Adds field trial parser.

Bug: webrtc:9346
Change-Id: Ibd07a1753feaa40d4be4d465d61f55bc8a8a9325
Reviewed-on: https://webrtc-review.googlesource.com/80263
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Christoffer Rodbro <crodbro@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23615}

rtc_base/experiments/field_trial_parser.cc

@@ -0,0 +1,134 @@
+/*
+ *  Copyright 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#include "rtc_base/experiments/field_trial_parser.h"
+
+#include <algorithm>
+#include <map>
+#include <type_traits>
+#include <utility>
+
+#include "rtc_base/logging.h"
+
+namespace webrtc {
+namespace {
+
+int FindOrEnd(std::string str, size_t start, char delimiter) {
+  size_t pos = str.find(delimiter, start);
+  pos = (pos == std::string::npos) ? str.length() : pos;
+  return static_cast<int>(pos);
+}
+}  // namespace
+
+FieldTrialParameterInterface::FieldTrialParameterInterface(std::string key)
+    : key_(key) {}
+FieldTrialParameterInterface::~FieldTrialParameterInterface() = default;
+std::string FieldTrialParameterInterface::Key() const {
+  return key_;
+}
+
+void ParseFieldTrial(
+    std::initializer_list<FieldTrialParameterInterface*> fields,
+    std::string trial_string) {
+  std::map<std::string, FieldTrialParameterInterface*> field_map;
+  for (FieldTrialParameterInterface* field : fields) {
+    field_map[field->Key()] = field;
+  }
+  size_t i = 0;
+  while (i < trial_string.length()) {
+    int val_end = FindOrEnd(trial_string, i, ',');
+    int colon_pos = FindOrEnd(trial_string, i, ':');
+    int key_end = std::min(val_end, colon_pos);
+    int val_begin = key_end + 1;
+    std::string key = trial_string.substr(i, key_end - i);
+    rtc::Optional<std::string> opt_value;
+    if (val_end >= val_begin)
+      opt_value = trial_string.substr(val_begin, val_end - val_begin);
+    i = val_end + 1;
+    auto field = field_map.find(key);
+    if (field != field_map.end()) {
+      if (!field->second->Parse(std::move(opt_value))) {
+        RTC_LOG(LS_WARNING) << "Failed to read field with key: '" << key
+                            << "' in trial: \"" << trial_string << "\"";
+      }
+    } else {
+      RTC_LOG(LS_INFO) << "No field with key: '" << key
+                       << "' (found in trial: \"" << trial_string << "\")";
+    }
+  }
+}
+
+template <>
+rtc::Optional<bool> ParseTypedParameter<bool>(std::string str) {
+  if (str == "true" || str == "1") {
+    return true;
+  } else if (str == "false" || str == "0") {
+    return false;
+  }
+  return rtc::nullopt;
+}
+
+template <>
+rtc::Optional<double> ParseTypedParameter<double>(std::string str) {
+  double value;
+  if (sscanf(str.c_str(), "%lf", &value) == 1) {
+    return value;
+  } else {
+    return rtc::nullopt;
+  }
+}
+
+template <>
+rtc::Optional<int> ParseTypedParameter<int>(std::string str) {
+  int value;
+  if (sscanf(str.c_str(), "%i", &value) == 1) {
+    return value;
+  } else {
+    return rtc::nullopt;
+  }
+}
+
+template <>
+rtc::Optional<std::string> ParseTypedParameter<std::string>(std::string str) {
+  return std::move(str);
+}
+
+FieldTrialFlag::FieldTrialFlag(std::string key) : FieldTrialFlag(key, false) {}
+
+FieldTrialFlag::FieldTrialFlag(std::string key, bool default_value)
+    : FieldTrialParameterInterface(key), value_(default_value) {}
+
+bool FieldTrialFlag::Get() const {
+  return value_;
+}
+
+bool FieldTrialFlag::Parse(rtc::Optional<std::string> str_value) {
+  // Only set the flag if there is no argument provided.
+  if (str_value) {
+    rtc::Optional<bool> opt_value = ParseTypedParameter<bool>(*str_value);
+    if (!opt_value)
+      return false;
+    value_ = *opt_value;
+  } else {
+    value_ = true;
+  }
+  return true;
+}
+
+template class FieldTrialParameter<bool>;
+template class FieldTrialParameter<double>;
+template class FieldTrialParameter<int>;
+template class FieldTrialParameter<std::string>;
+
+template class FieldTrialOptional<double>;
+template class FieldTrialOptional<int>;
+template class FieldTrialOptional<bool>;
+template class FieldTrialOptional<std::string>;
+
+}  // namespace webrtc