f: Introduce TLV_OVERHEAD

Author: shaavan

lightning/src/blinded_path/utils.rs

@@ -229,6 +229,12 @@ impl Writeable for BlindedPathPadding {
 	}
 }
 
+/// Padding storage requires two extra bytes:
+/// - One byte for the type.
+/// - One byte for the padding length.
+/// This constant accounts for that overhead.
+const TLV_OVERHEAD: usize = 2;
+
 /// A generic struct that applies padding to blinded path TLVs, rounding their size off to `round_off`
 pub(crate) struct BlindedPathWithPadding<T: Writeable> {
 	pub(crate) tlvs: T,
@@ -237,11 +243,13 @@ pub(crate) struct BlindedPathWithPadding<T: Writeable> {
 
 impl<T: Writeable> Writeable for BlindedPathWithPadding<T> {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
-		let length = self.tlvs.serialized_length();
+		let tlv_length = self.tlvs.serialized_length();
+		let total_length = tlv_length + TLV_OVERHEAD;
+
 		let padding_length =
-			(length + self.round_off - 1) / self.round_off * self.round_off - length;
+			(total_length + self.round_off - 1) / self.round_off * self.round_off - total_length;
 
-		let padding = Some(BlindedPathPadding::new(padding_length));
+		let padding = BlindedPathPadding::new(padding_length).into();
 
 		encode_tlv_stream!(writer, {
 			(1, padding, option),