Adding ExperimentLabels helper class.

chrome/installer/util/experiment_labels.cc

+// Copyright 2017 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 "chrome/installer/util/experiment_labels.h"
+
+#include <vector>
+
+#include "base/strings/string_split.h"
+#include "base/strings/stringprintf.h"
+
+namespace installer {
+
+namespace {
+
+constexpr base::StringPiece16::value_type kNameValueSeparator = L'=';
+constexpr base::StringPiece16::value_type kValueExpirationSeparator = L'|';
+constexpr base::StringPiece16::value_type kLabelSeparator = L';';
+
+// Returns a vector of string pieces, one for each "name=value|expiration"
+// group in |value|.
+std::vector<base::StringPiece16> Parse(base::StringPiece16 value) {
+  static constexpr base::char16 kLabelSeparatorString[] = {kLabelSeparator,
+                                                           L'\0'};
+  return base::SplitStringPiece(value, kLabelSeparatorString,
+                                base::TRIM_WHITESPACE,
+                                base::SPLIT_WANT_NONEMPTY);
+}
+
+// Returns an abbreviated day name for a zero-based |day_of_week|.
+const wchar_t* AbbreviatedDayOfWeek(int day_of_week) {
+  // Matches the abbreviated day names from the ICU "en" locale.
+  static constexpr const wchar_t* kDays[] = {L"Sun", L"Mon", L"Tue", L"Wed",
+                                             L"Thu", L"Fri", L"Sat"};
+  return kDays[day_of_week];
+}
+
+// Returns an abbreviated month name for a one-based |month|.
+const wchar_t* AbbreviatedMonth(int month) {
+  // Matches the abbreviated month names from the ICU "en" locale.
+  static constexpr const wchar_t* kMonths[] = {L"Jan", L"Feb", L"Mar", L"Apr",
+                                               L"May", L"Jun", L"Jul", L"Aug",
+                                               L"Sep", L"Oct", L"Nov", L"Dec"};
+  return kMonths[month - 1];
+}
+
+// Returns an RFC822-compliant representation of an expiration date that is
+// |lifetime| into the future.

[Patrick Monette, 2017/05/08 15:27:48]

Rewrite comment to use |expiration| instead of |lifetime|.

[grt (UTC plus 2), 2017/05/08 20:15:25]

Done.

+base::string16 FormatExpiration(base::Time expiration) {
+  base::Time::Exploded exploded_time;
+  expiration.UTCExplode(&exploded_time);
+
+  // "Fri, 14 Aug 2015 16:13:03 GMT"

[Patrick Monette, 2017/05/08 15:27:48]

It's weird that Omaha uses 4 digits for the year, but
http://www.ietf.org/rfc/rfc822.txt
specifies 2 digits. Not your fault though!

[grt (UTC plus 2), 2017/05/08 20:15:26]

Hmm, yeah. I've added pointers to the relevant Omaha code.

+  return base::StringPrintf(L"%ls, %02d %ls %04d %02d:%02d:%02d GMT",
+                            AbbreviatedDayOfWeek(exploded_time.day_of_week),
+                            exploded_time.day_of_month,
+                            AbbreviatedMonth(exploded_time.month),
+                            exploded_time.year, exploded_time.hour,
+                            exploded_time.minute, exploded_time.second);
+}
+
+// Appends "label_name=label_value|expiration" to |label|.
+void AppendLabel(base::StringPiece16 label_name,
+                 base::StringPiece16 label_value,
+                 base::Time expiration,
+                 base::string16* label) {

[Patrick Monette, 2017/05/08 15:27:48]

Is it possible to use reserve() here?

Maybe not given that the time format size can differ for 1 or 2 characters.

[grt (UTC plus 2), 2017/05/08 20:15:25]

Yes We Can!

+  label_name.AppendToString(label);
+  label->push_back(kNameValueSeparator);
+  label_value.AppendToString(label);
+  label->push_back(kValueExpirationSeparator);
+  label->append(FormatExpiration(expiration));
+}
+
+}  // namespace
+
+ExperimentLabels::ExperimentLabels(const base::string16& value)
+    : value_(value) {}
+
+base::StringPiece16 ExperimentLabels::GetValueForLabel(
+    base::StringPiece16 label_name) const {
+  DCHECK(!label_name.empty());
+
+  return FindLabel(label_name).second;
+}
+
+void ExperimentLabels::SetValueForLabel(base::StringPiece16 label_name,
+                                        base::StringPiece16 label_value,
+                                        base::TimeDelta lifetime) {
+  DCHECK(!label_name.empty());
+  DCHECK(!label_value.empty());
+  DCHECK(!lifetime.is_zero());  // Alternatively, delete if lifetime is zero.
+
+  SetValueForLabel(label_name, label_value, base::Time::Now() + lifetime);
+}
+
+void ExperimentLabels::SetValueForLabel(base::StringPiece16 label_name,
+                                        base::StringPiece16 label_value,
+                                        base::Time expiration) {
+  DCHECK(!label_name.empty());
+  DCHECK(!label_value.empty());
+
+  LabelAndValue label_and_value = FindLabel(label_name);
+  if (label_and_value.first.empty()) {
+    // This label doesn't already exist -- append it to the raw value.
+    if (!value_.empty())
+      value_.push_back(kLabelSeparator);
+    AppendLabel(label_name, label_value, expiration, &value_);
+  } else {
+    // Replace the existing value and expiration.
+    // Get the stuff before the old label.
+    base::string16 new_label(value_, 0,
+                             label_and_value.first.data() - value_.data());
+    // Append the new label.
+    AppendLabel(label_name, label_value, expiration, &new_label);
+    // Find the stuff after the old label and append it.
+    size_t next_separator = value_.find(
+        kLabelSeparator,
+        (label_and_value.second.data() + label_and_value.second.size()) -
+            value_.data());
+    if (next_separator != base::string16::npos)
+      new_label.append(value_, next_separator, base::string16::npos);
+    // Presto.
+    new_label.swap(value_);
+  }
+}
+
+ExperimentLabels::LabelAndValue ExperimentLabels::FindLabel(
+    base::StringPiece16 label_name) const {
+  DCHECK(!label_name.empty());
+
+  std::vector<base::StringPiece16> labels = Parse(value_);
+  for (const auto& label : labels) {
+    if (label.size() < label_name.size() + 2 ||
+        !label.starts_with(label_name) ||
+        label[label_name.size()] != kNameValueSeparator) {
+      continue;
+    }
+    size_t value_start = label_name.size() + 1;
+    size_t value_end = label.find(kValueExpirationSeparator, value_start);
+    if (value_end == base::StringPiece16::npos)
+      break;
+    return std::make_pair(label,
+                          label.substr(value_start, value_end - value_start));
+  }
+  return LabelAndValue();
+}
+
+}  // namespace installer