Create a histogram serialization mechanism in components/metrics

components/metrics/chromeos/metric_sample.h

+// 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.
+
+#ifndef COMPONENTS_METRICS_CHROMEOS_METRIC_SAMPLE_H_
+#define COMPONENTS_METRICS_CHROMEOS_METRIC_SAMPLE_H_
+
+#include <string>
+
+#include "base/gtest_prod_util.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+
+namespace metrics {
+
+// This class is used by libmetrics (ChromeOS) to serialize
+// and deserialize measurements to send them to a metrics sending service.
+// It is meant to be a simple container with serialization functions.
+class MetricSample {
+ public:
+  // Types of metric sample used.
+  enum SampleType {
+    CRASH,
+    HISTOGRAM,
+    LINEAR_HISTOGRAM,
+    SPARSE_HISTOGRAM,
+    USER_ACTION
+  };
+
+  ~MetricSample();
+
+  // Return true if the sample is valid (can be serialized without ambiguity).
+  //
+  // This function should be used to filter bad samples before serializing them.
+  bool IsValid() const;
+
+  // Getters for type and name. All types of metrics have these so we do not
+  // need to check the type.
+  SampleType type() const { return type_; }
+  const std::string& name() const { return name_; }
+
+  // Getters for sample, min, max, bucket_count.
+  // Check the metric type to make sure the request make sense. (ex: a crash
+  // sample does not have a bucket_count so we crash if we call bucket_count()
+  // on it.)
+  const int sample() const;
+  const int min() const;
+  const int max() const;
+  const int bucket_count() const;
+
+  // Return a serialized version of the sample.
+  //
+  // The serialized message for each type is:
+  // crash: crash\0|name_|\0
+  // user action: useraction\0|name_|\0
+  // histogram: histogram\0|name_| |sample_| |min_| |max_| |bucket_count_|\0
+  // sparsehistogram: sparsehistogram\0|name_| |sample_|\0
+  // linearhistogram: linearhistogram\0|name_| |sample_| |max_|\0
+  std::string ToString() const;
+
+  // Build a crash sample
+  static scoped_ptr<MetricSample> CrashSample(const std::string& crash_name);
+
+  // Build a histogram sample
+  static scoped_ptr<MetricSample> HistogramSample(
+      const std::string& histogram_name,
+      int sample,
+      int min,
+      int max,
+      int bucket_count);
+  // Deserialize a histogram sample
+  static scoped_ptr<MetricSample> ReadHistogram(const std::string& serialized);
+
+  // Build a sparse histogram sample
+  static scoped_ptr<MetricSample> SparseHistogramSample(
+      const std::string& histogram_name,
+      int sample);
+  // Deserialize a sparse histogram sample
+  static scoped_ptr<MetricSample> ReadSparseHistogram(
+      const std::string& serialized);
+
+  // Build a linear histogram sample
+  static scoped_ptr<MetricSample> LinearHistogramSample(
+      const std::string& histogram_name,
+      int sample,
+      int max);
+  // Deserialize a linear histogram sample
+  static scoped_ptr<MetricSample> ReadLinearHistogram(
+      const std::string& serialized);
+
+  // Build a user action sample
+  static scoped_ptr<MetricSample> UserActionSample(
+      const std::string& action_name);
+
+  // Returns true if sample and this object represent the same sample (type,
+  // name, sample, min, max, bucket_count match)
+  bool IsEqual(const MetricSample* sample);
+
+ private:
+  MetricSample(SampleType sample_type,
+               const std::string& metric_name,
+               const int sample,
+               const int min,
+               const int max,
+               const int bucket_count);
+
+  const SampleType type_;
+  const std::string name_;
+  const int sample_;
+  const int min_;
+  const int max_;
+  const int bucket_count_;
+
+  DISALLOW_COPY_AND_ASSIGN(MetricSample);
+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_CHROMEOS_METRIC_SAMPLE_H_