Introduce init_and_read_tlv_fields macro

We introduce a new macro that inits and reads tlv fields and DRY up `impl_writeable_tlv_based`.

Author: tnull

lightning/src/util/ser_macros.rs

@@ -391,6 +391,18 @@ macro_rules! init_tlv_field_var {
 	};
 }
 
+macro_rules! init_and_read_tlv_fields {
+	($reader: ident, {$(($type: expr, $field: ident, $fieldty: tt)),* $(,)*}) => {
+		$(
+			init_tlv_field_var!($field, $fieldty);
+		)*
+
+		read_tlv_fields!($reader, {
+			$(($type, $field, $fieldty)),*
+		});
+	}
+}
+
 /// Implements Readable/Writeable for a struct storing it as a set of TLVs
 /// If $fieldty is `required`, then $field is a required field that is not an Option nor a Vec.
 /// If $fieldty is `option`, then $field is optional field.
@@ -425,12 +437,10 @@ macro_rules! impl_writeable_tlv_based {
 
 		impl $crate::util::ser::Readable for $st {
 			fn read<R: $crate::io::Read>(reader: &mut R) -> Result<Self, $crate::ln::msgs::DecodeError> {
-				$(
-					init_tlv_field_var!($field, $fieldty);
-				)*
-				read_tlv_fields!(reader, {
+				init_and_read_tlv_fields!(reader, {
 					$(($type, $field, $fieldty)),*
 				});
+
 				Ok(Self {
 					$(
 						$field: init_tlv_based_struct_field!($field, $fieldty)