Wrap Directory.watch on linux for the watcher package.

pkg/watcher/lib/src/directory_watcher.dart

Index: pkg/watcher/lib/src/directory_watcher.dart
diff --git a/pkg/watcher/lib/src/directory_watcher.dart b/pkg/watcher/lib/src/directory_watcher.dart
index 679e227e8d181cefb7124a272e416824d5b5bc8b..4484c2b77bf194254f18cd14d4e499b07ef0b097 100644
--- a/pkg/watcher/lib/src/directory_watcher.dart
+++ b/pkg/watcher/lib/src/directory_watcher.dart
@@ -7,18 +7,15 @@ library watcher.directory_watcher;
 import 'dart:async';
 import 'dart:io';
 
-import 'package:crypto/crypto.dart';
-
-import 'async_queue.dart';
-import 'stat.dart';
-import 'utils.dart';
 import 'watch_event.dart';
+import 'directory_watcher/linux.dart';
+import 'directory_watcher/polling.dart';
 
 /// Watches the contents of a directory and emits [WatchEvent]s when something
 /// in the directory has changed.
-class DirectoryWatcher {
+abstract class DirectoryWatcher {
   /// The directory whose contents are being monitored.
-  final String directory;
+  String get directory;
 
   /// The broadcast [Stream] of events that have occurred to files in
   /// [directory].
@@ -26,10 +23,12 @@ class DirectoryWatcher {
   /// Changes will only be monitored while this stream has subscribers. Any
   /// file changes that occur during periods when there are no subscribers
   /// will not be reported the next time a subscriber is added.
-  Stream<WatchEvent> get events => _events.stream;
-  StreamController<WatchEvent> _events;
+  Stream<WatchEvent> get events;
 
-  _WatchState _state = _WatchState.UNSUBSCRIBED;
+  /// Whether the watcher is initialized and watching for file changes.
+  ///
+  /// This is true if and only if [ready] is complete.
+  bool get isReady;
 
   /// A [Future] that completes when the watcher is initialized and watching
   /// for file changes.
@@ -41,241 +40,20 @@ class DirectoryWatcher {
   ///
   /// If the watcher is already monitoring, this returns an already complete
   /// future.
-  Future get ready => _ready.future;
-  Completer _ready = new Completer();
-
-  /// The amount of time the watcher pauses between successive polls of the
-  /// directory contents.
-  final Duration pollingDelay;
-
-  /// The previous status of the files in the directory.
-  ///
-  /// Used to tell which files have been modified.
-  final _statuses = new Map<String, _FileStatus>();
-
-  /// The subscription used while [directory] is being listed.
-  ///
-  /// Will be `null` if a list is not currently happening.
-  StreamSubscription<FileSystemEntity> _listSubscription;
-
-  /// The queue of files waiting to be processed to see if they have been
-  /// modified.
-  ///
-  /// Processing a file is asynchronous, as is listing the directory, so the
-  /// queue exists to let each of those proceed at their own rate. The lister
-  /// will enqueue files as quickly as it can. Meanwhile, files are dequeued
-  /// and processed sequentially.
-  AsyncQueue<String> _filesToProcess;
-
-  /// The set of files that have been seen in the current directory listing.
-  ///
-  /// Used to tell which files have been removed: files that are in [_statuses]
-  /// but not in here when a poll completes have been removed.
-  final _polledFiles = new Set<String>();
+  Future get ready;
 
   /// Creates a new [DirectoryWatcher] monitoring [directory].
   ///
-  /// If [pollingDelay] is passed, it specifies the amount of time the watcher
-  /// will pause between successive polls of the directory contents. Making
-  /// this shorter will give more immediate feedback at the expense of doing
-  /// more IO and higher CPU usage. Defaults to one second.
-  DirectoryWatcher(this.directory, {Duration pollingDelay})
-      : pollingDelay = pollingDelay != null ? pollingDelay :
-                                              new Duration(seconds: 1) {
-    _events = new StreamController<WatchEvent>.broadcast(
-        onListen: _watch, onCancel: _cancel);
-
-    _filesToProcess = new AsyncQueue<String>(_processFile,
-        onError: _events.addError);
-  }
-
-  /// Scans to see which files were already present before the watcher was
-  /// subscribed to, and then starts watching the directory for changes.
-  void _watch() {
-    assert(_state == _WatchState.UNSUBSCRIBED);
-    _state = _WatchState.SCANNING;
-    _poll();
-  }
-
-  /// Stops watching the directory when there are no more subscribers.
-  void _cancel() {
-    assert(_state != _WatchState.UNSUBSCRIBED);
-    _state = _WatchState.UNSUBSCRIBED;
-
-    // If we're in the middle of listing the directory, stop.
-    if (_listSubscription != null) _listSubscription.cancel();
-
-    // Don't process any remaining files.
-    _filesToProcess.clear();
-    _polledFiles.clear();
-    _statuses.clear();
-
-    _ready = new Completer();
-  }
-
-  /// Scans the contents of the directory once to see which files have been
-  /// added, removed, and modified.
-  void _poll() {
-    _filesToProcess.clear();
-    _polledFiles.clear();
-
-    endListing() {
-      assert(_state != _WatchState.UNSUBSCRIBED);
-      _listSubscription = null;
-
-      // Null tells the queue consumer that we're done listing.
-      _filesToProcess.add(null);
-    }
-
-    var stream = new Directory(directory).list(recursive: true);
-    _listSubscription = stream.listen((entity) {
-      assert(_state != _WatchState.UNSUBSCRIBED);
-
-      if (entity is! File) return;
-      _filesToProcess.add(entity.path);
-    }, onError: (error, StackTrace stackTrace) {
-      if (!isDirectoryNotFoundException(error)) {
-        // It's some unknown error. Pipe it over to the event stream so the
-        // user can see it.
-        _events.addError(error, stackTrace);
-      }
-
-      // When an error occurs, we end the listing normally, which has the
-      // desired effect of marking all files that were in the directory as
-      // being removed.
-      endListing();
-    }, onDone: endListing, cancelOnError: true);
-  }
-
-  /// Processes [file] to determine if it has been modified since the last
-  /// time it was scanned.
-  Future _processFile(String file) {
-    assert(_state != _WatchState.UNSUBSCRIBED);
-
-    // `null` is the sentinel which means the directory listing is complete.
-    if (file == null) return _completePoll();
-
-    return getModificationTime(file).then((modified) {
-      if (_checkForCancel()) return null;
-
-      var lastStatus = _statuses[file];
-
-      // If its modification time hasn't changed, assume the file is unchanged.
-      if (lastStatus != null && lastStatus.modified == modified) {
-        // The file is still here.
-        _polledFiles.add(file);
-        return null;
-      }
-
-      return _hashFile(file).then((hash) {
-        if (_checkForCancel()) return;
-
-        var status = new _FileStatus(modified, hash);
-        _statuses[file] = status;
-        _polledFiles.add(file);
-
-        // Only notify while in the watching state.
-        if (_state != _WatchState.WATCHING) return;
-
-        // And the file is different.
-        var changed = lastStatus == null || !_sameHash(lastStatus.hash, hash);
-        if (!changed) return;
-
-        var type = lastStatus == null ? ChangeType.ADD : ChangeType.MODIFY;
-        _events.add(new WatchEvent(type, file));
-      });
-    });
-  }
-
-  /// After the directory listing is complete, this determines which files were
-  /// removed and then restarts the next poll.
-  Future _completePoll() {
-    // Any files that were not seen in the last poll but that we have a
-    // status for must have been removed.
-    var removedFiles = _statuses.keys.toSet().difference(_polledFiles);
-    for (var removed in removedFiles) {
-      if (_state == _WatchState.WATCHING) {
-        _events.add(new WatchEvent(ChangeType.REMOVE, removed));
-      }
-      _statuses.remove(removed);
-    }
-
-    if (_state == _WatchState.SCANNING) {
-      _state = _WatchState.WATCHING;
-      _ready.complete();
-    }
-
-    // Wait and then poll again.
-    return new Future.delayed(pollingDelay).then((_) {
-      if (_checkForCancel()) return;
-      _poll();
-    });
-  }
-
-  /// Returns `true` and clears the processing queue if the watcher has been
-  /// unsubscribed.
-  bool _checkForCancel() {
-    if (_state != _WatchState.UNSUBSCRIBED) return false;
-
-    // Don't process any more files.
-    _filesToProcess.clear();
-    return true;
-  }
-
-  /// Calculates the SHA-1 hash of the file at [path].
-  Future<List<int>> _hashFile(String path) {
-    return new File(path).readAsBytes().then((bytes) {
-      var sha1 = new SHA1();
-      sha1.add(bytes);
-      return sha1.close();
-    });
-  }
-
-  /// Returns `true` if [a] and [b] are the same hash value, i.e. the same
-  /// series of byte values.
-  bool _sameHash(List<int> a, List<int> b) {
-    // Hashes should always be the same size.
-    assert(a.length == b.length);
-
-    for (var i = 0; i < a.length; i++) {
-      if (a[i] != b[i]) return false;
-    }
-
-    return true;
-  }
-}
-
-/// Enum class for the states that the [DirectoryWatcher] can be in.
-class _WatchState {
-  /// There are no subscribers to the watcher's event stream and no watching
-  /// is going on.
-  static const UNSUBSCRIBED = const _WatchState("unsubscribed");
-
-  /// There are subscribers and the watcher is doing an initial scan of the
-  /// directory to see which files were already present before watching started.
+  /// If a native directory watcher is available for this platform, this will
+  /// use it. Otherwise, it will fall back to a [PollingDirectoryWatcher].
   ///
-  /// The watcher does not send notifications for changes that occurred while
-  /// there were no subscribers, or for files already present before watching.
-  /// The initial scan is used to determine what "before watching" state of
-  /// the file system was.
-  static const SCANNING = const _WatchState("scanning");
-
-  /// There are subscribers and the watcher is polling the directory to look
-  /// for changes.
-  static const WATCHING = const _WatchState("watching");
-
-  /// The name of the state.
-  final String name;
-
-  const _WatchState(this.name);
+  /// If [_pollingDelay] is passed, it specifies the amount of time the watcher
+  /// will pause between successive polls of the directory contents. Making this
+  /// shorter will give more immediate feedback at the expense of doing more IO
+  /// and higher CPU usage. Defaults to one second. Ignored for non-polling
+  /// watchers.
+  factory DirectoryWatcher(String directory, {Duration pollingDelay}) {
+    if (Platform.isLinux) return new LinuxDirectoryWatcher(directory);
+    return new PollingDirectoryWatcher(directory, pollingDelay: pollingDelay);
+  }
 }
-
-class _FileStatus {
-  /// The last time the file was modified.
-  DateTime modified;
-
-  /// The SHA-1 hash of the contents of the file.
-  List<int> hash;
-
-  _FileStatus(this.modified, this.hash);
-}