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// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "chromecast/base/cast_features.h"
#include <algorithm>
#include <utility>
#include "base/command_line.h"
#include "base/containers/contains.h"
#include "base/feature_list.h"
#include "base/metrics/field_trial.h"
#include "base/metrics/field_trial_param_associator.h"
#include "base/metrics/field_trial_params.h"
#include "base/no_destructor.h"
#include "base/strings/string_number_conversions.h"
#include "base/values.h"
#include "build/build_config.h"
namespace chromecast {
namespace {
// The name of the default group to use for Cast DCS features.
const char kDefaultDCSFeaturesGroup[] = "default_dcs_features_group";
std::unordered_set<int32_t>& GetExperimentIds() {
static base::NoDestructor<std::unordered_set<int32_t>> g_experiment_ids;
return *g_experiment_ids;
bool g_experiment_ids_initialized = false;
// The collection of features that have been registered by unit tests
std::vector<const base::Feature*>& GetTestFeatures() {
static base::NoDestructor<std::vector<const base::Feature*>>
return *features_for_test;
void SetExperimentIds(const base::Value::List& list) {
std::unordered_set<int32_t> ids;
for (const auto& it : list) {
if (it.is_int()) {
} else {
LOG(ERROR) << "Non-integer value found in experiment id list!";
g_experiment_ids_initialized = true;
} // namespace
// Cast Platform Features are listed below. These features may be
// toggled via configs fetched from DCS for devices in the field, or via
// command-line flags set by the developer. For the end-to-end details of the
// system design, please see go/dcs-experiments.
// Below are useful steps on how to use these features in your code.
// 1) Declaring and defining the feature.
// All Cast Platform Features should be declared in a common file with other
// Cast Platform Features (ex. chromecast/base/cast_features.h). When
// defining your feature, you will need to assign a default value. This is
// the value that the feature will hold until overriden by the server or the
// command line. Here's an exmaple:
// BASE_FEATURE(kSuperSecretSauce, "SuperSecretSauce",
// The first parameter that you pass in the definition is the feature's name.
// This MUST match the DCS experiment key for this feature.
// While Features elsewhere in Chromium alternatively use dashed-case or
// PascalCase for their names, Chromecast features should use snake_case
// (lowercase letters separated by underscores). This will ensure that DCS
// configs, which are passed around as JSON, remain conformant and readable.
// 2) Using the feature in client code.
// Using these features in your code is easy. Here's an example:
// #include “base/feature_list.h”
// #include “chromecast/base/chromecast_switches.h”
// std::unique_ptr<Foo> CreateFoo() {
// if (base::FeatureList::IsEnabled(kSuperSecretSauce))
// return std::make_unique<SuperSecretFoo>();
// return std::make_unique<BoringOldFoo>();
// }
// base::FeatureList can be called from any thread, in any process, at any
// time after PreCreateThreads(). It will return whether the feature is
// enabled.
// 3) Overriding the default value from the server.
// For devices in the field, DCS will issue different configs to different
// groups of devices, allowing us to run experiments on features. These
// feature settings will manifest on the next boot of cast_shell. In the
// example, if the latest config for a particular device set the value of
// kSuperSecretSauce to true, the appropriate code path would be taken.
// Otherwise, the default value, false, would be used. For more details on
// setting up experiments, see go/dcs-launch.
// 4) Overriding the default and server values from the command-line.
// While the server value trumps the default values, the command line trumps
// both. Enable features by passing this command line arg to cast_shell:
// --enable-features=enable_foo,enable_super_secret_sauce
// Features are separated by commas. Disable features by passing:
// --disable-features=enable_foo,enable_bar
// 5) If you add a new feature to the system you must include it in kFeatures
// This is because the system relies on knowing all of the features so
// it can properly iterate over all features to detect changes.
// Begin Chromecast Feature definitions.
// Allows applications to access media capture devices (webcams/microphones)
// through getUserMedia API.
// Enables the use of QUIC in Cast-specific NetworkContexts. See
// chromecast/browser/ for usage.
BASE_FEATURE(kEnableQuic, "enable_quic", base::FEATURE_DISABLED_BY_DEFAULT);
// Enables triple-buffer 720p graphics (overriding default graphics buffer
// settings for a platform).
// Enables single-buffered graphics (overriding default graphics buffer
// settings and takes precedence over triple-buffer feature).
// Disable idle sockets closing on memory pressure. See
// chromecast/browser/ for usage.
// Uses AudioManagerAndroid, instead of CastAudioManagerAndroid. This will
// disable lots of Cast features, so it should only be used for development and
// testing.
// Enables CastAudioOutputDevice for audio output on Android. When disabled,
// CastAudioManagerAndroid will be used.
// End Chromecast Feature definitions.
const base::Feature* kFeatures[] = {
std::vector<const base::Feature*> GetInternalFeatures();
const std::vector<const base::Feature*>& GetFeatures() {
static const base::NoDestructor<std::vector<const base::Feature*>> features(
[] {
std::vector<const base::Feature*> features(std::begin(kFeatures),
auto internal_features = GetInternalFeatures();
features.insert(features.end(), internal_features.begin(),
return features;
if (GetTestFeatures().size() > 0)
return GetTestFeatures();
return *features;
void InitializeFeatureList(const base::Value::Dict& dcs_features,
const base::Value::List& dcs_experiment_ids,
const std::string& cmd_line_enable_features,
const std::string& cmd_line_disable_features,
const std::string& extra_enable_features,
const std::string& extra_disable_features) {
// Set the experiments.
std::string all_enable_features =
cmd_line_enable_features + "," + extra_enable_features;
std::string all_disable_features =
cmd_line_disable_features + "," + extra_disable_features;
// Initialize the FeatureList from the command line.
auto feature_list = std::make_unique<base::FeatureList>();
feature_list->InitFromCommandLine(all_enable_features, all_disable_features);
// Override defaults from the DCS config.
for (const auto kv : dcs_features) {
// Each feature must have its own FieldTrial object. Since experiments are
// controlled server-side for Chromecast, and this class is designed with a
// client-side experimentation framework in mind, these parameters are
// carefully chosen:
// - The field trial name is unused for our purposes. However, we need to
// maintain a 1:1 mapping with Features in order to properly store and
// access parameters associated with each Feature. Therefore, use the
// Feature's name as the FieldTrial name to ensure uniqueness.
// - We don't care about the group_id.
const std::string& feature_name = kv.first;
auto* field_trial = base::FieldTrialList::CreateFieldTrial(
feature_name, kDefaultDCSFeaturesGroup);
// |field_trial| is null only if the trial has already been forced to
// another group. This shouldn't happen, unless we've processed a
// --force-fieldtrial commandline argument that overrides this to some other
// group.
if (!field_trial) {
LOG(ERROR) << "A trial was already created for a DCS feature: "
<< feature_name;
if (kv.second.is_bool()) {
// A boolean entry simply either enables or disables a feature.
kv.second.GetBool() ? base::FeatureList::OVERRIDE_ENABLE_FEATURE
if (kv.second.is_dict()) {
// A dictionary entry implies that the feature is enabled.
feature_name, base::FeatureList::OVERRIDE_ENABLE_FEATURE,
// If the feature has not been overriden from the command line, set its
// parameters accordingly.
if (!feature_list->IsFeatureOverriddenFromCommandLine(
feature_name, base::FeatureList::OVERRIDE_DISABLE_FEATURE)) {
// Build a map of the FieldTrial parameters and associate it to the
// FieldTrial.
base::FieldTrialParams params;
for (const auto params_kv : kv.second.GetDict()) {
if (params_kv.second.is_string()) {
params[params_kv.first] = params_kv.second.GetString();
} else {
LOG(ERROR) << "Entry in params dict for \"" << feature_name << "\""
<< " feature is not a string. Skipping.";
// Register the params, so that they can be queried by client code.
bool success = base::AssociateFieldTrialParams(
feature_name, kDefaultDCSFeaturesGroup, params);
// Other base::Value types are not supported.
LOG(ERROR) << "A DCS feature mapped to an unsupported value. key: "
<< feature_name << " type: " << kv.second.type();
bool IsFeatureEnabled(const base::Feature& feature) {
DCHECK(base::Contains(GetFeatures(), &feature)) <<;
return base::FeatureList::IsEnabled(feature);
base::Value::Dict GetOverriddenFeaturesForStorage(
const base::Value::Dict& features) {
base::Value::Dict persistent_dict;
// |features| maps feature names to either a boolean or a dict of params.
for (const auto feature : features) {
if (feature.second.is_bool()) {
persistent_dict.Set(feature.first, feature.second.GetBool());
if (feature.second.is_dict()) {
const base::Value* params_dict = &feature.second;
base::Value::Dict params;
for (const auto [param_key, param_val] : params_dict->GetDict()) {
if (param_val.is_bool()) {
params.Set(param_key, param_val.GetBool() ? "true" : "false");
} else if (param_val.is_int()) {
params.Set(param_key, base::NumberToString(param_val.GetInt()));
} else if (param_val.is_double()) {
params.Set(param_key, base::NumberToString(param_val.GetDouble()));
} else if (param_val.is_string()) {
params.Set(param_key, param_val.GetString());
} else {
LOG(ERROR) << "Entry in params dict for \"" << feature.first << "\""
<< " is not of a supported type (key: " << param_key
<< ", type: " << param_val.type();
persistent_dict.Set(feature.first, std::move(params));
// Other base::Value types are not supported.
LOG(ERROR) << "A DCS feature mapped to an unsupported value. key: "
<< feature.first << " type: " << feature.second.type();
return persistent_dict;
const std::unordered_set<int32_t>& GetDCSExperimentIds() {
return GetExperimentIds();
void ResetCastFeaturesForTesting() {
g_experiment_ids_initialized = false;
void SetFeaturesForTest(std::vector<const base::Feature*> features) {
GetTestFeatures() = std::move(features);
} // namespace chromecast