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- // Copyright 2020 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.
- #ifndef COMPONENTS_METRICS_ENTROPY_STATE_H_
- #define COMPONENTS_METRICS_ENTROPY_STATE_H_
- #include <string>
- #include "base/gtest_prod_util.h"
- #include "base/memory/raw_ptr.h"
- #include "components/prefs/pref_registry_simple.h"
- class PrefService;
- namespace metrics {
- // A class to get entropy source values from the PrefService.
- class EntropyState final {
- public:
- // Creates the EntropyState with the given |local_state| to get
- // the entropy source value from this helper class.
- explicit EntropyState(PrefService* local_state);
- EntropyState(const EntropyState&) = delete;
- EntropyState& operator=(const EntropyState&) = delete;
- // Clears low_entropy_source and old_low_entropy_source in the prefs.
- static void ClearPrefs(PrefService* local_state);
- // Registers low_entropy_source and old_low_entropy_source in the prefs.
- static void RegisterPrefs(PrefRegistrySimple* registry);
- // Returns the high entropy source for this client, which is composed of a
- // client ID and the low entropy source. This is intended to be unique for
- // each install. |initial_client_id| is the client_id that was used to
- // randomize field trials and must not be empty.
- std::string GetHighEntropySource(const std::string& initial_client_id);
- // Returns the low entropy source that is used to randomize field trials on
- // startup for this client. Generates a new value if there is none. See the
- // |low_entropy_source_| comment for more info.
- int GetLowEntropySource();
- // Returns the pseudo low entropy source for this client. Generates a new
- // value if there is none. See the |pseudo_low_entropy_source_| comment
- // for more info.
- int GetPseudoLowEntropySource();
- // Returns the old low entropy source for this client. Does not generate a new
- // value, but instead returns |kLowEntropySourceNotSet|, if there is none. See
- // the |old_low_entropy_source_| comment for more info.
- int GetOldLowEntropySource();
- private:
- FRIEND_TEST_ALL_PREFIXES(EntropyStateTest, LowEntropySourceNotReset);
- FRIEND_TEST_ALL_PREFIXES(EntropyStateTest, PseudoLowEntropySourceNotReset);
- FRIEND_TEST_ALL_PREFIXES(EntropyStateTest, HaveNoLowEntropySource);
- FRIEND_TEST_ALL_PREFIXES(EntropyStateTest, HaveOnlyNewLowEntropySource);
- FRIEND_TEST_ALL_PREFIXES(EntropyStateTest, HaveOnlyOldLowEntropySource);
- FRIEND_TEST_ALL_PREFIXES(EntropyStateTest, CorruptNewLowEntropySources);
- FRIEND_TEST_ALL_PREFIXES(EntropyStateTest, CorruptOldLowEntropySources);
- // Default value for prefs::kMetricsLowEntropySource.
- static constexpr int kLowEntropySourceNotSet = -1;
- // Loads the low entropy source values from prefs. Creates the new source
- // value if it doesn't exist, but doesn't create the old source value. After
- // this function finishes, |low_entropy_source_| will be set, but
- // |old_low_entropy_source_| may still be |kLowEntropySourceNotSet|.
- void UpdateLowEntropySources();
- // Checks whether a value is on the range of allowed low entropy source
- // values.
- static bool IsValidLowEntropySource(int value);
- // The local state prefs store.
- const raw_ptr<PrefService> local_state_;
- // The non-identifying low entropy source values. These values seed the
- // pseudorandom generators which pick experimental groups. The "old" value is
- // thought to be biased in the wild, and is no longer used for experiments
- // requiring low entropy. Clients which already have an "old" value continue
- // incorporating it into the high entropy source, to avoid changing those
- // group assignments. New clients only have the new source.
- //
- // The pseudo-low entropy source is not used for experiment diversion, but
- // only for statistical validation. (Since it's not used for experiment
- // diversion, it won't be subject to drift over time as experiment effects
- // accumulate in actual low entropy source buckets.)
- //
- // During startup these are set to the values used for randomizing field
- // trials and won't be changed within the session even after calling
- // |ClearPrefs|
- int low_entropy_source_ = kLowEntropySourceNotSet;
- int old_low_entropy_source_ = kLowEntropySourceNotSet;
- int pseudo_low_entropy_source_ = kLowEntropySourceNotSet;
- };
- } // namespace metrics
- #endif // COMPONENTS_METRICS_ENTROPY_STATE_H_
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