feat: add an option to skip resumption on nil ext

feat: update examples

common.go

@@ -700,6 +700,19 @@ type Config struct {
 	// This field is ignored when InsecureSkipVerify is true.
 	InsecureServerNameToVerify string // [uTLS]
 
+	// PreferSkipResumptionOnNilExtension controls the behavior when session resumption is enabled but the corresponding session extensions are nil.
+	//
+	// To successfully use session resumption, ensure that the following requirements are met:
+	//  - SessionTicketsDisabled is set to false
+	//  - ClientSessionCache is non-nil
+	//  - For TLS 1.2, SessionTicketExtension is non-nil
+	//  - For TLS 1.3, PreSharedKeyExtension is non-nil
+	//
+	// There may be cases where users enable session resumption (SessionTicketsDisabled: false && ClientSessionCache: non-nil), but they do not provide SessionTicketExtension or PreSharedKeyExtension in the ClientHelloSpec. This could be intentional or accidental.
+	//
+	// By default, utls throws an exception in such scenarios. Set this to true to skip the resumption and suppress the exception.
+	PreferSkipResumptionOnNilExtension bool // [uTLS]
+
 	// CipherSuites is a list of enabled TLS 1.0–1.2 cipher suites. The order of
 	// the list is ignored. Note that TLS 1.3 ciphersuites are not configurable.
 	//

examples/tls-resumption/main.go

@@ -38,7 +38,16 @@ func (csc *ClientSessionCache) Put(sessionKey string, cs *tls.ClientSessionState
 	}
 }
 
-func runResumptionCheck(helloID tls.ClientHelloID, serverAddr string, retry int, verbose bool) {
+type ResumptionType int
+
+const (
+	noResumption     ResumptionType = 0
+	pskResumption    ResumptionType = 1
+	ticketResumption ResumptionType = 2
+)
+
+func runResumptionCheck(helloID tls.ClientHelloID, getCustomSpec func() *tls.ClientHelloSpec, expectResumption ResumptionType, serverAddr string, retry int, verbose bool) {
+	fmt.Printf("checking: hello [%s], expectResumption [%v], serverAddr [%s]\n", helloID.Client, expectResumption, serverAddr)
 	csc := NewClientSessionCache()
 	tcpConn, err := net.Dial("tcp", serverAddr)
 	if err != nil {
@@ -55,6 +64,10 @@ func runResumptionCheck(helloID tls.ClientHelloID, serverAddr string, retry int,
 		OmitEmptyPsk:       true,
 	}, helloID)
 
+	if getCustomSpec != nil {
+		tlsConn.ApplyPreset(getCustomSpec())
+	}
+
 	// HS
 	err = tlsConn.Handshake()
 	if err != nil {
@@ -96,6 +109,7 @@ func runResumptionCheck(helloID tls.ClientHelloID, serverAddr string, retry int,
 	}
 	tlsConn.Close()
 
+	resumption := noResumption
 	for i := 0; i < retry; i++ {
 		tcpConnPSK, err := net.Dial("tcp", serverAddr)
 		if err != nil {
@@ -108,6 +122,10 @@ func runResumptionCheck(helloID tls.ClientHelloID, serverAddr string, retry int,
 			OmitEmptyPsk:       true,
 		}, helloID)
 
+		if getCustomSpec != nil {
+			tlsConnPSK.ApplyPreset(getCustomSpec())
+		}
+
 		// HS
 		err = tlsConnPSK.Handshake()
 		if verbose {
@@ -133,27 +151,47 @@ func runResumptionCheck(helloID tls.ClientHelloID, serverAddr string, retry int,
 
 			if tlsVer == tls.VersionTLS13 && tlsConnPSK.HandshakeState.State13.UsingPSK {
 				fmt.Println("[PSK used]")
-				return
+				resumption = pskResumption
+				break
 			} else if tlsVer == tls.VersionTLS12 && tlsConnPSK.DidTls12Resume() {
 				fmt.Println("[session ticket used]")
-				return
+				resumption = ticketResumption
+				break
 			}
 		}
 		time.Sleep(700 * time.Millisecond)
 	}
-	panic(fmt.Sprintf("PSK or session ticket not used for a resumption session, server %s, helloID: %s", serverAddr, helloID.Client))
+
+	if resumption != expectResumption {
+		panic(fmt.Sprintf("Expecting resumption type: %v, actual %v; session, server %s, helloID: %s", expectResumption, resumption, serverAddr, helloID.Client))
+	} else {
+		fmt.Println("[expected]")
+	}
 }
 
 func main() {
 	tls13Url := "www.microsoft.com:443"
 	tls12Url1 := "spocs.getpocket.com:443"
 	tls12Url2 := "marketplace.visualstudio.com:443"
-	runResumptionCheck(tls.HelloChrome_100_PSK, tls13Url, 1, false) // psk + utls
+	runResumptionCheck(tls.HelloChrome_100, nil, noResumption, tls13Url, 3, false) // no-resumption + utls
-	runResumptionCheck(tls.HelloGolang, tls13Url, 1, false)         // psk + crypto/tls
+	func() {
+		defer func() {
+			if err := recover(); err == nil {
+				panic("must throw")
+			}
+		}()
 
-	runResumptionCheck(tls.HelloChrome_100_PSK, tls12Url1, 10, false) // session ticket + utls
+		runResumptionCheck(tls.HelloCustom, func() *tls.ClientHelloSpec {
-	runResumptionCheck(tls.HelloGolang, tls12Url1, 10, false)         // session ticket + crypto/tls
+			spec, _ := tls.UTLSIdToSpec(tls.HelloChrome_100)
-	runResumptionCheck(tls.HelloChrome_100_PSK, tls12Url2, 10, false) // session ticket + utls
+			return &spec
-	runResumptionCheck(tls.HelloGolang, tls12Url2, 10, false)         // session ticket + crypto/tls
+		}, noResumption, tls13Url, 3, false) // no-resumption + utls custom + no psk extension
+	}()
+	runResumptionCheck(tls.HelloChrome_100_PSK, nil, pskResumption, tls13Url, 1, false) // psk + utls
+	runResumptionCheck(tls.HelloGolang, nil, pskResumption, tls13Url, 1, false)         // psk + crypto/tls
+
+	runResumptionCheck(tls.HelloChrome_100_PSK, nil, ticketResumption, tls12Url1, 10, false) // session ticket + utls
+	runResumptionCheck(tls.HelloGolang, nil, ticketResumption, tls12Url1, 10, false)         // session ticket + crypto/tls
+	runResumptionCheck(tls.HelloChrome_100_PSK, nil, ticketResumption, tls12Url2, 10, false) // session ticket + utls
+	runResumptionCheck(tls.HelloGolang, nil, ticketResumption, tls12Url2, 10, false)         // session ticket + crypto/tls
 
 }

u_conn.go

@@ -39,6 +39,11 @@ type UConn struct {
 
 	omitSNIExtension bool
 
+	// skipResumptionOnNilExtension is copied from `Config.PreferSkipResumptionOnNilExtension`.
+	//
+	// By default, if ClientHelloSpec is predefined or utls-generated (as opposed to HelloCustom), this flag will be updated to true.
+	skipResumptionOnNilExtension bool
+
 	// certCompressionAlgs represents the set of advertised certificate compression
 	// algorithms, as specified in the ClientHello. This is only relevant client-side, for the
 	// server certificate. All other forms of certificate compression are unsupported.
@@ -58,6 +63,7 @@ func UClient(conn net.Conn, config *Config, clientHelloID ClientHelloID) *UConn
 	uconn.handshakeFn = uconn.clientHandshake
 	uconn.sessionController = newSessionController(&uconn)
 	uconn.utls.sessionController = uconn.sessionController
+	uconn.skipResumptionOnNilExtension = config.PreferSkipResumptionOnNilExtension || clientHelloID.Client != helloCustom
 	return &uconn
 }
 

u_session_controller.go

@@ -121,6 +121,12 @@ func (s *sessionController) assertNotLocked(caller string) {
 	}
 }
 
+func (s *sessionController) assertCanSkip(caller, extensionName string) {
+	if !s.uconnRef.skipResumptionOnNilExtension {
+		panic(fmt.Sprintf("tls: %s failed: session resumption is enabled, but there is no %s in the ClientHelloSpec; Please consider provide one in the ClientHelloSpec; If this is intentional, you may consider disable resumption by setting Config.SessionTicketsDisabled to true, or set Config.PreferSkipResumptionOnNilExtension to true to suppress this exception", caller, extensionName))
+	}
+}
+
 // finalCheck performs a comprehensive check on the updated state to ensure the correctness of the changes.
 // If the checks pass successfully, the sessionController's state will be locked.
 // Any failure in passing the tests indicates incorrect implementations in the utls, which will result in triggering a panic.
@@ -141,7 +147,11 @@ func (s *sessionController) initSessionTicketExt(session *SessionState, ticket [
 	s.assertNotLocked("initSessionTicketExt")
 	s.assertHelloNotBuilt("initSessionTicketExt")
 	s.assertControllerState("initSessionTicketExt", NoSession)
-	panicOnNil("initSessionTicketExt", s.sessionTicketExt, session, ticket)
+	panicOnNil("initSessionTicketExt", session, ticket)
+	if s.sessionTicketExt == nil {
+		s.assertCanSkip("initSessionTicketExt", "session ticket extension")
+		return
+	}
 	initializationGuard(s.sessionTicketExt, func(e ISessionTicketExtension) {
 		s.sessionTicketExt.InitializeByUtls(session, ticket)
 	})
@@ -155,8 +165,11 @@ func (s *sessionController) initPskExt(session *SessionState, earlySecret []byte
 	s.assertNotLocked("initPskExt")
 	s.assertHelloNotBuilt("initPskExt")
 	s.assertControllerState("initPskExt", NoSession)
-	panicOnNil("initPskExt", s.pskExtension, session, earlySecret, pskIdentities)
+	panicOnNil("initPskExt", session, earlySecret, pskIdentities)
-
+	if s.pskExtension == nil {
+		s.assertCanSkip("initPskExt", "pre-shared key extension")
+		return
+	}
 	initializationGuard(s.pskExtension, func(e PreSharedKeyExtension) {
 		publicPskIdentities := mapSlice(pskIdentities, func(private pskIdentity) PskIdentity {
 			return PskIdentity{