fix: add stale-while-revalidate to limits

api/_utils.ts

@@ -1246,3 +1246,28 @@ export function getDefaultRelayerAddress(
     return sdk.constants.DEFAULT_SIMULATED_RELAYER_ADDRESS;
   }
 }
+
+/**
+ * Performs the needed function calls to return a Vercel Response
+ * @param response The response client provided by Vercel
+ * @param body A payload in JSON format to send to the client
+ * @param statusCode The status code - defaults to 200
+ * @param cache The cache time in seconds - defaults to 300
+ * @returns The response object
+ */
+export function sendResponse(
+  response: VercelResponse,
+  body: Record<string, unknown>,
+  statusCode = 200,
+  cache?: number
+) {
+  // We only want to cache if the status code is 200 and the
+  // caching time has been defined.
+  if (statusCode === 200 && sdk.utils.isDefined(cache)) {
+    response.setHeader(
+      "Cache-Control",
+      `s-max-age=${cache}, stale-while-revalidate=${cache}`
+    );
+  }
+  return response.status(statusCode).json(body);
+}

api/limits.ts

@@ -31,6 +31,7 @@ import {
   HUB_POOL_CHAIN_ID,
   ENABLED_ROUTES,
   getDefaultRelayerAddress,
+  sendResponse,
 } from "./_utils";
 
 const LimitsQueryParamsSchema = object({
@@ -235,8 +236,7 @@ const handler = async (
       message: "Response data",
       responseJson,
     });
-    response.setHeader("Cache-Control", "s-maxage=300");
-    response.status(200).json(responseJson);
+    sendResponse(response, responseJson, 200, 300);
   } catch (error: unknown) {
     return handleErrorCondition("limits", response, logger, error);
   }