io: redo GetVarSize for Serializable things

Use writes to a fake io.Writer that counts the bytes. Allows us to kill Size()
methods as useless and duplicating lots of functionality.

pkg/io/size.go

@@ -17,6 +17,20 @@ var (
 	i64  int64
 )
 
+// This structure is used to calculate the wire size of the serializable
+// structure. It's an io.Writer that doesn't do any real writes, but instead
+// just counts the number of bytes to be written.
+type counterWriter struct {
+	counter int
+}
+
+// Write implements the io.Writer interface
+func (cw *counterWriter) Write(p []byte) (int, error) {
+	n := len(p)
+	cw.counter += n
+	return n, nil
+}
+
 // GetVarIntSize returns the size in number of bytes of a variable integer
 // (reference: GetVarSize(int value),  https://github.com/neo-project/neo/blob/master/neo/IO/Helper.cs)
 func GetVarIntSize(value int) int {
@@ -59,6 +73,18 @@ func GetVarSize(value interface{}) int {
 		reflect.Uint32,
 		reflect.Uint64:
 		return GetVarIntSize(int(v.Uint()))
+	case reflect.Ptr:
+		vser, ok := v.Interface().(Serializable)
+		if !ok {
+			panic(fmt.Sprintf("unable to calculate GetVarSize for a non-Serializable pointer"))
+		}
+		cw := counterWriter{}
+		w := NewBinWriterFromIO(&cw)
+		err := vser.EncodeBinary(w)
+		if err != nil {
+			panic(fmt.Sprintf("error serializing %s: %s", reflect.TypeOf(value), err.Error()))
+		}
+		return cw.counter
 	case reflect.Slice, reflect.Array:
 		valueLength := v.Len()
 		valueSize := 0
@@ -67,8 +93,7 @@ func GetVarSize(value interface{}) int {
 			switch reflect.ValueOf(value).Index(0).Interface().(type) {
 			case Serializable:
 				for i := 0; i < valueLength; i++ {
-					elem := v.Index(i).Interface().(Serializable)
-					valueSize += elem.Size()
+					valueSize += GetVarSize(v.Index(i).Interface())
 				}
 			case uint8, int8:
 				valueSize = valueLength

pkg/io/size_test.go

@@ -10,13 +10,15 @@ import (
 
 // Mock structure to test getting size of an array of serializable things
 type smthSerializable struct {
+	some [42]byte
 }
 
 func (*smthSerializable) DecodeBinary(*BinReader) error {
 	return nil
 }
 
-func (*smthSerializable) EncodeBinary(*BinWriter) error {
+func (ss *smthSerializable) EncodeBinary(bw *BinWriter) error {
+	bw.WriteLE(ss.some)
 	return nil
 }