[build-tools] Forward network capture through local egress

.changeset/serve-sim-pr-4598.md

@@ -0,0 +1,5 @@
+---
+'@expo/build-tools': patch
+---
+
+Forward captured Simulator traffic through the local egress proxy.

packages/build-tools/src/steps/utils/__tests__/deviceSessionHost.test.ts

@@ -12,6 +12,7 @@ import { IosSimulatorUtils } from '../../../utils/IosSimulatorUtils';
 import { verifyLocalEgressGuardAsync } from '../localEgressGuard';
 import { type ServeSimApplicationOptions } from '../remoteDeviceRunSession';
 
+import { readLocalEgressHandoffAsync } from '../localEgress';
 import { runServeSimActionAsync, stageServeSimAppAsync } from '../serveSimActions';
 import { startServeSimActivityPolling } from '../serveSimActivity';
 import { readServeSimServersAsync } from '../serveSimMetricsRecorder';
@@ -46,6 +47,10 @@ jest.mock('../../../utils/IosSimulatorUtils', () => ({
 jest.mock('../localEgressGuard', () => ({ verifyLocalEgressGuardAsync: jest.fn() }));
 jest.mock('../serveSimActions');
 jest.mock('../serveSimActivity');
+jest.mock('../localEgress', () => ({
+  ...jest.requireActual('../localEgress'),
+  readLocalEgressHandoffAsync: jest.fn().mockResolvedValue(null),
+}));
 jest.mock('../deviceRunSessionArtifacts');
 jest.mock('../../../sentry');
 jest.mock('../serveSimMetricsRecorder', () => ({
@@ -131,6 +136,7 @@ beforeEach(() => {
   jest.clearAllMocks();
   jest.mocked(IosSimulatorUtils.disableApsdAsync).mockReset().mockResolvedValue(undefined);
   jest.mocked(verifyLocalEgressGuardAsync).mockReset().mockResolvedValue(undefined);
+  jest.mocked(readLocalEgressHandoffAsync).mockReset().mockResolvedValue(null);
   stopSessionPreview.mockResolvedValue(undefined);
   jest.mocked(startDeviceRunSessionPreview).mockReturnValue({ stopAsync: stopSessionPreview });
   jest.mocked(ensureFfmpegInstalledOnceAsync).mockResolvedValue(undefined);
@@ -1377,6 +1383,35 @@ it('uses the existing step logger for startup and shutdown output', async () =>
   ).toBe(false);
 });
 
+it('passes the active local-egress address to serve-sim without tunnel credentials', async () => {
+  jest.mocked(readLocalEgressHandoffAsync).mockResolvedValue({
+    port: 8899,
+    url: 'https://tunnel.example',
+    token: 'tunnel-secret',
+    fingerprint: 'fingerprint',
+  });
+  const host = await startDeviceSessionHostAsync(ctx, {
+    runtimePlatform: BuildRuntimePlatform.DARWIN,
+    env,
+    logger,
+    timeoutMs: 10_000,
+    networkCapture: true,
+  });
+  const spawned = jest.mocked(spawnDetached).mock.calls[0][0];
+  expect(spawned.args).toEqual(
+    expect.arrayContaining(['--network-capture-proxy', 'http://127.0.0.1:8899'])
+  );
+  expect(spawned.args).toContain('--network-capture');
+  expect(JSON.stringify(spawned)).not.toContain('tunnel-secret');
+  await host.finishAsync();
+});
+
+it('does not read the iOS egress handoff for an Android host', async () => {
+  const host = await startHostAsync();
+  expect(readLocalEgressHandoffAsync).not.toHaveBeenCalled();
+  await host.finishAsync();
+});
+
 it.each([true, false])(
   'waits for setup before launch or boot-only readiness (app: %s)',
   async hasApp => {

packages/build-tools/src/steps/utils/__tests__/remoteDeviceRunSession.test.ts

@@ -661,6 +661,14 @@ describe(createServeSimArgs, () => {
     );
   });
 
+  it('passes a capture proxy as one argument, including when capture will be enabled later', () => {
+    const proxy = 'http://user:p%40ss%20word@proxy.example:8899';
+    const args = createServeSimArgs({ port: 4321, networkCaptureProxy: proxy });
+    expect(args.slice(-2)).toEqual(['--network-capture-proxy', proxy]);
+    expect(args).not.toContain('--network-capture');
+    expect(createServeSimArgs({ port: 4321 })).not.toContain('--network-capture-proxy');
+  });
+
   it('appends --network-capture when enabled, which also covers an already booted simulator', () => {
     const args = createServeSimArgs({ port: 4321, networkCapture: true });
     expect(args).toContain('--network-capture');

packages/build-tools/src/steps/utils/deviceSessionHost.ts

@@ -40,6 +40,7 @@ import {
   spawnDetached,
   startNgrokTunnelAsync,
 } from './remoteDeviceRunSession';
+import { LOCAL_EGRESS_PROXY_HOST, readLocalEgressHandoffAsync } from './localEgress';
 import { withDeviceRunSessionTimeoutAsync } from './deviceRunSessionTimeout';
 import {
   IosSimulatorRecordingUtils,
@@ -137,6 +138,7 @@ export function createServeSimArgs({
   openUrl,
   networkCapture = false,
   networkCaptureFields = [],
+  networkCaptureProxy,
 }: {
   port: number;
   turnArgs?: string[];
@@ -150,6 +152,7 @@ export function createServeSimArgs({
   installAppPath?: string;
   networkCapture?: boolean;
   networkCaptureFields?: string[];
+  networkCaptureProxy?: string;
 } & ServeSimLaunchOptions): string[] {
   return [
     createServeSimPackageSpec(packageVersion),
@@ -189,6 +192,7 @@ export function createServeSimArgs({
           ...networkCaptureFields.flatMap(field => ['--network-capture-field', field]),
         ]
       : []),
+    ...(networkCaptureProxy !== undefined ? ['--network-capture-proxy', networkCaptureProxy] : []),
   ];
 }
 
@@ -496,6 +500,7 @@ async function startDeviceSessionHostInternalAsync(
     ? createExpoDeviceHubPackageSpec(packageVersion)
     : createServeSimPackageSpec(packageVersion);
   const turnArgs = await fetchWebPreviewTurnArgsAsync(ctx, { logger });
+  const localEgress = !isAndroid ? await readLocalEgressHandoffAsync() : null;
   const previewExec = resolvePackageExec(
     resolveConfiguredPackageManager(env, PackageManager.NPM),
     isAndroid
@@ -525,6 +530,9 @@ async function startDeviceSessionHostInternalAsync(
           openUrl: iosSimulatorUdid ? undefined : openUrl,
           networkCapture,
           networkCaptureFields,
+          networkCaptureProxy: localEgress
+            ? `http://${LOCAL_EGRESS_PROXY_HOST}:${localEgress.port}`
+            : undefined,
         })
   );
   logger.info(