diff --git a/go/state/state.go b/go/state/state.go
index 7feb550..c8c9087 100644
--- a/go/state/state.go
+++ b/go/state/state.go
@@ -13,7 +13,8 @@ type State struct {
 	CacheMap map[string]string
 	ExecPath []string
 	Arg *string
-	Idx uint16
+	sizes map[string]uint16
+	idx uint16
 }
 
 func NewState(bitSize uint64) State {
@@ -63,6 +64,7 @@ func(st *State) Down(input string) {
 	m := make(map[string]string)
 	st.Cache = append(st.Cache, m)
 	st.CacheMap = make(map[string]string)
+	st.sizes = make(map[string]uint16)
 	st.ExecPath = append(st.ExecPath, input)
 }
 
@@ -84,10 +86,18 @@ func(st *State) Add(key string, value string, sizeHint uint16) error {
 	log.Printf("add key %s value size %v", key, sz)
 	st.Cache[len(st.Cache)-1][key] = value
 	st.CacheUseSize += sz
+	st.sizes[key] = sizeHint
 	return nil
 }
 
 func(st *State) Update(key string, value string) error {
+	sizeHint := st.sizes[key]
+	if st.sizes[key] > 0 {
+		l := uint16(len(value))
+		if l > sizeHint {
+			return fmt.Errorf("update value length %v exceeds value size limit %v", l, sizeHint)
+		}
+	}
 	checkFrame := st.frameOf(key)
 	if checkFrame == -1 {
 		return fmt.Errorf("key %v not defined", key)
@@ -167,6 +177,16 @@ func(st *State) Check(key string) bool {
 	return st.frameOf(key) == -1
 }
 
+func(st *State) Size() (uint32, uint32) {
+	var l int
+	var c uint16
+	for k, v := range st.CacheMap {
+		l += len(v)
+		c += st.sizes[k]
+	}
+	return uint32(l), uint32(c)
+}
+
 // return 0-indexed frame number where key is defined. -1 if not defined
 func(st *State) frameOf(key string) int {
 	log.Printf("--- %s", key)
diff --git a/go/state/state_test.go b/go/state/state_test.go
index 4183279..8697a9c 100644
--- a/go/state/state_test.go
+++ b/go/state/state_test.go
@@ -113,3 +113,36 @@ func TestStateLoadDup(t *testing.T) {
 		t.Errorf("expected fail on duplicate load")
 	}
 }
+
+func TestStateCurrentSize(t *testing.T) {
+	st := NewState(17)
+	st.Down("one")
+	err := st.Add("foo", "bar", 0)
+	if err != nil {
+		t.Error(err)
+	}
+	st.Down("two")
+	err = st.Add("bar", "xyzzy", 10)
+	if err != nil {
+		t.Error(err)
+	}
+	err = st.Map("bar")
+	if err != nil {
+		t.Error(err)
+	}
+	err = st.Add("baz", "inkypinkyblinkyclyde", 40)
+	if err != nil {
+		t.Error(err)
+	}
+	err = st.Map("baz")
+	if err != nil {
+		t.Error(err)
+	}
+	l, c := st.Size()
+	if l != 25 {
+		t.Errorf("expected actual length 25, got %v", l)
+	}
+	if c != 50 {
+		t.Errorf("expected actual length 50, got %v", c)
+	}
+}