save the max_datagram_frame_size transport parameter in the session ticket (#4013)

* Add MaxDatagramFrameSize parameter in session ticket

* fix gofumpt issues

* Update integrationtests/self/zero_rtt_test.go

Co-authored-by: Marten Seemann <martenseemann@gmail.com>

* fix: correct comparsion of max_datagram_frame_size

* test: use constant MaxDatagramFrameSize for session ticket test

* fix grammar

---------

Co-authored-by: Marten Seemann <martenseemann@gmail.com>

integrationtests/self/zero_rtt_oldgo_test.go

@@ -801,4 +801,116 @@ var _ = Describe("0-RTT", func() {
 		Expect(len(zeroRTTPackets)).To(BeNumerically(">", 10))
 		Expect(zeroRTTPackets[0]).To(Equal(protocol.PacketNumber(0)))
 	})
+
+	It("sends 0-RTT datagrams", func() {
+		tlsConf, clientTLSConf := dialAndReceiveSessionTicket(getQuicConfig(&quic.Config{
+			EnableDatagrams: true,
+		}))
+
+		tracer := newPacketTracer()
+		ln, err := quic.ListenAddrEarly(
+			"localhost:0",
+			tlsConf,
+			getQuicConfig(&quic.Config{
+				Allow0RTT:       true,
+				EnableDatagrams: true,
+				Tracer:          newTracer(tracer),
+			}),
+		)
+		Expect(err).ToNot(HaveOccurred())
+		defer ln.Close()
+
+		proxy, num0RTTPackets := runCountingProxy(ln.Addr().(*net.UDPAddr).Port)
+		defer proxy.Close()
+
+		// second connection
+		sentMessage := GeneratePRData(100)
+		var receivedMessage []byte
+		received := make(chan struct{})
+		go func() {
+			defer GinkgoRecover()
+			defer close(received)
+			conn, err := ln.Accept(context.Background())
+			Expect(err).ToNot(HaveOccurred())
+			receivedMessage, err = conn.ReceiveMessage(context.Background())
+			Expect(err).ToNot(HaveOccurred())
+			Expect(conn.ConnectionState().Used0RTT).To(BeTrue())
+		}()
+		conn, err := quic.DialAddrEarly(
+			context.Background(),
+			fmt.Sprintf("localhost:%d", proxy.LocalPort()),
+			clientTLSConf,
+			getQuicConfig(&quic.Config{
+				EnableDatagrams: true,
+			}),
+		)
+		Expect(err).ToNot(HaveOccurred())
+		Expect(conn.ConnectionState().SupportsDatagrams).To(BeTrue())
+		Expect(conn.SendMessage(sentMessage)).To(Succeed())
+		<-conn.HandshakeComplete()
+		<-received
+
+		Expect(conn.ConnectionState().Used0RTT).To(BeTrue())
+		Expect(receivedMessage).To(Equal(sentMessage))
+		num0RTT := atomic.LoadUint32(num0RTTPackets)
+		fmt.Fprintf(GinkgoWriter, "Sent %d 0-RTT packets.", num0RTT)
+		Expect(num0RTT).ToNot(BeZero())
+		zeroRTTPackets := get0RTTPackets(tracer.getRcvdLongHeaderPackets())
+		Expect(zeroRTTPackets).To(HaveLen(1))
+		Expect(conn.CloseWithError(0, "")).To(Succeed())
+	})
+
+	It("rejects 0-RTT datagrams when the server doesn't support datagrams anymore", func() {
+		tlsConf, clientTLSConf := dialAndReceiveSessionTicket(getQuicConfig(&quic.Config{
+			EnableDatagrams: true,
+		}))
+
+		tracer := newPacketTracer()
+		ln, err := quic.ListenAddrEarly(
+			"localhost:0",
+			tlsConf,
+			getQuicConfig(&quic.Config{
+				Allow0RTT:       true,
+				EnableDatagrams: false,
+				Tracer:          newTracer(tracer),
+			}),
+		)
+		Expect(err).ToNot(HaveOccurred())
+		defer ln.Close()
+
+		proxy, num0RTTPackets := runCountingProxy(ln.Addr().(*net.UDPAddr).Port)
+		defer proxy.Close()
+
+		// second connection
+		go func() {
+			defer GinkgoRecover()
+			conn, err := ln.Accept(context.Background())
+			Expect(err).ToNot(HaveOccurred())
+			_, err = conn.ReceiveMessage(context.Background())
+			Expect(err.Error()).To(Equal("datagram support disabled"))
+			<-conn.HandshakeComplete()
+			Expect(conn.ConnectionState().Used0RTT).To(BeFalse())
+		}()
+		conn, err := quic.DialAddrEarly(
+			context.Background(),
+			fmt.Sprintf("localhost:%d", proxy.LocalPort()),
+			clientTLSConf,
+			getQuicConfig(&quic.Config{
+				EnableDatagrams: true,
+			}),
+		)
+		Expect(err).ToNot(HaveOccurred())
+		// the client can temporarily send datagrams but the server doesn't process them.
+		Expect(conn.ConnectionState().SupportsDatagrams).To(BeTrue())
+		Expect(conn.SendMessage(make([]byte, 100))).To(Succeed())
+		<-conn.HandshakeComplete()
+
+		Expect(conn.ConnectionState().SupportsDatagrams).To(BeFalse())
+		Expect(conn.ConnectionState().Used0RTT).To(BeFalse())
+		num0RTT := atomic.LoadUint32(num0RTTPackets)
+		fmt.Fprintf(GinkgoWriter, "Sent %d 0-RTT packets.", num0RTT)
+		Expect(num0RTT).ToNot(BeZero())
+		Expect(get0RTTPackets(tracer.getRcvdLongHeaderPackets())).To(BeEmpty())
+		Expect(conn.CloseWithError(0, "")).To(Succeed())
+	})
 })