Piggybacking simulcast id and ALR experiment id into video content type extension.

webrtc/modules/pacing/alr_detector.cc

 /*
  *  Copyright (c) 2016 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 "webrtc/modules/pacing/alr_detector.h"
 
+#include <map>
 #include <string>
 
 #include "webrtc/rtc_base/checks.h"
 #include "webrtc/rtc_base/format_macros.h"
 #include "webrtc/rtc_base/logging.h"
 #include "webrtc/rtc_base/timeutils.h"
 #include "webrtc/system_wrappers/include/field_trial.h"
 
 namespace webrtc {
 
@@ skipping 51 matching lines @@
 rtc::Optional<int64_t> AlrDetector::GetApplicationLimitedRegionStartTime()
     const {
   return alr_started_time_ms_;
 }
 
 rtc::Optional<AlrDetector::AlrExperimentSettings>
 AlrDetector::ParseAlrSettingsFromFieldTrial(const char* experiment_name) {
   rtc::Optional<AlrExperimentSettings> ret;
   std::string group_name = field_trial::FindFullName(experiment_name);
 
+  static std::map<const char*,
+                  rtc::Optional<AlrDetector::AlrExperimentSettings>>
+      computed_results;
+
+  auto it = computed_results.find(experiment_name);
+  if (it != computed_results.end()) {
+    return it->second;
+  }
+  computed_results[experiment_name] = ret;

[sprang_webrtc, 2017/08/24 09:13:16]

Looks like you can drop this insertion?

[ilnik, 2017/08/25 12:35:07]

No. Currently the function may exit below if it fails to parse a string.
In that case map will already contain correct empty value. Future calls will
never attempt to parse the string again.

If this insertion is removed, incorrect strings will be parsed on each call.

+
   const std::string kIgnoredSuffix = "_Dogfood";
   if (group_name.rfind(kIgnoredSuffix) ==
       group_name.length() - kIgnoredSuffix.length()) {
     group_name.resize(group_name.length() - kIgnoredSuffix.length());
   }
 
   if (group_name.empty())
     return ret;
 
   AlrExperimentSettings settings;
-  if (sscanf(group_name.c_str(), "%f,%" PRId64 ",%d,%d,%d",
+  if (sscanf(group_name.c_str(), "%f,%" PRId64 ",%d,%d,%d,%d",
              &settings.pacing_factor, &settings.max_paced_queue_time,
              &settings.alr_bandwidth_usage_percent,
              &settings.alr_start_budget_level_percent,
-             &settings.alr_stop_budget_level_percent) == 5) {
+             &settings.alr_stop_budget_level_percent,
+             &settings.group_id) == 6) {
     ret.emplace(settings);
     LOG(LS_INFO) << "Using ALR experiment settings: "
                     "pacing factor: "
                  << settings.pacing_factor << ", max pacer queue length: "
                  << settings.max_paced_queue_time
                  << ", ALR start bandwidth usage percent: "
                  << settings.alr_bandwidth_usage_percent
                  << ", ALR end budget level percent: "
                  << settings.alr_start_budget_level_percent
                  << ", ALR end budget level percent: "
-                 << settings.alr_stop_budget_level_percent;
+                 << settings.alr_stop_budget_level_percent
+                 << ", ALR experiment group ID: " << settings.group_id;
   } else {
     LOG(LS_INFO) << "Failed to parse ALR experiment: " << experiment_name;
   }
 
+  computed_results[experiment_name] = ret;
   return ret;
 }
 
 }  // namespace webrtc