Fix error response types for rate limiting in service

Replace hardcoded BuyError responses with appropriate error types based on
the actual request (GetInfo vs Buy) when rate limiting is triggered.

This fixes incorrect error response types and provides an easy way to test
the error event handling added in this PR.

Author: martinsaposnic

lightning-liquidity/src/lsps2/service.rs

@@ -1348,45 +1348,43 @@ where
 		&self, peer_state_lock: &mut MutexGuard<'a, PeerState>, request_id: LSPSRequestId,
 		counterparty_node_id: PublicKey, request: LSPS2Request,
 	) -> (Result<(), LightningError>, Option<LSPSMessage>) {
-		if self.total_pending_requests.load(Ordering::Relaxed) >= MAX_TOTAL_PENDING_REQUESTS {
-			let response = LSPS2Response::BuyError(LSPSResponseError {
+		let create_pending_request_limit_exceeded_response = |error_message: String| {
+			let error_details = LSPSResponseError {
 				code: LSPS0_CLIENT_REJECTED_ERROR_CODE,
-				message: "Reached maximum number of pending requests. Please try again later."
-					.to_string(),
+				message: error_message.clone(),
 				data: None,
+			};
+			let response = match &request {
+				LSPS2Request::GetInfo(_) => LSPS2Response::GetInfoError(error_details),
+				LSPS2Request::Buy(_) => LSPS2Response::BuyError(error_details),
+			};
+			let msg = Some(LSPS2Message::Response(request_id.clone(), response).into());
+
+			let result = Err(LightningError {
+				err: error_message,
+				action: ErrorAction::IgnoreAndLog(Level::Debug),
 			});
-			let msg = Some(LSPS2Message::Response(request_id, response).into());
+			(result, msg)
+		};
 
-			let err = format!(
-				"Peer {} reached maximum number of total pending requests: {}",
+		if self.total_pending_requests.load(Ordering::Relaxed) >= MAX_TOTAL_PENDING_REQUESTS {
+			let error_message = format!(
+				"reached maximum number of total pending requests {}: {}",
 				counterparty_node_id, MAX_TOTAL_PENDING_REQUESTS
 			);
-			let result =
-				Err(LightningError { err, action: ErrorAction::IgnoreAndLog(Level::Debug) });
-			return (result, msg);
+			return create_pending_request_limit_exceeded_response(error_message);
 		}
 
 		if peer_state_lock.pending_requests_and_channels() < MAX_PENDING_REQUESTS_PER_PEER {
 			peer_state_lock.pending_requests.insert(request_id, request);
 			self.total_pending_requests.fetch_add(1, Ordering::Relaxed);
 			(Ok(()), None)
 		} else {
-			let response = LSPS2Response::BuyError(LSPSResponseError {
-				code: LSPS0_CLIENT_REJECTED_ERROR_CODE,
-				message: "Reached maximum number of pending requests. Please try again later."
-					.to_string(),
-				data: None,
-			});
-			let msg = Some(LSPS2Message::Response(request_id, response).into());
-
-			let err = format!(
-				"Peer {} reached maximum number of pending requests: {}",
+			let error_message = format!(
+				"reached maximum number of pending requests for peer {}: {}",
 				counterparty_node_id, MAX_PENDING_REQUESTS_PER_PEER
 			);
-			let result =
-				Err(LightningError { err, action: ErrorAction::IgnoreAndLog(Level::Debug) });
-
-			(result, msg)
+			create_pending_request_limit_exceeded_response(error_message)
 		}
 	}