feature(dev-middleware): add custom message handlers to extend CDP capabilities (#43291)

Summary:
This is a proposal for the `react-native/dev-middleware` package, to allow implementers to extend the CDP capabilities of the `InspectorProxy`. It's unfortunately needed until we can move to the native Hermes CDP layer.

At Expo, we extend the CDP capabilities of this `InspectorProxy` by injecting functionality on the device level. This proposed API does the same, but without having to overwrite internal functions of both the `InspectorProxy` and `InspectorDevice`.

A good example of this is the network inspector's capabilities. This currently works through the inspection proxy, and roughly like:
- Handle any incoming `Expo(Network.receivedResponseBody)` from the _**device**_, store it, and stop event from propagating
- Handle the incoming `Network.getResponseBody` from the _**debugger**_, return the data, and stop event from propagating.

This API brings back that capability in a more structured way.

## API:

```ts
import { createDevMiddleware } from 'react-native/dev-middleware';

const { middleware, websocketEndpoints } = createDevMiddleware({
  unstable_customInspectorMessageHandler: ({ page, deviceInfo, debuggerInfo }) => {
    // Do not enable handler for page other than "SOMETHING", or for vscode debugging
    // Can also include `page.capabilities` to determine if handler is required
    if (page.title !== 'SOMETHING' || debuggerInfo.userAgent?.includes('vscode')) {
      return null;
    }

    return {
      handleDeviceMessage(message) {
        if (message.type === 'CDP_MESSAGE') {
          // Do something and stop message from propagating with return `true`
          return true;
        }
      },
      handleDebuggerMessage(message) {
        if (message.type === 'CDP_MESSAGE') {
          // Do something and stop message from propagating with return `true`
          return true;
        }
      },
    };
  },
});
```

## Changelog:

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[GENERAL] [ADDED] - Add inspector proxy device message middleware API

Pull Request resolved: https://github.com/facebook/react-native/pull/43291

Test Plan: See added tests and code above

Reviewed By: huntie

Differential Revision: D54804503

Pulled By: motiz88

fbshipit-source-id: ae918dcd5b7e76d3fb31db4c84717567ae60fa96

packages/dev-middleware/src/inspector-proxy/CustomMessageHandler.js

@@ -0,0 +1,54 @@
+/**
+ * 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 strict-local
+ * @format
+ */
+
+import type {JSONSerializable, Page} from './types';
+
+type ExposedDevice = $ReadOnly<{
+  appId: string,
+  id: string,
+  name: string,
+  sendMessage: (message: JSONSerializable) => void,
+}>;
+
+type ExposedDebugger = $ReadOnly<{
+  userAgent: string | null,
+  sendMessage: (message: JSONSerializable) => void,
+}>;
+
+export type CustomMessageHandlerConnection = $ReadOnly<{
+  page: Page,
+  device: ExposedDevice,
+  debugger: ExposedDebugger,
+}>;
+
+export type CreateCustomMessageHandlerFn = (
+  connection: CustomMessageHandlerConnection,
+) => ?CustomMessageHandler;
+
+/**
+ * The device message middleware allows implementers to handle unsupported CDP messages.
+ * It is instantiated per device and may contain state that is specific to that device.
+ * The middleware can also mark messages from the device or debugger as handled, which stops propagating.
+ */
+export interface CustomMessageHandler {
+  /**
+   * Handle a CDP message coming from the device.
+   * This is invoked before the message is sent to the debugger.
+   * When returning true, the message is considered handled and will not be sent to the debugger.
+   */
+  handleDeviceMessage(message: JSONSerializable): true | void;
+
+  /**
+   * Handle a CDP message coming from the debugger.
+   * This is invoked before the message is sent to the device.
+   * When returning true, the message is considered handled and will not be sent to the device.
+   */
+  handleDebuggerMessage(message: JSONSerializable): true | void;
+}

packages/dev-middleware/src/inspector-proxy/Device.js

@@ -16,6 +16,10 @@ import type {
   CDPResponse,
   CDPServerMessage,
 } from './cdp-types/messages';
+import type {
+  CreateCustomMessageHandlerFn,
+  CustomMessageHandler,
+} from './CustomMessageHandler';
 import type {
   MessageFromDevice,
   MessageToDevice,
@@ -51,6 +55,11 @@ type DebuggerInfo = {
   userAgent: string | null,
 };
 
+type DebuggerConnection = {
+  ...DebuggerInfo,
+  customHandler: ?CustomMessageHandler,
+};
+
 const REACT_NATIVE_RELOADABLE_PAGE_ID = '-1';
 
 /**
@@ -74,7 +83,7 @@ export default class Device {
   #pages: $ReadOnlyMap<string, Page>;
 
   // Stores information about currently connected debugger (if any).
-  #debuggerConnection: ?DebuggerInfo = null;
+  #debuggerConnection: ?DebuggerConnection = null;
 
   // Last known Page ID of the React Native page.
   // This is used by debugger connections that don't have PageID specified
@@ -97,6 +106,9 @@ export default class Device {
 
   #pagesPollingIntervalId: ReturnType<typeof setInterval>;
 
+  // The device message middleware factory function allowing implementers to handle unsupported CDP messages.
+  #createCustomMessageHandler: ?CreateCustomMessageHandlerFn;
+
   constructor(
     id: string,
     name: string,
@@ -104,6 +116,7 @@ export default class Device {
     socket: WS,
     projectRoot: string,
     eventReporter: ?EventReporter,
+    createMessageMiddleware: ?CreateCustomMessageHandlerFn,
   ) {
     this.#id = id;
     this.#name = name;
@@ -118,6 +131,7 @@ export default class Device {
           appId: app,
         })
       : null;
+    this.#createCustomMessageHandler = createMessageMiddleware;
 
     // $FlowFixMe[incompatible-call]
     this.#deviceSocket.on('message', (message: string) => {
@@ -205,6 +219,7 @@ export default class Device {
       prependedFilePrefix: false,
       pageId,
       userAgent: metadata.userAgent,
+      customHandler: null,
     };
 
     // TODO(moti): Handle null case explicitly, e.g. refuse to connect to
@@ -215,6 +230,50 @@ export default class Device {
 
     debug(`Got new debugger connection for page ${pageId} of ${this.#name}`);
 
+    if (page && this.#debuggerConnection && this.#createCustomMessageHandler) {
+      this.#debuggerConnection.customHandler = this.#createCustomMessageHandler(
+        {
+          page,
+          debugger: {
+            userAgent: debuggerInfo.userAgent,
+            sendMessage: message => {
+              try {
+                const payload = JSON.stringify(message);
+                debug('(Debugger) <- (Proxy)    (Device): ' + payload);
+                socket.send(payload);
+              } catch {}
+            },
+          },
+          device: {
+            appId: this.#app,
+            id: this.#id,
+            name: this.#name,
+            sendMessage: message => {
+              try {
+                const payload = JSON.stringify({
+                  event: 'wrappedEvent',
+                  payload: {
+                    pageId: this.#mapToDevicePageId(pageId),
+                    wrappedEvent: JSON.stringify(message),
+                  },
+                });
+                debug('(Debugger) -> (Proxy)    (Device): ' + payload);
+                this.#deviceSocket.send(payload);
+              } catch {}
+            },
+          },
+        },
+      );
+
+      if (this.#debuggerConnection.customHandler) {
+        debug('Created new custom message handler for debugger connection');
+      } else {
+        debug(
+          'Skipping new custom message handler for debugger connection, factory function returned null',
+        );
+      }
+    }
+
     this.#sendMessageToDevice({
       event: 'connect',
       payload: {
@@ -231,6 +290,15 @@ export default class Device {
         frontendUserAgent: metadata.userAgent,
       });
       let processedReq = debuggerRequest;
+
+      if (
+        this.#debuggerConnection?.customHandler?.handleDebuggerMessage(
+          debuggerRequest,
+        ) === true
+      ) {
+        return;
+      }
+
       if (!page || !this.#pageHasCapability(page, 'nativeSourceCodeFetching')) {
         processedReq = this.#interceptClientMessageForSourceFetching(
           debuggerRequest,
@@ -411,12 +479,21 @@ export default class Device {
         });
       }
 
-      if (this.#debuggerConnection != null) {
+      const debuggerConnection = this.#debuggerConnection;
+      if (debuggerConnection != null) {
+        if (
+          debuggerConnection.customHandler?.handleDeviceMessage(
+            parsedPayload,
+          ) === true
+        ) {
+          return;
+        }
+
         // Wrapping just to make flow happy :)
         // $FlowFixMe[unused-promise]
         this.#processMessageFromDeviceLegacy(
           parsedPayload,
-          this.#debuggerConnection,
+          debuggerConnection,
           pageId,
         ).then(() => {
           const messageToSend = JSON.stringify(parsedPayload);
@@ -499,7 +576,7 @@ export default class Device {
   // Allows to make changes in incoming message from device.
   async #processMessageFromDeviceLegacy(
     payload: CDPServerMessage,
-    debuggerInfo: DebuggerInfo,
+    debuggerInfo: DebuggerConnection,
     pageId: ?string,
   ) {
     // TODO(moti): Handle null case explicitly, or ideally associate a copy
@@ -616,7 +693,7 @@ export default class Device {
    */
   #interceptClientMessageForSourceFetching(
     req: CDPClientMessage,
-    debuggerInfo: DebuggerInfo,
+    debuggerInfo: DebuggerConnection,
     socket: WS,
   ): CDPClientMessage | null {
     switch (req.method) {
@@ -633,7 +710,7 @@ export default class Device {
 
   #processDebuggerSetBreakpointByUrl(
     req: CDPRequest<'Debugger.setBreakpointByUrl'>,
-    debuggerInfo: DebuggerInfo,
+    debuggerInfo: DebuggerConnection,
   ): CDPRequest<'Debugger.setBreakpointByUrl'> {
     // If we replaced Android emulator's address to localhost we need to change it back.
     if (debuggerInfo.originalSourceURLAddress != null) {

packages/dev-middleware/src/inspector-proxy/InspectorProxy.js

@@ -11,6 +11,7 @@
 
 import type {EventReporter} from '../types/EventReporter';
 import type {Experiments} from '../types/Experiments';
+import type {CreateCustomMessageHandlerFn} from './CustomMessageHandler';
 import type {
   JsonPagesListResponse,
   JsonVersionResponse,
@@ -58,17 +59,22 @@ export default class InspectorProxy implements InspectorProxyQueries {
 
   #experiments: Experiments;
 
+  // custom message handler factory allowing implementers to handle unsupported CDP messages.
+  #customMessageHandler: ?CreateCustomMessageHandlerFn;
+
   constructor(
     projectRoot: string,
     serverBaseUrl: string,
     eventReporter: ?EventReporter,
     experiments: Experiments,
+    customMessageHandler: ?CreateCustomMessageHandlerFn,
   ) {
     this.#projectRoot = projectRoot;
     this.#serverBaseUrl = serverBaseUrl;
     this.#devices = new Map();
     this.#eventReporter = eventReporter;
     this.#experiments = experiments;
+    this.#customMessageHandler = customMessageHandler;
   }
 
   getPageDescriptions(): Array<PageDescription> {
@@ -204,6 +210,7 @@ export default class InspectorProxy implements InspectorProxyQueries {
           socket,
           this.#projectRoot,
           this.#eventReporter,
+          this.#customMessageHandler,
         );
 
         if (oldDevice) {