[netlify] allow opting out of Image CDN (#120)

* chore: add image CDN tests

* feat: allow image cdn opt-out

* write docs

* add changeset

* fix: put proper jsdoc values

.changeset/slimy-donuts-lick.md

@@ -0,0 +1,5 @@
+---
+'@astrojs/netlify': minor
+---
+
+Adds opt-out option for Image CDN.

packages/netlify/src/index.ts

@@ -49,9 +49,19 @@ export interface NetlifyIntegrationConfig {
 	 * If enabled, Astro Middleware is deployed as an Edge Function and applies to all routes.
 	 * Caveat: Locals set in Middleware are not applied to prerendered pages, because they've been rendered at build-time and are served from the CDN.
 	 *
-	 * @default disabled
+	 * @default {false}
 	 */
 	edgeMiddleware?: boolean;
+
+	/**
+	 * If enabled, Netlify Image CDN is used for image optimization.
+	 * This transforms images on-the-fly without impacting build times.
+	 * 
+	 * If disabled, Astro's built-in image optimization is run at build-time instead.
+	 * 
+	 * @default {true}
+	 */
+	imageCDN?: boolean
 }
 
 export default function netlifyIntegration(
@@ -226,6 +236,8 @@ export default function netlifyIntegration(
 
 				outDir = new URL('./dist/', rootDir);
 
+				const enableImageCDN = isRunningInNetlify && (integrationConfig?.imageCDN ?? true);
+
 				updateConfig({
 					outDir,
 					build: {
@@ -242,7 +254,7 @@ export default function netlifyIntegration(
 					},
 					image: {
 						service: {
-							entrypoint: isRunningInNetlify ? '@astrojs/netlify/image-service.js' : undefined,
+							entrypoint: enableImageCDN ? '@astrojs/netlify/image-service.js' : undefined,
 						},
 					},
 				});

packages/netlify/test/functions/fixtures/middleware/astro.config.mjs

@@ -5,6 +5,7 @@ export default defineConfig({
   output: 'server',
   adapter: netlify({
     edgeMiddleware: process.env.EDGE_MIDDLEWARE === 'true',
+    imageCDN: process.env.DISABLE_IMAGE_CDN ? false : undefined,
   }),
   site: `http://example.com`,
 });

packages/netlify/test/functions/fixtures/middleware/src/pages/astronaut.astro

@@ -0,0 +1,9 @@
+---
+import { Image } from 'astro:assets';
+import astronautImage from "../astronaut.jpg"
+
+export const prerender = true;
+---
+
+<Image src={astronautImage} alt="an astronaut floating in space" />
+

packages/netlify/test/functions/image-cdn.test.js

@@ -0,0 +1,43 @@
+import { loadFixture } from '@astrojs/test-utils';
+import { expect } from 'chai';
+import { describe } from 'node:test';
+
+describe('Image CDN', () => {
+	const root = new URL('./fixtures/middleware/', import.meta.url);
+
+  describe("when running outside of netlify", () => {
+    it("does not enable Image CDN", async () => {
+      const fixture = await loadFixture({ root });
+			await fixture.build();
+
+      const astronautPage = await fixture.readFile('astronaut/index.html');
+      expect(astronautPage).contains(`src="/_astro/astronaut.`)
+    })
+  })
+
+  describe("when running inside of netlify", () => {
+    it("enables Netlify Image CDN", async () => {
+      process.env.NETLIFY = 'true'
+      const fixture = await loadFixture({ root });
+			await fixture.build();
+
+      const astronautPage = await fixture.readFile('astronaut/index.html');
+      expect(astronautPage).contains(`src="/.netlify/image`)
+
+      process.env.NETLIFY = undefined
+    })
+
+    it("respects image CDN opt-out", async () => {
+      process.env.NETLIFY = 'true'
+      process.env.DISABLE_IMAGE_CDN = 'true'
+      const fixture = await loadFixture({ root });
+			await fixture.build();
+
+      const astronautPage = await fixture.readFile('astronaut/index.html');
+      expect(astronautPage).contains(`src="/_astro/astronaut.`)
+
+      process.env.NETLIFY = undefined
+      process.env.DISABLE_IMAGE_CDN = undefined
+    })
+  })
+});