1 files changed, 57 insertions, 0 deletions
diff --git a/lib/binstruct/size.go b/lib/binstruct/size.go
new file mode 100644
index 0000000..6563455
--- /dev/null
+++ b/lib/binstruct/size.go
@@ -0,0 +1,57 @@
+package binstruct
+
+import (
+	"fmt"
+	"reflect"
+)
+
+type StaticSizer interface {
+	BinaryStaticSize() int
+}
+
+func StaticSize(obj any) int {
+	sz, err := staticSize(reflect.TypeOf(obj))
+	if err != nil {
+		panic(err)
+	}
+	return sz
+}
+
+var (
+	staticSizerType = reflect.TypeOf((*StaticSizer)(nil)).Elem()
+	marshalerType   = reflect.TypeOf((*Marshaler)(nil)).Elem()
+	unmarshalerType = reflect.TypeOf((*Unmarshaler)(nil)).Elem()
+)
+
+func staticSize(typ reflect.Type) (int, error) {
+	if typ.Implements(staticSizerType) {
+		return reflect.New(typ).Elem().Interface().(StaticSizer).BinaryStaticSize(), nil
+	}
+	switch typ.Kind() {
+	case reflect.Uint8, reflect.Int8:
+		return 1, nil
+	case reflect.Uint16, reflect.Int16:
+		return 2, nil
+	case reflect.Uint32, reflect.Int32:
+		return 4, nil
+	case reflect.Uint64, reflect.Int64:
+		return 8, nil
+	case reflect.Ptr:
+		return staticSize(typ.Elem())
+	case reflect.Array:
+		elemSize, err := staticSize(typ.Elem())
+		if err != nil {
+			return 0, err
+		}
+		return elemSize * typ.Len(), nil
+	case reflect.Struct:
+		if !(typ.Implements(marshalerType) || typ.Implements(unmarshalerType)) {
+			return getStructHandler(typ).Size, nil
+		}
+		return 0, fmt.Errorf("type=%v (kind=%v) does not implement binfmt.StaticSizer but does implement binfmt.Marshaler or binfmt.Unmarshaler",
+			typ, typ.Kind())
+	default:
+		return 0, fmt.Errorf("type=%v does not implement binfmt.StaticSizer and kind=%v is not a supported statically-sized kind",
+			typ, typ.Kind())
+	}
+}