add a http3.RoundTripper.EnableDatagram option

http3/client.go

@@ -37,6 +37,7 @@ var dialAddr = quic.DialAddrEarly
 
 type roundTripperOpts struct {
 	DisableCompression bool
+	EnableDatagram     bool
 	MaxHeaderBytes     int64
 }
 
@@ -68,7 +69,7 @@ func newClient(
 	dialer func(network, addr string, tlsCfg *tls.Config, cfg *quic.Config) (quic.EarlySession, error),
 ) (*client, error) {
 	if quicConfig == nil {
-		quicConfig = defaultQuicConfig
+		quicConfig = defaultQuicConfig.Clone()
 	} else if len(quicConfig.Versions) == 0 {
 		quicConfig = quicConfig.Clone()
 		quicConfig.Versions = []quic.VersionNumber{defaultQuicConfig.Versions[0]}
@@ -77,6 +78,7 @@ func newClient(
 		return nil, errors.New("can only use a single QUIC version for dialing a HTTP/3 connection")
 	}
 	quicConfig.MaxIncomingStreams = -1 // don't allow any bidirectional streams
+	quicConfig.EnableDatagrams = opts.EnableDatagram
 	logger := utils.DefaultLogger.WithPrefix("h3 client")
 
 	if tlsConf == nil {
@@ -131,7 +133,7 @@ func (c *client) setupSession() error {
 	buf := &bytes.Buffer{}
 	utils.WriteVarInt(buf, streamTypeControlStream)
 	// send the SETTINGS frame
-	(&settingsFrame{}).Write(buf)
+	(&settingsFrame{Datagram: c.opts.EnableDatagram}).Write(buf)
 	_, err = str.Write(buf.Bytes())
 	return err
 }

http3/client_test.go

@@ -136,6 +136,18 @@ var _ = Describe("Client", func() {
 		Expect(dialerCalled).To(BeTrue())
 	})
 
+	It("enables HTTP/3 Datagrams", func() {
+		testErr := errors.New("handshake error")
+		client, err := newClient("localhost:1337", nil, &roundTripperOpts{EnableDatagram: true}, nil, nil)
+		Expect(err).ToNot(HaveOccurred())
+		dialAddr = func(hostname string, _ *tls.Config, quicConf *quic.Config) (quic.EarlySession, error) {
+			Expect(quicConf.EnableDatagrams).To(BeTrue())
+			return nil, testErr
+		}
+		_, err = client.RoundTrip(req)
+		Expect(err).To(MatchError(testErr))
+	})
+
 	It("errors when dialing fails", func() {
 		testErr := errors.New("handshake error")
 		client, err := newClient("localhost:1337", nil, &roundTripperOpts{}, nil, nil)

http3/roundtrip.go

@@ -41,6 +41,11 @@ type RoundTripper struct {
 	// If nil, reasonable default values will be used.
 	QuicConfig *quic.Config
 
+	// Enable support for HTTP/3 datagrams.
+	// If set to true, QuicConfig.EnableDatagram will be set.
+	// See https://www.ietf.org/archive/id/draft-schinazi-masque-h3-datagram-02.html.
+	EnableDatagrams bool
+
 	// Dial specifies an optional dial function for creating QUIC
 	// connections for requests.
 	// If Dial is nil, quic.DialAddr will be used.
@@ -135,6 +140,7 @@ func (r *RoundTripper) getClient(hostname string, onlyCached bool) (http.RoundTr
 			hostname,
 			r.TLSClientConfig,
 			&roundTripperOpts{
+				EnableDatagram:     r.EnableDatagrams,
 				DisableCompression: r.DisableCompression,
 				MaxHeaderBytes:     r.MaxResponseHeaderBytes,
 			},