http3: simplify ConfigureTLSConfig (#5011)

The previous logic allowed for setting different ALPN
values depending on the QUIC version in use. This was
needed to set the draft ALPN value before publication of
the RFC.

http3/server.go

@@ -57,55 +57,24 @@ type QUICEarlyListener interface {
 
 var _ QUICEarlyListener = &quic.EarlyListener{}
 
-func versionToALPN(v protocol.Version) string {
-	//nolint:exhaustive // These are all the versions we care about.
-	switch v {
-	case protocol.Version1, protocol.Version2:
-		return NextProtoH3
-	default:
-		return ""
-	}
-}
-
 // ConfigureTLSConfig creates a new tls.Config which can be used
-// to create a quic.Listener meant for serving http3. The created
-// tls.Config adds the functionality of detecting the used QUIC version
-// in order to set the correct ALPN value for the http3 connection.
+// to create a quic.Listener meant for serving HTTP/3.
 func ConfigureTLSConfig(tlsConf *tls.Config) *tls.Config {
-	// The tls.Config used to setup the quic.Listener needs to have the GetConfigForClient callback set.
-	// That way, we can get the QUIC version and set the correct ALPN value.
-	return &tls.Config{
-		GetConfigForClient: func(ch *tls.ClientHelloInfo) (*tls.Config, error) {
-			// determine the ALPN from the QUIC version used
-			proto := NextProtoH3
-			val := ch.Context().Value(quic.QUICVersionContextKey)
-			if v, ok := val.(quic.Version); ok {
-				proto = versionToALPN(v)
+	// Workaround for https://github.com/golang/go/issues/60506.
+	// This initializes the session tickets _before_ cloning the config.
+	_, _ = tlsConf.DecryptTicket(nil, tls.ConnectionState{})
+	config := tlsConf.Clone()
+	config.NextProtos = []string{NextProtoH3}
+	if gfc := config.GetConfigForClient; gfc != nil {
+		config.GetConfigForClient = func(ch *tls.ClientHelloInfo) (*tls.Config, error) {
+			conf, err := gfc(ch)
+			if conf == nil || err != nil {
+				return conf, err
 			}
-			config := tlsConf
-			if tlsConf.GetConfigForClient != nil {
-				getConfigForClient := tlsConf.GetConfigForClient
-				var err error
-				conf, err := getConfigForClient(ch)
-				if err != nil {
-					return nil, err
-				}
-				if conf != nil {
-					config = conf
-				}
-			}
-			if config == nil {
-				return nil, nil
-			}
-			// Workaround for https://github.com/golang/go/issues/60506.
-			// This initializes the session tickets _before_ cloning the config.
-			_, _ = config.DecryptTicket(nil, tls.ConnectionState{})
-
-			config = config.Clone()
-			config.NextProtos = []string{proto}
-			return config, nil
-		},
+			return ConfigureTLSConfig(conf), nil
+		}
 	}
+	return config
 }
 
 // contextKey is a value for use with context.WithValue. It's used as
@@ -407,28 +376,10 @@ func (s *Server) generateAltSvcHeader() {
 	}
 
 	// This code assumes that we will use protocol.SupportedVersions if no quic.Config is passed.
-	supportedVersions := protocol.SupportedVersions
-	if s.QUICConfig != nil && len(s.QUICConfig.Versions) > 0 {
-		supportedVersions = s.QUICConfig.Versions
-	}
-
-	// keep track of which have been seen so we don't yield duplicate values
-	seen := make(map[string]struct{}, len(supportedVersions))
-	var versionStrings []string
-	for _, version := range supportedVersions {
-		if v := versionToALPN(version); len(v) > 0 {
-			if _, ok := seen[v]; !ok {
-				versionStrings = append(versionStrings, v)
-				seen[v] = struct{}{}
-			}
-		}
-	}
 
 	var altSvc []string
 	addPort := func(port int) {
-		for _, v := range versionStrings {
-			altSvc = append(altSvc, fmt.Sprintf(`%s=":%d"; ma=2592000`, v, port))
-		}
+		altSvc = append(altSvc, fmt.Sprintf(`%s=":%d"; ma=2592000`, NextProtoH3, port))
 	}
 
 	if s.Port != 0 {

http3/transport.go

@@ -322,7 +322,7 @@ func (t *Transport) dial(ctx context.Context, hostname string) (quic.EarlyConnec
 		tlsConf.ServerName = sni
 	}
 	// Replace existing ALPNs by H3
-	tlsConf.NextProtos = []string{versionToALPN(t.QUICConfig.Versions[0])}
+	tlsConf.NextProtos = []string{NextProtoH3}
 
 	dial := t.Dial
 	if dial == nil {