From 3a359027b51064d633d6f0faf530833fa4d788c6 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Sun, 27 Jun 2021 15:29:29 -0700
Subject: [PATCH] add a config option to disable sending of Version Negotiation
 packets

---
 config.go      | 35 ++++++++++++++++++-----------------
 config_test.go |  3 +++
 interface.go   |  4 ++++
 server.go      |  4 +++-
 server_test.go | 19 +++++++++++++++++++
 5 files changed, 47 insertions(+), 18 deletions(-)

diff --git a/config.go b/config.go
index 61ee7a21..8e439c26 100644
--- a/config.go
+++ b/config.go
@@ -101,22 +101,23 @@ func populateConfig(config *Config) *Config {
 	}
 
 	return &Config{
-		Versions:                       versions,
-		HandshakeIdleTimeout:           handshakeIdleTimeout,
-		MaxIdleTimeout:                 idleTimeout,
-		AcceptToken:                    config.AcceptToken,
-		KeepAlive:                      config.KeepAlive,
-		InitialStreamReceiveWindow:     initialStreamReceiveWindow,
-		MaxStreamReceiveWindow:         maxStreamReceiveWindow,
-		InitialConnectionReceiveWindow: initialConnectionReceiveWindow,
-		MaxConnectionReceiveWindow:     maxConnectionReceiveWindow,
-		MaxIncomingStreams:             maxIncomingStreams,
-		MaxIncomingUniStreams:          maxIncomingUniStreams,
-		ConnectionIDLength:             config.ConnectionIDLength,
-		StatelessResetKey:              config.StatelessResetKey,
-		TokenStore:                     config.TokenStore,
-		EnableDatagrams:                config.EnableDatagrams,
-		DisablePathMTUDiscovery:        config.DisablePathMTUDiscovery,
-		Tracer:                         config.Tracer,
+		Versions:                         versions,
+		HandshakeIdleTimeout:             handshakeIdleTimeout,
+		MaxIdleTimeout:                   idleTimeout,
+		AcceptToken:                      config.AcceptToken,
+		KeepAlive:                        config.KeepAlive,
+		InitialStreamReceiveWindow:       initialStreamReceiveWindow,
+		MaxStreamReceiveWindow:           maxStreamReceiveWindow,
+		InitialConnectionReceiveWindow:   initialConnectionReceiveWindow,
+		MaxConnectionReceiveWindow:       maxConnectionReceiveWindow,
+		MaxIncomingStreams:               maxIncomingStreams,
+		MaxIncomingUniStreams:            maxIncomingUniStreams,
+		ConnectionIDLength:               config.ConnectionIDLength,
+		StatelessResetKey:                config.StatelessResetKey,
+		TokenStore:                       config.TokenStore,
+		EnableDatagrams:                  config.EnableDatagrams,
+		DisablePathMTUDiscovery:          config.DisablePathMTUDiscovery,
+		DisableVersionNegotiationPackets: config.DisableVersionNegotiationPackets,
+		Tracer:                           config.Tracer,
 	}
 }
diff --git a/config_test.go b/config_test.go
index 6cb2ce91..b8454b10 100644
--- a/config_test.go
+++ b/config_test.go
@@ -75,6 +75,8 @@ var _ = Describe("Config", func() {
 				f.Set(reflect.ValueOf(true))
 			case "EnableDatagrams":
 				f.Set(reflect.ValueOf(true))
+			case "DisableVersionNegotiationPackets":
+				f.Set(reflect.ValueOf(true))
 			case "DisablePathMTUDiscovery":
 				f.Set(reflect.ValueOf(true))
 			case "Tracer":
@@ -152,6 +154,7 @@ var _ = Describe("Config", func() {
 			Expect(c.MaxConnectionReceiveWindow).To(BeEquivalentTo(protocol.DefaultMaxReceiveConnectionFlowControlWindow))
 			Expect(c.MaxIncomingStreams).To(BeEquivalentTo(protocol.DefaultMaxIncomingStreams))
 			Expect(c.MaxIncomingUniStreams).To(BeEquivalentTo(protocol.DefaultMaxIncomingUniStreams))
+			Expect(c.DisableVersionNegotiationPackets).To(BeFalse())
 			Expect(c.DisablePathMTUDiscovery).To(BeFalse())
 		})
 
diff --git a/interface.go b/interface.go
index 0b1a1891..df8a95d9 100644
--- a/interface.go
+++ b/interface.go
@@ -298,6 +298,10 @@ type Config struct {
 	// DisablePathMTUDiscovery disables Path MTU Discovery (RFC 8899).
 	// Packets will then be at most 1252 (IPv4) / 1232 (IPv6) bytes in size.
 	DisablePathMTUDiscovery bool
+	// DisableVersionNegotiationPackets disables the sending of Version Negotiation packets.
+	// This can be useful if version information is exchanged out-of-band.
+	// It has no effect for a client.
+	DisableVersionNegotiationPackets bool
 	// See https://datatracker.ietf.org/doc/draft-ietf-quic-datagram/.
 	// Datagrams will only be available when both peers enable datagram support.
 	EnableDatagrams bool
diff --git a/server.go b/server.go
index f2b94c42..6ab869c0 100644
--- a/server.go
+++ b/server.go
@@ -366,7 +366,9 @@ func (s *baseServer) handlePacketImpl(p *receivedPacket) bool /* is the buffer s
 			}
 			return false
 		}
-		go s.sendVersionNegotiationPacket(p, hdr)
+		if !s.config.DisableVersionNegotiationPackets {
+			go s.sendVersionNegotiationPacket(p, hdr)
+		}
 		return false
 	}
 	if hdr.IsLongHeader && hdr.Type != protocol.PacketTypeInitial {
diff --git a/server_test.go b/server_test.go
index 3abb5341..80f199c1 100644
--- a/server_test.go
+++ b/server_test.go
@@ -406,6 +406,25 @@ var _ = Describe("Server", func() {
 				Eventually(done).Should(BeClosed())
 			})
 
+			It("doesn't send a Version Negotiation packets if sending them is disabled", func() {
+				serv.config.DisableVersionNegotiationPackets = true
+				srcConnID := protocol.ConnectionID{1, 2, 3, 4, 5}
+				destConnID := protocol.ConnectionID{1, 2, 3, 4, 5, 6}
+				packet := getPacket(&wire.Header{
+					IsLongHeader:     true,
+					Type:             protocol.PacketTypeHandshake,
+					SrcConnectionID:  srcConnID,
+					DestConnectionID: destConnID,
+					Version:          0x42,
+				}, make([]byte, protocol.MinUnknownVersionPacketSize))
+				raddr := &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1), Port: 1337}
+				packet.remoteAddr = raddr
+				done := make(chan struct{})
+				conn.EXPECT().WriteTo(gomock.Any(), raddr).Do(func() { close(done) }).Times(0)
+				serv.handlePacket(packet)
+				Consistently(done, 50*time.Millisecond).ShouldNot(BeClosed())
+			})
+
 			It("ignores Version Negotiation packets", func() {
 				data, err := wire.ComposeVersionNegotiation(
 					protocol.ConnectionID{1, 2, 3, 4},