perf(middleware): optimize route-check with WeakMap cache

src/middleware/route-check/index.ts

@@ -16,6 +16,32 @@ type RouteCheckOptions = {
   onNotFound?: (c: Context) => Response | Promise<Response>
 }
 
+/**
+ * Cache to store the result of handler checks.
+ *
+ * Determining if a handler is a "middleware" or an "actual handler" involves:
+ * 1. Unwrapping composed handlers recursively via `findTargetHandler`.
+ * 2. Checking the function length via `isMiddleware`.
+ *
+ * Since Hono handlers are immutable references in runtime, performing this calculation
+ * for every request is redundant. We use a `WeakMap` to cache the boolean result.
+ * This optimization:
+ * - Reduces CPU overhead by changing O(depth) recursion to O(1) map lookup.
+ * - Handles dynamic route registration safely (new handlers get new entries).
+ * - Prevents memory leaks (entries are GC'd when handlers are released).
+ */
+const handlerTypeCache = new WeakMap<Function, boolean>()
+
+const isActualHandler = (handler: Function): boolean => {
+  if (handlerTypeCache.has(handler)) {
+    return handlerTypeCache.get(handler)!
+  }
+  const targetHandler = findTargetHandler(handler)
+  const result = !isMiddleware(targetHandler)
+  handlerTypeCache.set(handler, result)
+  return result
+}
+
 /**
  * Route Check Middleware for Hono.
  *
@@ -50,10 +76,7 @@ export const routeCheck = (options?: RouteCheckOptions): MiddlewareHandler => {
     const routes = matchedRoutes(c)
 
     // Check if there's at least one actual handler (not middleware)
-    const hasActualHandler = routes.some((route) => {
-      const targetHandler = findTargetHandler(route.handler)
-      return !isMiddleware(targetHandler)
-    })
+    const hasActualHandler = routes.some((route) => isActualHandler(route.handler))
 
     if (!hasActualHandler) {
       // No actual handler found - return 404 immediately