f: Use FixedLengthReader and WithoutLength

Author: arik-so

lightning/src/ln/msgs.rs

@@ -1859,23 +1859,15 @@ impl Writeable for TrampolineOnionPacket {
 
 impl LengthReadable for TrampolineOnionPacket {
 	fn read<R: LengthRead>(r: &mut R) -> Result<Self, DecodeError> {
-		const READ_BUFFER_SIZE: usize = 4096;
-
 		let version = Readable::read(r)?;
 		let public_key = Readable::read(r)?;
 
-		let mut hop_data = Vec::new();
 		let hop_data_len = r.total_bytes().saturating_sub(66) as usize; // 1 (version) + 33 (pubkey) + 32 (HMAC) = 66
-		let mut read_idx = 0;
-		while read_idx < hop_data_len {
-			let mut read_buffer = [0; READ_BUFFER_SIZE];
-			let read_amt = cmp::min(hop_data_len - read_idx, READ_BUFFER_SIZE);
-			r.read_exact(&mut read_buffer[..read_amt])?;
-			hop_data.extend_from_slice(&read_buffer[..read_amt]);
-			read_idx += read_amt;
-		}
+		let mut rd = FixedLengthReader::new(r, hop_data_len as u64);
+		let hop_data = WithoutLength::<Vec<u8>>::read(&mut rd)?.0;
 
 		let hmac = Readable::read(r)?;
+
 		Ok(TrampolineOnionPacket {
 			version,
 			public_key,