3 files changed, 80 insertions, 3 deletions

diff --git a/libgo/go/encoding/json/decode.go b/libgo/go/encoding/json/decode.go
index 110c6fd6238..d61f8870646 100644
--- a/libgo/go/encoding/json/decode.go
+++ b/libgo/go/encoding/json/decode.go
@@ -273,9 +273,14 @@ func (d *decodeState) indirect(v reflect.Value, decodingNull bool) (Unmarshaler,
 			_, isUnmarshaler = v.Interface().(Unmarshaler)
 		}
 
+		// Load value from interface, but only if the result will be
+		// usefully addressable.
 		if iv := v; iv.Kind() == reflect.Interface && !iv.IsNil() {
-			v = iv.Elem()
-			continue
+			e := iv.Elem()
+			if e.Kind() == reflect.Ptr && !e.IsNil() && (!decodingNull || e.Elem().Kind() == reflect.Ptr) {
+				v = e
+				continue
+			}
 		}
 
 		pv := v
@@ -588,6 +593,11 @@ func (d *decodeState) literal(v reflect.Value) {
 // produce more helpful error messages.
 func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool) {
 	// Check for unmarshaler.
+	if len(item) == 0 {
+		//Empty string given
+		d.saveError(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
+		return
+	}
 	wantptr := item[0] == 'n' // null
 	unmarshaler, pv := d.indirect(v, wantptr)
 	if unmarshaler != nil {
diff --git a/libgo/go/encoding/json/decode_test.go b/libgo/go/encoding/json/decode_test.go
index d758758d978..6fac22c4a35 100644
--- a/libgo/go/encoding/json/decode_test.go
+++ b/libgo/go/encoding/json/decode_test.go
@@ -638,3 +638,68 @@ func TestAnonymous(t *testing.T) {
 		t.Fatal("Unmarshal: did set T.Y")
 	}
 }
+
+// Test that the empty string doesn't panic decoding when ,string is specified
+// Issue 3450
+func TestEmptyString(t *testing.T) {
+	type T2 struct {
+		Number1 int `json:",string"`
+		Number2 int `json:",string"`
+	}
+	data := `{"Number1":"1", "Number2":""}`
+	dec := NewDecoder(strings.NewReader(data))
+	var t2 T2
+	err := dec.Decode(&t2)
+	if err == nil {
+		t.Fatal("Decode: did not return error")
+	}
+	if t2.Number1 != 1 {
+		t.Fatal("Decode: did not set Number1")
+	}
+}
+
+func intp(x int) *int {
+	p := new(int)
+	*p = x
+	return p
+}
+
+func intpp(x *int) **int {
+	pp := new(*int)
+	*pp = x
+	return pp
+}
+
+var interfaceSetTests = []struct {
+	pre  interface{}
+	json string
+	post interface{}
+}{
+	{"foo", `"bar"`, "bar"},
+	{"foo", `2`, 2.0},
+	{"foo", `true`, true},
+	{"foo", `null`, nil},
+
+	{nil, `null`, nil},
+	{new(int), `null`, nil},
+	{(*int)(nil), `null`, nil},
+	{new(*int), `null`, new(*int)},
+	{(**int)(nil), `null`, nil},
+	{intp(1), `null`, nil},
+	{intpp(nil), `null`, intpp(nil)},
+	{intpp(intp(1)), `null`, intpp(nil)},
+}
+
+func TestInterfaceSet(t *testing.T) {
+	for _, tt := range interfaceSetTests {
+		b := struct{ X interface{} }{tt.pre}
+		blob := `{"X":` + tt.json + `}`
+		if err := Unmarshal([]byte(blob), &b); err != nil {
+			t.Errorf("Unmarshal %#q: %v", blob, err)
+			continue
+		}
+		if !reflect.DeepEqual(b.X, tt.post) {
+			t.Errorf("Unmarshal %#q into %#v: X=%#v, want %#v", blob, tt.pre, b.X, tt.post)
+		}
+	}
+}
diff --git a/libgo/go/encoding/json/encode.go b/libgo/go/encoding/json/encode.go
index 842672c3974..b6e1cb16e5a 100644
--- a/libgo/go/encoding/json/encode.go
+++ b/libgo/go/encoding/json/encode.go
@@ -96,7 +96,7 @@ import (
 //
 // Channel, complex, and function values cannot be encoded in JSON.
 // Attempting to encode such a value causes Marshal to return
-// an InvalidTypeError.
+// an UnsupportedTypeError.
 //
 // JSON cannot represent cyclic data structures and Marshal does not
 // handle them.  Passing cyclic structures to Marshal will result in
@@ -157,6 +157,8 @@ type Marshaler interface {
 	MarshalJSON() ([]byte, error)
 }
 
+// An UnsupportedTypeError is returned by Marshal when attempting
+// to encode an unsupported value type.
 type UnsupportedTypeError struct {
 	Type reflect.Type
 }