Alternative Multi-dimensional Rappor

components/rappor/sample.cc

+// Copyright 2015 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/sample.h"
+
+#include <map>
+#include <string>
+
+#include "base/logging.h"
+#include "components/metrics/metrics_hashes.h"
+#include "components/rappor/bloom_filter.h"
+#include "components/rappor/byte_vector_utils.h"
+#include "components/rappor/proto/rappor_metric.pb.h"
+#include "components/rappor/reports.h"
+
+namespace rappor {
+
+Sample::Sample(int32_t cohort_seed, const RapporParameters& parameters)
+  : parameters_(parameters),
+    bloom_offset_((cohort_seed % parameters_.num_cohorts) *
+          parameters_.bloom_filter_hash_function_count) {
+  // Must use bloom filter size that fits in uint64.
+  DCHECK_LE(parameters_.bloom_filter_size_bytes, 8);
+}
+
+Sample::~Sample() {
+}
+
+void Sample::SetStringField(const std::string& field_name,
+                            const std::string& value) {
+  DCHECK_EQ(0u, sizes_[field_name]);
+  fields_[field_name] = internal::GetBloomBits(
+      parameters_.bloom_filter_size_bytes,
+      parameters_.bloom_filter_hash_function_count,
+      bloom_offset_,
+      value);
+  sizes_[field_name] = parameters_.bloom_filter_size_bytes;
+}
+
+void Sample::SetFlagsField(const std::string& field_name,
+                           uint64_t flags,
+                           size_t num_flags) {
+  DCHECK_EQ(0u, sizes_[field_name]);
+  DCHECK_GT(num_flags, 0u);
+  DCHECK_LE(num_flags, 64u);
+  DCHECK(num_flags == 64u || flags >> num_flags == 0);
+  fields_[field_name] = flags;
+  sizes_[field_name] = (num_flags + 7) / 8;
+}
+
+void Sample::ExportMetrics(const std::string& secret,
+                           const std::string& metric_name,
+                           RapporReports* reports) const {
+  for (const auto& kv : fields_) {
+    uint64_t value = kv.second;
+    const auto it = sizes_.find(kv.first);
+    DCHECK(it != sizes_.end());
+    uint64_t size = it->second;
+    ByteVector value_bytes(size);
+    for (size_t i = 0; i < size; i++) {
+      // Get the value of the i-th smallest byte and copy it to the byte vector.
+      uint64_t shift = i * 8;
+      uint64_t byte_mask = 0xff << shift;
+      value_bytes[i] = (value & byte_mask) >> shift;
+    }
+    ByteVector report_bytes = internal::GenerateReport(
+        secret, parameters_, value_bytes);
+
+    RapporReports::Report* report = reports->add_report();
+    report->set_name_hash(metrics::HashMetricName(
+        metric_name + "." + kv.first));
+    report->set_bits(std::string(report_bytes.begin(), report_bytes.end()));
+  }
+}
+
+}  // namespace rappor