feat(experimental): add fetchable environment interface

docs/guide/api-environment-frameworks.md

@@ -38,7 +38,48 @@ if (isRunnableDevEnvironment(server.environments.ssr)) {
 ```
 
 :::warning
-The `runner` is evaluated eagerly when it's accessed for the first time. Beware that Vite enables source map support when the `runner` is created by calling `process.setSourceMapsEnabled` or by overriding `Error.prepareStackTrace` if it's not available.
+The `runner` is evaluated lazily only when it's accessed for the first time. Beware that Vite enables source map support when the `runner` is created by calling `process.setSourceMapsEnabled` or by overriding `Error.prepareStackTrace` if it's not available.
+:::
+
+Frameworks that communicate with their runtime via the [Fetch API](https://developer.mozilla.org/en-US/docs/Web/API/Window/fetch) can utilize the `FetchableDevEnvironment` that provides a standardized way of handling requests via the `handleRequest` method:
+
+```ts
+import {
+  createServer,
+  createFetchableDevEnvironment,
+  isFetchableDevEnvironment,
+} from 'vite'
+
+const server = await createServer({
+  server: { middlewareMode: true },
+  appType: 'custom',
+  environments: {
+    custom: {
+      dev: {
+        createEnvironment(name, config) {
+          return createFetchableDevEnvironment(name, config, {
+            handleRequest(request: Request): Promise<Response> | Response {
+              // handle Request and return a Response
+            },
+          })
+        },
+      },
+    },
+  },
+})
+
+// Any consumer of the environment API can now call `dispatchFetch`
+if (isFetchableDevEnvironment(server.environments.custom)) {
+  const response: Response = await server.environments.custom.dispatchFetch(
+    new Request('/request-to-handle'),
+  )
+}
+```
+
+:::warning
+Vite validates the input and output of the `dispatchFetch` method: the request must be an instance of the global `Request` class and the response must be the instance of the global `Response` class. Vite will throw a `TypeError` if this is not the case.
+
+Note that although the `FetchableDevEnvironment` is implemented as a class, it is considered an implementation detail by the Vite team and might change at any moment.
 :::
 
 ## Default `RunnableDevEnvironment`

eslint.config.js

@@ -63,7 +63,13 @@ export default tseslint.config(
       'n/no-exports-assign': 'error',
       'n/no-unpublished-bin': 'error',
       'n/no-unsupported-features/es-builtins': 'error',
-      'n/no-unsupported-features/node-builtins': 'error',
+      'n/no-unsupported-features/node-builtins': [
+        'error',
+        {
+          // TODO: remove this when we don't support Node 18 anymore
+          ignores: ['Response', 'Request', 'fetch'],
+        },
+      ],
       'n/process-exit-as-throw': 'error',
       'n/hashbang': 'error',
 

packages/vite/index.cjs

@@ -48,6 +48,8 @@ const disallowedVariables = [
   'createServerModuleRunner',
   'createServerModuleRunnerTransport',
   'isRunnableDevEnvironment',
+  'createFetchableDevEnvironment',
+  'isFetchableDevEnvironment',
 ]
 disallowedVariables.forEach((name) => {
   Object.defineProperty(module.exports, name, {

packages/vite/src/node/index.ts

@@ -27,6 +27,12 @@ export {
   type RunnableDevEnvironment,
   type RunnableDevEnvironmentContext,
 } from './server/environments/runnableEnvironment'
+export {
+  createFetchableDevEnvironment,
+  isFetchableDevEnvironment,
+  type FetchableDevEnvironment,
+  type FetchableDevEnvironmentContext,
+} from './server/environments/fetchableEnvironments'
 export {
   DevEnvironment,
   type DevEnvironmentContext,

packages/vite/src/node/server/environments/fetchableEnvironments.ts

@@ -0,0 +1,64 @@
+import type { ResolvedConfig } from '../../config'
+import type { DevEnvironmentContext } from '../environment'
+import { DevEnvironment } from '../environment'
+import type { Environment } from '../../environment'
+
+export interface FetchableDevEnvironmentContext extends DevEnvironmentContext {
+  handleRequest(request: Request): Promise<Response> | Response
+}
+
+export function createFetchableDevEnvironment(
+  name: string,
+  config: ResolvedConfig,
+  context: FetchableDevEnvironmentContext,
+): FetchableDevEnvironment {
+  if (typeof Request === 'undefined' || typeof Response === 'undefined') {
+    throw new TypeError(
+      'FetchableDevEnvironment requires a global `Request` and `Response` object.',
+    )
+  }
+
+  if (!context.handleRequest) {
+    throw new TypeError(
+      'FetchableDevEnvironment requires a `handleRequest` method during initialisation.',
+    )
+  }
+
+  return new FetchableDevEnvironment(name, config, context)
+}
+
+export function isFetchableDevEnvironment(
+  environment: Environment,
+): environment is FetchableDevEnvironment {
+  return environment instanceof FetchableDevEnvironment
+}
+
+class FetchableDevEnvironment extends DevEnvironment {
+  private _handleRequest: (request: Request) => Promise<Response> | Response
+
+  constructor(
+    name: string,
+    config: ResolvedConfig,
+    context: FetchableDevEnvironmentContext,
+  ) {
+    super(name, config, context)
+    this._handleRequest = context.handleRequest
+  }
+
+  public async dispatchFetch(request: Request): Promise<Response> {
+    if (!(request instanceof Request)) {
+      throw new TypeError(
+        'FetchableDevEnvironment `dispatchFetch` must receive a `Request` object.',
+      )
+    }
+    const response = await this._handleRequest(request)
+    if (!(response instanceof Response)) {
+      throw new TypeError(
+        'FetchableDevEnvironment `context.handleRequest` must return a `Response` object.',
+      )
+    }
+    return response
+  }
+}
+
+export type { FetchableDevEnvironment }