feat: support custom response headers on images served via IPX

README.md

@@ -53,6 +53,19 @@ In order to deliver the correct format to a visitor's browser, this uses a Netli
 site may not support Edge Functions, in which case it will instead fall back to delivering the original file format. You
 may also manually disable the Edge Function by setting the environment variable `NEXT_DISABLE_EDGE_IMAGES` to `true`.
 
+## Returning custom response headers on images handled by `ipx`
+
+Should you wish to return custom response headers on images handled by the [`netlify-ipx`](https://github.com/netlify/netlify-ipx) package, you can add them within your project's `netlify.toml` by targeting the `/_next/image/*` route:
+
+```
+[[headers]]
+  for = "/_next/image/*"
+
+  [headers.values]
+    Strict-Transport-Security = "max-age=31536000"
+    X-Test = 'foobar'
+```
+
 ## Next.js Middleware on Netlify
 
 Next.js Middleware works out of the box on Netlify, but check out the

demos/default/netlify.toml

@@ -11,6 +11,13 @@ CYPRESS_CACHE_FOLDER = "../node_modules/.CypressBinary"
 TERM = "xterm"
 NODE_VERSION = "16.15.1"
 
+[[headers]]
+  for = "/_next/image/*"
+
+  [headers.values]
+    Strict-Transport-Security = "max-age=31536000"
+    X-Test = 'foobar'
+
 [dev]
 framework = "#static"
 

packages/runtime/package.json

@@ -74,4 +74,4 @@
   "engines": {
     "node": ">=12.0.0"
   }
-}
+}

packages/runtime/src/helpers/functions.ts

@@ -60,12 +60,14 @@ export const setupImageFunction = async ({
   netlifyConfig,
   basePath,
   remotePatterns,
+  responseHeaders,
 }: {
   constants: NetlifyPluginConstants
   netlifyConfig: NetlifyConfig
   basePath: string
   imageconfig: Partial<ImageConfigComplete>
   remotePatterns: RemotePattern[]
+  responseHeaders?: Record<string, string>
 }): Promise<void> => {
   const functionsPath = INTERNAL_FUNCTIONS_SRC || FUNCTIONS_SRC
   const functionName = `${IMAGE_FUNCTION_NAME}.js`
@@ -76,6 +78,7 @@ export const setupImageFunction = async ({
     ...imageconfig,
     basePath: [basePath, IMAGE_FUNCTION_NAME].join('/'),
     remotePatterns,
+    responseHeaders,
   })
   await copyFile(join(__dirname, '..', '..', 'lib', 'templates', 'ipx.js'), join(functionDirectory, functionName))
 

packages/runtime/src/helpers/utils.ts

@@ -1,4 +1,6 @@
+/* eslint-disable max-lines */
 import type { NetlifyConfig } from '@netlify/build'
+import type { Header } from '@netlify/build/types/config/netlify_config'
 import globby from 'globby'
 import { join } from 'pathe'
 
@@ -185,3 +187,13 @@ export const isNextAuthInstalled = (): boolean => {
     return false
   }
 }
+
+export const getCustomImageResponseHeaders = (headers: Header[]): Record<string, string> | null => {
+  const customImageResponseHeaders = headers.find((header) => header.for?.startsWith('/_next/image/'))
+
+  if (customImageResponseHeaders) {
+    return customImageResponseHeaders?.values as Record<string, string>
+  }
+  return null
+}
+/* eslint-enable max-lines */

packages/runtime/src/index.ts

@@ -19,7 +19,7 @@ import { updateConfig, writeEdgeFunctions, loadMiddlewareManifest } from './help
 import { moveStaticPages, movePublicFiles, patchNextFiles, unpatchNextFiles } from './helpers/files'
 import { generateFunctions, setupImageFunction, generatePagesResolver } from './helpers/functions'
 import { generateRedirects, generateStaticRedirects } from './helpers/redirects'
-import { shouldSkip, isNextAuthInstalled } from './helpers/utils'
+import { shouldSkip, isNextAuthInstalled, getCustomImageResponseHeaders } from './helpers/utils'
 import {
   verifyNetlifyBuildVersion,
   checkNextSiteHasBuilt,
@@ -129,6 +129,7 @@ const plugin: NetlifyPlugin = {
       netlifyConfig,
       basePath,
       remotePatterns: experimentalRemotePatterns,
+      responseHeaders: getCustomImageResponseHeaders(netlifyConfig.headers),
     })
 
     await generateRedirects({

packages/runtime/src/templates/ipx.ts

@@ -3,11 +3,12 @@ import { Handler } from '@netlify/functions'
 import { createIPXHandler } from '@netlify/ipx'
 
 // @ts-ignore Injected at build time
-import { basePath, domains, remotePatterns } from './imageconfig.json'
+import { basePath, domains, remotePatterns, responseHeaders } from './imageconfig.json'
 
 export const handler: Handler = createIPXHandler({
   basePath,
   domains,
   remotePatterns,
+  responseHeaders,
 }) as Handler
 /* eslint-enable n/no-missing-import, import/no-unresolved, @typescript-eslint/ban-ts-comment  */

test/helpers/utils.spec.ts

@@ -0,0 +1,33 @@
+import Chance from 'chance'
+import { getCustomImageResponseHeaders } from '../../plugin/src/helpers/utils'
+
+const chance = new Chance()
+
+describe('getCustomImageResponseHeaders', () => {
+  it('returns null when no custom image response headers are found', () => {
+    const mockHeaders = [{
+      for: '/test',
+      values: {
+        'X-Foo': chance.string()
+      }
+    }]
+
+    expect(getCustomImageResponseHeaders(mockHeaders)).toBe(null)
+  })
+
+  it('returns header values when custom image response headers are found', () => {
+    const mockFooValue = chance.string()
+
+    const mockHeaders = [{
+      for: '/_next/image/',
+      values: {
+        'X-Foo': mockFooValue
+      }
+    }]
+
+    const result = getCustomImageResponseHeaders(mockHeaders)
+    expect(result).toStrictEqual({
+      'X-Foo': mockFooValue,
+    })
+  })
+})

test/index.js

@@ -530,13 +530,32 @@ describe('onBuild()', () => {
     expect(await plugin.onBuild(defaultArgs)).toBeUndefined()
   })
 
-  test('generates imageconfig file with entries for domains and remotePatterns', async () => {
+  test('generates imageconfig file with entries for domains, remotePatterns, and custom response headers', async () => {
     await moveNextDist()
-    await plugin.onBuild(defaultArgs)
+    const mockHeaderValue = chance.string()
+
+    const updatedArgs = {
+      ...defaultArgs,
+      netlifyConfig: {
+        ...defaultArgs.netlifyConfig,
+        headers: [{
+          for: '/_next/image/',
+          values: {
+            'X-Foo': mockHeaderValue
+          }
+        }]
+      }
+    }
+    await plugin.onBuild(updatedArgs)
+
     const imageConfigPath = path.join(constants.INTERNAL_FUNCTIONS_SRC, IMAGE_FUNCTION_NAME, 'imageconfig.json')
     const imageConfigJson = await readJson(imageConfigPath)
+
     expect(imageConfigJson.domains.length).toBe(1)
     expect(imageConfigJson.remotePatterns.length).toBe(1)
+    expect(imageConfigJson.responseHeaders).toStrictEqual({
+      'X-Foo': mockHeaderValue
+    })
   })
 })