Measure packet loss so we can use it to select ICE candidate pairs.

webrtc/p2p/base/packetlossestimator.cc

+/*
+ *  Copyright 2017 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/p2p/base/packetlossestimator.h"
+
+#include "webrtc/base/checks.h"
+
+namespace cricket {
+
+PacketLossEstimator::PacketLossEstimator(int64_t consider_lost_after_ms,
+                                         int64_t forget_after_ms)
+    : consider_lost_after_ms_(consider_lost_after_ms),
+      forget_after_ms_(forget_after_ms) {
+  RTC_DCHECK_LT(consider_lost_after_ms, forget_after_ms);
+}
+
+void PacketLossEstimator::ExpectResponse(std::string id, int64_t sent_time) {
+  tracked_packets_[id] = PacketInfo{sent_time, false};
+
+  // Called to free memory in case the client hasn't called UpdateResponseRate
+  // in a while.
+  MaybeForgetOldRequests(sent_time);
+}
+
+void PacketLossEstimator::ReceivedResponse(std::string id,
+                                           int64_t received_time) {
+  auto iter = tracked_packets_.find(id);
+  if (iter != tracked_packets_.end()) {
+    auto& packet_info = iter->second;
+    packet_info.response_received = true;
+  }
+
+  // Called to free memory in case the client hasn't called UpdateResponseRate
+  // in a while.
+  MaybeForgetOldRequests(received_time);
+}
+
+void PacketLossEstimator::UpdateResponseRate(int64_t now) {
+  int responses_expected = 0;
+  int responses_received = 0;
+
+  for (auto iter = tracked_packets_.begin(); iter != tracked_packets_.end();) {
+    const auto& packet_info = iter->second;
+    if (Forget(packet_info, now)) {
+      iter = tracked_packets_.erase(iter);
+      continue;
+    }
+    if (packet_info.response_received) {
+      responses_expected += 1;
+      responses_received += 1;
+    } else if (ConsiderLost(packet_info, now)) {
+      responses_expected += 1;
+    }
+    ++iter;
+  }
+
+  if (responses_expected > 0) {
+    response_rate_ =
+        static_cast<double>(responses_received) / responses_expected;
+  } else {
+    response_rate_ = 1.0;
+  }
+
+  last_forgot_at_ = now;
+}
+
+void PacketLossEstimator::MaybeForgetOldRequests(int64_t now) {
+  if (now - last_forgot_at_ <= forget_after_ms_) {
+    return;
+  }
+
+  for (auto iter = tracked_packets_.begin(); iter != tracked_packets_.end();) {
+    const auto& packet_info = iter->second;
+    if (Forget(packet_info, now)) {
+      iter = tracked_packets_.erase(iter);
+    } else {
+      ++iter;
+    }
+  }
+
+  last_forgot_at_ = now;
+}
+
+bool PacketLossEstimator::ConsiderLost(const PacketInfo& packet_info,
+                                       int64_t now) const {
+  return packet_info.sent_time < now - consider_lost_after_ms_;
+}
+
+bool PacketLossEstimator::Forget(const PacketInfo& packet_info,
+                                 int64_t now) const {
+  return now - packet_info.sent_time > forget_after_ms_;
+}
+
+}  // namespace cricket