1 files changed, 107 insertions, 0 deletions
diff --git a/third_party/libwebrtc/api/field_trials.cc b/third_party/libwebrtc/api/field_trials.cc
new file mode 100644
index 0000000000..4bd11271dc
--- /dev/null
+++ b/third_party/libwebrtc/api/field_trials.cc
@@ -0,0 +1,107 @@
+/*
+ *  Copyright (c) 2020 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 "api/field_trials.h"
+
+#include <atomic>
+
+#include "rtc_base/checks.h"
+#include "system_wrappers/include/field_trial.h"
+
+namespace {
+
+// This part is copied from system_wrappers/field_trial.cc.
+webrtc::flat_map<std::string, std::string> InsertIntoMap(const std::string& s) {
+  std::string::size_type field_start = 0;
+  webrtc::flat_map<std::string, std::string> key_value_map;
+  while (field_start < s.size()) {
+    std::string::size_type separator_pos = s.find('/', field_start);
+    RTC_CHECK_NE(separator_pos, std::string::npos)
+        << "Missing separator '/' after field trial key.";
+    RTC_CHECK_GT(separator_pos, field_start)
+        << "Field trial key cannot be empty.";
+    std::string key = s.substr(field_start, separator_pos - field_start);
+    field_start = separator_pos + 1;
+
+    RTC_CHECK_LT(field_start, s.size())
+        << "Missing value after field trial key. String ended.";
+    separator_pos = s.find('/', field_start);
+    RTC_CHECK_NE(separator_pos, std::string::npos)
+        << "Missing terminating '/' in field trial string.";
+    RTC_CHECK_GT(separator_pos, field_start)
+        << "Field trial value cannot be empty.";
+    std::string value = s.substr(field_start, separator_pos - field_start);
+    field_start = separator_pos + 1;
+
+    // If a key is specified multiple times, only the value linked to the first
+    // key is stored. note: This will crash in debug build when calling
+    // InitFieldTrialsFromString().
+    key_value_map.emplace(key, value);
+  }
+  // This check is technically redundant due to earlier checks.
+  // We nevertheless keep the check to make it clear that the entire
+  // string has been processed, and without indexing past the end.
+  RTC_CHECK_EQ(field_start, s.size());
+
+  return key_value_map;
+}
+
+// Makes sure that only one instance is created, since the usage
+// of global string makes behaviour unpredicatable otherwise.
+// TODO(bugs.webrtc.org/10335): Remove once global string is gone.
+std::atomic<bool> instance_created_{false};
+
+}  // namespace
+
+namespace webrtc {
+
+FieldTrials::FieldTrials(const std::string& s)
+    : uses_global_(true),
+      field_trial_string_(s),
+      previous_field_trial_string_(webrtc::field_trial::GetFieldTrialString()),
+      key_value_map_(InsertIntoMap(s)) {
+  // TODO(bugs.webrtc.org/10335): Remove the global string!
+  field_trial::InitFieldTrialsFromString(field_trial_string_.c_str());
+  RTC_CHECK(!instance_created_.exchange(true))
+      << "Only one instance may be instanciated at any given time!";
+}
+
+std::unique_ptr<FieldTrials> FieldTrials::CreateNoGlobal(const std::string& s) {
+  return std::unique_ptr<FieldTrials>(new FieldTrials(s, true));
+}
+
+FieldTrials::FieldTrials(const std::string& s, bool)
+    : uses_global_(false),
+      previous_field_trial_string_(nullptr),
+      key_value_map_(InsertIntoMap(s)) {}
+
+FieldTrials::~FieldTrials() {
+  // TODO(bugs.webrtc.org/10335): Remove the global string!
+  if (uses_global_) {
+    field_trial::InitFieldTrialsFromString(previous_field_trial_string_);
+    RTC_CHECK(instance_created_.exchange(false));
+  }
+}
+
+std::string FieldTrials::GetValue(absl::string_view key) const {
+  auto it = key_value_map_.find(std::string(key));
+  if (it != key_value_map_.end())
+    return it->second;
+
+  // Check the global string so that programs using
+  // a mix between FieldTrials and the global string continue to work
+  // TODO(bugs.webrtc.org/10335): Remove the global string!
+  if (uses_global_) {
+    return field_trial::FindFullName(std::string(key));
+  }
+  return "";
+}
+
+}  // namespace webrtc