Downgrading rst stream codes which wouldn't be recognized by the peer.

net/quic/quic_protocol.h

 // 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.
 
 #ifndef NET_QUIC_QUIC_PROTOCOL_H_
 #define NET_QUIC_QUIC_PROTOCOL_H_
 
 #include <stddef.h>
 #include <limits>
 #include <map>
@@ skipping 338 matching lines @@
   QUIC_STREAM_PEER_GOING_AWAY,
   // The stream has been cancelled.
   QUIC_STREAM_CANCELLED,
   // Sending a RST to allow for proper flow control accounting.
   QUIC_RST_FLOW_CONTROL_ACCOUNTING,
 
   // No error. Used as bound while iterating.
   QUIC_STREAM_LAST_ERROR,
 };
 
+// Because receiving an unknown QuicRstStreamErrorCode results in connection
+// teardown, we use this to make sure any errors predating a given version are
+// downgraded to the most appropriate existing error.
+QuicRstStreamErrorCode AdjustErrorForVersion(
+    QuicRstStreamErrorCode error_code,
+    QuicVersion version);
+
 // These values must remain stable as they are uploaded to UMA histograms.
 // To add a new error code, use the current value of QUIC_LAST_ERROR and
 // increment QUIC_LAST_ERROR.
 enum QuicErrorCode {
   QUIC_NO_ERROR = 0,
 
   // Connection has reached an invalid state.
   QUIC_INTERNAL_ERROR = 1,
   // There were data frames after the a fin or reset.
   QUIC_STREAM_DATA_AFTER_TERMINATION = 2,
@@ skipping 652 matching lines @@
   WriteStatus status;
   union {
     int bytes_written;  // only valid when status is OK
     int error_code;  // only valid when status is ERROR
   };
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_PROTOCOL_H_