Reset user data directory and disk cache directory after downgrade.

chrome/browser/downgrade/user_data_downgrade.cc

+// Copyright 2016 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/downgrade/user_data_downgrade.h"
+
+#include <string>
+
+#include "base/bind.h"
+#include "base/command_line.h"
+#include "base/files/file_enumerator.h"
+#include "base/files/file_path.h"
+#include "base/files/file_util.h"
+#include "base/path_service.h"
+#include "base/strings/string_util.h"
+#include "base/strings/stringprintf.h"
+#include "base/strings/utf_string_conversions.h"
+#include "base/time/time.h"
+#include "base/version.h"
+#include "base/win/registry.h"
+#include "chrome/browser/policy/policy_path_parser.h"
+#include "chrome/common/chrome_constants.h"
+#include "chrome/common/chrome_paths.h"
+#include "chrome/common/chrome_switches.h"
+#include "chrome/common/chrome_version.h"
+#include "chrome/installer/util/install_util.h"
+#include "content/public/browser/browser_thread.h"
+
+namespace {
+
+constexpr base::FilePath::CharType g_delete_suffix[] =
+    FILE_PATH_LITERAL(".CHROME_DELETE");
+bool g_is_browser_test = false;
+
+// Return the disk cache dir override value if exists or empty path for default
+// disk cache dir.
+base::FilePath GetDiskCacheDir() {
+  base::FilePath disk_cache_dir;
+  policy::path_parser::CheckDiskCacheDirPolicy(&disk_cache_dir);
+  if (disk_cache_dir.empty()) {
+    base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
+    disk_cache_dir = command_line->GetSwitchValuePath(switches::kDiskCacheDir);
+  }
+  if (disk_cache_dir.ReferencesParent())
+    return base::MakeAbsoluteFilePath(disk_cache_dir);
+  return disk_cache_dir;
+}
+
+base::FilePath GetLastChromeVersionFile(const base::FilePath& user_data_dir) {
+  const base::FilePath::StringType last_chrome_version =
+      FILE_PATH_LITERAL("Last Chrome Version");

[sky, 2016/06/03 00:04:24]

nit: Chrome Version? Generally we don't use 'Last' for things that are current.
For example, we have Bookmarks, not 'Last Bookmarks'.

[zmin, 2016/06/03 15:46:52]

I use 'Last' here because this file is used to indicate the version of last
launched Chrome so that we're able to know whether the profiles needs to be
deleted or not.

What's more, I think Chrome use 'last' in 'Local State' file for chrome version
too.

[sky, 2016/06/03 18:18:03]

I'm still of the opinion 'Last' is unnecessary here. I would also avoid 'Chrome'
too as I assume this will be written for chromium builds too.

+  return user_data_dir.Append(last_chrome_version);
+}
+
+base::Version GetLastChromeVersion(const base::FilePath& user_data_dir) {
+  std::string last_chrome_version_str;
+  if (base::ReadFileToString(GetLastChromeVersionFile(user_data_dir),
+                             &last_chrome_version_str)) {
+    return base::Version(
+        base::TrimWhitespaceASCII(last_chrome_version_str, base::TRIM_ALL)
+            .as_string());
+  }
+  return base::Version();
+}
+
+// Return the temporary path that |source_path| will be renamed to later.
+base::FilePath GetTempDirNameForDelete(const base::FilePath& source_path) {
+  if (source_path.empty())
+    return base::FilePath();
+
+  base::FilePath target_path(source_path.AddExtension(g_delete_suffix));
+  int uniquifier = base::GetUniquePathNumber(source_path, g_delete_suffix);
+  if (uniquifier < 0)
+    return base::FilePath();
+  if (uniquifier > 0) {
+    return target_path.InsertBeforeExtensionASCII(
+        base::StringPrintf(" (%d)", uniquifier));
+  }
+
+  return target_path;
+}
+
+// Rename the |source| directory to |target|. Create |source| directory after
+// rename if |recreate| is true.
+void RenameDirectory(const base::FilePath& source,
+                     const base::FilePath& target,
+                     bool recreate) {
+  if (!source.empty() && !target.empty() && base::Move(source, target) &&

[sky, 2016/06/03 00:04:24]

What if Move fails? Doesn't that leave things in a weird state?

[zmin, 2016/06/03 15:46:52]

If move failed, we just end up with a higher version profile with lower version
Chrome and a pop up error window if the format is different.

[sky, 2016/06/03 18:18:03]

That's assuming every file deals with a version from the future, which I don't
believe is the case. If it did, then we wouldn't need to nuke it, right?

+      recreate) {
+    base::CreateDirectory(source);
+  }
+}
+
+void DeleteAllRenamedUserDirectories(const base::FilePath& path) {
+  if (path.empty())
+    return;
+  base::FilePath dir_name = path.DirName();
+  // Does not support root directory
+  if (dir_name == path)
+    return;
+
+  base::FilePath::StringType pattern =
+      path.BaseName().value() + FILE_PATH_LITERAL("*") + g_delete_suffix;
+  base::FileEnumerator enumerator(dir_name, false,
+                                  base::FileEnumerator::DIRECTORIES, pattern);
+  for (base::FilePath dir = enumerator.Next(); !dir.empty();
+       dir = enumerator.Next()) {
+    base::DeleteFile(dir, true);
+  }
+}
+
+void DeleteMovedUserData(const base::FilePath& user_data_dir,
+                         const base::FilePath& disk_cache_dir) {
+  DeleteAllRenamedUserDirectories(user_data_dir);
+  DeleteAllRenamedUserDirectories(disk_cache_dir);
+}
+
+}  // namespace
+
+void MoveUserDataForFirstRunAfterDowngrade() {
+  base::FilePath user_data_dir;
+  PathService::Get(chrome::DIR_USER_DATA, &user_data_dir);

[sky, 2016/06/03 00:04:23]

Check return value.

[zmin, 2016/06/03 15:46:52]

Done.

+  base::Version current_version(chrome::kChromeVersion);
+  base::FilePath cur_chrome_exe;
+  if (!PathService::Get(base::FILE_EXE, &cur_chrome_exe))
+    return;
+  base::Version downgrade_version = InstallUtil::GetDowngradeVersion(
+      !InstallUtil::IsPerUserInstall(cur_chrome_exe),
+      BrowserDistribution::GetDistribution());
+  if (downgrade_version.IsValid() && downgrade_version > current_version) {
+    base::FilePath disk_cache_dir(GetDiskCacheDir());
+    // Without the browser process singleton protection, the directory may be
+    // copied multiple times. In order to prevent that from happening, the temp
+    // directory's name will be computed before the LastChromeVersion file is
+    // read. Because the deletion will be scheduled after the singleton is
+    // acquired, the directory can only be moved twice in the worst case.
+    // Also, doing this after the downgrade version check to reduce performance
+    // cost for the normal launch.
+    base::FilePath temp_disk_cache_dir(GetTempDirNameForDelete(disk_cache_dir));
+    base::FilePath temp_user_data_dir(GetTempDirNameForDelete(user_data_dir));
+    base::Version last_chrome_version = GetLastChromeVersion(user_data_dir);
+    if (last_chrome_version.IsValid() &&

[sky, 2016/06/03 00:04:24]

Move this earlier on. You don't need to figure out temp dirs name is the
last_chrome_version is bogus.

[zmin, 2016/06/03 15:46:52]

Finding temp dir name is put before this on purpose. It is used to prevent
multiple moving without singleton protection. The comments above describes more
details.

+        last_chrome_version > current_version) {
+      // Do not recreate |disk_cache_dir| as it will be initialized later.
+      RenameDirectory(disk_cache_dir, temp_disk_cache_dir, false);
+      RenameDirectory(user_data_dir, temp_user_data_dir, true);
+    }
+  }
+  base::WriteFile(GetLastChromeVersionFile(user_data_dir),

[sky, 2016/06/03 00:04:23]

I find it confusing that a function named
MoveUserDataForFirstRunAfterDowngrade() is also responsible for updating the
version string. I think this code would be clearer if there is a specific
function for updating the version string.

[zmin, 2016/06/03 15:46:52]

Done.

+                  chrome::kChromeVersion, strlen(chrome::kChromeVersion));
+}
+
+void DeleteMovedUserDataSoon() {
+  base::FilePath user_data_dir;
+  PathService::Get(chrome::DIR_USER_DATA, &user_data_dir);
+  if (g_is_browser_test) {
+    // Delete task will always be posted and executed for browser test.
+    content::BrowserThread::PostBlockingPoolTask(
+        FROM_HERE,
+        base::Bind(&DeleteMovedUserData, user_data_dir, GetDiskCacheDir()));
+  } else {
+    content::BrowserThread::PostAfterStartupTask(
+        FROM_HERE, content::BrowserThread::GetBlockingPool()
+                       ->GetTaskRunnerWithShutdownBehavior(
+                           base::SequencedWorkerPool::CONTINUE_ON_SHUTDOWN),
+        base::Bind(&DeleteMovedUserData, user_data_dir, GetDiskCacheDir()));
+  }
+}
+
+void SimulateDowngradeForTest(bool is_browser_test) {
+  g_is_browser_test = is_browser_test;
+}