Alternative Multi-dimensional Rappor

components/rappor/sampler.h

+// 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.
+
+#ifndef COMPONENTS_RAPPOR_SAMPLER_H_
+#define COMPONENTS_RAPPOR_SAMPLER_H_
+
+#include <map>
+#include <string>
+
+#include "base/containers/scoped_ptr_hash_map.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "components/rappor/rappor_parameters.h"
+#include "components/rappor/sample.h"
+
+namespace rappor {
+
+class RapporReports;
+
+namespace internal {
+
+// Sampler manages the collection and storage of Sample objects.
+// For each metric name, it will randomly select one Sample to store and
+// use when generating RapporReports.
+class Sampler {
+ public:
+  Sampler();
+  ~Sampler();
+
+  // Store this sample for metric name, randomly selecting a sample if
+  // others have already been recorded.
+  void AddSample(const std::string& metric_name, scoped_ptr<Sample> sample);
+
+  // Generate randomized reports for all stored samples and store them
+  // in |reports|, then discard the samples.
+  void ExportMetrics(const std::string& secret, RapporReports* reports);

[Alexei Svitkine (slow), 2015/04/22 21:00:13]

Could you add a unit test for this class?

i.e. that ExportMetrics really does clear them and that logging multiple times
has one or the other metric (e.g. log two values for the same metric and check
that the export of that is either one or the other).

[Steven Holte, 2015/04/22 21:59:32]

Done.

+
+ private:
+  // The number of samples recorded for each metric since the last export.
+  std::map<std::string, int> sample_counts_;
+
+  // We keep all registered metrics in a map, from name to metric.
+  // The map owns the metrics it contains.

[Alexei Svitkine (slow), 2015/04/22 21:00:13]

Nit: Last line is uneccessary since the map type implies that. Also, rephrase
first line without using "we".

[Steven Holte, 2015/04/22 21:59:32]

Done.

+  base::ScopedPtrHashMap<std::string, Sample> samples_;
+
+  DISALLOW_COPY_AND_ASSIGN(Sampler);
+};
+
+}  // namespace internal
+
+}  // namespace rappor
+
+#endif  // COMPONENTS_RAPPOR_SAMPLER_H_