Only inform QUIC's SentPacketManager of packets that are actually sent, not those that failed to be…

net/quic/core/quic_connection.cc

Index: net/quic/core/quic_connection.cc
diff --git a/net/quic/core/quic_connection.cc b/net/quic/core/quic_connection.cc
index 91bf216ba0766b8d6a3002c7c6046d7dcd352894..6985d7dfd0d62c312a7d73d53be1a2d1f66371ad 100644
--- a/net/quic/core/quic_connection.cc
+++ b/net/quic/core/quic_connection.cc
@@ -1607,6 +1607,9 @@ bool QuicConnection::WritePacket(SerializedPacket* packet) {
   }
 
   QuicPacketNumber packet_number = packet->packet_number;
+  // TODO(ianswett): Remove packet_number_of_last_sent_packet_ because it's
+  // redundant to SentPacketManager_->GetLargestPacket in most cases, and wrong
+  // for multipath.
   DCHECK_LE(packet_number_of_last_sent_packet_, packet_number);
   packet_number_of_last_sent_packet_ = packet_number;
 
@@ -1664,6 +1667,34 @@ bool QuicConnection::WritePacket(SerializedPacket* packet) {
       return false;
     }
   }
+
+  if (FLAGS_quic_only_track_sent_packets) {
+    // In some cases, an MTU probe can cause EMSGSIZE. This indicates that the
+    // MTU discovery is permanently unsuccessful.
+    if (FLAGS_graceful_emsgsize_on_mtu_probe &&
+        result.status == WRITE_STATUS_ERROR &&
+        result.error_code == kMessageTooBigErrorCode &&
+        packet->retransmittable_frames.empty() &&
+        packet->encrypted_length > long_term_mtu_) {
+      mtu_discovery_target_ = 0;
+      mtu_discovery_alarm_->Cancel();
+      // The write failed, but the writer is not blocked, so return true.
+      return true;
+    }
+
+    if (result.status == WRITE_STATUS_ERROR) {
+      OnWriteError(result.error_code);
+      DLOG(ERROR) << ENDPOINT << "failed writing " << encrypted_length
+                  << " from host "
+                  << (self_address().address().empty()
+                          ? " empty address "
+                          : self_address().ToStringWithoutPort())
+                  << " to address " << peer_address().ToString()
+                  << " with error code " << result.error_code;
+      return false;
+    }
+  }
+
   if (result.status != WRITE_STATUS_ERROR && debug_visitor_ != nullptr) {
     // Pass the write result to the visitor.
     debug_visitor_->OnPacketSent(*packet, packet->original_path_id,
@@ -1715,28 +1746,30 @@ bool QuicConnection::WritePacket(SerializedPacket* packet) {
     ++stats_.packets_retransmitted;
   }
 
-  // In some cases, an MTU probe can cause ERR_MSG_TOO_BIG. This indicates that
-  // the MTU discovery is permanently unsuccessful.
-  if (FLAGS_graceful_emsgsize_on_mtu_probe &&
-      result.status == WRITE_STATUS_ERROR &&
-      result.error_code == kMessageTooBigErrorCode &&
-      packet->retransmittable_frames.empty() &&
-      packet->encrypted_length > long_term_mtu_) {
-    mtu_discovery_target_ = 0;
-    mtu_discovery_alarm_->Cancel();
-    return true;
-  }
+  if (!FLAGS_quic_only_track_sent_packets) {
+    // In some cases, an MTU probe can cause EMSGSIZE. This indicates that the
+    // MTU discovery is permanently unsuccessful.
+    if (FLAGS_graceful_emsgsize_on_mtu_probe &&
+        result.status == WRITE_STATUS_ERROR &&
+        result.error_code == kMessageTooBigErrorCode &&
+        packet->retransmittable_frames.empty() &&
+        packet->encrypted_length > long_term_mtu_) {
+      mtu_discovery_target_ = 0;
+      mtu_discovery_alarm_->Cancel();
+      return true;
+    }
 
-  if (result.status == WRITE_STATUS_ERROR) {
-    OnWriteError(result.error_code);
-    DLOG(ERROR) << ENDPOINT << "failed writing " << encrypted_length
-                << " bytes "
-                << " from host " << (self_address().address().empty()
-                                         ? " empty address "
-                                         : self_address().ToStringWithoutPort())
-                << " to address " << peer_address().ToString()
-                << " with error code " << result.error_code;
-    return false;
+    if (result.status == WRITE_STATUS_ERROR) {
+      OnWriteError(result.error_code);
+      DLOG(ERROR) << ENDPOINT << "failed writing " << encrypted_length
+                  << " from host "
+                  << (self_address().address().empty()
+                          ? " empty address "
+                          : self_address().ToStringWithoutPort())
+                  << " to address " << peer_address().ToString()
+                  << " with error code " << result.error_code;
+      return false;
+    }
   }
 
   return true;