perf(netlify-legacy): exclude static paths from SSR function

Backporting nitrojs#2822 to the netlify-legacy preset.

Since it's using "v1" Netlify Functions
(https://docs.netlify.com/functions/lambda-compatibility), it doesn't have access to
`excludedPath` and `preferStatic`, so we implement this with redirects.

src/presets/netlify/legacy/preset.ts

@@ -24,7 +24,7 @@ const netlify = defineNitroPreset(
       },
       async compiled(nitro: Nitro) {
         await writeHeaders(nitro);
-        await writeRedirects(nitro);
+        await writeRedirects(nitro, "/.netlify/functions/server");
 
         if (nitro.options.netlify) {
           const configPath = join(

src/presets/netlify/legacy/utils.ts

@@ -2,7 +2,25 @@ import { existsSync, promises as fsp } from "node:fs";
 import type { Nitro } from "nitropack/types";
 import { join } from "pathe";
 
-export async function writeRedirects(nitro: Nitro) {
+export function generateCatchAllRedirects(
+  nitro: Nitro,
+  catchAllPath?: string
+): string {
+  if (!catchAllPath) return "";
+
+  return [
+    // e.g.: /_nuxt/* /_nuxt/:splat 200
+    // Because of Netlify CDN shadowing
+    // (https://docs.netlify.com/routing/redirects/rewrites-proxies/#shadowing),
+    // this config avoids function invocations for all static paths, even 404s.
+    ...getStaticPaths(nitro).map(
+      (path) => `${path} ${path.replace("/*", "/:splat")} 200`
+    ),
+    `/* ${catchAllPath} 200`,
+  ].join("\n");
+}
+
+export async function writeRedirects(nitro: Nitro, catchAllPath?: string) {
   const redirectsPath = join(nitro.options.output.publicDir, "_redirects");
   const staticFallback = existsSync(
     join(nitro.options.output.publicDir, "404.html")
@@ -11,7 +29,7 @@ export async function writeRedirects(nitro: Nitro) {
     : "";
   let contents = nitro.options.static
     ? staticFallback
-    : "/* /.netlify/functions/server 200";
+    : generateCatchAllRedirects(nitro, catchAllPath);
 
   const rules = Object.entries(nitro.options.routeRules).sort(
     (a, b) => a[0].split(/\/(?!\*)/).length - b[0].split(/\/(?!\*)/).length
@@ -103,6 +121,13 @@ export async function writeHeaders(nitro: Nitro) {
   await fsp.writeFile(headersPath, contents);
 }
 
+export function getStaticPaths(nitro: Nitro): string[] {
+  const publicAssets = nitro.options.publicAssets.filter(
+    (dir) => dir.fallthrough !== true && dir.baseURL && dir.baseURL !== "/"
+  );
+  return ["/.netlify/*", ...publicAssets.map((dir) => `${dir.baseURL}/*`)];
+}
+
 export function deprecateSWR(nitro: Nitro) {
   if (nitro.options.future.nativeSWR) {
     return;

test/presets/netlify-legacy.test.ts

@@ -70,6 +70,10 @@ describe("nitro:preset:netlify-legacy", async () => {
         /rules/isr-ttl/*	/.netlify/builders/server 200
         /rules/isr/*	/.netlify/builders/server 200
         /rules/dynamic	/.netlify/functions/server 200
+        /.netlify/* /.netlify/:splat 200
+        /build/* /build/:splat 200
+        /with-default-fallthrough/* /with-default-fallthrough/:splat 200
+        /nested/no-fallthrough/* /nested/no-fallthrough/:splat 200
         /* /.netlify/functions/server 200"
       `);
       });