wire: apply the default value for the active_connection_id_limit (#3806)

connection.go

@@ -312,9 +312,14 @@ var newConnection = func(
  DisableActiveMigration: true,
  StatelessResetToken: &statelessResetToken,
  OriginalDestinationConnectionID: origDestConnID,
- ActiveConnectionIDLimit: protocol.MaxActiveConnectionIDs,
- InitialSourceConnectionID: srcConnID,
- RetrySourceConnectionID: retrySrcConnID,
+ // For interoperability with quic-go versions before May 2023, this value must be set to a value
+ // different from protocol.DefaultActiveConnectionIDLimit.
+ // If set to the default value, it will be omitted from the transport parameters, which will make
+ // old quic-go versions interpret it as 0, instead of the default value of 2.
+ // See https://github.com/quic-go/quic-go/pull/3806.
+ ActiveConnectionIDLimit: protocol.MaxActiveConnectionIDs,
+ InitialSourceConnectionID: srcConnID,
+ RetrySourceConnectionID: retrySrcConnID,
  }
  if s.config.EnableDatagrams {
  params.MaxDatagramFrameSize = protocol.MaxDatagramFrameSize
@@ -426,8 +431,13 @@ var newClientConnection = func(
  MaxAckDelay: protocol.MaxAckDelayInclGranularity,
  AckDelayExponent: protocol.AckDelayExponent,
  DisableActiveMigration: true,
- ActiveConnectionIDLimit: protocol.MaxActiveConnectionIDs,
- InitialSourceConnectionID: srcConnID,
+ // For interoperability with quic-go versions before May 2023, this value must be set to a value
+ // different from protocol.DefaultActiveConnectionIDLimit.
+ // If set to the default value, it will be omitted from the transport parameters, which will make
+ // old quic-go versions interpret it as 0, instead of the default value of 2.
+ // See https://github.com/quic-go/quic-go/pull/3806.
+ ActiveConnectionIDLimit: protocol.MaxActiveConnectionIDs,
+ InitialSourceConnectionID: srcConnID,
  }
  if s.config.EnableDatagrams {
  params.MaxDatagramFrameSize = protocol.MaxDatagramFrameSize

internal/protocol/protocol.go

@@ -77,6 +77,9 @@ const MinConnectionIDLenInitial = 8
 // DefaultAckDelayExponent is the default ack delay exponent
 const DefaultAckDelayExponent = 3
 
+// DefaultActiveConnectionIDLimit is the default active connection ID limit
+const DefaultActiveConnectionIDLimit = 2
+
 // MaxAckDelayExponent is the maximum ack delay exponent
 const MaxAckDelayExponent = 20
 

internal/wire/transport_parameter_test.go

@@ -289,15 +289,16 @@ var _ = Describe("Transport Parameters", func() {
  Expect(float32(dataLen) / num).To(BeNumerically("~", float32(defaultLen)/num+float32(entryLen), 1))
  })
 
- It("sets the default value for the ack_delay_exponent, when no value was sent", func() {
+ It("sets the default value for the ack_delay_exponent and max_active_connection_id_limit, when no values were sent", func() {
  data := (&TransportParameters{
  AckDelayExponent: protocol.DefaultAckDelayExponent,
  StatelessResetToken: &protocol.StatelessResetToken{},
- ActiveConnectionIDLimit: 2,
+ ActiveConnectionIDLimit: protocol.DefaultActiveConnectionIDLimit,
  }).Marshal(protocol.PerspectiveServer)
  p := &TransportParameters{}
  Expect(p.Unmarshal(data, protocol.PerspectiveServer)).To(Succeed())
  Expect(p.AckDelayExponent).To(BeEquivalentTo(protocol.DefaultAckDelayExponent))
+ Expect(p.ActiveConnectionIDLimit).To(BeEquivalentTo(protocol.DefaultActiveConnectionIDLimit))
  })
 
  It("errors when the varint value has the wrong length", func() {

internal/wire/transport_parameters.go

@@ -118,6 +118,7 @@ func (p *TransportParameters) unmarshal(r *bytes.Reader, sentBy protocol.Perspec
  var (
  readOriginalDestinationConnectionID bool
  readInitialSourceConnectionID bool
+ readActiveConnectionIDLimit bool
  )
 
  p.AckDelayExponent = protocol.DefaultAckDelayExponent
@@ -139,6 +140,9 @@ func (p *TransportParameters) unmarshal(r *bytes.Reader, sentBy protocol.Perspec
  }
  parameterIDs = append(parameterIDs, paramID)
  switch paramID {
+ case activeConnectionIDLimitParameterID:
+ readActiveConnectionIDLimit = true
+ fallthrough
  case maxIdleTimeoutParameterID,
  maxUDPPayloadSizeParameterID,
  initialMaxDataParameterID,
@@ -148,7 +152,6 @@ func (p *TransportParameters) unmarshal(r *bytes.Reader, sentBy protocol.Perspec
  initialMaxStreamsBidiParameterID,
  initialMaxStreamsUniParameterID,
  maxAckDelayParameterID,
- activeConnectionIDLimitParameterID,
  maxDatagramFrameSizeParameterID,
  ackDelayExponentParameterID:
  if err := p.readNumericTransportParameter(r, paramID, int(paramLen)); err != nil {
@@ -196,6 +199,9 @@ func (p *TransportParameters) unmarshal(r *bytes.Reader, sentBy protocol.Perspec
  }
  }
 
+ if !readActiveConnectionIDLimit {
+ p.ActiveConnectionIDLimit = protocol.DefaultActiveConnectionIDLimit
+ }
  if !fromSessionTicket {
  if sentBy == protocol.PerspectiveServer && !readOriginalDestinationConnectionID {
  return errors.New("missing original_destination_connection_id")
@@ -402,7 +408,9 @@ func (p *TransportParameters) Marshal(pers protocol.Perspective) []byte {
  }
  }
  // active_connection_id_limit
- b = p.marshalVarintParam(b, activeConnectionIDLimitParameterID, p.ActiveConnectionIDLimit)
+ if p.ActiveConnectionIDLimit != protocol.DefaultActiveConnectionIDLimit {
+ b = p.marshalVarintParam(b, activeConnectionIDLimitParameterID, p.ActiveConnectionIDLimit)
+ }
  // initial_source_connection_id
  b = quicvarint.Append(b, uint64(initialSourceConnectionIDParameterID))
  b = quicvarint.Append(b, uint64(p.InitialSourceConnectionID.Len()))