Create gVisor stack by default in NE

stack.go

@@ -24,6 +24,7 @@ type StackOptions struct {
 	UDPTimeout             int64
 	Handler                Handler
 	Logger                 logger.Logger
+	UnderPlatform          bool
 }
 
 func NewStack(
@@ -32,7 +33,7 @@ func NewStack(
 ) (Stack, error) {
 	switch stack {
 	case "":
-		return NewSystem(options)
+		return defaultStack(options)
 	case "gvisor":
 		return NewGVisor(options)
 	case "system":

stack_default.go

@@ -0,0 +1,7 @@
+//go:build !darwin
+
+package tun
+
+func defaultStack(options StackOptions) (Stack, error) {
+	return NewSystem(options)
+}

stack_default_darwin.go

@@ -0,0 +1,10 @@
+package tun
+
+func defaultStack(options StackOptions) (Stack, error) {
+	if options.UnderPlatform {
+		// Apple Network Extension conflicts with system stack.
+		return NewGVisor(options)
+	} else {
+		return NewSystem(options)
+	}
+}