Block smokescreen init incase of invalid config

pkg/smokescreen/config.go

@@ -85,9 +85,11 @@ type Config struct {
 	ProxyDialTimeout func(ctx context.Context, network, address string, timeout time.Duration) (net.Conn, error)
 
 	// Custom handler to allow clients to modify reject responses
+	// Deprecated: RejectResponseHandler is deprecated.Please use RejectResponseHandlerWithCtx instead.
 	RejectResponseHandler func(*http.Response)
 
 	// Custom handler to allow clients to modify reject responses
+	// In case RejectResponseHandler is set, this cannot be used.
 	RejectResponseHandlerWithCtx func(*SmokescreenContext, *http.Response)
 
 	// Custom handler to allow clients to modify successful CONNECT responses
@@ -421,6 +423,13 @@ func (config *Config) SetupTls(certFile, keyFile string, clientCAFiles []string)
 	return nil
 }
 
+func (config *Config) Validate() error {
+	if config.RejectResponseHandler != nil && config.RejectResponseHandlerWithCtx != nil {
+		return errors.New("RejectResponseHandler and RejectResponseHandlerWithCtx cannot be used together")
+	}
+	return nil
+}
+
 func (config *Config) populateClientCaMap(pemCerts []byte) (ok bool) {
 
 	for len(pemCerts) > 0 {

pkg/smokescreen/smokescreen.go

@@ -736,9 +736,14 @@ func findListener(ip string, defaultPort uint16) (net.Listener, error) {
 
 func StartWithConfig(config *Config, quit <-chan interface{}) {
 	config.Log.Println("starting")
+	var err error
+
+	if err = config.Validate(); err != nil {
+		config.Log.Fatal("invalid config", err)
+	}
+
 	proxy := BuildProxy(config)
 	listener := config.Listener
-	var err error
 
 	if listener == nil {
 		listener, err = findListener(config.Ip, config.Port)
@@ -782,6 +787,10 @@ func StartWithConfig(config *Config, quit <-chan interface{}) {
 		server.IdleTimeout = config.IdleTimeout
 	}
 
+	if config.RejectResponseHandler != nil && config.RejectResponseHandlerWithCtx != nil {
+		config.Log.Fatal("RejectResponseHandler and RejectResponseHandlerWithCtx cannot be set simultaneously")
+	}
+
 	config.MetricsClient.SetStarted()
 	config.ShuttingDown.Store(false)
 	runServer(config, &server, listener, quit)

pkg/smokescreen/smokescreen_test.go

@@ -1535,6 +1535,38 @@ func TestMitm(t *testing.T) {
 	})
 }
 
+func TestConfigValidate(t *testing.T) {
+	t.Run("Test invalid config", func(t *testing.T) {
+		conf := NewConfig()
+		conf.ConnectTimeout = 10 * time.Second
+		conf.ExitTimeout = 10 * time.Second
+		conf.AdditionalErrorMessageOnDeny = "Proxy denied"
+		conf.RejectResponseHandlerWithCtx = func(smokescreenContext *SmokescreenContext, response *http.Response) {
+			fmt.Println("RejectResponseHandlerWithCtx")
+		}
+		conf.RejectResponseHandler = func(response *http.Response) {
+			fmt.Println("RejectResponseHandler")
+		}
+		err := conf.Validate()
+		require.Error(t, err)
+
+	})
+
+	t.Run("Test valid config", func(t *testing.T) {
+		conf := NewConfig()
+		conf.ConnectTimeout = 10 * time.Second
+		conf.ExitTimeout = 10 * time.Second
+		conf.AdditionalErrorMessageOnDeny = "Proxy denied"
+
+		conf.RejectResponseHandler = func(response *http.Response) {
+			fmt.Println("RejectResponseHandler")
+		}
+		err := conf.Validate()
+		require.NoError(t, err)
+
+	})
+}
+
 func findCanonicalProxyDecision(logs []*logrus.Entry) *logrus.Entry {
 	for _, entry := range logs {
 		if entry.Message == CanonicalProxyDecision {