Add minimumCacheTTL config for Image Optimization (vercel#27200)

- Closes vercel#23328  
- Related to vercel#19914 
- Related to vercel#22319 


## Feature

- [x] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [x] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [x] Errors have helpful link attached, see `contributing.md`

docs/basic-features/image-optimization.md

@@ -136,9 +136,11 @@ Images are optimized dynamically upon request and stored in the `<distDir>/cache
 
 The expiration (or rather Max Age) is defined by the upstream server's `Cache-Control` header.
 
-If `s-maxage` is found in `Cache-Control`, it is used. If no `s-maxage` is found, then `max-age` is used. If no `max-age` is found, then 60 seconds is used.
+If `s-maxage` is found in `Cache-Control`, it is used. If no `s-maxage` is found, then `max-age` is used. If no `max-age` is found, then [`minimumCacheTTL`](#minimum-cache-ttl) is used.
 
-You can configure [`deviceSizes`](#device-sizes) and [`imageSizes`](#device-sizes) to reduce the total number of possible generated images.
+You can configure [`minimumCacheTTL`](#minimum-cache-ttl) to increase the cache duration when the upstream image does not include `max-age`.
+
+You can also configure [`deviceSizes`](#device-sizes) and [`imageSizes`](#device-sizes) to reduce the total number of possible generated images.
 
 ## Advanced
 
@@ -172,6 +174,18 @@ module.exports = {
 }
 ```
 
+### Minimum Cache TTL
+
+You can configure the time to live (TTL) in seconds for cached optimized images. This will configure the server's image cache as well as the `Cache-Control` header sent to the browser. This is a global setting that will affect all images. In most cases, its better to use a [Static Image Import](#image-Imports) which will handle hashing file contents and caching the file. You can also configure the `Cache-Control` header on an individual upstream image instead.
+
+```js
+module.exports = {
+  images: {
+    minimumCacheTTL: 60,
+  },
+}
+```
+
 ### Disable Static Imports
 
 The default behavior allows you to import static files such as `import icon from './icon.png` and then pass that to the `src` property.

errors/invalid-images-config.md

@@ -18,8 +18,12 @@ module.exports = {
     // limit of 50 domains values
     domains: [],
     path: '/_next/image',
-    // loader can be 'default', 'imgix', 'cloudinary', or 'akamai'
+    // loader can be 'default', 'imgix', 'cloudinary', 'akamai', or 'custom'
     loader: 'default',
+    // disable static imports for image files
+    disableStaticImages: false,
+    // minimumCacheTTL is in seconds, must be integer 0 or more
+    minimumCacheTTL: 60,
   },
 }
 ```

packages/next/server/config.ts

@@ -291,6 +291,17 @@ function assignDefaults(userConfig: { [key: string]: any }) {
     if (images.path === imageConfigDefault.path && result.basePath) {
       images.path = `${result.basePath}${images.path}`
     }
+
+    if (
+      images.minimumCacheTTL &&
+      (!Number.isInteger(images.minimumCacheTTL) || images.minimumCacheTTL < 0)
+    ) {
+      throw new Error(
+        `Specified images.minimumCacheTTL should be an integer 0 or more
+          ', '
+        )}), received  (${images.minimumCacheTTL}).\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
+      )
+    }
   }
 
   if (result.i18n) {

packages/next/server/image-config.ts

@@ -15,6 +15,7 @@ export type ImageConfig = {
   path: string
   domains?: string[]
   disableStaticImages?: boolean
+  minimumCacheTTL?: number
 }
 
 export const imageConfigDefault: ImageConfig = {
@@ -24,4 +25,5 @@ export const imageConfigDefault: ImageConfig = {
   loader: 'default',
   domains: [],
   disableStaticImages: false,
+  minimumCacheTTL: 60,
 }

packages/next/server/image-optimizer.ts

@@ -39,7 +39,13 @@ export async function imageOptimizer(
   isDev = false
 ) {
   const imageData: ImageConfig = nextConfig.images || imageConfigDefault
-  const { deviceSizes = [], imageSizes = [], domains = [], loader } = imageData
+  const {
+    deviceSizes = [],
+    imageSizes = [],
+    domains = [],
+    loader,
+    minimumCacheTTL = 60,
+  } = imageData
 
   if (loader !== 'default') {
     await server.render404(req, res, parsedUrl)
@@ -206,7 +212,10 @@ export async function imageOptimizer(
       upstreamType =
         detectContentType(upstreamBuffer) ||
         upstreamRes.headers.get('Content-Type')
-      maxAge = getMaxAge(upstreamRes.headers.get('Cache-Control'))
+      maxAge = getMaxAge(
+        upstreamRes.headers.get('Cache-Control'),
+        minimumCacheTTL
+      )
     } else {
       try {
         const resBuffers: Buffer[] = []
@@ -261,7 +270,7 @@ export async function imageOptimizer(
         upstreamBuffer = Buffer.concat(resBuffers)
         upstreamType =
           detectContentType(upstreamBuffer) || mockRes.getHeader('Content-Type')
-        maxAge = getMaxAge(mockRes.getHeader('Cache-Control'))
+        maxAge = getMaxAge(mockRes.getHeader('Cache-Control'), minimumCacheTTL)
       } catch (err) {
         res.statusCode = 500
         res.end('"url" parameter is valid but upstream response is invalid')
@@ -529,8 +538,7 @@ export function detectContentType(buffer: Buffer) {
   return null
 }
 
-export function getMaxAge(str: string | null): number {
-  const minimum = 60
+export function getMaxAge(str: string | null, minimumCacheTTL: number): number {
   const map = parseCacheControl(str)
   if (map) {
     let age = map.get('s-maxage') || map.get('max-age') || ''
@@ -539,8 +547,8 @@ export function getMaxAge(str: string | null): number {
     }
     const n = parseInt(age, 10)
     if (!isNaN(n)) {
-      return Math.max(n, minimum)
+      return Math.max(n, minimumCacheTTL)
     }
   }
-  return minimum
+  return minimumCacheTTL
 }

test/integration/image-optimizer/test/get-max-age.test.js

@@ -3,42 +3,42 @@ import { getMaxAge } from '../../../../packages/next/dist/server/image-optimizer
 
 describe('getMaxAge', () => {
   it('should return default when no cache-control provided', () => {
-    expect(getMaxAge()).toBe(60)
+    expect(getMaxAge(undefined, 60)).toBe(60)
   })
   it('should return default when cache-control is null', () => {
-    expect(getMaxAge(null)).toBe(60)
+    expect(getMaxAge(null, 60)).toBe(60)
   })
   it('should return default when cache-control is empty string', () => {
-    expect(getMaxAge('')).toBe(60)
+    expect(getMaxAge('', 60)).toBe(60)
   })
   it('should return default when cache-control max-age is less than default', () => {
-    expect(getMaxAge('max-age=30')).toBe(60)
+    expect(getMaxAge('max-age=30', 60)).toBe(60)
   })
   it('should return default when cache-control max-age is not a number', () => {
-    expect(getMaxAge('max-age=foo')).toBe(60)
+    expect(getMaxAge('max-age=foo', 60)).toBe(60)
   })
   it('should return default when cache-control is no-cache', () => {
-    expect(getMaxAge('no-cache')).toBe(60)
+    expect(getMaxAge('no-cache', 60)).toBe(60)
   })
   it('should return cache-control max-age lowercase', () => {
-    expect(getMaxAge('max-age=9999')).toBe(9999)
+    expect(getMaxAge('max-age=9999', 60)).toBe(9999)
   })
   it('should return cache-control MAX-AGE uppercase', () => {
-    expect(getMaxAge('MAX-AGE=9999')).toBe(9999)
+    expect(getMaxAge('MAX-AGE=9999', 60)).toBe(9999)
   })
   it('should return cache-control s-maxage lowercase', () => {
-    expect(getMaxAge('s-maxage=9999')).toBe(9999)
+    expect(getMaxAge('s-maxage=9999', 60)).toBe(9999)
   })
   it('should return cache-control S-MAXAGE', () => {
-    expect(getMaxAge('S-MAXAGE=9999')).toBe(9999)
+    expect(getMaxAge('S-MAXAGE=9999', 60)).toBe(9999)
   })
   it('should return cache-control s-maxage with spaces', () => {
-    expect(getMaxAge('public, max-age=5555, s-maxage=9999')).toBe(9999)
+    expect(getMaxAge('public, max-age=5555, s-maxage=9999', 60)).toBe(9999)
   })
   it('should return cache-control s-maxage without spaces', () => {
-    expect(getMaxAge('public,s-maxage=9999,max-age=5555')).toBe(9999)
+    expect(getMaxAge('public,s-maxage=9999,max-age=5555', 60)).toBe(9999)
   })
   it('should return cache-control for a quoted value', () => {
-    expect(getMaxAge('public, s-maxage="9999", max-age="5555"')).toBe(9999)
+    expect(getMaxAge('public, s-maxage="9999", max-age="5555"', 60)).toBe(9999)
   })
 })