Improving support for third-party hosted image services (#3957)

* WIP: always use the built-in sharp service for local images in `dev`

* adding type definitions for the integration's use of globalThis

* simplifying the globalThis type checking

* chore: adding changeset

* removing temp hosted service used for testing

6 files changed, 59 insertions, 15 deletions

diff --git a/.changeset/purple-vans-bake.md b/.changeset/purple-vans-bake.md
new file mode 100644
index 000000000..3af99ba74
--- /dev/null
+++ b/.changeset/purple-vans-bake.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/image': patch
+---
+
+Improves the `astro dev` experience when using a third-party hosted image service
diff --git a/packages/integrations/image/README.md b/packages/integrations/image/README.md
index b14587d71..ee9fdf3c9 100644
--- a/packages/integrations/image/README.md
+++ b/packages/integrations/image/README.md
@@ -73,6 +73,8 @@ The included `sharp` transformer supports resizing images and encoding them to d
 
 The intergration can be configured to run with a different image service, either a hosted image service or a full image transformer that runs locally in your build or SSR deployment.
 
+> During development, local images may not have been published yet and would not be available to hosted image services. Local images will always use the built-in `sharp` service when using `astro dev`.
+
 There are currently no other configuration options for the `@astrojs/image` integration. Please [open an issue](https://github.com/withastro/astro/issues/new/choose) if you have a compelling use case to share.
 
 <details>
diff --git a/packages/integrations/image/src/endpoints/dev.ts b/packages/integrations/image/src/endpoints/dev.ts
index 3d8b28993..67b37b177 100644
--- a/packages/integrations/image/src/endpoints/dev.ts
+++ b/packages/integrations/image/src/endpoints/dev.ts
@@ -1,10 +1,10 @@
 import type { APIRoute } from 'astro';
 import { lookup } from 'mrmime';
-// @ts-ignore
-import loader from 'virtual:image-loader';
 import { loadImage } from '../utils.js';
 
 export const get: APIRoute = async ({ request }) => {
+	const loader = globalThis.astroImage.ssrLoader;
+
 	try {
 		const url = new URL(request.url);
 		const transform = loader.parseTransform(url.searchParams);
diff --git a/packages/integrations/image/src/get-image.ts b/packages/integrations/image/src/get-image.ts
index 5eb41cf73..83ac2e5ba 100644
--- a/packages/integrations/image/src/get-image.ts
+++ b/packages/integrations/image/src/get-image.ts
@@ -8,7 +8,7 @@ import {
 	OutputFormat,
 	TransformOptions,
 } from './types.js';
-import { parseAspectRatio } from './utils.js';
+import { isRemoteImage, parseAspectRatio } from './utils.js';
 
 export interface GetImageTransform extends Omit<TransformOptions, 'src'> {
 	src: string | ImageMetadata | Promise<{ default: ImageMetadata }>;
@@ -105,23 +105,32 @@ export async function getImage(
 	loader: ImageService,
 	transform: GetImageTransform
 ): Promise<ImageAttributes> {
-	(globalThis as any).loader = loader;
+	globalThis.astroImage.loader = loader;
 
 	const resolved = await resolveTransform(transform);
+
 	const attributes = await loader.getImageAttributes(resolved);
 
+	const isDev = globalThis.astroImage.command === 'dev';
+	const isLocalImage = !isRemoteImage(resolved.src);
+	
+	const _loader = isDev && isLocalImage ? globalThis.astroImage.ssrLoader : loader;
+
+	if (!_loader) {
+		throw new Error('@astrojs/image: loader not found!');
+	}
+
 	// For SSR services, build URLs for the injected route
-	if (isSSRService(loader)) {
-		const { searchParams } = loader.serializeTransform(resolved);
+	if (isSSRService(_loader)) {
+		const { searchParams } = _loader.serializeTransform(resolved);
 
 		// cache all images rendered to HTML
-		if (globalThis && (globalThis as any).addStaticImage) {
-			(globalThis as any)?.addStaticImage(resolved);
+		if (globalThis?.astroImage) {
+			globalThis.astroImage.addStaticImage(resolved);
 		}
 
-		const src =
-			globalThis && (globalThis as any).filenameFormat
-				? (globalThis as any).filenameFormat(resolved, searchParams)
+		const src = globalThis?.astroImage
+				? globalThis.astroImage.filenameFormat(resolved, searchParams)
 				: `${ROUTE_PATTERN}?${searchParams.toString()}`;
 
 		return {
diff --git a/packages/integrations/image/src/index.ts b/packages/integrations/image/src/index.ts
index 3721f9667..da1ec1d4b 100644
--- a/packages/integrations/image/src/index.ts
+++ b/packages/integrations/image/src/index.ts
@@ -3,6 +3,7 @@ import fs from 'fs/promises';
 import path from 'path';
 import { fileURLToPath } from 'url';
 import { OUTPUT_DIR, PKG_NAME, ROUTE_PATTERN } from './constants.js';
+import sharp from './loaders/sharp.js';
 import { IntegrationOptions, TransformOptions } from './types.js';
 import {
 	ensureDir,
@@ -51,15 +52,15 @@ const createIntegration = (options: IntegrationOptions = {}): AstroIntegration =
 
 				// Used to cache all images rendered to HTML
 				// Added to globalThis to share the same map in Node and Vite
-				(globalThis as any).addStaticImage = (transform: TransformOptions) => {
+				function addStaticImage(transform: TransformOptions) {
 					staticImages.set(propsToFilename(transform), transform);
 				};
 
 				// TODO: Add support for custom, user-provided filename format functions
-				(globalThis as any).filenameFormat = (
+				function filenameFormat(
 					transform: TransformOptions,
 					searchParams: URLSearchParams
-				) => {
+				) {
 					if (mode === 'ssg') {
 						return isRemoteImage(transform.src)
 							? path.join(OUTPUT_DIR, path.basename(propsToFilename(transform)))
@@ -73,6 +74,16 @@ const createIntegration = (options: IntegrationOptions = {}): AstroIntegration =
 					}
 				};
 
+				// Initialize the integration's globalThis namespace
+				// This is needed to share scope between Node and Vite
+				globalThis.astroImage = {
+					loader: undefined, // initialized in first getImage() call
+					ssrLoader: sharp,
+					command,
+					addStaticImage,
+					filenameFormat,
+				}
+
 				if (mode === 'ssr') {
 					injectRoute({
 						pattern: ROUTE_PATTERN,
@@ -83,7 +94,12 @@ const createIntegration = (options: IntegrationOptions = {}): AstroIntegration =
 			},
 			'astro:build:done': async ({ dir }) => {
 				for await (const [filename, transform] of staticImages) {
-					const loader = (globalThis as any).loader;
+					const loader = globalThis.astroImage.loader;
+
+					if (!loader || !('transform' in loader)) {
+						// this should never be hit, how was a staticImage added without an SSR service?
+						return;
+					}
 
 					let inputBuffer: Buffer | undefined = undefined;
 					let outputFile: string;
diff --git a/packages/integrations/image/src/types.ts b/packages/integrations/image/src/types.ts
index 96067e828..e6c315c23 100644
--- a/packages/integrations/image/src/types.ts
+++ b/packages/integrations/image/src/types.ts
@@ -2,6 +2,18 @@
 export type { Image, Picture } from '../components/index.js';
 export * from './index.js';
 
+interface ImageIntegration {
+	loader?: ImageService;
+	ssrLoader: SSRImageService;
+	command: 'dev' | 'build';
+	addStaticImage: (transform: TransformOptions) => void;
+	filenameFormat: (transform: TransformOptions, searchParams: URLSearchParams) => string;
+}
+
+declare global {
+	var astroImage: ImageIntegration;
+}
+
 export type InputFormat =
 	| 'heic'
 	| 'heif'