WIP: Fuzz test onion message replies

Author: jkczyz

fuzz/src/onion_message.rs

@@ -101,7 +101,7 @@ struct TestCustomMessageHandler {}
 impl CustomOnionMessageHandler for TestCustomMessageHandler {
 	type CustomMessage = TestCustomMessage;
 	fn handle_custom_message(&self, _msg: Self::CustomMessage) -> Option<Self::CustomMessage> {
-		None
+		Some(TestCustomMessage {})
 	}
 	fn read_custom_message<R: io::Read>(&self, _message_type: u64, buffer: &mut R) -> Result<Option<Self::CustomMessage>, msgs::DecodeError> {
 		let mut buf = Vec::new();
@@ -111,9 +111,7 @@ impl CustomOnionMessageHandler for TestCustomMessageHandler {
 }
 
 impl ResponseErrorHandler for TestCustomMessageHandler {
-	fn handle_response_error(&self, _error: ResponseError) {
-		unreachable!()
-	}
+	fn handle_response_error(&self, _error: ResponseError) {}
 }
 
 pub struct VecWriter(pub Vec<u8>);
@@ -209,6 +207,9 @@ mod tests {
 			let log_entries = logger.lines.lock().unwrap();
 			assert_eq!(log_entries.get(&("lightning::onion_message::messenger".to_string(),
 						"Received an onion message with path_id None and no reply_path".to_string())), Some(&1));
+			// TODO: Add reply path to one_hop_om instead?
+			assert_eq!(log_entries.get(&("lightning::onion_message::messenger".to_string(),
+						"No reply path to respond to onion message with path_id None".to_string())), Some(&1));
 		}
 
 		let two_unblinded_hops_om = "020000000000000000000000000000000000000000000000000000000000000e01055600020000000000000000000000000000000000000000000000000000000000000e0135043304210200000000000000000000000000000000000000000000000000000000000000029500000000000000000000000000000036000000000000000000000000000000000000000000000000000000000000003604104b000000000000000000000000000000fd1092202a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a2a00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000b200000000000000000000000000000000000000000000000000000000000000";