perf: accelerate production request hot paths

packages/dev-server/src/public.ts

@@ -41,6 +41,11 @@ function cachePolicy(filePath: string, mode: Mode): string {
 
 /** Cache the public-dir existence check so it isn't a sync stat on every request. */
 const publicDirExistsCache = new Map<string, boolean>();
+const productionPublicFileCache = new Map<
+  string,
+  { body: Uint8Array; contentType: string; cacheControl: string }
+>();
+const PRODUCTION_PUBLIC_FILE_CACHE_MAX = 256;
 function publicDirExists(dir: string): boolean {
   let exists = publicDirExistsCache.get(dir);
   if (exists === undefined) {
@@ -73,6 +78,21 @@ export async function servePublicAsset(
   let filePath = resolve(base, rel);
   if (!isInside(base, filePath)) return fallback;
 
+  if (mode === "production") {
+    const cached = productionPublicFileCache.get(filePath);
+    if (cached) {
+      productionPublicFileCache.delete(filePath);
+      productionPublicFileCache.set(filePath, cached);
+      return new Response(cached.body.slice(), {
+        headers: {
+          "content-type": cached.contentType,
+          "cache-control": cached.cacheControl,
+          "x-content-type-options": "nosniff",
+        },
+      });
+    }
+  }
+
   try {
     const info = await stat(filePath);
     if (info.isDirectory()) {
@@ -86,10 +106,22 @@ export async function servePublicAsset(
     const body = await readFile(filePath);
     const contentType =
       CONTENT_TYPES[extname(filePath).toLowerCase()] ?? "application/octet-stream";
+    const cacheControl = cachePolicy(filePath, mode);
+    if (mode === "production") {
+      productionPublicFileCache.set(filePath, {
+        body: new Uint8Array(body),
+        contentType,
+        cacheControl,
+      });
+      if (productionPublicFileCache.size > PRODUCTION_PUBLIC_FILE_CACHE_MAX) {
+        const oldest = productionPublicFileCache.keys().next().value;
+        if (oldest) productionPublicFileCache.delete(oldest);
+      }
+    }
     return new Response(body, {
       headers: {
         "content-type": contentType,
-        "cache-control": cachePolicy(filePath, mode),
+        "cache-control": cacheControl,
         "x-content-type-options": "nosniff",
       },
     });