Introduce a new framework for back-and-forth tracked/protected preferences migration.

chrome/browser/prefs/tracked/tracked_preferences_migration.cc

Index: chrome/browser/prefs/tracked/tracked_preferences_migration.cc
diff --git a/chrome/browser/prefs/tracked/tracked_preferences_migration.cc b/chrome/browser/prefs/tracked/tracked_preferences_migration.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c358256f06b4f50ff9e88b6045c82634d2b41586
--- /dev/null
+++ b/chrome/browser/prefs/tracked/tracked_preferences_migration.cc
@@ -0,0 +1,267 @@
+// Copyright 2014 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/prefs/tracked/tracked_preferences_migration.h"
+
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/values.h"
+#include "chrome/browser/prefs/interceptable_pref_filter.h"
+
+namespace {
+
+class TrackedPreferencesMigrator
+    : public base::RefCounted<TrackedPreferencesMigrator> {
+ public:
+  TrackedPreferencesMigrator(
+      const std::set<std::string>& unprotected_pref_names,
+      const std::set<std::string>& protected_pref_names,
+      const base::Callback<void(const std::string& key)>&
+          unprotected_store_cleaner,
+      const base::Callback<void(const std::string& key)>&
+          protected_store_cleaner,
+      const base::Callback<void(const base::Closure&)>&
+          register_on_successful_unprotected_store_write_callback,
+      const base::Callback<void(const base::Closure&)>&
+          register_on_successful_protected_store_write_callback,
+      InterceptablePrefFilter* unprotected_pref_filter,
+      InterceptablePrefFilter* protected_pref_filter);
+
+ private:
+  friend class base::RefCounted<TrackedPreferencesMigrator>;
+
+  enum PrefFilterID {
+    UNPROTECTED_PREF_FILTER,
+    PROTECTED_PREF_FILTER
+  };
+
+  ~TrackedPreferencesMigrator();
+
+  // Stores the data coming in from the filter identified by |id| into this
+  // class and then calls MigrateIfReady();
+  void InterceptFilterOnLoad(
+      PrefFilterID id,
+      const InterceptablePrefFilter::FinalizeFilterOnLoadCallback&
+          finalize_filter_on_load,
+      scoped_ptr<base::DictionaryValue> prefs);
+
+  // Proceeds with migration if both |unprotected_prefs_| and |protected_prefs_|
+  // have been set.
+  void MigrateIfReady();
+
+  const std::set<std::string> unprotected_pref_names_;
+  const std::set<std::string> protected_pref_names_;
+
+  const base::Callback<void(const std::string& key)> unprotected_store_cleaner_;
+  const base::Callback<void(const std::string& key)> protected_store_cleaner_;
+  const base::Callback<void(const base::Closure&)>
+      register_on_successful_unprotected_store_write_callback_;
+  const base::Callback<void(const base::Closure&)>
+      register_on_successful_protected_store_write_callback_;
+
+  InterceptablePrefFilter::FinalizeFilterOnLoadCallback
+      finalize_unprotected_filter_on_load_;
+  InterceptablePrefFilter::FinalizeFilterOnLoadCallback
+      finalize_protected_filter_on_load_;
+
+  scoped_ptr<base::DictionaryValue> unprotected_prefs_;
+  scoped_ptr<base::DictionaryValue> protected_prefs_;
+
+  DISALLOW_COPY_AND_ASSIGN(TrackedPreferencesMigrator);
+};
+
+// Invokes |store_cleaner| for every |keys_to_clean|.
+void CleanupPrefStore(
+    const base::Callback<void(const std::string& key)>& store_cleaner,
+    const std::set<std::string>& keys_to_clean) {
+  for (std::set<std::string>::const_iterator it = keys_to_clean.begin();
+       it != keys_to_clean.end(); ++it) {
+    store_cleaner.Run(*it);
+  }
+}
+
+// If |wait_for_commit_to_destination_store|: schedules (via
+// |register_on_successful_destination_store_write_callback|) a cleanup of the
+// |keys_to_clean| from the source pref store (through |source_store_cleaner|)
+// once the destination pref store they were migrated to was successfully
+// written to disk. Otherwise, executes the cleanup right away.
+void ScheduleSourcePrefStoreCleanup(
+    const base::Callback<void(const base::Closure&)>&
+        register_on_successful_destination_store_write_callback,
+    const base::Callback<void(const std::string& key)>& source_store_cleaner,
+    const std::set<std::string>& keys_to_clean,
+    bool wait_for_commit_to_destination_store) {
+  DCHECK(!keys_to_clean.empty());
+  if (wait_for_commit_to_destination_store) {
+    register_on_successful_destination_store_write_callback.Run(
+        base::Bind(&CleanupPrefStore, source_store_cleaner, keys_to_clean));
+  } else {
+    CleanupPrefStore(source_store_cleaner, keys_to_clean);
+  }
+}
+
+// Copies the value of each pref in |pref_names| which is set in |old_store|,
+// but not in |new_store| into |new_store|. Sets |old_store_needs_cleanup| to
+// true if any old duplicates remain in |old_store| and sets |new_store_altered|
+// to true if any value was copied to |new_store|.
+void MigratePrefsFromOldToNewStore(const std::set<std::string>& pref_names,
+                                   const base::DictionaryValue* old_store,
+                                   base::DictionaryValue* new_store,
+                                   bool* old_store_needs_cleanup,
+                                   bool* new_store_altered) {
+  for (std::set<std::string>::const_iterator it = pref_names.begin();
+       it != pref_names.end(); ++it) {
+    const std::string& pref_name = *it;
+
+    const base::Value* value_in_old_store = NULL;
+    if (!old_store->Get(pref_name, &value_in_old_store))
+      continue;
+
+    // Whether this value ends up being copied below or was left behind by a
+    // previous incomplete migration, it should be cleaned up.
+    *old_store_needs_cleanup = true;
+
+    if (new_store->Get(pref_name, NULL))
+      continue;
+
+    // Copy the value from |old_store| to |new_store| rather than moving it to
+    // avoid data loss should |old_store| be flushed to disk without |new_store|
+    // having equivalently been successfully flushed to disk (e.g., on crash or
+    // in cases where |new_store| is read-only following a read error on
+    // startup).
+    new_store->Set(pref_name, value_in_old_store->DeepCopy());
+    *new_store_altered = true;
+  }
+}
+
+TrackedPreferencesMigrator::TrackedPreferencesMigrator(
+    const std::set<std::string>& unprotected_pref_names,
+    const std::set<std::string>& protected_pref_names,
+    const base::Callback<void(const std::string& key)>&
+        unprotected_store_cleaner,
+    const base::Callback<void(const std::string& key)>& protected_store_cleaner,
+    const base::Callback<void(const base::Closure&)>&
+        register_on_successful_unprotected_store_write_callback,
+    const base::Callback<void(const base::Closure&)>&
+        register_on_successful_protected_store_write_callback,
+    InterceptablePrefFilter* unprotected_pref_filter,
+    InterceptablePrefFilter* protected_pref_filter)
+    : unprotected_pref_names_(unprotected_pref_names),
+      protected_pref_names_(protected_pref_names),
+      unprotected_store_cleaner_(unprotected_store_cleaner),
+      protected_store_cleaner_(protected_store_cleaner),
+      register_on_successful_unprotected_store_write_callback_(
+          register_on_successful_unprotected_store_write_callback),
+      register_on_successful_protected_store_write_callback_(
+          register_on_successful_protected_store_write_callback) {
+  // The callbacks bound below will own this TrackedPreferencesMigrator by
+  // reference.
+  unprotected_pref_filter->InterceptNextFilterOnLoad(
+      base::Bind(&TrackedPreferencesMigrator::InterceptFilterOnLoad,
+                 this,
+                 UNPROTECTED_PREF_FILTER));
+  protected_pref_filter->InterceptNextFilterOnLoad(
+      base::Bind(&TrackedPreferencesMigrator::InterceptFilterOnLoad,
+                 this,
+                 PROTECTED_PREF_FILTER));
+}
+
+TrackedPreferencesMigrator::~TrackedPreferencesMigrator() {}
+
+void TrackedPreferencesMigrator::InterceptFilterOnLoad(
+    PrefFilterID id,
+    const InterceptablePrefFilter::FinalizeFilterOnLoadCallback&
+        finalize_filter_on_load,
+    scoped_ptr<base::DictionaryValue> prefs) {
+  switch (id) {
+    case UNPROTECTED_PREF_FILTER:
+      finalize_unprotected_filter_on_load_ = finalize_filter_on_load;
+      unprotected_prefs_ = prefs.Pass();
+      break;
+    case PROTECTED_PREF_FILTER:
+      finalize_protected_filter_on_load_ = finalize_filter_on_load;
+      protected_prefs_ = prefs.Pass();
+      break;
+  }
+
+  MigrateIfReady();
+}
+
+void TrackedPreferencesMigrator::MigrateIfReady() {
+  // Wait for both stores to have been read before proceeding.
+  if (!protected_prefs_ || !unprotected_prefs_)
+    return;
+
+  bool protected_prefs_need_cleanup = false;
+  bool unprotected_prefs_altered = false;
+  MigratePrefsFromOldToNewStore(unprotected_pref_names_,
+                                protected_prefs_.get(),
+                                unprotected_prefs_.get(),
+                                &protected_prefs_need_cleanup,
+                                &unprotected_prefs_altered);
+  bool unprotected_prefs_need_cleanup = false;
+  bool protected_prefs_altered = false;
+  MigratePrefsFromOldToNewStore(protected_pref_names_,
+                                unprotected_prefs_.get(),
+                                protected_prefs_.get(),
+                                &unprotected_prefs_need_cleanup,
+                                &protected_prefs_altered);
+
+  // Hand the processed prefs back to their respective filters.
+  finalize_unprotected_filter_on_load_.Run(unprotected_prefs_.Pass(),
+                                           unprotected_prefs_altered);
+  finalize_protected_filter_on_load_.Run(protected_prefs_.Pass(),
+                                         protected_prefs_altered);
+
+  if (unprotected_prefs_need_cleanup) {
+    // Schedule a cleanup of the |protected_pref_names_| from the unprotected
+    // prefs once the protected prefs were successfully written to disk (or
+    // do it immediately if |!protected_prefs_altered|).
+    ScheduleSourcePrefStoreCleanup(
+        register_on_successful_protected_store_write_callback_,
+        unprotected_store_cleaner_,
+        protected_pref_names_,
+        protected_prefs_altered);
+  }
+
+  if (protected_prefs_need_cleanup) {
+    // Schedule a cleanup of the |unprotected_pref_names_| from the protected
+    // prefs once the unprotected prefs were successfully written to disk (or
+    // do it immediately if |!unprotected_prefs_altered|).
+    ScheduleSourcePrefStoreCleanup(
+        register_on_successful_unprotected_store_write_callback_,
+        protected_store_cleaner_,
+        unprotected_pref_names_,
+        unprotected_prefs_altered);
+  }
+}
+
+}  // namespace
+
+void SetupTrackedPreferencesMigration(
+    const std::set<std::string>& unprotected_pref_names,
+    const std::set<std::string>& protected_pref_names,
+    const base::Callback<void(const std::string& key)>&
+        unprotected_store_cleaner,
+    const base::Callback<void(const std::string& key)>& protected_store_cleaner,
+    const base::Callback<void(const base::Closure&)>&
+        register_on_successful_unprotected_store_write_callback,
+    const base::Callback<void(const base::Closure&)>&
+        register_on_successful_protected_store_write_callback,
+    InterceptablePrefFilter* unprotected_pref_filter,
+    InterceptablePrefFilter* protected_pref_filter) {
+  scoped_refptr<TrackedPreferencesMigrator> prefs_migrator(
+      new TrackedPreferencesMigrator(
+          unprotected_pref_names,
+          protected_pref_names,
+          unprotected_store_cleaner,
+          protected_store_cleaner,
+          register_on_successful_unprotected_store_write_callback,
+          register_on_successful_protected_store_write_callback,
+          unprotected_pref_filter,
+          protected_pref_filter));
+}