fix #6200: if we cannot parse an onion, send a failure code that has the BADONION bit

electrum/lnpeer.py

@@ -1534,7 +1534,6 @@ class Peer(Logger):
                     onion_packet_bytes = bytes.fromhex(onion_packet_hex)
                     onion_packet = None
                     try:
-                        if self.network.config.get('test_fail_malformed_htlc'): raise InvalidOnionPubkey()
                         onion_packet = OnionPacket.from_bytes(onion_packet_bytes)
                         processed_onion = process_onion_packet(onion_packet, associated_data=payment_hash, our_onion_private_key=self.privkey)
                     except UnsupportedOnionPacketVersion:
@@ -1545,11 +1544,15 @@ class Peer(Logger):
                         error_reason = OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_HMAC, data=sha256(onion_packet_bytes))
                     except Exception as e:
                         self.logger.info(f"error processing onion packet: {e!r}")
-                        error_reason = OnionRoutingFailureMessage(code=OnionFailureCode.TEMPORARY_NODE_FAILURE, data=b'')
+                        error_reason = OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_VERSION, data=sha256(onion_packet_bytes))
                     else:
+                        if self.network.config.get('test_fail_malformed_htlc'):
+                            error_reason = OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_VERSION, data=sha256(onion_packet_bytes))
                         if self.network.config.get('test_fail_htlcs_with_temp_node_failure'):
                             error_reason = OnionRoutingFailureMessage(code=OnionFailureCode.TEMPORARY_NODE_FAILURE, data=b'')
-                        elif processed_onion.are_we_final:
+
+                    if not error_reason:
+                        if processed_onion.are_we_final:
                             preimage, error_reason = self.maybe_fulfill_htlc(
                                 chan=chan,
                                 htlc=htlc,