add simple stack depth limit mechanism

otto.go

@@ -367,6 +367,10 @@ func (self Otto) SetRandomSource(fn func() float64) {
 	self.runtime.random = fn
 }
 
+func (self Otto) SetStackDepthLimit(limit int) {
+	self.runtime.stackLimit = limit
+}
+
 // Context is a structure that contains information about the current execution
 // context.
 type Context struct {

otto_test.go

@@ -1650,6 +1650,56 @@ func Test_objectLength(t *testing.T) {
 	})
 }
 
+func Test_stackLimit(t *testing.T) {
+	code := `
+        function a() {}
+        function b() { a(); }
+        function c() { b(); }
+        function d() { c(); }
+        function e() { d(); }
+        e();
+    `
+
+	tt(t, func() {
+		_, vm := test()
+
+		_, err := vm.Run(code)
+
+		is(err == nil, true)
+	})
+
+	tt(t, func() {
+		_, vm := test()
+
+		vm.vm.SetStackDepthLimit(2)
+
+		_, err := vm.Run(code)
+
+		is(err == nil, false)
+	})
+
+	tt(t, func() {
+		_, vm := test()
+
+		vm.vm.SetStackDepthLimit(6)
+
+		_, err := vm.Run(code)
+
+		is(err == nil, true)
+	})
+
+	tt(t, func() {
+		_, vm := test()
+
+		vm.vm.SetStackDepthLimit(1)
+		vm.vm.SetStackDepthLimit(0)
+
+		_, err := vm.Run(code)
+
+		is(err == nil, true)
+	})
+}
+
 func BenchmarkNew(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		New()

runtime.go

@@ -56,6 +56,7 @@ type _runtime struct {
 	eval         *_object // The builtin eval, for determine indirect versus direct invocation
 	debugger     func(*Otto)
 	random       func() float64
+	stackLimit   int
 
 	labels []string // FIXME
 	lck    sync.Mutex
@@ -63,6 +64,14 @@ type _runtime struct {
 
 func (self *_runtime) enterScope(scope *_scope) {
 	scope.outer = self.scope
+	if self.scope != nil {
+		scope.depth = self.scope.depth + 1
+	}
+
+	if self.stackLimit != 0 && scope.depth >= self.stackLimit {
+		panic(self.panicRangeError("RangeError: Maximum call stack size exceeded"))
+	}
+
 	self.scope = scope
 }
 

scope.go

@@ -21,6 +21,7 @@ type _scope struct {
 	this     *_object
 	eval     bool // Replace this with kind?
 	outer    *_scope
+	depth    int
 
 	frame _frame
 }