Fix a bug where the packet was put into unacked packets when it was

net/quic/quic_connection.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/quic/quic_connection.h"
 
 #include <string.h>
 #include <sys/types.h>
 #include <algorithm>
 #include <iterator>
@@ skipping 1178 matching lines @@
   if (encryption_level_ == ENCRYPTION_FORWARD_SECURE &&
       level == ENCRYPTION_NONE) {
     // Drop packets that are NULL encrypted since the peer won't accept them
     // anymore.
     DVLOG(1) << ENDPOINT << "Dropping packet: " << sequence_number
                << " since the packet is NULL encrypted.";
     sent_packet_manager_.DiscardUnackedPacket(sequence_number);
     return true;
   }
 
+  // If the packet has been discarded before sending, don't send it.
+  // This occurs if a packet gets serialized, queued, then discarded.
+  if (!sent_packet_manager_.IsUnacked(sequence_number)) {
+    DVLOG(1) << ENDPOINT << "Dropping packet before sending: "
+             << sequence_number << " since it has already been discarded.";
+    return true;
+  }
+
   if (retransmittable == HAS_RETRANSMITTABLE_DATA) {
-    if (!sent_packet_manager_.IsUnacked(sequence_number)) {
-      // This is a crazy edge case, but if we retransmit a packet,
-      // (but have to queue it for some reason) then receive an ack
-      // for the previous transmission (but not the retransmission)
-      // then receive a truncated ACK which causes us to raise the
-      // high water mark, all before we're able to send the packet
-      // then we can simply drop it.
-      DVLOG(1) << ENDPOINT << "Dropping packet: " << sequence_number
-                 << " since it has already been acked.";
-      return true;
-    }
-
     if (sent_packet_manager_.IsPreviousTransmission(sequence_number)) {
       // If somehow we have already retransmitted this packet *before*
       // we actually send it for the first time (I think this is probably
       // impossible in the real world), then don't bother sending it.
       // We don't want to call DiscardUnackedPacket because in this case
       // the peer has not yet ACK'd the data.  We need the subsequent
       // retransmission to be sent.
       DVLOG(1) << ENDPOINT << "Dropping packet: " << sequence_number
                  << " since it has already been retransmitted.";
       return true;
@@ skipping 431 matching lines @@
   // If we changed the generator's batch state, restore original batch state.
   if (!already_in_batch_mode_) {
     DVLOG(1) << "Leaving Batch Mode.";
     connection_->packet_generator_.FinishBatchOperations();
   }
   DCHECK_EQ(already_in_batch_mode_,
             connection_->packet_generator_.InBatchMode());
 }
 
 }  // namespace net