dev-middleware: Redefine "serverBaseUrl" as server-relative, '/json/list' by requestor

Summary:
`serverBaseUrl` is currently documented as:

> The base URL to the dev server, as addressible from the local developer machine

This is problematic in general because `dev-middleware` on a server doesn't necessarily know about where clients might be reaching it from, how tunnels or port-forwards are set up, etc., and this can change over the lifetime of the server and vary between clients.

Indeed, our own use of `serverBaseUrl` from both `community-cli-plugin` and internally simply sets it to the host and port the dev server is listening on - ie it's the address of the dev server accessible *from the server*.

This PR changes the docs, redefining `serverBaseUrl`, to match the way we currently specify it.

One usage where we *do* want the previously documented behaviour is in responses to `/json/list` (`getPageDescriptions`) where the URLs in the response should be reachable by a browser requesting `/json/list`. 

Here, we use the request (host header, etc.) to attempt to get working base URL.

History:
It should be mentioned that this is the latest in a series of changes like this:
 - https://github.com/facebook/react-native/pull/39394
 - https://github.com/facebook/react-native/pull/39456

Learning from those:
 - This change does *not* break Android emulators, which routes `10.0.2.2` to localhost, or other routed devices, because `/open-debugger` still uses server-relative URLs, and now formally delegates to `BrowserLauncher` to decide what to do with those URLs (internally, VSCode / `xdg-open` handles port forwarding)
 - Middleware configuration is no longer required to specify how it is reachable from clients.

This sets up some subsequent changes for more robust handling of tunnelled connections.

Changelog:
[General][Breaking] dev-middleware: Frameworks should specify `serverBaseUrl` relative to the middleware host.

Differential Revision: D65974487

packages/dev-middleware/src/__tests__/getBaseUrlFromRequest-test.js

@@ -0,0 +1,49 @@
+/**
+ * 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
+ * @oncall react_native
+ */
+
+import getBaseUrlFromRequest from '../utils/getBaseUrlFromRequest';
+
+test('returns a base url based on req.headers.host', () => {
+  expect(
+    getBaseUrlFromRequest(makeRequest('localhost:8081', false))?.href,
+  ).toEqual('http://localhost:8081/');
+});
+
+test('identifies https using socket.encrypted', () => {
+  expect(
+    getBaseUrlFromRequest(makeRequest('secure.net:8443', true))?.href,
+  ).toEqual('https://secure.net:8443/');
+});
+
+test('works with ipv6 hosts', () => {
+  expect(getBaseUrlFromRequest(makeRequest('[::1]:8081', false))?.href).toEqual(
+    'http://[::1]:8081/',
+  );
+});
+
+test('returns null on an invalid host header', () => {
+  expect(getBaseUrlFromRequest(makeRequest('local[]host', false))).toBeNull();
+});
+
+test('returns null on an empty host header', () => {
+  expect(getBaseUrlFromRequest(makeRequest(null, false))).toBeNull();
+});
+
+function makeRequest(
+  host: ?string,
+  encrypted: boolean,
+): http$IncomingMessage<> | http$IncomingMessage<tls$TLSSocket> {
+  // $FlowIgnore[incompatible-return] Partial mock of request
+  return {
+    socket: encrypted ? {encrypted: true} : {},
+    headers: host != null ? {host} : {},
+  };
+}

packages/dev-middleware/src/createDevMiddleware.js

@@ -28,11 +28,8 @@ type Options = $ReadOnly<{
   projectRoot: string,
 
   /**
-   * The base URL to the dev server, as addressible from the local developer
-   * machine. This is used in responses which return URLs to other endpoints,
-   * e.g. the debugger frontend and inspector proxy targets.
-   *
-   * Example: `'http://localhost:8081'`.
+   * The base URL to the dev server, as reachable from the machine on which
+   * dev-middleware is hosted. Typically `http://localhost:${metroPort}`.
    */
   serverBaseUrl: string,
 

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

@@ -133,6 +133,7 @@ export default class Device {
     projectRoot: string,
     eventReporter: ?EventReporter,
     createMessageMiddleware: ?CreateCustomMessageHandlerFn,
+    serverBaseUrl?: URL,
   ) {
     this.#dangerouslyConstruct(
       id,

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

@@ -22,6 +22,7 @@ import type {IncomingMessage, ServerResponse} from 'http';
 // $FlowFixMe[cannot-resolve-module] libdef missing in RN OSS
 import type {Timeout} from 'timers';
 
+import getBaseUrlFromRequest from '../utils/getBaseUrlFromRequest';
 import Device from './Device';
 import nullthrows from 'nullthrows';
 // Import these from node:timers to get the correct Flow types.
@@ -47,7 +48,7 @@ export interface InspectorProxyQueries {
    * Returns list of page descriptions ordered by device connection order, then
    * page addition order.
    */
-  getPageDescriptions(): Array<PageDescription>;
+  getPageDescriptions(requestorRelativeBaseUrl: URL): Array<PageDescription>;
 }
 
 /**
@@ -57,8 +58,8 @@ export default class InspectorProxy implements InspectorProxyQueries {
   // Root of the project used for relative to absolute source path conversion.
   #projectRoot: string;
 
-  /** The base URL to the dev server from the developer machine. */
-  #serverBaseUrl: string;
+  // The base URL to the dev server from the dev-middleware host.
+  #serverBaseUrl: URL;
 
   // Maps device ID to Device instance.
   #devices: Map<string, Device>;
@@ -81,14 +82,14 @@ export default class InspectorProxy implements InspectorProxyQueries {
     customMessageHandler: ?CreateCustomMessageHandlerFn,
   ) {
     this.#projectRoot = projectRoot;
-    this.#serverBaseUrl = serverBaseUrl;
+    this.#serverBaseUrl = new URL(serverBaseUrl);
     this.#devices = new Map();
     this.#eventReporter = eventReporter;
     this.#experiments = experiments;
     this.#customMessageHandler = customMessageHandler;
   }
 
-  getPageDescriptions(): Array<PageDescription> {
+  getPageDescriptions(requestorRelativeBaseUrl: URL): Array<PageDescription> {
     // Build list of pages from all devices.
     let result: Array<PageDescription> = [];
     Array.from(this.#devices.entries()).forEach(([deviceId, device]) => {
@@ -96,7 +97,12 @@ export default class InspectorProxy implements InspectorProxyQueries {
         device
           .getPagesList()
           .map((page: Page) =>
-            this.#buildPageDescription(deviceId, device, page),
+            this.#buildPageDescription(
+              deviceId,
+              device,
+              page,
+              requestorRelativeBaseUrl,
+            ),
           ),
       );
     });
@@ -117,7 +123,12 @@ export default class InspectorProxy implements InspectorProxyQueries {
       pathname === PAGES_LIST_JSON_URL ||
       pathname === PAGES_LIST_JSON_URL_2
     ) {
-      this.#sendJsonResponse(response, this.getPageDescriptions());
+      this.#sendJsonResponse(
+        response,
+        this.getPageDescriptions(
+          getBaseUrlFromRequest(request) ?? this.#serverBaseUrl,
+        ),
+      );
     } else if (pathname === PAGES_LIST_JSON_VERSION_URL) {
       this.#sendJsonResponse(response, {
         Browser: 'Mobile JavaScript',
@@ -143,8 +154,9 @@ export default class InspectorProxy implements InspectorProxyQueries {
     deviceId: string,
     device: Device,
     page: Page,
+    requestorRelativeBaseUrl: URL,
   ): PageDescription {
-    const {host, protocol} = new URL(this.#serverBaseUrl);
+    const {host, protocol} = requestorRelativeBaseUrl;
     const webSocketScheme = protocol === 'https:' ? 'wss' : 'ws';
 
     const webSocketUrlWithoutProtocol = `${host}${WS_DEBUGGER_URL}?device=${deviceId}&page=${page.id}`;

packages/dev-middleware/src/middleware/openDebuggerMiddleware.js

@@ -72,12 +72,14 @@ export default function openDebuggerMiddleware({
         ...
       } = query;
 
-      const targets = inspectorProxy.getPageDescriptions().filter(
-        // Only use targets with better reloading support
-        app =>
-          app.title === LEGACY_SYNTHETIC_PAGE_TITLE ||
-          app.reactNative.capabilities?.nativePageReloads === true,
-      );
+      const targets = inspectorProxy
+        .getPageDescriptions(new URL(serverBaseUrl))
+        .filter(
+          // Only use targets with better reloading support
+          app =>
+            app.title === LEGACY_SYNTHETIC_PAGE_TITLE ||
+            app.reactNative.capabilities?.nativePageReloads === true,
+        );
 
       let target;
 

packages/dev-middleware/src/types/BrowserLauncher.js

@@ -18,6 +18,10 @@ export interface BrowserLauncher {
    * Attempt to open a debugger frontend URL in a browser app window,
    * optionally returning an object to control the launched browser instance.
    * The browser used should be capable of running Chrome DevTools.
+   *
+   * The provided url is based on serverBaseUrl, and therefore reachable from
+   * the host of dev-middleware. Implementations are responsible for rewriting
+   * this as necessary where the server is remote.
    */
   launchDebuggerAppWindow: (url: string) => Promise<void>;
 }

packages/dev-middleware/src/utils/getBaseUrlFromRequest.js

@@ -0,0 +1,28 @@
+/**
+ * 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
+ * @oncall react_native
+ */
+
+// Determine the base URL (scheme and host) used by a client to reach this
+// server.
+//
+// TODO: Support X-Forwarded-Host, etc. for trusted proxies
+export default function getBaseUrlFromRequest(
+  req: http$IncomingMessage<tls$TLSSocket> | http$IncomingMessage<net$Socket>,
+): ?URL {
+  const hostHeader = req.headers.host;
+  if (hostHeader == null) {
+    return null;
+  }
+  // `encrypted` is always true for TLS sockets and undefined for net
+  // https://github.com/nodejs/node/issues/41863#issuecomment-1030709186
+  const scheme = req.socket.encrypted === true ? 'https' : 'http';
+  const url = `${scheme}://${req.headers.host}`;
+  return URL.canParse(url) ? new URL(url) : null;
+}

packages/dev-middleware/src/utils/getDevToolsFrontendUrl.js

@@ -65,7 +65,11 @@ function getWsParam({
   const serverHost = new URL(devServerUrl).host;
   let value;
   if (wsUrl.host === serverHost) {
-    // Use a path-absolute (host-relative) URL
+    // Use a path-absolute (host-relative) URL if the WS server and frontend
+    // server are colocated. This is more robust for cases where the frontend
+    // may actually load through a tunnel or proxy, and the WS connection
+    // should therefore do the same.
+    //
     // Depends on https://github.com/facebookexperimental/rn-chrome-devtools-frontend/pull/4
     value = wsUrl.pathname + wsUrl.search + wsUrl.hash;
   } else {