Create a histogram serialization mechanism in components/metrics

components/metrics/export/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/export/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_vector.h"
+#include "base/strings/string_split.h"
+#include "base/strings/string_util.h"
+#include "components/metrics/export/crash_sample.h"
+#include "components/metrics/export/histogram_sample.h"
+#include "components/metrics/export/linearhistogram_sample.h"
+#include "components/metrics/export/metric_sample.h"
+#include "components/metrics/export/sparsehistogram_sample.h"
+#include "components/metrics/export/useraction_sample.h"
+
+using base::File;
+using base::FilePath;
+using base::SplitString;
+using std::string;
+using std::vector;
+
+namespace metrics {
+
+MetricSample* MetricsUtils::ReadSample(const string& sample) {
+  vector<string> vector;
+  SplitString(sample, '\0', &vector);
+  // We should have a two null terminated strings so split should produce
+  // three chuncks.
+  if (vector.size() != 3) {
+    DLOG(ERROR) << "wrong length" << vector.size();
+    return NULL;
+  }
+  const string& name = vector[0];
+  const string& value = vector[1];
+
+  if (LowerCaseEqualsASCII(name, "crash")) {
+    return CrashSample::ReadCrash(value);
+  } else if (LowerCaseEqualsASCII(name, "histogram")) {
+    return HistogramSample::ReadHistogram(value);
+  } else if (LowerCaseEqualsASCII(name, "linearhistogram")) {
+    return LinearHistogramSample::ReadLinearHistogram(value);
+  } else if (LowerCaseEqualsASCII(name, "sparsehistogram")) {
+    return SparseHistogramSample::ReadSparseHistogram(value);
+  } else if (LowerCaseEqualsASCII(name, "useraction")) {
+    return UserActionSample::ReadUserAction(value);
+  } else {
+    DLOG(ERROR) << "invalid event type: " << name
+                << ", value: " << value;
+  }
+  return NULL;
+}
+
+bool MetricsUtils::WriteMetricToFile(const MetricSample& sample,
+                                     const std::string& filename) {
+  if (!sample.IsValid()) return false;

[Alexei Svitkine (slow), 2014/04/30 15:25:24]

Put return on next line.

[bsimonnet, 2014/04/30 20:28:40]

Done.

+  File file =
+      File(FilePath(filename), File::FLAG_OPEN_ALWAYS | File::FLAG_APPEND);

[Alexei Svitkine (slow), 2014/04/30 15:25:24]

Nit: You can just do:

File file(FilePath(filename), ...);

[bsimonnet, 2014/04/30 20:28:40]

Done.

+  File::Error err = file.Lock();
+  if (err != File::FILE_OK) {
+    DLOG(ERROR) << "could not lock the file";
+    return false;
+  }
+
+  const 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) {
+  File file = File(FilePath(filename),
+                   File::FLAG_OPEN | File::FLAG_READ | File::FLAG_WRITE);
+  File::Error err = file.Lock();
+  if (err != 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(File::FROM_CURRENT, message_length) != -1) continue;
+
+      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(string(serialized_sample, message_length)));
+  }
+  file.SetLength(0);
+}
+
+}  // namespace metrics