Modify rappor parameters.

components/rappor/rappor_service.cc

 // 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 "components/rappor/rappor_service.h"
 
 #include "base/base64.h"
 #include "base/metrics/field_trial.h"
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/pref_service.h"
 #include "base/rand_util.h"
 #include "base/stl_util.h"
 #include "base/time/time.h"
 #include "components/metrics/metrics_hashes.h"
 #include "components/rappor/log_uploader.h"
 #include "components/rappor/proto/rappor_metric.pb.h"
 #include "components/rappor/rappor_metric.h"
 #include "components/rappor/rappor_pref_names.h"
 #include "components/variations/variations_associated_data.h"
 
 namespace rappor {
 
 namespace {
 
-// The number of cohorts we divide clients into.
-const int kNumCohorts = 32;
-
 // Seconds before the initial log is generated.
 const int kInitialLogIntervalSeconds = 15;
 // Interval between ongoing logs.
 const int kLogIntervalSeconds = 30 * 60;
 
 const char kMimeType[] = "application/vnd.chrome.rappor";
 
 // Constants for the RAPPOR rollout field trial.
 const char kRapporRolloutFieldTrialName[] = "RapporRollout";
 
 // Constant for the finch parameter name for the server URL
 const char kRapporRolloutServerUrlParam[] = "ServerUrl";
 
 GURL GetServerUrl() {
   return GURL(chrome_variations::GetVariationParamValue(
       kRapporRolloutFieldTrialName,
       kRapporRolloutServerUrlParam));
 }
 
 const RapporParameters kRapporParametersForType[NUM_RAPPOR_TYPES] = {
     // ETLD_PLUS_ONE_RAPPOR_TYPE
-    {16 /* Bloom filter size bytes */,
+    {128 /* Num cohorts */,
+     16 /* Bloom filter size bytes */,
      2 /* Bloom filter hash count */,
-     rappor::PROBABILITY_75 /* Fake data probability */,
+     rappor::PROBABILITY_50 /* Fake data probability */,
      rappor::PROBABILITY_50 /* Fake one probability */,
      rappor::PROBABILITY_75 /* One coin probability */,
-     rappor::PROBABILITY_50 /* Zero coin probability */},
+     rappor::PROBABILITY_25 /* Zero coin probability */},
 };
 
 }  // namespace
 
 RapporService::RapporService() : cohort_(-1) {}
 
 RapporService::~RapporService() {
   STLDeleteValues(&metrics_map_);
 }
 
@@ skipping 24 matching lines @@
   }
   log_rotation_timer_.Start(FROM_HERE,
                             base::TimeDelta::FromSeconds(kLogIntervalSeconds),
                             this,
                             &RapporService::OnLogInterval);
 }
 
 // static
 void RapporService::RegisterPrefs(PrefRegistrySimple* registry) {
   registry->RegisterStringPref(prefs::kRapporSecret, std::string());
-  registry->RegisterIntegerPref(prefs::kRapporCohort, -1);
+  registry->RegisterIntegerPref(prefs::kRapporCohortDeprecated, -1);
+  registry->RegisterIntegerPref(prefs::kRapporCohortSeed, -1);
 }
 
 void RapporService::LoadCohort(PrefService* pref_service) {
   DCHECK(!IsInitialized());
-  cohort_ = pref_service->GetInteger(prefs::kRapporCohort);
+  // Ignore and delete old cohort parameter.
+  pref_service->ClearPref(prefs::kRapporCohortDeprecated);
+
+  cohort_ = pref_service->GetInteger(prefs::kRapporCohortSeed);
   // If the user is already assigned to a valid cohort, we're done.
-  if (cohort_ >= 0 && cohort_ < kNumCohorts)
+  if (cohort_ >= 0 && cohort_ < RapporParameters::kMaxCohorts)
     return;
 
   // This is the first time the client has started the service (or their
   // preferences were corrupted).  Randomly assign them to a cohort.
-  cohort_ = base::RandGenerator(kNumCohorts);
-  pref_service->SetInteger(prefs::kRapporCohort, cohort_);
+  cohort_ = base::RandGenerator(RapporParameters::kMaxCohorts);
+  pref_service->SetInteger(prefs::kRapporCohortSeed, cohort_);
 }
 
 void RapporService::LoadSecret(PrefService* pref_service) {
   DCHECK(secret_.empty());
   std::string secret_base64 = pref_service->GetString(prefs::kRapporSecret);
   if (!secret_base64.empty()) {
     bool decoded = base::Base64Decode(secret_base64, &secret_);
     if (decoded && secret_.size() == HmacByteVectorGenerator::kEntropyInputSize)
       return;
     // If the preference fails to decode, or is the wrong size, it must be
@@ skipping 59 matching lines @@
     DCHECK_EQ(parameters.ToString(), metric->parameters().ToString());
     return metric;
   }
 
   RapporMetric* new_metric = new RapporMetric(metric_name, parameters, cohort_);
   metrics_map_[metric_name] = new_metric;
   return new_metric;
 }
 
 }  // namespace rappor