better

hack/packetgen/templates/length.tmpl

+{{$name := index . 0 -}}
+{{$pointer := index . 1 -}}
+{{$value := index . 2 -}}
+
+{{if some $value.Map -}}
+    {{$ifaceName := printf "%s%s" $name $value.Map.Name -}}
+
+    {{$prefixPointer := printf "%s.%s()" $pointer $ifaceName -}}
+
+    {{template "length" (list $name $prefixPointer $value.Map.Prefix)}}
+
+	length += {{$pointer}}.Length()
+{{else if some $value.Remaining -}}
+
+{{else if some $value.Basic -}}
+
+{{else if some $value.Array -}}
+
+{{else if some $value.Struct -}}
+    {{$structName := printf "%s%s" $name $value.Struct.Name -}}
+
+    {{range $field := $value.Struct.Fields -}}
+        {{$fieldPointer := printf "%s.%s" $pointer $field.Name -}}
+
+        {{template "length" (list $structName $fieldPointer $field)}}
+    {{end -}}
+{{else if some $value.LengthPrefixedSlice -}}
+
+{{else if some $value.NullableLengthPrefixedSlice -}}
+
+{{else if some $value.ZeroByteTerminatedSlice -}}
+
+{{else if some $value.ZeroTerminatedSlice -}}
+
+{{end -}}

hack/packetgen/templates/packets.tmpl

@@ -24,6 +24,12 @@ const (
 
 	type {{$name}} {{template "type" (list $name $packet)}}
 
+	func (T *{{$name}}) Length() (length int) {
+		{{template "length" (list $name "(*T)" $packet)}}
+
+		return
+	}
+
 	func (T *{{$name}}) ReadFrom(decoder *fed.Decoder) (err error) {
 		{{if some $packet.Type -}}
 			if decoder.Type() != {{$name}}Type {

hack/packetgen/templates/preType.tmpl

@@ -15,6 +15,12 @@
 			return {{$item.Type}}
 		}
 
+		func (T *{{$itemName}}) Length() (length int) {
+			{{template "length" (list $name "(*T)" $item)}}
+
+			return
+		}
+
 		func (T *{{$itemName}}) ReadFrom(decoder *fed.Decoder) (err error) {
 			{{template "decode" (list $itemName "(*T)" $item)}}
 
@@ -32,6 +38,7 @@
 	type {{$ifaceName}} interface{
 		{{$ifaceName}}() {{template "type" (list $name $value.Map.Prefix)}}
 
+		Length() int
 		ReadFrom(decoder *fed.Decoder) error
 		WriteTo(encoder *fed.Encoder) error
 	}