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// Copyright (c) 2014 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 <string>
#include "absl/strings/string_view.h"
#include "rtc_base/containers/flat_set.h"
// Field trials allow webrtc clients (such as Chrome) to turn on feature code
// in binaries out in the field and gather information with that.
// By default WebRTC provides an implementation of field trials that can be
// found in system_wrappers/source/ If clients want to provide
// a custom version, they will have to:
// 1. Compile WebRTC defining the preprocessor macro
// WEBRTC_EXCLUDE_FIELD_TRIAL_DEFAULT (if GN is used this can be achieved
// by setting the GN arg rtc_exclude_field_trial_default to true).
// 2. Provide an implementation of:
// std::string webrtc::field_trial::FindFullName(absl::string_view trial).
// They are designed to wire up directly to chrome field trials and to speed up
// developers by reducing the need to wire APIs to control whether a feature is
// on/off. E.g. to experiment with a new method that could lead to a different
// trade-off between CPU/bandwidth:
// 1 - Develop the feature with default behaviour off:
// if (FieldTrial::FindFullName("WebRTCExperimentMethod2") == "Enabled")
// method2();
// else
// method1();
// 2 - Once the changes are rolled to chrome, the new code path can be
// controlled as normal chrome field trials.
// 3 - Evaluate the new feature and clean the code paths.
// Notes:
// - NOT every feature is a candidate to be controlled by this mechanism as
// it may require negotiation between involved parties (e.g. SDP).
// TODO(andresp): since chrome --force-fieldtrials does not marks the trial
// as active it does not get propagated to the renderer process. For now one
// needs to push a config with start_active:true or run a local finch
// server.
// TODO(andresp): find out how to get bots to run tests with trials enabled.
namespace webrtc {
namespace field_trial {
// Returns the group name chosen for the named trial, or the empty string
// if the trial does not exists.
// Note: To keep things tidy append all the trial names with WebRTC.
std::string FindFullName(absl::string_view name);
// Convenience method, returns true iff FindFullName(name) return a string that
// starts with "Enabled".
// TODO(tommi): Make sure all implementations support this.
inline bool IsEnabled(absl::string_view name) {
return FindFullName(name).find("Enabled") == 0;
// Convenience method, returns true iff FindFullName(name) return a string that
// starts with "Disabled".
inline bool IsDisabled(absl::string_view name) {
return FindFullName(name).find("Disabled") == 0;
// Optionally initialize field trial from a string.
// This method can be called at most once before any other call into webrtc.
// E.g. before the peer connection factory is constructed.
// Note: trials_string must never be destroyed.
void InitFieldTrialsFromString(const char* trials_string);
const char* GetFieldTrialString();
// Validates the given field trial string.
bool FieldTrialsStringIsValid(absl::string_view trials_string);
// Merges two field trial strings.
// If a key (trial) exists twice with conflicting values (groups), the value
// in 'second' takes precedence.
// Shall only be called with valid FieldTrial strings.
std::string MergeFieldTrialsStrings(absl::string_view first,
absl::string_view second);
// This helper allows to temporary "register" a field trial within the current
// scope. This is only useful for tests that use the global field trial string,
// otherwise you can use `webrtc::FieldTrialsRegistry`.
// If you want to isolate changes to the global field trial string itself within
// the current scope you should use `webrtc::test::ScopedFieldTrials`.
class FieldTrialsAllowedInScopeForTesting {
explicit FieldTrialsAllowedInScopeForTesting(flat_set<std::string> keys);
} // namespace field_trial
} // namespace webrtc