Reland 56341 - Add support for watching directories to FileWatcher.

BUG=none
TEST=Unit tests in file_watcher_unittest.cc.

Review URL: http://codereview.chromium.org/3184010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@56670 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 243 insertions, 0 deletions

diff --git a/chrome/browser/file_path_watcher_win.cc b/chrome/browser/file_path_watcher_win.cc
new file mode 100644
index 0000000..194e91e
--- /dev/null
+++ b/chrome/browser/file_path_watcher_win.cc
@@ -0,0 +1,243 @@
+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/file_path_watcher.h"
+
+#include "base/file_path.h"
+#include "base/file_util.h"
+#include "base/logging.h"
+#include "base/object_watcher.h"
+#include "base/ref_counted.h"
+#include "base/time.h"
+
+namespace {
+
+class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate,
+                            public base::ObjectWatcher::Delegate {
+ public:
+  FilePathWatcherImpl() : delegate_(NULL), handle_(INVALID_HANDLE_VALUE) {}
+
+  virtual bool Watch(const FilePath& path, FilePathWatcher::Delegate* delegate);
+  virtual void Cancel();
+
+  // Callback from MessageLoopForIO.
+  virtual void OnObjectSignaled(HANDLE object);
+
+ private:
+  virtual ~FilePathWatcherImpl();
+
+  // Setup a watch handle for directory |dir|. Returns true if no fatal error
+  // occurs. |handle| will receive the handle value if |dir| is watchable,
+  // otherwise INVALID_HANDLE_VALUE.
+  static bool SetupWatchHandle(const FilePath& dir, HANDLE* handle)
+      WARN_UNUSED_RESULT;
+
+  // (Re-)Initialize the watch handle.
+  bool UpdateWatch() WARN_UNUSED_RESULT;
+
+  // Destroy the watch handle.
+  void DestroyWatch();
+
+  // Delegate to notify upon changes.
+  scoped_refptr<FilePathWatcher::Delegate> delegate_;
+
+  // Path we're supposed to watch (passed to delegate).
+  FilePath target_;
+
+  // Handle for FindFirstChangeNotification.
+  HANDLE handle_;
+
+  // ObjectWatcher to watch handle_ for events.
+  base::ObjectWatcher watcher_;
+
+  // Keep track of the last modified time of the file.  We use nulltime
+  // to represent the file not existing.
+  base::Time last_modified_;
+
+  // The time at which we processed the first notification with the
+  // |last_modified_| time stamp.
+  base::Time first_notification_;
+
+  DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl);
+};
+
+bool FilePathWatcherImpl::Watch(const FilePath& path,
+                                FilePathWatcher::Delegate* delegate) {
+  DCHECK(target_.value().empty());  // Can only watch one path.
+  delegate_ = delegate;
+  target_ = path;
+
+  if (!UpdateWatch())
+    return false;
+
+  watcher_.StartWatching(handle_, this);
+
+  return true;
+}
+
+void FilePathWatcherImpl::Cancel() {
+  // Switch to the file thread if necessary so we can stop |watcher_|.
+  if (!ChromeThread::CurrentlyOn(ChromeThread::FILE)) {
+    ChromeThread::PostTask(ChromeThread::FILE, FROM_HERE,
+        NewRunnableMethod(this, &FilePathWatcherImpl::Cancel));
+    return;
+  }
+
+  if (handle_ != INVALID_HANDLE_VALUE)
+    DestroyWatch();
+}
+
+void FilePathWatcherImpl::OnObjectSignaled(HANDLE object) {
+  DCHECK(object == handle_);
+  // Make sure we stay alive through the body of this function.
+  scoped_refptr<FilePathWatcherImpl> keep_alive(this);
+
+  if (!UpdateWatch()) {
+    delegate_->OnError();
+    return;
+  }
+
+  // Check whether the event applies to |target_| and notify the delegate.
+  file_util::FileInfo file_info;
+  bool file_exists = file_util::GetFileInfo(target_, &file_info);
+  if (file_exists && (last_modified_.is_null() ||
+      last_modified_ != file_info.last_modified)) {
+    last_modified_ = file_info.last_modified;
+    first_notification_ = base::Time::Now();
+    delegate_->OnFilePathChanged(target_);
+  } else if (file_exists && !first_notification_.is_null()) {
+    // The target's last modification time is equal to what's on record. This
+    // means that either an unrelated event occurred, or the target changed
+    // again (file modification times only have a resolution of 1s). Comparing
+    // file modification times against the wall clock is not reliable to find
+    // out whether the change is recent, since this code might just run too
+    // late. Moreover, there's no guarantee that file modification time and wall
+    // clock times come from the same source.
+    //
+    // Instead, the time at which the first notification carrying the current
+    // |last_notified_| time stamp is recorded. Later notifications that find
+    // the same file modification time only need to be forwarded until wall
+    // clock has advanced one second from the initial notification. After that
+    // interval, client code is guaranteed to having seen the current revision
+    // of the file.
+    if (base::Time::Now() - first_notification_ >
+        base::TimeDelta::FromSeconds(1)) {
+      // Stop further notifications for this |last_modification_| time stamp.
+      first_notification_ = base::Time();
+    }
+    delegate_->OnFilePathChanged(target_);
+  } else if (!file_exists && !last_modified_.is_null()) {
+    last_modified_ = base::Time();
+    delegate_->OnFilePathChanged(target_);
+  }
+
+  // The watch may have been cancelled by the callback.
+  if (handle_ != INVALID_HANDLE_VALUE)
+    watcher_.StartWatching(handle_, this);
+}
+
+FilePathWatcherImpl::~FilePathWatcherImpl() {
+  if (handle_ != INVALID_HANDLE_VALUE)
+    DestroyWatch();
+}
+
+// static
+bool FilePathWatcherImpl::SetupWatchHandle(const FilePath& dir,
+                                           HANDLE* handle) {
+  *handle = FindFirstChangeNotification(
+      dir.value().c_str(),
+      false,  // Don't watch subtrees
+      FILE_NOTIFY_CHANGE_FILE_NAME | FILE_NOTIFY_CHANGE_SIZE |
+      FILE_NOTIFY_CHANGE_LAST_WRITE | FILE_NOTIFY_CHANGE_DIR_NAME |
+      FILE_NOTIFY_CHANGE_ATTRIBUTES | FILE_NOTIFY_CHANGE_SECURITY);
+  if (*handle != INVALID_HANDLE_VALUE) {
+    // Make sure the handle we got points to an existing directory. It seems
+    // that windows sometimes hands out watches to direectories that are
+    // about to go away, but doesn't sent notifications if that happens.
+    if (!file_util::DirectoryExists(dir)) {
+      FindCloseChangeNotification(*handle);
+      *handle = INVALID_HANDLE_VALUE;
+    }
+    return true;
+  }
+
+  // If FindFirstChangeNotification failed because the target directory
+  // doesn't exist, access is denied (happens if the file is already gone but
+  // there are still handles open), or the target is not a directory, try the
+  // immediate parent directory instead.
+  DWORD error_code = GetLastError();
+  if (error_code != ERROR_FILE_NOT_FOUND &&
+      error_code != ERROR_PATH_NOT_FOUND &&
+      error_code != ERROR_ACCESS_DENIED &&
+      error_code != ERROR_DIRECTORY) {
+    PLOG(ERROR) << "FindFirstChangeNotification failed for "
+                << dir.value();
+    return false;
+  }
+
+  return true;
+}
+
+bool FilePathWatcherImpl::UpdateWatch() {
+  if (handle_ != INVALID_HANDLE_VALUE)
+    DestroyWatch();
+
+  file_util::FileInfo file_info;
+  if (file_util::GetFileInfo(target_, &file_info)) {
+    last_modified_ = file_info.last_modified;
+    first_notification_ = base::Time::Now();
+  }
+
+  // Start at the target and walk up the directory chain until we succesfully
+  // create a watch handle in |handle_|. |child_dirs| keeps a stack of child
+  // directories stripped from target, in reverse order.
+  std::vector<FilePath> child_dirs;
+  FilePath watched_path(target_);
+  while (true) {
+    if (!SetupWatchHandle(watched_path, &handle_))
+      return false;
+
+    // Break if a valid handle is returned. Try the parent directory otherwise.
+    if (handle_ != INVALID_HANDLE_VALUE)
+      break;
+
+    // Abort if we hit the root directory.
+    child_dirs.push_back(watched_path.BaseName());
+    FilePath parent(watched_path.DirName());
+    if (parent == watched_path) {
+      LOG(ERROR) << "Reached the root directory";
+      return false;
+    }
+    watched_path = parent;
+  }
+
+  // At this point, handle_ is valid. However, the bottom-up search that the
+  // above code performs races against directory creation. So try to walk back
+  // down and see whether any children appeared in the mean time.
+  while (!child_dirs.empty()) {
+    watched_path = watched_path.Append(child_dirs.back());
+    child_dirs.pop_back();
+    HANDLE temp_handle = INVALID_HANDLE_VALUE;
+    if (!SetupWatchHandle(watched_path, &temp_handle))
+      return false;
+    if (temp_handle == INVALID_HANDLE_VALUE)
+      break;
+    FindCloseChangeNotification(handle_);
+    handle_ = temp_handle;
+  }
+
+  return true;
+}
+
+void FilePathWatcherImpl::DestroyWatch() {
+  watcher_.StopWatching();
+  FindCloseChangeNotification(handle_);
+  handle_ = INVALID_HANDLE_VALUE;
+}
+
+}  // namespace
+
+FilePathWatcher::FilePathWatcher() {
+  impl_ = new FilePathWatcherImpl();
+}