make the connection ID length configurable

client.go

@@ -74,6 +74,7 @@ func DialAddrContext(
 	tlsConf *tls.Config,
 	config *Config,
 ) (Session, error) {
+	config = populateClientConfig(config, false)
 	udpAddr, err := net.ResolveUDPAddr("udp", addr)
 	if err != nil {
 		return nil, err
@@ -115,8 +116,12 @@ func DialContext(
 	tlsConf *tls.Config,
 	config *Config,
 ) (Session, error) {
+	config = populateClientConfig(config, true)
 	multiplexer := getClientMultiplexer()
-	manager := multiplexer.AddConn(pconn)
+	manager, err := multiplexer.AddConn(pconn, config.ConnectionIDLength)
+	if err != nil {
+		return nil, err
+	}
 	c, err := newClient(pconn, remoteAddr, config, tlsConf, host, manager.Remove)
 	if err != nil {
 		return nil, err
@@ -138,9 +143,6 @@ func newClient(
 	host string,
 	closeCallback func(protocol.ConnectionID),
 ) (*client, error) {
-	clientConfig := populateClientConfig(config)
-	version := clientConfig.Versions[0]
-
 	var hostname string
 	if tlsConf != nil {
 		hostname = tlsConf.ServerName
@@ -169,8 +171,8 @@ func newClient(
 		conn:          &conn{pconn: pconn, currentAddr: remoteAddr},
 		hostname:      hostname,
 		tlsConf:       tlsConf,
-		config:        clientConfig,
-		version:       version,
+		config:        config,
+		version:       config.Versions[0],
 		handshakeChan: make(chan struct{}),
 		closeCallback: onClose,
 		logger:        utils.DefaultLogger.WithPrefix("client"),
@@ -180,7 +182,7 @@ func newClient(
 
 // populateClientConfig populates fields in the quic.Config with their default values, if none are set
 // it may be called with nil
-func populateClientConfig(config *Config) *Config {
+func populateClientConfig(config *Config, onPacketConn bool) *Config {
 	if config == nil {
 		config = &Config{}
 	}
@@ -218,12 +220,17 @@ func populateClientConfig(config *Config) *Config {
 	} else if maxIncomingUniStreams < 0 {
 		maxIncomingUniStreams = 0
 	}
+	connIDLen := config.ConnectionIDLength
+	if connIDLen == 0 && onPacketConn {
+		connIDLen = protocol.DefaultConnectionIDLength
+	}
 
 	return &Config{
 		Versions:                              versions,
 		HandshakeTimeout:                      handshakeTimeout,
 		IdleTimeout:                           idleTimeout,
 		RequestConnectionIDOmission:           config.RequestConnectionIDOmission,
+		ConnectionIDLength:                    connIDLen,
 		MaxReceiveStreamFlowControlWindow:     maxReceiveStreamFlowControlWindow,
 		MaxReceiveConnectionFlowControlWindow: maxReceiveConnectionFlowControlWindow,
 		MaxIncomingStreams:                    maxIncomingStreams,
@@ -233,7 +240,11 @@ func populateClientConfig(config *Config) *Config {
 }
 
 func (c *client) generateConnectionIDs() error {
-	srcConnID, err := generateConnectionID(protocol.ConnectionIDLenGQUIC)
+	connIDLen := protocol.ConnectionIDLenGQUIC
+	if c.version.UsesTLS() {
+		connIDLen = c.config.ConnectionIDLength
+	}
+	srcConnID, err := generateConnectionID(connIDLen)
 	if err != nil {
 		return err
 	}
@@ -370,7 +381,7 @@ func (c *client) handleRead(remoteAddr net.Addr, packet []byte) {
 	rcvTime := time.Now()
 
 	r := bytes.NewReader(packet)
-	iHdr, err := wire.ParseInvariantHeader(r, protocol.ConnectionIDLenGQUIC)
+	iHdr, err := wire.ParseInvariantHeader(r, c.config.ConnectionIDLength)
 	// drop the packet if we can't parse the header
 	if err != nil {
 		c.logger.Errorf("error parsing invariant header: %s", err)