fix issue 26

json/codec.go

@@ -156,7 +156,7 @@ func constructCodec(t reflect.Type, seen map[reflect.Type]*structType, canAddr b
 		c = codec{encode: encoder.encodeString, decode: decoder.decodeString}
 
 	case reflect.Interface:
-		c = codec{encode: encoder.encodeInterface, decode: constructNonEmptyInterfaceDecoderFunc(t)}
+		c = codec{encode: encoder.encodeInterface, decode: constructMaybeEmptyInterfaceDecoderFunc(t)}
 
 	case reflect.Array:
 		c = constructArrayCodec(t, seen, canAddr)
@@ -711,9 +711,9 @@ func constructPointerDecodeFunc(t reflect.Type, decode decodeFunc) decodeFunc {
 	}
 }
 
-func constructNonEmptyInterfaceDecoderFunc(t reflect.Type) decodeFunc {
+func constructMaybeEmptyInterfaceDecoderFunc(t reflect.Type) decodeFunc {
 	return func(d decoder, b []byte, p unsafe.Pointer) ([]byte, error) {
-		return d.decodeNonEmptyInterface(b, p, t)
+		return d.decodeMaybeEmptyInterface(b, p, t)
 	}
 }
 

json/decode.go

@@ -1087,7 +1087,7 @@ func (d decoder) decodeInterface(b []byte, p unsafe.Pointer) ([]byte, error) {
 	return b, nil
 }
 
-func (d decoder) decodeNonEmptyInterface(b []byte, p unsafe.Pointer, t reflect.Type) ([]byte, error) {
+func (d decoder) decodeMaybeEmptyInterface(b []byte, p unsafe.Pointer, t reflect.Type) ([]byte, error) {
 	if hasNullPrefix(b) {
 		*(*interface{})(p) = nil
 		return b[4:], nil
@@ -1097,6 +1097,8 @@ func (d decoder) decodeNonEmptyInterface(b []byte, p unsafe.Pointer, t reflect.T
 		if e := x.Elem(); e.Kind() == reflect.Ptr {
 			return Parse(b, e.Interface(), d.flags)
 		}
+	} else if t.NumMethod() == 0 { // empty interface
+		return Parse(b, (*interface{})(p), d.flags)
 	}
 
 	return d.decodeUnmarshalTypeError(b, p, t)

json/json_test.go

@@ -1464,3 +1464,14 @@ func TestGithubIssue23(t *testing.T) {
 		}
 	})
 }
+
+func TestGithubIssue26(t *testing.T) {
+	type interfaceType interface{}
+
+	var value interfaceType
+	var data = []byte(`{}`)
+
+	if err := Unmarshal(data, &value); err != nil {
+		t.Error(err)
+	}
+}