From 55f6613fc02323f0b65ee6794c782c1e2aea41b8 Mon Sep 17 00:00:00 2001
From: Per K <perkj@webrtc.org>
Date: Thu, 2 May 2024 10:23:32 +0000
Subject: [PATCH] Retry initial probe if it times out and BWE has not been
 updated.

This is to avoid the case where the initial probe fail and the BWE is not updated, which can lead to a long period of low bandwidth.

Bug: webrtc:14928
Change-Id: Ie8f84270507b59995d57e4ab6e2a984570191529
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/349580
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Diep Bui <diepbp@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42208}
---
 .../goog_cc/probe_controller.cc               |  8 +++
 .../goog_cc/probe_controller_unittest.cc      | 49 +++++++++++++++++--
 2 files changed, 54 insertions(+), 3 deletions(-)

diff --git a/modules/congestion_controller/goog_cc/probe_controller.cc b/modules/congestion_controller/goog_cc/probe_controller.cc
index 36d61bf9fc..8961675f9c 100644
--- a/modules/congestion_controller/goog_cc/probe_controller.cc
+++ b/modules/congestion_controller/goog_cc/probe_controller.cc
@@ -476,6 +476,14 @@ std::vector<ProbeClusterConfig> ProbeController::Process(Timestamp at_time) {
   if (at_time - time_last_probing_initiated_ >
       kMaxWaitingTimeForProbingResult) {
     if (state_ == State::kWaitingForProbingResult) {
+      // If the initial probe timed out, and the estimate has not changed by
+      // other means, (likely because normal media packets are not being sent
+      // yet), then send a probe again.
+      if (waiting_for_initial_probe_result_ &&
+          estimated_bitrate_ == start_bitrate_ && first_probe_to_max_bitrate_) {
+        UpdateState(State::kInit);
+        return InitiateExponentialProbing(at_time);
+      }
       RTC_LOG(LS_INFO) << "kWaitingForProbingResult: timeout";
       UpdateState(State::kProbingComplete);
     }
diff --git a/modules/congestion_controller/goog_cc/probe_controller_unittest.cc b/modules/congestion_controller/goog_cc/probe_controller_unittest.cc
index 8024fec4dd..6691e87d3d 100644
--- a/modules/congestion_controller/goog_cc/probe_controller_unittest.cc
+++ b/modules/congestion_controller/goog_cc/probe_controller_unittest.cc
@@ -438,7 +438,7 @@ TEST(ProbeControllerTest,
   EXPECT_EQ(probes[0].target_data_rate.bps(), 2 * kStartBitrate.bps());
 }
 
-TEST(ProbeControllerTest, TestExponentialProbingTimeout) {
+TEST(ProbeControllerTest, InitialProbingTimeout) {
   ProbeControllerFixture fixture;
   std::unique_ptr<ProbeController> probe_controller =
       fixture.CreateController();
@@ -447,14 +447,57 @@ TEST(ProbeControllerTest, TestExponentialProbingTimeout) {
       IsEmpty());
   auto probes = probe_controller->SetBitrates(
       kMinBitrate, kStartBitrate, kMaxBitrate, fixture.CurrentTime());
+  EXPECT_THAT(probes, SizeIs(Gt(0)));
   // Advance far enough to cause a time out in waiting for probing result.
   fixture.AdvanceTime(kExponentialProbingTimeout);
   probes = probe_controller->Process(fixture.CurrentTime());
-
+  EXPECT_THAT(probes, IsEmpty());
   probes = probe_controller->SetEstimatedBitrate(
       DataRate::BitsPerSec(1800), BandwidthLimitedCause::kDelayBasedLimited,
       fixture.CurrentTime());
-  EXPECT_TRUE(probes.empty());
+  EXPECT_THAT(probes, IsEmpty());
+}
+
+TEST(
+    ProbeControllerTest,
+    InitialProbingRetriedAfterTimeoutIfFirstProbeToMaxBitrateAndBweNotUpdated) {
+  ProbeControllerFixture fixture;
+  std::unique_ptr<ProbeController> probe_controller =
+      fixture.CreateController();
+  probe_controller->SetFirstProbeToMaxBitrate(true);
+  ASSERT_THAT(
+      probe_controller->OnNetworkAvailability({.network_available = true}),
+      IsEmpty());
+  auto probes = probe_controller->SetBitrates(
+      kMinBitrate, kStartBitrate, kMaxBitrate, fixture.CurrentTime());
+  EXPECT_THAT(probes, SizeIs(Gt(0)));
+  // Advance far enough to cause a time out in waiting for probing result.
+  fixture.AdvanceTime(kExponentialProbingTimeout);
+  probes = probe_controller->Process(fixture.CurrentTime());
+  EXPECT_THAT(probes, SizeIs(Gt(0)));
+}
+
+TEST(ProbeControllerTest,
+     InitialProbingNotRetriedAfterTimeoutIfFirstProbeAndBweUpdated) {
+  ProbeControllerFixture fixture;
+  std::unique_ptr<ProbeController> probe_controller =
+      fixture.CreateController();
+  probe_controller->SetFirstProbeToMaxBitrate(true);
+  ASSERT_THAT(
+      probe_controller->OnNetworkAvailability({.network_available = true}),
+      IsEmpty());
+  auto probes = probe_controller->SetBitrates(
+      kMinBitrate, kStartBitrate, kMaxBitrate, fixture.CurrentTime());
+  EXPECT_THAT(probes, SizeIs(Gt(0)));
+  fixture.AdvanceTime(TimeDelta::Millis(700));
+  probes = probe_controller->SetEstimatedBitrate(
+      DataRate::BitsPerSec(180), BandwidthLimitedCause::kDelayBasedLimited,
+      fixture.CurrentTime());
+  EXPECT_THAT(probes, IsEmpty());
+  // Advance far enough to cause a time out in waiting for probing result.
+  fixture.AdvanceTime(kExponentialProbingTimeout);
+  probes = probe_controller->Process(fixture.CurrentTime());
+  EXPECT_THAT(probes, IsEmpty());
 }
 
 TEST(ProbeControllerTest, RequestProbeInAlr) {