Create a histogram serialization mechanism in components/metrics

components/metrics/chromeos/metrics_utils.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/metrics/chromeos/metrics_utils.h"
+
+#include <string>
+#include <vector>
+
+#include "base/file_util.h"
+#include "base/files/file_path.h"
+#include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
+#include "base/strings/string_split.h"
+#include "base/strings/string_util.h"
+#include "components/metrics/chromeos/crash_sample.h"
+#include "components/metrics/chromeos/histogram_sample.h"
+#include "components/metrics/chromeos/linearhistogram_sample.h"
+#include "components/metrics/chromeos/metric_sample.h"
+#include "components/metrics/chromeos/sparsehistogram_sample.h"
+#include "components/metrics/chromeos/useraction_sample.h"
+
+namespace metrics {
+
+scoped_ptr<MetricSample> MetricsUtils::ReadSample(const std::string& sample) {
+  std::vector<std::string> parts;
+  base::SplitString(sample, '\0', &parts);
+  // We should have a two null terminated strings so split should produce

[Luigi Semenzato, 2014/05/08 17:19:37]

Typo: "... have a two null ..."

+  // three chuncks.

[Luigi Semenzato, 2014/05/08 17:19:37]

Chunks.

+  if (parts.size() != 3) {
+    DLOG(ERROR) << "wrong length" << parts.size();

[Luigi Semenzato, 2014/05/08 17:19:37]

I like more descriptive messages, for instance:

"unexpected length " << parts.size() << " of serialized sample"

+    return scoped_ptr<MetricSample>();
+  }
+  const std::string& name = parts[0];
+  const std::string& value = parts[1];
+
+  if (LowerCaseEqualsASCII(name, "crash")) {
+    return CrashSample::ReadCrash(value).PassAs<MetricSample>();
+  } else if (LowerCaseEqualsASCII(name, "histogram")) {
+    return HistogramSample::ReadHistogram(value).PassAs<MetricSample>();
+  } else if (LowerCaseEqualsASCII(name, "linearhistogram")) {
+    return LinearHistogramSample::ReadLinearHistogram(value)
+        .PassAs<MetricSample>();
+  } else if (LowerCaseEqualsASCII(name, "sparsehistogram")) {
+    return SparseHistogramSample::ReadSparseHistogram(value)
+        .PassAs<MetricSample>();
+  } else if (LowerCaseEqualsASCII(name, "useraction")) {
+    return UserActionSample::ReadUserAction(value).PassAs<MetricSample>();
+  } else {
+    DLOG(ERROR) << "invalid event type: " << name << ", value: " << value;
+  }
+  return scoped_ptr<MetricSample>();
+}
+
+bool MetricsUtils::WriteMetricToFile(const MetricSample& sample,
+                                     const std::string& filename) {
+  if (!sample.IsValid())
+    return false;
+  base::File file(base::FilePath(filename),
+                  base::File::FLAG_OPEN_ALWAYS | base::File::FLAG_APPEND);
+  base::File::Error err = file.Lock();
+  if (err != base::File::FILE_OK) {
+    DLOG(ERROR) << "could not lock the file";
+    return false;
+  }
+
+  const std::string msg = sample.ToString();
+  int32_t size = msg.length() + sizeof(int32_t);
+  if (msg.length() > size_t(kMessageMaxLength)) {
+    DLOG(ERROR) << "cannot write message: too long";
+    return false;
+  }
+  file.WriteAtCurrentPos(reinterpret_cast<char*>(&size), sizeof(int32_t));
+  file.WriteAtCurrentPos(msg.c_str(), msg.length());
+
+  return true;
+}
+
+void MetricsUtils::ReadAndTruncateMetricsFromFile(
+    const std::string& filename,
+    ScopedVector<MetricSample>* metrics) {
+  base::File file(
+      base::FilePath(filename),
+      base::File::FLAG_OPEN | base::File::FLAG_READ | base::File::FLAG_WRITE);
+  base::File::Error err = file.Lock();
+  if (err != base::File::FILE_OK) {
+    DLOG(ERROR) << "could not lock the file";
+    return;
+  }
+  for (;;) {
+    int32 message_length;
+    int read = file.ReadAtCurrentPos(reinterpret_cast<char*>(&message_length),
+                                     sizeof(message_length));
+    if (read != sizeof(message_length))
+      break;
+
+    message_length -= sizeof(message_length);
+    if (message_length > kMessageMaxLength) {
+      DLOG(ERROR) << "cannot read message: too long";
+
+      // Skip the invalid message and continue reading.
+      if (file.Seek(base::File::FROM_CURRENT, message_length) != -1) continue;

[Luigi Semenzato, 2014/05/08 17:19:37]

I am not sure the style code accepts a statement on the same line of the IF
condition.

[bsimonnet, 2014/05/08 20:02:58]

It is authorized to enhance readability but I feel like it hurts readability
everytime.
I stopped using it but forgot some on older CLs.

+
+      DLOG(ERROR) << "cannot skip long message";
+      // We do not know the size of the message. The rest of the file is not
+      // readable. Truncate the file and exit.
+      break;
+    }
+    char serialized_sample[kMessageMaxLength];
+    read = file.ReadAtCurrentPos(serialized_sample, message_length);
+    if (read != message_length) {
+      DLOG(ERROR) << "could not read message" << read;
+      break;
+    }
+    metrics->push_back(
+        ReadSample(std::string(serialized_sample, message_length)).release());
+  }
+  file.SetLength(0);
+}
+
+}  // namespace metrics