Implement Readable for LengthReadable

Inbound Trampoline entrypoint packets will contain inner onions, which
only implement LengthReadable. Until now, we never had to decode
LengthReadable-only structs in TLV streams, so this issue never
surfaced before, but going forward, this will allow us to parse inbound
Trampoline data.

Author: arik-so

lightning/src/ln/msgs.rs

@@ -1964,7 +1964,7 @@ impl LengthReadable for TrampolineOnionPacket {
 
 		let hop_data_len = r.total_bytes().saturating_sub(66); // 1 (version) + 33 (pubkey) + 32 (HMAC) = 66
 		let mut rd = FixedLengthReader::new(r, hop_data_len);
-		let hop_data = WithoutLength::<Vec<u8>>::read(&mut rd)?.0;
+		let hop_data = <WithoutLength::<Vec<u8>> as LengthReadable>::read(&mut rd)?.0;
 
 		let hmac = Readable::read(r)?;
 
@@ -2854,7 +2854,7 @@ impl<NS: Deref> ReadableArgs<(Option<PublicKey>, NS)> for InboundOnionPayload wh
 		let mut keysend_preimage: Option<PaymentPreimage> = None;
 		let mut custom_tlvs = Vec::new();
 
-		let tlv_len = BigSize::read(r)?;
+		let tlv_len = <BigSize as Readable>::read(r)?;
 		let mut rd = FixedLengthReader::new(r, tlv_len.0);
 		decode_tlv_stream_with_custom_tlv_decode!(&mut rd, {
 			(2, amt, (option, encoding: (u64, HighZeroBytesDroppedBigSize))),
@@ -4313,7 +4313,7 @@ mod tests {
 		let encoded_value = closing_signed.encode();
 		let target_value = <Vec<u8>>::from_hex("020202020202020202020202020202020202020202020202020202020202020200083a840000034dd977cb9b53d93a6ff64bb5f1e158b4094b66e798fb12911168a3ccdf80a83096340a6a95da0ae8d9f776528eecdbb747eb6b545495a4319ed5378e35b21e073a").unwrap();
 		assert_eq!(encoded_value, target_value);
-		assert_eq!(msgs::ClosingSigned::read(&mut Cursor::new(&target_value)).unwrap(), closing_signed);
+		assert_eq!(<msgs::ClosingSigned as Readable>::read(&mut Cursor::new(&target_value)).unwrap(), closing_signed);
 
 		let closing_signed_with_range = msgs::ClosingSigned {
 			channel_id: ChannelId::from_bytes([2; 32]),
@@ -4327,7 +4327,7 @@ mod tests {
 		let encoded_value_with_range = closing_signed_with_range.encode();
 		let target_value_with_range = <Vec<u8>>::from_hex("020202020202020202020202020202020202020202020202020202020202020200083a840000034dd977cb9b53d93a6ff64bb5f1e158b4094b66e798fb12911168a3ccdf80a83096340a6a95da0ae8d9f776528eecdbb747eb6b545495a4319ed5378e35b21e073a011000000000deadbeef1badcafe01234567").unwrap();
 		assert_eq!(encoded_value_with_range, target_value_with_range);
-		assert_eq!(msgs::ClosingSigned::read(&mut Cursor::new(&target_value_with_range)).unwrap(),
+		assert_eq!(<msgs::ClosingSigned as Readable>::read(&mut Cursor::new(&target_value_with_range)).unwrap(),
 			closing_signed_with_range);
 	}
 
@@ -4491,7 +4491,7 @@ mod tests {
 		let encoded_value = init_msg.encode();
 		let target_value = <Vec<u8>>::from_hex("0000000001206fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d61900000000000307017f00000103e8").unwrap();
 		assert_eq!(encoded_value, target_value);
-		assert_eq!(msgs::Init::read(&mut Cursor::new(&target_value)).unwrap(), init_msg);
+		assert_eq!(<msgs::Init as Readable>::read(&mut Cursor::new(&target_value)).unwrap(), init_msg);
 	}
 
 	#[test]

lightning/src/util/ser.rs

@@ -374,6 +374,13 @@ where
 	fn read<R: LengthRead>(reader: &mut R) -> Result<Self, DecodeError>;
 }
 
+impl<T: Readable> LengthReadable for T {
+	#[inline]
+	fn read<R: Read>(reader: &mut R) -> Result<T, DecodeError> {
+		Readable::read(reader)
+	}
+}
+
 /// A trait that various LDK types implement allowing them to (maybe) be read in from a [`Read`].
 ///
 /// This is not exported to bindings users as we only export serialization to/from byte arrays instead

lightning/src/util/ser_macros.rs

@@ -385,7 +385,7 @@ macro_rules! _decode_tlv {
 	($outer_reader: expr, $reader: expr, $field: ident, (static_value, $value: expr)) => {{
 	}};
 	($outer_reader: expr, $reader: expr, $field: ident, required) => {{
-		$field = $crate::util::ser::Readable::read(&mut $reader)?;
+		$field = $crate::util::ser::LengthReadable::read(&mut $reader)?;
 	}};
 	($outer_reader: expr, $reader: expr, $field: ident, (required: $trait: ident $(, $read_arg: expr)?)) => {{
 		$field = $trait::read(&mut $reader $(, $read_arg)*)?;
@@ -395,7 +395,7 @@ macro_rules! _decode_tlv {
 		$field = f.0;
 	}};
 	($outer_reader: expr, $reader: expr, $field: ident, option) => {{
-		$field = Some($crate::util::ser::Readable::read(&mut $reader)?);
+		$field = Some($crate::util::ser::LengthReadable::read(&mut $reader)?);
 	}};
 	($outer_reader: expr, $reader: expr, $field: ident, (option, explicit_type: $fieldty: ty)) => {{
 		let _field: &Option<$fieldty> = &$field;
@@ -453,7 +453,7 @@ macro_rules! _decode_tlv {
 	}};
 	($outer_reader: expr, $reader: expr, $field: ident, (option, encoding: ($fieldty: ty, $encoding: ident))) => {{
 		$field = {
-			let field: $encoding<$fieldty> = ser::Readable::read(&mut $reader)?;
+			let field: $encoding<$fieldty> = ser::LengthReadable::read(&mut $reader)?;
 			Some(field.0)
 		};
 	}};