Move metro-inspector-proxy into dev-middleware (#39045)

Summary:
Pull Request resolved: #39045

## Context

RFC: Decoupling Flipper from React Native core: react-native-community/discussions-and-proposals#641

## Changes

- Relocates `metro-inspector-proxy` source from the Metro repo into the React Native repo as part of the `react-native/dev-middleware` package.
    - Drops the `runInspectorProxy` entry point.
- Attaches the Inspector Proxy to the `createDevMiddleware()` API as the new integration point for this functionality.
- Documents migrated endpoints + usage of `createDevMiddleware()` in README.

Changelog: [Internal]
Metro changelog: None (`metro-inspector-proxy` is now an internal component of `react-native`, covered in the [release notes for 0.78.1](https://github.com/facebook/metro/releases/tag/v0.78.1))

Reviewed By: motiz88, blakef

Differential Revision: D48066213

fbshipit-source-id: 3fbef5d881f6f451cb5955dcbbc362c53347437e

Author: huntie

flow-typed/npm/@react-native-community/cli-server-api_v12.x.x.js

@@ -23,9 +23,7 @@ declare module '@react-native-community/cli-server-api' {
   ): {
     middleware: Server,
     websocketEndpoints: {
-      '/debugger-proxy': ws$WebSocketServer,
-      '/message': ws$WebSocketServer,
-      '/events': ws$WebSocketServer,
+      [path: string]: ws$WebSocketServer,
     },
     debuggerProxyEndpoint: {
       server: ws$WebSocketServer,

flow-typed/npm/debug_v2.x.x.js

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ * @format
+ */
+
+// https://github.com/visionmedia/debug
+// https://www.npmjs.com/package/debug
+
+declare module 'debug' {
+  declare module.exports: (namespace: string) => (...Array<mixed>) => void;
+}

packages/dev-middleware/README.md

@@ -1,11 +1,82 @@
 # @react-native/dev-middleware
 
-![https://img.shields.io/npm/v/@react-native/dev-middleware?color=brightgreen&label=npm%20package](https://www.npmjs.com/package/@react-native/dev-middleware)
+![npm package](https://img.shields.io/npm/v/@react-native/dev-middleware?color=brightgreen&label=npm%20package)
 
 Dev server middleware supporting core React Native development features. This package is preconfigured in all React Native projects.
 
-## Endpoints
+## Usage
 
-### `/open-debugger`
+Middleware can be attached to a dev server (e.g. [Metro](https://facebook.github.io/metro/docs/getting-started)) using the `createDevMiddleware` API.
+
+```js
+import { createDevMiddleware } from '@react-native/dev-middleware';
+
+function myDevServerImpl(args) {
+  ...
+
+  const {middleware, websocketEndpoints} = createDevMiddleware({
+    host: args.host,
+    port: metroConfig.server.port,
+    projectRoot: metroConfig.projectRoot,
+    logger,
+  });
+
+  await Metro.runServer(metroConfig, {
+    host: args.host,
+    ...,
+    unstable_extraMiddleware: [
+      middleware,
+      // Optionally extend with additional HTTP middleware
+    ],
+    websocketEndpoints: {
+      ...websocketEndpoints,
+      // Optionally extend with additional WebSocket endpoints
+    },
+  });
+}
+```
+
+## Included middleware
+
+`@react-native/dev-middleware` is designed for integrators such as [`@expo/dev-server`](https://www.npmjs.com/package/@expo/dev-server) and [`@react-native/community-cli-plugin`](https://github.com/facebook/react-native/tree/main/packages/community-cli-plugin). It provides a common default implementation for core React Native dev server responsibilities.
+
+We intend to keep this to a narrow set of functionality, based around:
+
+- **Debugging** — The [Chrome DevTools protocol (CDP)](https://chromedevtools.github.io/devtools-protocol/) endpoints supported by React Native, including the Inspector Proxy, which facilitates connections with multiple devices.
+- **Dev actions** — Endpoints implementing core [Dev Menu](https://reactnative.dev/docs/debugging#accessing-the-dev-menu) actions, e.g. reloading the app, opening the debugger frontend.
+
+### HTTP endpoints
+
+<small>`DevMiddlewareAPI.middleware`</small>
+
+These are exposed as a [`connect`](https://www.npmjs.com/package/connect) middleware handler, assignable to `Metro.runServer` or other compatible HTTP servers.
+
+#### GET `/json/list`, `/json` ([CDP](https://chromedevtools.github.io/devtools-protocol/#endpoints))
+
+Returns the list of available WebSocket targets for all connected React Native app sessions.
+
+#### GET `/json/version` ([CDP](https://chromedevtools.github.io/devtools-protocol/#endpoints))
+
+Returns version metadata used by Chrome DevTools.
+
+#### POST `/open-debugger`
 
 Open the JavaScript debugger for a given CDP target (direct Hermes debugging).
+
+<details>
+<summary>Example</summary>
+
+    curl -X POST 'http://localhost:8081/open-debugger?appId=com.meta.RNTester'
+</details>
+
+### WebSocket endpoints
+
+<small>`DevMiddlewareAPI.websocketEndpoints`</small>
+
+#### `/inspector/device`
+
+WebSocket handler for registering device connections.
+
+#### `/inspector/debug`
+
+WebSocket handler that proxies CDP messages to/from the corresponding device.

packages/dev-middleware/package.json

@@ -24,6 +24,7 @@
   "dependencies": {
     "chrome-launcher": "^0.15.2",
     "connect": "^3.6.5",
+    "debug": "^2.2.0",
     "node-fetch": "^2.2.0",
     "temp-dir": "^2.0.0"
   },

packages/dev-middleware/src/createDevMiddleware.js

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict
+ * @flow strict-local
  * @format
  * @oncall react_native
  */
@@ -14,18 +14,36 @@ import type {Logger} from './types/Logger';
 
 import connect from 'connect';
 import openDebuggerMiddleware from './middleware/openDebuggerMiddleware';
+import InspectorProxy from './inspector-proxy/InspectorProxy';
 
 type Options = $ReadOnly<{
+  host: string,
+  port: number,
+  projectRoot: string,
   logger?: Logger,
 }>;
 
-export default function createDevMiddleware({logger}: Options = {}): {
+type DevMiddlewareAPI = $ReadOnly<{
   middleware: NextHandleFunction,
-} {
-  const middleware = connect().use(
-    '/open-debugger',
-    openDebuggerMiddleware({logger}),
-  );
+  websocketEndpoints: {[path: string]: ws$WebSocketServer},
+}>;
+
+export default function createDevMiddleware({
+  host,
+  port,
+  projectRoot,
+  logger,
+}: Options): DevMiddlewareAPI {
+  const inspectorProxy = new InspectorProxy(projectRoot);
+
+  const middleware = connect()
+    .use('/open-debugger', openDebuggerMiddleware({logger}))
+    .use((...args) => inspectorProxy.processRequest(...args));
 
-  return {middleware};
+  return {
+    middleware,
+    websocketEndpoints: inspectorProxy.createWebSocketListeners(
+      `${host}:${port}`,
+    ),
+  };
 }

packages/dev-middleware/src/index.flow.js

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict
+ * @flow strict-local
  * @format
  * @oncall react_native
  */