Allow etags to be disabled with config option (#3915)

* Allow etags to be disabled with config option

- CR Change: Rename option to generateEtags
- CR Change: Add tests for etag generation
- CR Change: Refactor to use next.config.js
- Update documentation

* Use renderOpts instead of passing nextConfig

readme.md

@@ -1047,6 +1047,17 @@ module.exports = {
 }
 ```
 
+#### Disabling etag generation
+
+You can disable etag generation for HTML pages depending on your cache strategy. If no configuration is specified then Next will generate etags for every page.
+
+```js
+// next.config.js
+module.exports = {
+  generateEtags: false
+}
+```
+
 #### Configuring the onDemandEntries
 
 Next exposes some options that give you some control over how the server will dispose or keep in memories pages built:

server/config.js

@@ -10,6 +10,7 @@ const defaultConfig = {
   assetPrefix: '',
   configOrigin: 'default',
   useFileSystemPublicRoutes: true,
+  generateEtags: true,
   pageExtensions: ['jsx', 'js'] // jsx before js because otherwise regex matching will match js first
 }
 

server/index.js

@@ -45,6 +45,10 @@ export default class Server {
       updateNotifier(pkg, 'next')
     }
 
+    // Only serverRuntimeConfig needs the default
+    // publicRuntimeConfig gets it's default in client/index.js
+    const {serverRuntimeConfig = {}, publicRuntimeConfig, assetPrefix, generateEtags} = this.nextConfig
+
     if (!dev && !fs.existsSync(resolve(dir, this.dist, 'BUILD_ID'))) {
       console.error(`> Could not find a valid build in the '${this.dist}' directory! Try building your app with 'next build' before starting the server.`)
       process.exit(1)
@@ -57,13 +61,10 @@ export default class Server {
       dist: this.dist,
       hotReloader: this.hotReloader,
       buildId: this.buildId,
-      availableChunks: dev ? {} : getAvailableChunks(this.dir, this.dist)
+      availableChunks: dev ? {} : getAvailableChunks(this.dir, this.dist),
+      generateEtags
     }
 
-    // Only serverRuntimeConfig needs the default
-    // publicRuntimeConfig gets it's default in client/index.js
-    const {serverRuntimeConfig = {}, publicRuntimeConfig, assetPrefix} = this.nextConfig
-
     // Only the `publicRuntimeConfig` key is exposed to the client side
     // It'll be rendered as part of __NEXT_DATA__ on the client side
     if (publicRuntimeConfig) {

server/render.js

@@ -138,9 +138,9 @@ export async function renderScriptError (req, res, page, error) {
   res.end('500 - Internal Error')
 }
 
-export function sendHTML (req, res, html, method, { dev }) {
+export function sendHTML (req, res, html, method, { dev, generateEtags }) {
   if (isResSent(res)) return
-  const etag = generateETag(html)
+  const etag = generateEtags && generateETag(html)
 
   if (fresh(req.headers, { etag })) {
     res.statusCode = 304
@@ -154,7 +154,10 @@ export function sendHTML (req, res, html, method, { dev }) {
     res.setHeader('Cache-Control', 'no-store, must-revalidate')
   }
 
+  if (etag) {
     res.setHeader('ETag', etag)
+  }
+
   if (!res.getHeader('Content-Type')) {
     res.setHeader('Content-Type', 'text/html; charset=utf-8')
   }

test/integration/custom-server/next.config.js

@@ -2,5 +2,6 @@ module.exports = {
   onDemandEntries: {
     // Make sure entries are not getting disposed.
     maxInactiveAge: 1000 * 60 * 60
-  }
+  },
+  generateEtags: process.env.GENERATE_ETAGS === 'true'
 }

test/integration/custom-server/test/index.test.js

@@ -7,7 +7,8 @@ import cheerio from 'cheerio'
 import {
   initNextServerScript,
   killApp,
-  renderViaHTTP
+  renderViaHTTP,
+  fetchViaHTTP
 } from 'next-test-utils'
 import webdriver from 'next-webdriver'
 
@@ -18,18 +19,24 @@ jasmine.DEFAULT_TIMEOUT_INTERVAL = 1000 * 60 * 2
 
 const context = {}
 
-describe('Custom Server', () => {
-  beforeAll(async () => {
+const startServer = async (optEnv = {}) => {
   const scriptPath = join(appDir, 'server.js')
   context.appPort = appPort = await getPort()
-    const env = clone(process.env)
-    env.PORT = `${appPort}`
+  const env = Object.assign(
+    {},
+    clone(process.env),
+    { PORT: `${appPort}` },
+    optEnv
+  )
 
   server = await initNextServerScript(scriptPath, /Ready on/, env)
-  })
+}
+
+describe('Custom Server', () => {
+  describe('with dynamic assetPrefix', () => {
+    beforeAll(() => startServer())
     afterAll(() => killApp(server))
 
-  describe('with dynamic assetPrefix', () => {
     it('should set the assetPrefix dynamically', async () => {
       const normalUsage = await renderViaHTTP(appPort, '/asset')
       expect(normalUsage).not.toMatch(/127\.0\.0\.1/)
@@ -83,4 +90,24 @@ describe('Custom Server', () => {
       browser2.close()
     })
   })
+
+  describe('with generateEtags enabled', () => {
+    beforeAll(() => startServer({ GENERATE_ETAGS: 'true' }))
+    afterAll(() => killApp(server))
+
+    it('response includes etag header', async () => {
+      const response = await fetchViaHTTP(appPort, '/')
+      expect(response.headers.get('etag')).toBeTruthy()
+    })
+  })
+
+  describe('with generateEtags disabled', () => {
+    beforeAll(() => startServer({ GENERATE_ETAGS: 'false' }))
+    afterAll(() => killApp(server))
+
+    it('response does not include etag header', async () => {
+      const response = await fetchViaHTTP(appPort, '/')
+      expect(response.headers.get('etag')).toBeNull()
+    })
+  })
 })