Set error code and friends when processing an error within a blinded path

We don't bother actually parsing errors from within a blinded path, since all
errors should be wiped by the introduction node by the time it gets back to us
(the sender).

Author: valentinewallace

lightning/src/ln/onion_utils.rs

@@ -413,6 +413,11 @@ where L::Target: Logger {
 	let mut error_packet_ret = None;
 	let mut is_from_final_node = false;
 
+	const BADONION: u16 = 0x8000;
+	const PERM: u16 = 0x4000;
+	const NODE: u16 = 0x2000;
+	const UPDATE: u16 = 0x1000;
+
 	// Handle packed channel/node updates for passing back for the route handler
 	construct_onion_keys_callback(secp_ctx, &path, session_priv,
 		|shared_secret, _, _, route_hop_opt, route_hop_idx|
@@ -421,7 +426,13 @@ where L::Target: Logger {
 
 		let route_hop = match route_hop_opt {
 			Some(hop) => hop,
-			None => return,
+			None => {
+				// Got an error from within a blinded route.
+				error_code_ret = Some(BADONION | PERM | 24); // invalid_onion_blinding
+				error_packet_ret = Some(vec![0; 32]);
+				is_from_final_node = false;
+				return
+			},
 		};
 
 		let amt_to_forward = htlc_msat - route_hop.fee_msat;
@@ -463,10 +474,6 @@ where L::Target: Logger {
 				return
 			}
 		};
-		const BADONION: u16 = 0x8000;
-		const PERM: u16 = 0x4000;
-		const NODE: u16 = 0x2000;
-		const UPDATE: u16 = 0x1000;
 
 		let error_code = u16::from_be_bytes(error_code_slice.try_into().expect("len is 2"));
 		error_code_ret = Some(error_code);