RAPPOR implementation

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 "components/rappor/proto/rappor_metric.pb.h"
+#include "components/rappor/rappor_pref_names.h"
+#include "components/variations/metrics_util.h"
+#include "components/variations/variations_associated_data.h"
+
+namespace rappor {
+
+namespace {
+
+// Version which is incremented when changes are made in the reporting scheme.
+const int kRapporVersion = 1;
+
+// The number of cohorts we divide clients into.
+const int kNumCohorts = 32;
+
+// Length of the rappor secret in bytes.
+const int kRapporSecretSize = 128;

[edknapp, 2014/02/11 17:28:00]

kRapporSecretSize = HmacByteVectorGenerator::kKeySize
and create that constant in HmacByteVectorGenerator. 

Possible security levels for the SHA256 instantiation are 80, 112, 128, 192,
256. I'd recommend 128 bits. 

[Steven Holte, 2014/02/11 22:08:14]

Done.

[edknapp, 2014/02/12 00:27:17]

The new constant was created but I still see 128 here. 

[Steven Holte, 2014/02/12 04:02:55]

Oops.  Removed it.

+
+// 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 */,
+        2 /* Bloom filter hash count */,
+        rappor::PROBABILITY_75 /* Fake data probability */,
+        rappor::PROBABILITY_50 /* Fake one probability */,
+        rappor::PROBABILITY_75 /* One coin probability */,
+        rappor::PROBABILITY_50 /* Zero coin probability */
+    },
+};
+
+}  // namespace
+
+RapporService::RapporService() : cohort_(-1) {}
+
+RapporService::~RapporService() {}
+
+void RapporService::Start(PrefService* pref_service,
+                          net::URLRequestContextGetter* request_context) {
+  GURL server_url = GetServerUrl();
+  if (!server_url.is_valid())
+    return;
+  DCHECK(!uploader_);
+  LoadSecret(pref_service);
+  LoadCohort(pref_service);
+  uploader_.reset(new LogUploader(server_url, kMimeType, request_context));
+  log_rotation_timer_.Start(
+      FROM_HERE,
+      base::TimeDelta::FromSeconds(kInitialLogIntervalSeconds),
+      this,
+      &RapporService::OnLogInterval);
+}
+
+void RapporService::OnLogInterval() {
+  DCHECK(uploader_);
+  RapporReports reports;
+  if (ExportMetrics(&reports)) {
+    std::string log_text;
+    bool success = reports.SerializeToString(&log_text);
+    DCHECK(success);
+    uploader_->QueueLog(log_text);
+  }
+  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);
+}
+
+void RapporService::LoadCohort(PrefService* pref_service) {
+  DCHECK_EQ(cohort_, -1);
+  cohort_ = pref_service->GetInteger(prefs::kRapporCohort);
+  if (cohort_ >= 0 && cohort_ < kNumCohorts)
+    return;
+
+  cohort_ = base::RandGenerator(kNumCohorts);
+  pref_service->SetInteger(prefs::kRapporCohort, 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)
+      return;
+    // If the preference fails to decode, it must be corrupt, so continue as
+    // though it didn't exist yet and generate a new one.
+  }
+
+  secret_ = base::RandBytesAsString(kRapporSecretSize);
+  base::Base64Encode(secret_, &secret_base64);
+  pref_service->SetString(prefs::kRapporSecret, secret_base64);
+}
+
+bool RapporService::ExportMetrics(RapporReports* reports) {
+  base::AutoLock auto_lock(lock_);
+  if (metrics_map_.empty())
+    return false;
+
+  DCHECK_GE(cohort_, 0);
+  reports->set_version(kRapporVersion);
+  reports->set_cohort(cohort_);
+
+  for (std::map<std::string, RapporMetric*>::iterator it = metrics_map_.begin();
+       metrics_map_.end() != it;
+       ++it) {
+    const RapporMetric* metric = it->second;
+    RapporReports::Report* report = reports->add_report();
+    report->set_name_hash(metrics::HashMetricName(it->first));
+    ByteVector bytes = metric->GetReport(secret_);
+    report->set_bits(std::string(bytes.begin(), bytes.end()));
+  }
+  STLDeleteContainerPairSecondPointers(
+      metrics_map_.begin(), metrics_map_.end());
+  metrics_map_.clear();
+  return true;
+}
+
+bool RapporService::IsInitialized() const {
+  return cohort_ >= 0;
+}
+
+void RapporService::RecordSample(const std::string& metric_name,
+                                 RapporType type,
+                                 const std::string& sample) {
+  // Ignore the sample if the service hasn't started yet.
+  if (!IsInitialized())
+    return;
+  DCHECK_LT(type, NUM_RAPPOR_TYPES);
+  RecordSampleInternal(metric_name, kRapporParametersForType[type], sample);
+}
+
+void RapporService::RecordSampleInternal(const std::string& metric_name,
+                                         const RapporParameters& parameters,
+                                         const std::string& sample) {
+  DCHECK(IsInitialized());
+  base::AutoLock auto_lock(lock_);
+
+  RapporMetric* metric = LookupMetric(metric_name, parameters);
+  metric->AddSample(sample);
+}
+
+RapporMetric* RapporService::LookupMetric(const std::string& metric_name,
+                                          const RapporParameters& parameters) {
+  DCHECK(IsInitialized());
+  std::map<std::string, RapporMetric*>::iterator it =
+      metrics_map_.find(metric_name);
+  if (metrics_map_.end() != it) {
+    RapporMetric* metric = it->second;
+    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