fix(perf): exclude /_next/static/ dir from function

See inline comment. This only matters because of browsers requesting assets from previous
deploys or bots crawling for garbage. This will avoid unnecessary function invocations in
those cases, improving performance and reducing customer bills in some cases.

Author: serhalp

src/build/templates/handler-monorepo.tmpl.js

@@ -53,4 +53,9 @@ export default async function (req, context) {
 export const config = {
   path: '/*',
   preferStatic: true,
+  excludedPath: [
+    // We use `preferStatic: true` so we already won't run this on *existing* static assets,
+    // but by excluding this entire path we also avoid invoking the function just to 404.
+    '/_next/static/*',
+  ],
 }

src/build/templates/handler.tmpl.js

@@ -46,4 +46,9 @@ export default async function handler(req, context) {
 export const config = {
   path: '/*',
   preferStatic: true,
+  excludedPath: [
+    // We use `preferStatic: true` so we already won't run this on *existing* static assets,
+    // but by excluding this entire path we also avoid invoking the function just to 404.
+    '/_next/static/*',
+  ],
 }

tests/e2e/simple-app.test.ts

@@ -1,6 +1,8 @@
 import { expect, type Locator } from '@playwright/test'
 import { nextVersionSatisfies } from '../utils/next-version-helpers.mjs'
 import { test } from '../utils/playwright-helpers.js'
+import { join } from 'node:path'
+import { readdir } from 'node:fs/promises'
 
 const expectImageWasLoaded = async (locator: Locator) => {
   expect(await locator.evaluate((img: HTMLImageElement) => img.naturalHeight)).toBeGreaterThan(0)
@@ -282,3 +284,27 @@ test('can require CJS module that is not bundled', async ({ simple }) => {
   expect(parsedBody.notBundledCJSModule.isBundled).toEqual(false)
   expect(parsedBody.bundledCJSModule.isBundled).toEqual(true)
 })
+
+test('serves a 200 for an existing static asset without invoking a function', async ({
+  page,
+  simple,
+}) => {
+  // Since assets are hashed, we can't hardcode anything here. Find something to fetch.
+  const [staticAsset] = await readdir(join(simple.isolatedFixtureRoot, '.next', 'static', 'chunks'))
+  expect(staticAsset).toBeDefined()
+
+  const response = await page.goto(`${simple.url}/_next/static/chunks/${staticAsset}`)
+
+  expect(response?.status()).toBe(200)
+  expect(response?.headers()).not.toHaveProperty('x-nf-function-type')
+})
+
+test('serves a 404 for a nonexistent static asset without invoking a function', async ({
+  page,
+  simple,
+}) => {
+  const response = await page.goto(`${simple.url}/_next/static/stale123abcdef.js`)
+
+  expect(response?.status()).toBe(404)
+  expect(response?.headers()).not.toHaveProperty('x-nf-function-type')
+})

tests/utils/create-e2e-fixture.ts

@@ -20,6 +20,7 @@ export interface DeployResult {
   deployID: string
   url: string
   logs: string
+  isolatedFixtureRoot: string
 }
 
 type PackageManager = 'npm' | 'pnpm' | 'yarn' | 'bun' | 'berry'
@@ -91,6 +92,7 @@ export const createE2EFixture = async (fixture: string, config: E2EConfig = {})
       cleanup: _cleanup,
       deployID: result.deployID,
       url: result.url,
+      isolatedFixtureRoot,
     }
   } catch (error) {
     await _cleanup(true)