Do not switch best connection on the controlled side too frequently

webrtc/p2p/base/port.cc

Index: webrtc/p2p/base/port.cc
diff --git a/webrtc/p2p/base/port.cc b/webrtc/p2p/base/port.cc
index c0e8d9770d8b11fb5e63b3c0221247d6eb2e7e82..3a00738d33dd3e92e2cf604ce33eb0325f727b9b 100644
--- a/webrtc/p2p/base/port.cc
+++ b/webrtc/p2p/base/port.cc
@@ -956,11 +956,14 @@ void Connection::OnReadPacket(
     recv_rate_tracker_.AddSamples(size);
     SignalReadPacket(this, data, size, packet_time);
 
-    // If timed out sending writability checks, start up again
-    if (!pruned_ && (write_state_ == STATE_WRITE_TIMEOUT)) {
+    // If the connection has timed out, it might be because it was pruned or
+    // it failed the writability check. Start it up again if it was not pruned
+    // (so it is due to writability check failure), or it was pruned but it has
+    // been nominated by the controlling side.
+    if (write_state_ == STATE_WRITE_TIMEOUT && (nominated() || !pruned_)) {
       LOG(LS_WARNING) << "Received a data packet on a timed-out Connection. "
                       << "Resetting state to STATE_WRITE_INIT.";
-      set_write_state(STATE_WRITE_INIT);
+      ResetWriteStateAndUnprune();
     }
   } else if (!msg) {
     // The packet was STUN, but failed a check and was handled internally.
@@ -1035,19 +1038,21 @@ void Connection::HandleBindingRequest(IceMessage* msg) {
   // This is a validated stun request from remote peer.
   port_->SendBindingResponse(msg, remote_addr);
 
-  // If it timed out on writing check, start up again
-  if (!pruned_ && write_state_ == STATE_WRITE_TIMEOUT) {
-    set_write_state(STATE_WRITE_INIT);
-  }
-
+  bool nominated = false;
   if (port_->GetIceRole() == ICEROLE_CONTROLLED) {
-    const StunByteStringAttribute* use_candidate_attr =
-        msg->GetByteString(STUN_ATTR_USE_CANDIDATE);
-    if (use_candidate_attr) {
+    bool nominated = msg->GetByteString(STUN_ATTR_USE_CANDIDATE) != nullptr;
+    if (nominated) {
       set_nominated(true);
       SignalNominated(this);
     }
   }
+  // If it timed out on writing check, start up again if it is not pruned or
+  // it is just nominated now, because the nomination may increase its priority
+  // in the pruning process.
+  if (write_state_ == STATE_WRITE_TIMEOUT && (nominated || !pruned_)) {
+    ResetWriteStateAndUnprune();
+  }
+
   // Set the remote cost if the network_info attribute is available.
   // Note: If packets are re-ordered, we may get incorrect network cost
   // temporarily, but it should get the correct value shortly after that.
@@ -1081,7 +1086,6 @@ void Connection::Prune() {
 }
 
 void Connection::Destroy() {
-  LOG_J(LS_VERBOSE, this) << "Connection destroyed";
   port_->thread()->Post(RTC_FROM_HERE, this, MSG_DELETE);
 }
 
@@ -1424,6 +1428,14 @@ int64_t Connection::last_received() const {
              std::max(last_ping_received_, last_ping_response_received_));
 }
 
+void Connection::ResetWriteStateAndUnprune() {
+  write_state_ = STATE_WRITE_INIT;
+  LOG_J(INFO, this) << "Connection unpruned";
+  if (pruned_) {
+    pruned_ = false;
+  }
+}
+
 ConnectionInfo Connection::stats() {
   stats_.recv_bytes_second = round(recv_rate_tracker_.ComputeRate());
   stats_.recv_total_bytes = recv_rate_tracker_.TotalSampleCount();