Implement static 1.3 CID negotiation

Author: JoTurk

conn.go

@@ -591,8 +591,6 @@ func (c *Conn) Write(payload []byte) (int, error) {
 		return 0, err
 	}
 
-	//nolint:godox
-	// TODO: check for version
 	ctx, cancel := c.contextWithClose(c.writeDeadline)
 	defer cancel()
 
@@ -606,7 +604,7 @@ func (c *Conn) Write(payload []byte) (int, error) {
 					Data: payload,
 				},
 			},
-			ShouldWrapCID: len(dtlsstate.CommonState(c.state).RemoteConnectionID) > 0,
+			ShouldWrapCID: c.state.ShouldWrapConnectionID(),
 			ShouldEncrypt: true,
 		},
 	})
@@ -2269,7 +2267,6 @@ func (c *Conn) notify(ctx context.Context, level alert.Level, desc alert.Descrip
 		}
 	}
 
-	// This should be updated with DTLS 1.3 record encoding.
 	return c.writePackets(ctx, []*dtlsflight.Packet{
 		{
 			Record: &recordlayer.RecordLayer{
@@ -2282,7 +2279,7 @@ func (c *Conn) notify(ctx context.Context, level alert.Level, desc alert.Descrip
 					Description: desc,
 				},
 			},
-			ShouldWrapCID: len(common.RemoteConnectionID) > 0,
+			ShouldWrapCID: c.state.ShouldWrapConnectionID(),
 			ShouldEncrypt: c.isHandshakeCompletedSuccessfully(),
 		},
 	})

internal/state/active_state.go

@@ -11,6 +11,7 @@ import (
 // Active is a concrete DTLS version state that shares common connection fields.
 type Active interface {
 	CommonFields() *Common
+	ShouldWrapConnectionID() bool
 }
 
 // NewActive creates a DTLS 1.2 active state with initialized common fields.

internal/state/state12.go

@@ -38,6 +38,12 @@ type State12 struct {
 	PeerCertificatesVerified bool
 }
 
+// ShouldWrapConnectionID reports whether outgoing DTLS 1.2 records should
+// use CID record encoding.
+func (s *State12) ShouldWrapConnectionID() bool {
+	return s != nil && s.Common != nil && len(s.RemoteConnectionID) > 0
+}
+
 func (s *State12) InitCipherSuite() error {
 	if s.CipherSuite == nil {
 		return dtlserrors.ErrCipherSuiteNotSet

internal/state/state13.go

@@ -119,3 +119,9 @@ type State13 struct {
 	RemoteSignatureSchemes     []signaturehash.Algorithm // signature_algorithms from peer
 	RemoteCertSignatureSchemes []signaturehash.Algorithm // signature_algorithms_cert from peer
 }
+
+// ShouldWrapConnectionID reports whether outgoing records should use the
+// legacy DTLS 1.2 CID record encoding.
+func (*State13) ShouldWrapConnectionID() bool {
+	return false
+}