components/rappor/rappor_metric.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "components/rappor/rappor_metric.h"
   6
   7 #include "base/logging.h"
   8 #include "base/rand_util.h"
   9 #include "components/rappor/reports.h"
  10
  11 namespace rappor {
  12
  13 RapporMetric::RapporMetric(const std::string& metric_name,
  14                            const RapporParameters& parameters,
  15                            int32_t cohort_seed)
  16     : metric_name_(metric_name),
  17       parameters_(parameters),
  18       sample_count_(0),
  19       bloom_filter_(parameters.bloom_filter_size_bytes,
  20                     parameters.bloom_filter_hash_function_count,
  21                     (cohort_seed % parameters.num_cohorts) *
  22                         parameters.bloom_filter_hash_function_count) {
  23   DCHECK_GE(cohort_seed, 0);
  24   DCHECK_LT(cohort_seed, RapporParameters::kMaxCohorts);
  25   // Since cohort_seed is in the range [0, kMaxCohorts), num_cohorts should
  26   // divide kMaxCohorts for each cohort to have equal weight.
  27   DCHECK_EQ(0, RapporParameters::kMaxCohorts % parameters.num_cohorts);
  28 }
  29
  30 RapporMetric::~RapporMetric() {}
  31
  32 void RapporMetric::AddSample(const std::string& str) {
  33   ++sample_count_;
  34   // Replace the previous sample with a 1 in sample_count_ chance so that each
  35   // sample has equal probability of being reported.
  36   if (base::RandGenerator(sample_count_) == 0) {
  37     bloom_filter_.SetString(str);
  38   }
  39 }
  40
  41 ByteVector RapporMetric::GetReport(const std::string& secret) const {
  42   return internal::GenerateReport(secret, parameters(), bytes());
  43 }
  44
  45 void RapporMetric::SetBytesForTesting(const ByteVector& bytes) {
  46   bloom_filter_.SetBytesForTesting(bytes);
  47 }
  48
  49 }  // namespace rappor