Pull hmac out of OnionHopData.

Its a bit awkward to have an hmac field covering the struct that
its in, and there is little difference in removing it, so just pull
it out and use a [u8; 32] where we care about the hmac.

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -922,22 +922,24 @@ impl<ChanSigner: ChannelKeys> ChannelManager<ChanSigner> {
 		}
 
 		let mut chacha = ChaCha20::new(&rho, &[0u8; 8]);
-		let next_hop_data = {
+		let (next_hop_data, next_hop_hmac) = {
 			let mut decoded = [0; 65];
 			chacha.process(&msg.onion_routing_packet.hop_data[0..65], &mut decoded);
-			match msgs::OnionHopData::read(&mut Cursor::new(&decoded[..])) {
+			let mut hmac = [0; 32];
+			hmac.copy_from_slice(&decoded[33..]);
+			match msgs::OnionHopData::read(&mut Cursor::new(&decoded[..33])) {
 				Err(err) => {
 					let error_code = match err {
 						msgs::DecodeError::UnknownVersion => 0x4000 | 1, // unknown realm byte
 						_ => 0x2000 | 2, // Should never happen
 					};
 					return_err!("Unable to decode our hop data", error_code, &[0;0]);
 				},
-				Ok(msg) => msg
+				Ok(msg) => (msg, hmac)
 			}
 		};
 
-		let pending_forward_info = if next_hop_data.hmac == [0; 32] {
+		let pending_forward_info = if next_hop_hmac == [0; 32] {
 				#[cfg(test)]
 				{
 					// In tests, make sure that the initial onion pcket data is, at least, non-0.
@@ -1002,7 +1004,7 @@ impl<ChanSigner: ChannelKeys> ChannelManager<ChanSigner> {
 					version: 0,
 					public_key,
 					hop_data: new_packet_data,
-					hmac: next_hop_data.hmac.clone(),
+					hmac: next_hop_hmac.clone(),
 				};
 
 				PendingHTLCStatus::Forward(PendingForwardHTLCInfo {

lightning/src/ln/msgs.rs

@@ -830,7 +830,6 @@ mod fuzzy_internal_msgs {
 		pub(crate) amt_to_forward: u64,
 		pub(crate) outgoing_cltv_value: u32,
 		// 12 bytes of 0-padding
-		pub(crate) hmac: [u8; 32],
 	}
 
 	pub struct DecodedOnionErrorPacket {
@@ -1205,7 +1204,7 @@ impl_writeable!(UpdateAddHTLC, 32+8+8+32+4+1366, {
 
 impl Writeable for OnionHopData {
 	fn write<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
-		w.size_hint(65);
+		w.size_hint(33);
 		match self.format {
 			OnionHopDataFormat::Legacy => 0u8.write(w)?,
 			#[cfg(test)]
@@ -1215,7 +1214,6 @@ impl Writeable for OnionHopData {
 		self.amt_to_forward.write(w)?;
 		self.outgoing_cltv_value.write(w)?;
 		w.write_all(&[0;12])?;
-		self.hmac.write(w)?;
 		Ok(())
 	}
 }
@@ -1237,7 +1235,6 @@ impl<R: Read> Readable<R> for OnionHopData {
 				r.read_exact(&mut [0; 12])?;
 				v
 			},
-			hmac: Readable::read(r)?,
 		})
 	}
 }

lightning/src/ln/onion_utils.rs

@@ -125,7 +125,6 @@ pub(super) fn build_onion_payloads(route: &Route, starting_htlc_offset: u32) ->
 			short_channel_id: last_short_channel_id,
 			amt_to_forward: value_msat,
 			outgoing_cltv_value: cltv,
-			hmac: [0; 32],
 		});
 		cur_value_msat += hop.fee_msat;
 		if cur_value_msat >= 21000000 * 100000000 * 1000 {
@@ -193,8 +192,8 @@ fn construct_onion_packet_with_init_noise(mut payloads: Vec<msgs::OnionHopData>,
 
 	for (i, (payload, keys)) in payloads.iter_mut().zip(onion_keys.iter()).rev().enumerate() {
 		shift_arr_right(&mut packet_data);
-		payload.hmac = hmac_res;
-		packet_data[0..65].copy_from_slice(&payload.encode()[..]);
+		packet_data[0..33].copy_from_slice(&payload.encode()[..]);
+		packet_data[33..65].copy_from_slice(&hmac_res);
 
 		let mut chacha = ChaCha20::new(&keys.rho, &[0u8; 8]);
 		chacha.process(&packet_data, &mut buf[0..20*65]);
@@ -517,35 +516,30 @@ mod tests {
 				short_channel_id: 0,
 				amt_to_forward: 0,
 				outgoing_cltv_value: 0,
-				hmac: [0; 32],
 			},
 			msgs::OnionHopData {
 				format: msgs::OnionHopDataFormat::Legacy,
 				short_channel_id: 0x0101010101010101,
 				amt_to_forward: 0x0100000001,
 				outgoing_cltv_value: 0,
-				hmac: [0; 32],
 			},
 			msgs::OnionHopData {
 				format: msgs::OnionHopDataFormat::Legacy,
 				short_channel_id: 0x0202020202020202,
 				amt_to_forward: 0x0200000002,
 				outgoing_cltv_value: 0,
-				hmac: [0; 32],
 			},
 			msgs::OnionHopData {
 				format: msgs::OnionHopDataFormat::Legacy,
 				short_channel_id: 0x0303030303030303,
 				amt_to_forward: 0x0300000003,
 				outgoing_cltv_value: 0,
-				hmac: [0; 32],
 			},
 			msgs::OnionHopData {
 				format: msgs::OnionHopDataFormat::Legacy,
 				short_channel_id: 0x0404040404040404,
 				amt_to_forward: 0x0400000004,
 				outgoing_cltv_value: 0,
-				hmac: [0; 32],
 			},
 		);