Refactor code structure for improved readability and maintainability

server/limits.js

@@ -1,3 +1,5 @@
+import { apiError } from "./errors.js";
+
 /**
  * Limits for the expensive endpoints: parsing an uploaded Word file can take a LibreOffice
  * conversion and seconds of CPU, so one client must not be able to occupy the server.
@@ -15,7 +17,7 @@ export function rateLimit({ max, windowMs, message }) {
     windows.set(req.ip, w);
     if (w.count <= max) return next();
     res.set("Retry-After", String(Math.ceil((w.start + windowMs - now) / 1000)));
-    res.status(429).json({ error: message });
+    res.status(429).json({ error: message, code: "too_many_requests" });
   };
 }
 
@@ -29,7 +31,7 @@ export function semaphore({ limit, queue, message }) {
   return async function run(task) {
     if (active < limit) active++;
     else if (waiting.length < queue) await new Promise((resolve) => waiting.push(resolve));
-    else throw Object.assign(new Error(message), { status: 429 });
+    else throw apiError(429, "busy", message);
     try {
       return await task();
     } finally {