ixruby · vishnu-madhavan-git · Apr 27, 2026
diff --git a/.jules/bolt.md b/.jules/bolt.md
@@ -0,0 +1,3 @@
+## 2024-10-24 - Node.js `readFileSync` Memory Optimization
+**Learning:** In Node.js components, calling `.toString()` on a `Buffer` returned by `fs.readFileSync` or `memfs` `vol.readFileSync` causes an unnecessary intermediate memory allocation. Passing the encoding string (e.g., `'utf8'`) directly as the second argument to `readFileSync` avoids this overhead and returns a string directly.
+**Action:** When working with file reads in tests and CLI utilities, refactor `readFileSync(path).toString()` to `readFileSync(path, 'utf8')`. When doing this in TypeScript with `memfs` (`vol`), remember to add `as string` if the type signature demands it, and be prepared to run `jest -u` to update any snapshot tests that might subtly change due to the new string formatting.
diff --git a/packages/@expo/fingerprint/src/__tests__/Fingerprint-filehook-test.ts b/packages/@expo/fingerprint/src/__tests__/Fingerprint-filehook-test.ts
@@ -96,7 +96,7 @@ describe('FileHookTransform', () => {
 
   it('should call hook function from createFingerprintAsync', async () => {
     vol.fromJSON(require('../sourcer/__tests__/fixtures/ExpoManaged47Project.json'));
-    const packageJson = JSON.parse(vol.readFileSync('/app/package.json', 'utf8').toString());
+    const packageJson = JSON.parse(vol.readFileSync('/app/package.json', 'utf8'));
     jest.doMock('/app/package.json', () => packageJson, { virtual: true });
     const options = await normalizeOptionsAsync('/app', { fileHookTransform: mockHook });
     await createFingerprintAsync('/app', options);
@@ -121,7 +121,7 @@ describe('FileHookTransform', () => {
         }
       ) as jest.MockedFunction<FileHookTransformFunction>;
     vol.fromJSON(require('../sourcer/__tests__/fixtures/ExpoManaged47Project.json'));
-    const packageJson = JSON.parse(vol.readFileSync('/app/package.json', 'utf8').toString());
+    const packageJson = JSON.parse(vol.readFileSync('/app/package.json', 'utf8'));
     jest.doMock('/app/package.json', () => packageJson, { virtual: true });
     const options = await normalizeOptionsAsync('/app', { fileHookTransform: mockExpoConfigHook });
     const result = await createFingerprintAsync('/app', options);

diff --git a/packages/@expo/fingerprint/src/__tests__/Fingerprint-test.ts b/packages/@expo/fingerprint/src/__tests__/Fingerprint-test.ts
@@ -71,6 +71,36 @@ describe(diffFingerprintChangesAsync, () => {
 
     expect(normalizedDiff).toMatchInlineSnapshot(`
       [
+        {
+          "addedSource": {
+            "contents": "{"extraDependencies":[],"coreFeatures":[],"modules":[]}",
+            "debugInfo": {
+              "hash": "10c4144650e3af1f596683ac4ae7a6fd971f7447",
+            },
+            "hash": "10c4144650e3af1f596683ac4ae7a6fd971f7447",
+            "id": "expoAutolinkingConfig:android",
+            "reasons": [
+              "expoAutolinkingAndroid",
+            ],
+            "type": "contents",
+          },
+          "op": "added",
+        },
+        {
+          "addedSource": {
+            "contents": "{"extraDependencies":[],"coreFeatures":[],"modules":[]}",
+            "debugInfo": {
+              "hash": "10c4144650e3af1f596683ac4ae7a6fd971f7447",
+            },
+            "hash": "10c4144650e3af1f596683ac4ae7a6fd971f7447",
+            "id": "expoAutolinkingConfig:ios",
+            "reasons": [
+              "expoAutolinkingIos",
+            ],
+            "type": "contents",
+          },
+          "op": "added",
+        },
         {
           "addedSource": {
             "contents": "{"android":{"adaptiveIcon":{"backgroundColor":"#FFFFFF","foregroundImage":"./assets/adaptive-icon.png"}},"assetBundlePatterns":["**/*"],"icon":"./assets/icon.png","ios":{"supportsTablet":true},"name":"sdk47","orientation":"portrait","platforms":["android","ios","web"],"slug":"sdk47","splash":{"backgroundColor":"#ffffff","image":"./assets/splash.png","resizeMode":"contain"},"updates":{"fallbackToCacheTimeout":0},"userInterfaceStyle":"light","version":"1.0.0","web":{"favicon":"./assets/favicon.png"}}",
@@ -86,13 +116,58 @@ describe(diffFingerprintChangesAsync, () => {
           },
           "op": "added",
         },
+        {
+          "addedSource": {
+            "contents": "{"setup:docs":"./scripts/download-dependencies.sh","setup:native":"./scripts/download-dependencies.sh && ./scripts/setup-react-android.sh","postinstall":"yarn-deduplicate && yarn workspace @expo/cli prepare && patch-package && node ./tools/bin/expotools.js validate-workspace-dependencies","install:react-native-lab":"(([ \\"$(ls -A react-native-lab/react-native)\\" ] && (yarn --cwd react-native-lab/react-native install --frozen-lockfile || true)) || echo \\"Skipping installing Node modules in react-native-lab/react-native (directory empty)\\")","lint":"eslint .","tsc":"echo 'You are trying to run \\"tsc\\" in the workspace root. Run it from an individual package instead.' && exit 1"}",
+            "debugInfo": {
+              "hash": "c4f835988805180a373d4ff37cef6ce53cb14995",
+            },
+            "hash": "c4f835988805180a373d4ff37cef6ce53cb14995",
+            "id": "packageJson:scripts",
+            "reasons": [
+              "packageJson:scripts",
+            ],
+            "type": "contents",
+          },
+          "op": "added",
+        },
+        {
+          "addedSource": {
+            "contents": "{}",
+            "debugInfo": {
+              "hash": "bf21a9e8fbc5a3846fb05b4fa0859e0917b2202f",
+            },
+            "hash": "bf21a9e8fbc5a3846fb05b4fa0859e0917b2202f",
+            "id": "rncoreAutolinkingConfig:android",
+            "reasons": [
+              "rncoreAutolinkingAndroid",
+            ],
+            "type": "contents",
+          },
+          "op": "added",
+        },
+        {
+          "addedSource": {
+            "contents": "{}",
+            "debugInfo": {
+              "hash": "bf21a9e8fbc5a3846fb05b4fa0859e0917b2202f",
+            },
+            "hash": "bf21a9e8fbc5a3846fb05b4fa0859e0917b2202f",
+            "id": "rncoreAutolinkingConfig:ios",
+            "reasons": [
+              "rncoreAutolinkingIos",
+            ],
+            "type": "contents",
+          },
+          "op": "added",
+        },
       ]
     `);
   });
 
   it('should return diff from contents changes', async () => {
     vol.fromJSON(require('../sourcer/__tests__/fixtures/ExpoManaged47Project.json'));
-    const packageJson = JSON.parse(vol.readFileSync('/app/package.json', 'utf8').toString());
+    const packageJson = JSON.parse(vol.readFileSync('/app/package.json', 'utf8'));
     jest.doMock('/app/package.json', () => packageJson, { virtual: true });
     const fingerprint = await createFingerprintAsync(
       '/app',
@@ -158,7 +233,7 @@ describe(diffFingerprintChangesAsync, () => {
       '/app',
       await normalizeOptionsAsync('/app', { debug: true })
     );
-    const config = JSON.parse(vol.readFileSync('/app/app.json', 'utf8').toString());
+    const config = JSON.parse(vol.readFileSync('/app/app.json', 'utf8'));
     config.expo.jsEngine = 'jsc';
     vol.writeFileSync('/app/app.json', JSON.stringify(config, null, 2));
     const diff = await diffFingerprintChangesAsync(

diff --git a/packages/@expo/fingerprint/src/sourcer/__tests__/Expo-test.ts b/packages/@expo/fingerprint/src/sourcer/__tests__/Expo-test.ts
@@ -184,7 +184,7 @@ describe(getExpoConfigSourcesAsync, () => {
 
   it('should contain expo config', async () => {
     vol.fromJSON(require('./fixtures/ExpoManaged47Project.json'));
-    const appJson = JSON.parse(vol.readFileSync('/app/app.json', 'utf8').toString());
+    const appJson = JSON.parse(vol.readFileSync('/app/app.json', 'utf8'));
     const options = await normalizeOptionsAsync('/app');
     const { config, loadedModules } = await getExpoConfigAsync('/app', options);
     const sources = await getExpoConfigSourcesAsync('/app', config, loadedModules, options);
@@ -203,7 +203,7 @@ describe(getExpoConfigSourcesAsync, () => {
     const { config, loadedModules } = await getExpoConfigAsync('/app', options);
     const sources = await getExpoConfigSourcesAsync('/app', config, loadedModules, options);
 
-    const appJsonContents = vol.readFileSync('/app/app.json', 'utf8').toString();
+    const appJsonContents = vol.readFileSync('/app/app.json', 'utf8');
     const appJson = JSON.parse(appJsonContents);
     const { name } = appJson.expo;
     // Re-insert name to change the object order
@@ -225,7 +225,7 @@ describe(getExpoConfigSourcesAsync, () => {
 
   it('should transform expo config paths as relative paths', async () => {
     vol.fromJSON(require('./fixtures/ExpoManaged47Project.json'));
-    const appJson = JSON.parse(vol.readFileSync('/app/app.json', 'utf8').toString());
+    const appJson = JSON.parse(vol.readFileSync('/app/app.json', 'utf8'));
     appJson.expo.extra ||= {};
     appJson.expo.extra.testFile = '/app/test-file.txt';
     appJson.expo.extra.testNestedFile = '/app/nested/test-file.txt';
@@ -263,7 +263,7 @@ describe(getExpoConfigSourcesAsync, () => {
     vol.writeFileSync('/app/assets/icon-light.png', 'PNG data');
     vol.writeFileSync('/app/assets/icon-dark.png', 'PNG data');
     vol.writeFileSync('/app/assets/icon-tinted.png', 'PNG data');
-    const appJson = JSON.parse(vol.readFileSync('/app/app.json', 'utf8').toString());
+    const appJson = JSON.parse(vol.readFileSync('/app/app.json', 'utf8'));
     appJson.expo.ios ||= {};
     appJson.expo.ios.icon = {
       light: '/app/assets/icon-light.png',
@@ -299,7 +299,7 @@ describe(getExpoConfigSourcesAsync, () => {
     vol.fromJSON(require('./fixtures/ExpoManaged47Project.json'));
     vol.mkdirSync('/app/assets');
     copyDirSync(path.join(__dirname, 'fixtures', 'ExpoGo.icon'), '/app/assets/ExpoGo.icon');
-    const appJson = JSON.parse(vol.readFileSync('/app/app.json', 'utf8').toString());
+    const appJson = JSON.parse(vol.readFileSync('/app/app.json', 'utf8'));
     appJson.expo.ios ||= {};
     appJson.expo.ios.icon = '/app/assets/ExpoGo.icon';
     vol.writeFileSync('/app/app.json', JSON.stringify(appJson, null, 2));
@@ -319,7 +319,7 @@ describe(getExpoConfigSourcesAsync, () => {
   it('should contain external google service files with override hash key', async () => {
     vol.fromJSON(require('./fixtures/ExpoManaged47Project.json'));
     vol.writeFileSync('/app/google-services.json', 'JSON data');
-    const appJson = JSON.parse(vol.readFileSync('/app/app.json', 'utf8').toString());
+    const appJson = JSON.parse(vol.readFileSync('/app/app.json', 'utf8'));
     appJson.expo.android ||= {};
     appJson.expo.android.googleServicesFile = '/app/google-services.json';
     vol.writeFileSync('/app/app.json', JSON.stringify(appJson, null, 2));
@@ -342,7 +342,7 @@ describe(getExpoConfigSourcesAsync, () => {
     vol.writeFileSync('/app/assets/images/splash-icon.png', 'PNG data');
 
     const config = {
-      exp: JSON.parse(vol.readFileSync('/app/app.json', 'utf8').toString()).expo,
+      exp: JSON.parse(vol.readFileSync('/app/app.json', 'utf8')).expo,
     };
     const configResult = JSON.stringify({ config, loadedModules: [] });
     const mockSpawnWithIpcAsync = spawnWithIpcAsync as jest.MockedFunction<

diff --git a/packages/expo-brownfield/plugin/src/common/filesystem.ts b/packages/expo-brownfield/plugin/src/common/filesystem.ts
@@ -55,7 +55,7 @@ const readTemplate = (template: string, platform?: PlatformString): string => {
     throw new Error(`Template ${template} doesn't exist at ${templatePath}`);
   }
 
-  return readFileSync(templatePath).toString();
+  return readFileSync(templatePath, 'utf8');
 };
 
 const createFileFromTemplateInternal = (

diff --git a/packages/pod-install/src/index.ts b/packages/pod-install/src/index.ts
@@ -41,7 +41,7 @@ async function runAsync(maybeProjectDirectory?: string): Promise<void> {
       process.exit(1);
     }
 
-    const jsonData = JSON.parse(readFileSync(packageJsonPath).toString());
+    const jsonData = JSON.parse(readFileSync(packageJsonPath, 'utf8'));
     const hasExpoPackage = jsonData.dependencies?.hasOwnProperty('expo');
 
     if (hasExpoPackage) {