change between the last known
+  /// state of [path] and its current state on the filesystem.
+  ///
+  /// This returns a list whose order should be reflected in the events emitted
+  /// to the user, unlike the batched events from [Directory.watch]. The
+  /// returned list may be empty, indicating that no changes occurred to [path]
+  /// (probably indicating that it was created and then immediately deleted).
+  List<FileSystemEvent> _eventsBasedOnFileSystem(String path) {
+    var fileExisted = _files.contains(path);
+    var dirExisted = _files.containsDir(path);
+    var fileExists = new File(path).existsSync();
+    var dirExists = new Directory(path).existsSync();
+
+    var events = [];
+    if (fileExisted) {
+      if (fileExists) {
+        events.add(new ConstructableFileSystemModifyEvent(path, false, false));
+      } else {
+        events.add(new ConstructableFileSystemDeleteEvent(path, false));
+      }
+    } else if (dirExisted) {
+      if (dirExists) {
+        // If we got contradictory events for a directory that used to exist and
+        // still exists, we need to rescan the whole thing in case it was
+        // replaced with a different directory.
+        events.add(new ConstructableFileSystemDeleteEvent(path, true));
+        events.add(new ConstructableFileSystemCreateEvent(path, true));
+      } else {
+        events.add(new ConstructableFileSystemDeleteEvent(path, true));
+      }
+    }
+
+    if (!fileExisted && fileExists) {
+      events.add(new ConstructableFileSystemCreateEvent(path, false));
+    } else if (!dirExisted && dirExists) {
+      events.add(new ConstructableFileSystemCreateEvent(path, true));
+    }
+
+    return events;
+  }
+
+  /// The callback that's run when the [Directory.watch] stream is closed.
+  void _onDone() {
+    _watchSubscription = null;
+
+    // If the directory still exists and we haven't seen more than one batch,
+    // this is probably issue 14849 rather than a real close event. We should
+    // just restart the watcher.
+    if (batches < 2 && new Directory(directory).existsSync()) {
+      _startWatch();
+      return;
+    }
+
+    // FSEvents can fail to report the contents of the directory being removed
+    // when the directory itself is removed, so we need to manually mark the as
+    // removed.
+    for (var file in _files.toSet()) {
+      _emitEvent(ChangeType.REMOVE, file);
+    }
+    _files.clear();
+    close();
+  }
+
+  /// Start or restart the underlying [Directory.watch] stream.
+  void _startWatch() {
+    // Batch the FSEvent changes together so that we can dedup events.
+    var innerStream = new Directory(directory).watch(recursive: true).transform(
+        new BatchedStreamTransformer<FileSystemEvent>());
+    _watchSubscription = innerStream.listen(_onBatch,
+        onError: _eventsController.addError,
+        onDone: _onDone);
+  }
+
+  /// Emit an event with the given [type] and [path].
+  void _emitEvent(ChangeType type, String path) {
+    if (!isReady) return;
+
+    // Don't emit ADD events for files that we already know about. Such an event
+    // probably comes from FSEvents reporting an add that happened prior to the
+    // watch beginning.
+    if (type == ChangeType.ADD && _files.contains(path)) return;
+
+    _eventsController.add(new WatchEvent(type, path));
+  }
+
+  /// Emit an error, then close the watcher.
+  void _emitError(error, StackTrace stackTrace) {
+    _eventsController.add(error, stackTrace);
+    close();
+  }
+
+  /// Like [Stream.listen], but automatically adds the subscription to
+  /// [_subscriptions] so that it can be canceled when [close] is called.
+  void _listen(Stream stream, void onData(event), {Function onError,
+      void onDone(), bool cancelOnError}) {
+    var subscription;
+    subscription = stream.listen(onData, onError: onError, onDone: () {
+      _subscriptions.remove(subscription);
+      if (onDone != null) onDone();
+    }, cancelOnError: cancelOnError);
+    _subscriptions.add(subscription);
+  }
+}