path: root/chromium/components/variations/service/variations_field_trial_creator.cc

// Copyright (c) 2012 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 "components/variations/service/variations_field_trial_creator.h"

#include <stddef.h>
#include <stdint.h>

#include <utility>
#include <vector>

#include "base/build_time.h"
#include "base/command_line.h"
#include "base/metrics/histogram_macros.h"
#include "base/metrics/sparse_histogram.h"
#include "base/sys_info.h"
#include "base/version.h"
#include "build/build_config.h"
#include "components/prefs/pref_service.h"
#include "components/variations/pref_names.h"
#include "components/variations/proto/variations_seed.pb.h"
#include "components/variations/service/variations_service_client.h"
#include "components/variations/variations_seed_processor.h"
#include "components/variations/variations_switches.h"
#include "ui/base/device_form_factor.h"

namespace variations {

// Maximum age permitted for a variations seed, in days.
const int kMaxVariationsSeedAgeDays = 30;

enum VariationsSeedExpiry {
  VARIATIONS_SEED_EXPIRY_NOT_EXPIRED,
  VARIATIONS_SEED_EXPIRY_FETCH_TIME_MISSING,
  VARIATIONS_SEED_EXPIRY_EXPIRED,
  VARIATIONS_SEED_EXPIRY_ENUM_SIZE,
};

// Gets current form factor and converts it from enum DeviceFormFactor to enum
// Study_FormFactor.
Study::FormFactor GetCurrentFormFactor() {
  switch (ui::GetDeviceFormFactor()) {
    case ui::DEVICE_FORM_FACTOR_PHONE:
      return Study::PHONE;
    case ui::DEVICE_FORM_FACTOR_TABLET:
      return Study::TABLET;
    case ui::DEVICE_FORM_FACTOR_DESKTOP:
      return Study::DESKTOP;
  }
  NOTREACHED();
  return Study::DESKTOP;
}

// Gets the hardware class and returns it as a string. This returns an empty
// string if the client is not ChromeOS.
std::string GetHardwareClass() {
#if defined(OS_CHROMEOS)
  return base::SysInfo::GetLsbReleaseBoard();
#endif  // OS_CHROMEOS
  return std::string();
}

// Returns the date that should be used by the VariationsSeedProcessor to do
// expiry and start date checks.
base::Time GetReferenceDateForExpiryChecks(PrefService* local_state) {
  const int64_t date_value = local_state->GetInt64(prefs::kVariationsSeedDate);
  const base::Time seed_date = base::Time::FromInternalValue(date_value);
  const base::Time build_time = base::GetBuildTime();
  // Use the build time for date checks if either the seed date is invalid or
  // the build time is newer than the seed date.
  base::Time reference_date = seed_date;
  if (seed_date.is_null() || seed_date < build_time)
    reference_date = build_time;
  return reference_date;
}

// Wrapper around channel checking, used to enable channel mocking for
// testing. If the current browser channel is not UNKNOWN, this will return
// that channel value. Otherwise, if the fake channel flag is provided, this
// will return the fake channel. Failing that, this will return the UNKNOWN
// channel.
Study::Channel GetChannelForVariations(version_info::Channel product_channel) {
  switch (product_channel) {
    case version_info::Channel::CANARY:
      return Study::CANARY;
    case version_info::Channel::DEV:
      return Study::DEV;
    case version_info::Channel::BETA:
      return Study::BETA;
    case version_info::Channel::STABLE:
      return Study::STABLE;
    case version_info::Channel::UNKNOWN:
      break;
  }
  const std::string forced_channel =
      base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
          switches::kFakeVariationsChannel);
  if (forced_channel == "stable")
    return Study::STABLE;
  if (forced_channel == "beta")
    return Study::BETA;
  if (forced_channel == "dev")
    return Study::DEV;
  if (forced_channel == "canary")
    return Study::CANARY;
  DVLOG(1) << "Invalid channel provided: " << forced_channel;
  return Study::UNKNOWN;
}

// Records UMA histogram with the result of the variations seed expiry check.
void RecordCreateTrialsSeedExpiry(VariationsSeedExpiry expiry_check_result) {
  UMA_HISTOGRAM_ENUMERATION("Variations.CreateTrials.SeedExpiry",
                            expiry_check_result,
                            VARIATIONS_SEED_EXPIRY_ENUM_SIZE);
}

VariationsFieldTrialCreator::VariationsFieldTrialCreator(
    PrefService* local_state,
    VariationsServiceClient* client,
    const UIStringOverrider& ui_string_overrider)
    : client_(client),
      ui_string_overrider_(ui_string_overrider),
      seed_store_(local_state),
      create_trials_from_seed_called_(false) {}

VariationsFieldTrialCreator::~VariationsFieldTrialCreator() {}

std::string VariationsFieldTrialCreator::GetLatestCountry() const {
  const std::string override_country =
      base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
          switches::kVariationsOverrideCountry);
  return !override_country.empty()
             ? override_country
             : local_state()->GetString(prefs::kVariationsCountry);
}

bool VariationsFieldTrialCreator::CreateTrialsFromSeed(
    std::unique_ptr<const base::FieldTrial::EntropyProvider>
        low_entropy_provider,
    base::FeatureList* feature_list) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  CHECK(!create_trials_from_seed_called_);

  create_trials_from_seed_called_ = true;

  VariationsSeed seed;
  if (!LoadSeed(&seed))
    return false;

  const int64_t last_fetch_time_internal =
      local_state()->GetInt64(prefs::kVariationsLastFetchTime);
  const base::Time last_fetch_time =
      base::Time::FromInternalValue(last_fetch_time_internal);
  if (last_fetch_time.is_null()) {
    // If the last fetch time is missing and we have a seed, then this must be
    // the first run of Chrome. Store the current time as the last fetch time.
    RecordLastFetchTime();
    RecordCreateTrialsSeedExpiry(VARIATIONS_SEED_EXPIRY_FETCH_TIME_MISSING);
  } else {
    // Reject the seed if it is more than 30 days old.
    const base::TimeDelta seed_age = base::Time::Now() - last_fetch_time;
    if (seed_age.InDays() > kMaxVariationsSeedAgeDays) {
      RecordCreateTrialsSeedExpiry(VARIATIONS_SEED_EXPIRY_EXPIRED);
      return false;
    }
    RecordCreateTrialsSeedExpiry(VARIATIONS_SEED_EXPIRY_NOT_EXPIRED);
  }

  const base::Version current_version(version_info::GetVersionNumber());
  if (!current_version.IsValid())
    return false;

  std::unique_ptr<ClientFilterableState> client_state =
      GetClientFilterableStateForVersion(current_version);

  // Note that passing |&ui_string_overrider_| via base::Unretained below is
  // safe because the callback is executed synchronously. It is not possible
  // to pass UIStringOverrider itself to VariationSeedProcessor as variations
  // components should not depends on //ui/base.
  VariationsSeedProcessor().CreateTrialsFromSeed(
      seed, *client_state,
      base::Bind(&UIStringOverrider::OverrideUIString,
                 base::Unretained(&ui_string_overrider_)),
      low_entropy_provider.get(), feature_list);

  const base::Time now = base::Time::Now();

  // Log the "freshness" of the seed that was just used. The freshness is the
  // time between the last successful seed download and now.
  if (!last_fetch_time.is_null()) {
    const base::TimeDelta delta = now - last_fetch_time;
    // Log the value in number of minutes.
    UMA_HISTOGRAM_CUSTOM_COUNTS("Variations.SeedFreshness", delta.InMinutes(),
                                1, base::TimeDelta::FromDays(30).InMinutes(),
                                50);
  }

  return true;
}

void VariationsFieldTrialCreator::SetCreateTrialsFromSeedCalledForTesting(
    bool called) {
  create_trials_from_seed_called_ = called;
}

std::unique_ptr<ClientFilterableState>
VariationsFieldTrialCreator::GetClientFilterableStateForVersion(
    const base::Version& version) {
  std::unique_ptr<ClientFilterableState> state =
      base::MakeUnique<ClientFilterableState>();
  state->locale = client_->GetApplicationLocale();
  state->reference_date = GetReferenceDateForExpiryChecks(local_state());
  state->version = version;
  state->channel = GetChannelForVariations(client_->GetChannel());
  state->form_factor = GetCurrentFormFactor();
  state->platform = ClientFilterableState::GetCurrentPlatform();
  state->hardware_class = GetHardwareClass();
#if defined(OS_ANDROID)
  // This is set on Android only currently, because the IsLowEndDevice() API
  // on other platforms has no intrinsic meaning outside of a field trial that
  // controls its value. Since this is before server-side field trials are
  // evaluated, that field trial would not be able to apply for this case.
  state->is_low_end_device = base::SysInfo::IsLowEndDevice();
#endif
  state->session_consistency_country = GetLatestCountry();
  state->permanent_consistency_country = LoadPermanentConsistencyCountry(
      version, state->session_consistency_country);
  return state;
}

std::string VariationsFieldTrialCreator::LoadPermanentConsistencyCountry(
    const base::Version& version,
    const std::string& latest_country) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK(version.IsValid());

  const std::string override_country =
      base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
          switches::kVariationsOverrideCountry);
  if (!override_country.empty())
    return override_country;

  const base::ListValue* list_value =
      local_state()->GetList(prefs::kVariationsPermanentConsistencyCountry);
  std::string stored_version_string;
  std::string stored_country;

  // Determine if the saved pref value is present and valid.
  const bool is_pref_empty = list_value->empty();
  const bool is_pref_valid = list_value->GetSize() == 2 &&
                             list_value->GetString(0, &stored_version_string) &&
                             list_value->GetString(1, &stored_country) &&
                             base::Version(stored_version_string).IsValid();

  // Determine if the version from the saved pref matches |version|.
  const bool does_version_match =
      is_pref_valid && version == base::Version(stored_version_string);

  // Determine if the country in the saved pref matches the country in
  // |latest_country|.
  const bool does_country_match = is_pref_valid && !latest_country.empty() &&
                                  stored_country == latest_country;

  // Record a histogram for how the saved pref value compares to the current
  // version and the country code in the variations seed.
  LoadPermanentConsistencyCountryResult result;
  if (is_pref_empty) {
    result = !latest_country.empty() ? LOAD_COUNTRY_NO_PREF_HAS_SEED
                                     : LOAD_COUNTRY_NO_PREF_NO_SEED;
  } else if (!is_pref_valid) {
    result = !latest_country.empty() ? LOAD_COUNTRY_INVALID_PREF_HAS_SEED
                                     : LOAD_COUNTRY_INVALID_PREF_NO_SEED;
  } else if (latest_country.empty()) {
    result = does_version_match ? LOAD_COUNTRY_HAS_PREF_NO_SEED_VERSION_EQ
                                : LOAD_COUNTRY_HAS_PREF_NO_SEED_VERSION_NEQ;
  } else if (does_version_match) {
    result = does_country_match ? LOAD_COUNTRY_HAS_BOTH_VERSION_EQ_COUNTRY_EQ
                                : LOAD_COUNTRY_HAS_BOTH_VERSION_EQ_COUNTRY_NEQ;
  } else {
    result = does_country_match ? LOAD_COUNTRY_HAS_BOTH_VERSION_NEQ_COUNTRY_EQ
                                : LOAD_COUNTRY_HAS_BOTH_VERSION_NEQ_COUNTRY_NEQ;
  }
  UMA_HISTOGRAM_ENUMERATION("Variations.LoadPermanentConsistencyCountryResult",
                            result, LOAD_COUNTRY_MAX);

  // Use the stored country if one is available and was fetched since the last
  // time Chrome was updated.
  if (does_version_match)
    return stored_country;

  if (latest_country.empty()) {
    if (!is_pref_valid)
      local_state()->ClearPref(prefs::kVariationsPermanentConsistencyCountry);
    // If we've never received a country code from the server, use an empty
    // country so that it won't pass any filters that specifically include
    // countries, but so that it will pass any filters that specifically exclude
    // countries.
    return std::string();
  }

  // Otherwise, update the pref with the current Chrome version and country.
  StorePermanentCountry(version, latest_country);
  return latest_country;
}

void VariationsFieldTrialCreator::StorePermanentCountry(
    const base::Version& version,
    const std::string& country) {
  base::ListValue new_list_value;
  new_list_value.AppendString(version.GetString());
  new_list_value.AppendString(country);
  local_state()->Set(prefs::kVariationsPermanentConsistencyCountry,
                     new_list_value);
}

void VariationsFieldTrialCreator::RecordLastFetchTime() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  local_state()->SetInt64(prefs::kVariationsLastFetchTime,
                          base::Time::Now().ToInternalValue());
}

bool VariationsFieldTrialCreator::LoadSeed(VariationsSeed* seed) {
  return seed_store_.LoadSeed(seed);
}

}  // namespace variations