caddyhttp: Option to disable 0-RTT

caddyconfig/httpcaddyfile/serveroptions.go

@@ -57,6 +57,9 @@ type serverOptions struct {
 	ShouldLogCredentials  bool
 	Metrics               *caddyhttp.Metrics
 	Trace                 bool // TODO: EXPERIMENTAL
+	// If set, overrides whether QUIC listeners allow 0-RTT (early data).
+	// If nil, the default behavior is used (currently allowed).
+	Allow0RTT *bool
 }
 
 func unmarshalCaddyfileServerOptions(d *caddyfile.Dispenser) (any, error) {
@@ -309,6 +312,17 @@ func unmarshalCaddyfileServerOptions(d *caddyfile.Dispenser) (any, error) {
 			}
 			serverOpts.Trace = true
 
+		case "0rtt":
+			// only supports "off" for now
+			if !d.NextArg() {
+				return nil, d.ArgErr()
+			}
+			if d.Val() != "off" {
+				return nil, d.Errf("unsupported 0rtt argument '%s' (only 'off' is supported)", d.Val())
+			}
+			boolVal := false
+			serverOpts.Allow0RTT = &boolVal
+
 		default:
 			return nil, d.Errf("unrecognized servers option '%s'", d.Val())
 		}
@@ -373,6 +387,7 @@ func applyServerOptions(
 		server.TrustedProxiesStrict = opts.TrustedProxiesStrict
 		server.TrustedProxiesUnix = opts.TrustedProxiesUnix
 		server.Metrics = opts.Metrics
+		server.Allow0RTT = opts.Allow0RTT
 		if opts.ShouldLogCredentials {
 			if server.Logs == nil {
 				server.Logs = new(caddyhttp.ServerLogConfig)

caddytest/integration/caddyfile_adapt/global_server_options_single.caddyfiletest

@@ -21,6 +21,7 @@
 		keepalive_interval 20s
 		keepalive_idle 20s
 		keepalive_count 10
+		0rtt off
 	}
 }
 
@@ -90,7 +91,8 @@ foo.com {
 						"h2",
 						"h2c",
 						"h3"
-					]
+					],
+					"allow_0rtt": false
 				}
 			}
 		}

listeners.go

@@ -511,7 +511,7 @@ func JoinNetworkAddress(network, host, port string) string {
 //
 // NOTE: This API is EXPERIMENTAL and may be changed or removed.
 // NOTE: user should close the returned listener twice, once to stop accepting new connections, the second time to free up the packet conn.
-func (na NetworkAddress) ListenQUIC(ctx context.Context, portOffset uint, config net.ListenConfig, tlsConf *tls.Config, pcWrappers []PacketConnWrapper) (http3.QUICListener, error) {
+func (na NetworkAddress) ListenQUIC(ctx context.Context, portOffset uint, config net.ListenConfig, tlsConf *tls.Config, pcWrappers []PacketConnWrapper, allow0rttconf *bool) (http3.QUICListener, error) {
 	lnKey := listenerKey("quic"+na.Network, na.JoinHostPort(portOffset))
 
 	sharedEarlyListener, _, err := listenerPool.LoadOrNew(lnKey, func() (Destructor, error) {
@@ -550,10 +550,14 @@ func (na NetworkAddress) ListenQUIC(ctx context.Context, portOffset uint, config
 			Conn:                h3ln,
 			VerifySourceAddress: func(addr net.Addr) bool { return !limiter.Allow() },
 		}
+		allow0rtt := true
+		if allow0rttconf != nil {
+			allow0rtt = *allow0rttconf
+		}
 		earlyLn, err := tr.ListenEarly(
 			http3.ConfigureTLSConfig(quicTlsConfig),
 			&quic.Config{
-				Allow0RTT: true,
+				Allow0RTT: allow0rtt,
 				Tracer:    h3qlog.DefaultConnectionTracer,
 			},
 		)

modules/caddyhttp/server.go

@@ -253,6 +253,16 @@ type Server struct {
 	// A nil value or element indicates that Protocols will be used instead.
 	ListenProtocols [][]string `json:"listen_protocols,omitempty"`
 
+	// If set, overrides whether QUIC listeners allow 0-RTT (early data).
+	// If nil, the default behavior is used (currently allowed).
+	//
+	// One reason to disable 0-RTT is if a remote IP matcher is used,
+	// which introduces a dependency on the remote address being verified
+	// if routing happens before the TLS handshake completes. An HTTP 425
+	// response is written in that case, but some clients misbehave and
+	// don't perform a retry, so disabling 0-RTT can smooth it out.
+	Allow0RTT *bool `json:"allow_0rtt,omitempty"`
+
 	// If set, metrics observations will be enabled.
 	// This setting is EXPERIMENTAL and subject to change.
 	// DEPRECATED: Use the app-level `metrics` field.
@@ -650,7 +660,7 @@ func (s *Server) serveHTTP3(addr caddy.NetworkAddress, tlsCfg *tls.Config) error
 		return fmt.Errorf("starting HTTP/3 QUIC listener: %v", err)
 	}
 	addr.Network = h3net
-	h3ln, err := addr.ListenQUIC(s.ctx, 0, net.ListenConfig{}, tlsCfg, s.packetConnWrappers)
+	h3ln, err := addr.ListenQUIC(s.ctx, 0, net.ListenConfig{}, tlsCfg, s.packetConnWrappers, s.Allow0RTT)
 	if err != nil {
 		return fmt.Errorf("starting HTTP/3 QUIC listener: %v", err)
 	}