relnote: Make QUIC version negotiation stateless. The QUIC dispatcher

net/tools/quic/quic_dispatcher.cc

Index: net/tools/quic/quic_dispatcher.cc
diff --git a/net/tools/quic/quic_dispatcher.cc b/net/tools/quic/quic_dispatcher.cc
index bcfd92b4c8d66f3e79781270c8577e4781678056..a4d43cdd1cb9dcf86c2354585234f7a21466b40b 100644
--- a/net/tools/quic/quic_dispatcher.cc
+++ b/net/tools/quic/quic_dispatcher.cc
@@ -90,6 +90,8 @@ void QuicDispatcher::ProcessPacket(const IPEndPoint& server_address,
 
 bool QuicDispatcher::OnUnauthenticatedPublicHeader(
     const QuicPacketPublicHeader& header) {
+  current_connection_id_ = header.connection_id;
+
   // Port zero is only allowed for unidirectional UDP, so is disallowed by QUIC.
   // Given that we can't even send a reply rejecting the packet, just drop the
   // packet.
@@ -137,12 +139,22 @@ bool QuicDispatcher::OnUnauthenticatedPublicHeader(
     if (framer_.IsSupportedVersion(packet_version)) {
       version = packet_version;
     } else {
-      // Packets set to be processed but having an unsupported version will
-      // cause a connection to be created.  The connection will handle
-      // sending a version negotiation packet.
-      // TODO(ianswett): This will malfunction if the full header of the packet
-      // causes a parsing error when parsed using the server's preferred
-      // version.
+      if (FLAGS_quic_stateless_version_negotiation) {
+        DVLOG(1) << "Version mismatch, connection ID " << connection_id;
+        // Since the version is not supported, send a version negotiation
+        // packet and stop processing the current packet.
+        time_wait_list_manager()->SendVersionNegotiationPacket(
+            connection_id, supported_versions_, current_server_address_,
+            current_client_address_);
+        return false;
+      } else {
+        // Packets set to be processed but having an unsupported version will
+        // cause a connection to be created.  The connection will handle
+        // sending a version negotiation packet.
+        // TODO(ianswett): This will malfunction if the full header of the
+        // packet causes a parsing error when parsed using the server's
+        // preferred version.
+      }
     }
   }
   // Set the framer's version and continue processing.
@@ -336,6 +348,11 @@ void QuicDispatcher::OnError(QuicFramer* framer) {
 
 bool QuicDispatcher::OnProtocolVersionMismatch(
     QuicVersion /*received_version*/) {
+  if (FLAGS_quic_stateless_version_negotiation) {
+    QUIC_BUG_IF(!time_wait_list_manager_->IsConnectionIdInTimeWait(
+        current_connection_id_));
+  }
+
   // Keep processing after protocol mismatch - this will be dealt with by the
   // time wait list or connection that we will create.
   return true;