Use LengthReadable trait for deserialization

Previously, our deserialization macros used the `Readable` trait by
default. Now that `LengthReadable` is public and all `Readable` types
also implement it, we can use `LengthReadable` instead.

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>>::read_from_fixed_length_buffer(&mut rd)?.0;
 
 		let hmac = Readable::read(r)?;
 

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_from_fixed_length_buffer(&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_from_fixed_length_buffer(&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_from_fixed_length_buffer(&mut $reader)?;
 			Some(field.0)
 		};
 	}};