Remove `should_update_expected_server_connection_id_length_` from QuicDispatcher.

Its value is always false, even in tests.

PiperOrigin-RevId: 651400527

quiche/quic/core/quic_dispatcher.cc

diff --git a/quiche/quic/core/quic_dispatcher.cc b/quiche/quic/core/quic_dispatcher.cc
index 4c59fc5..4ced4aa 100644
--- a/quiche/quic/core/quic_dispatcher.cc
+++ b/quiche/quic/core/quic_dispatcher.cc
@@ -238,7 +238,6 @@
           expected_server_connection_id_length),
       clear_stateless_reset_addresses_alarm_(alarm_factory_->CreateAlarm(
           new ClearStatelessResetAddressesAlarm(this))),
-      should_update_expected_server_connection_id_length_(false),
       connection_id_generator_(connection_id_generator) {
   QUIC_BUG_IF(quic_bug_12724_1, GetSupportedVersions().empty())
       << "Trying to create dispatcher without any supported versions";
@@ -290,7 +289,6 @@
   }
   if (packet_info.destination_connection_id.length() !=
           expected_server_connection_id_length_ &&
-      !should_update_expected_server_connection_id_length_ &&
       packet_info.version.IsKnown() &&
       !packet_info.version.AllowsVariableLengthConnectionIds()) {
     SetLastError(QUIC_INVALID_PACKET_HEADER);
@@ -317,14 +315,6 @@
     }
   }
 
-  // Before introducing the flag, it was impossible for a short header to
-  // update |expected_server_connection_id_length_|.
-  if (should_update_expected_server_connection_id_length_ &&
-      packet_info.version_flag) {
-    expected_server_connection_id_length_ =
-        packet_info.destination_connection_id.length();
-  }
-
   if (MaybeDispatchPacket(packet_info)) {
     // Packet has been dropped or successfully dispatched, stop processing.
     return;

quiche/quic/core/quic_dispatcher.h

diff --git a/quiche/quic/core/quic_dispatcher.h b/quiche/quic/core/quic_dispatcher.h
index 625f519..b88cd0e 100644
--- a/quiche/quic/core/quic_dispatcher.h
+++ b/quiche/quic/core/quic_dispatcher.h
@@ -314,14 +314,6 @@
   virtual void RestorePerPacketContext(
       std::unique_ptr<QuicPerPacketContext> /*context*/) {}
 
-  // If true, our framer will change its expected connection ID length
-  // to the received destination connection ID length of all IETF long headers.
-  void SetShouldUpdateExpectedServerConnectionIdLength(
-      bool should_update_expected_server_connection_id_length) {
-    should_update_expected_server_connection_id_length_ =
-        should_update_expected_server_connection_id_length;
-  }
-
   // Called if a packet from an unseen connection is reset or rejected.
   virtual void OnNewConnectionRejected() {}
 
@@ -461,10 +453,9 @@
   // IETF short headers contain a destination connection ID but do not
   // encode its length. This variable contains the length we expect to read.
   // This is also used to signal an error when a long header packet with
-  // different destination connection ID length is received when
-  // should_update_expected_server_connection_id_length_ is false and packet's
+  // different destination connection ID length is received when packet's
   // version does not allow variable length connection ID.
-  uint8_t expected_server_connection_id_length_;
+  const uint8_t expected_server_connection_id_length_;
 
   // Records client addresses that have been recently reset.
   absl::flat_hash_set<QuicSocketAddress, QuicSocketAddressHash>
@@ -473,10 +464,6 @@
   // An alarm which clear recent_stateless_reset_addresses_.
   std::unique_ptr<QuicAlarm> clear_stateless_reset_addresses_alarm_;
 
-  // If true, change expected_server_connection_id_length_ to be the received
-  // destination connection ID length of all IETF long headers.
-  bool should_update_expected_server_connection_id_length_;
-
   ConnectionIdGeneratorInterface& connection_id_generator_;
 };