Small fixes (paritytech#2126)

bridges/bin/runtime-common/src/messages.rs

@@ -216,7 +216,7 @@ pub mod source {
 		// the message itself. The proof is always larger than the message. But unless chain state
 		// is enormously large, it should be several dozens/hundreds of bytes. The delivery
 		// transaction also contains signatures and signed extensions. Because of this, we reserve
-		// 1/3 of the the maximal extrinsic weight for this data.
+		// 1/3 of the the maximal extrinsic size for this data.
 		if payload.len() > maximal_message_size::<B>() as usize {
 			return Err(VerificationError::MessageTooLarge)
 		}

bridges/bin/runtime-common/src/messages_call_ext.rs

@@ -47,7 +47,7 @@ pub struct BaseMessagesProofInfo {
 impl BaseMessagesProofInfo {
 	/// Returns true if `bundled_range` continues the `0..=best_stored_nonce` range.
 	fn appends_to_stored_nonce(&self) -> bool {
-		*self.bundled_range.start() == self.best_stored_nonce + 1
+		Some(*self.bundled_range.start()) == self.best_stored_nonce.checked_add(1)
 	}
 }
 

bridges/modules/messages/src/inbound_lane.rs

@@ -171,8 +171,7 @@ impl<S: InboundLaneStorage> InboundLane<S> {
 		message_data: DispatchMessageData<Dispatch::DispatchPayload>,
 	) -> ReceivalResult<Dispatch::DispatchLevelResult> {
 		let mut data = self.storage.get_or_init_data();
-		let is_correct_message = nonce == data.last_delivered_nonce() + 1;
-		if !is_correct_message {
+		if Some(nonce) != data.last_delivered_nonce().checked_add(1) {
 			return ReceivalResult::InvalidNonce
 		}