Writing Native Modules (Android & iOS)

1// === TURBOMODULE: Full Example ===
2
3// 1. TypeScript Spec (shared between platforms)
4// specs/NativeSecureStorage.ts
5import type { TurboModule } from 'react-native';
6import { TurboModuleRegistry } from 'react-native';
7
8export interface Spec extends TurboModule {
9  // Synchronous — uses iOS Keychain / Android Keystore
10  setItem(key: string, value: string): boolean;
11  getItem(key: string): string | null;
12  removeItem(key: string): boolean;
13  getAllKeys(): string[];
14  
15  // Async for potentially slow operations
16  clear(): Promise<void>;
17}
18
19export default TurboModuleRegistry.getEnforcing<Spec>('SecureStorage');
20
21// 2. Android Implementation (Kotlin)
22/*
23package com.myapp.modules
24
25import com.facebook.react.bridge.*
26import com.facebook.react.module.annotations.ReactModule
27import android.security.keystore.KeyGenParameterSpec
28import java.security.KeyStore
29
30@ReactModule(name = SecureStorageModule.NAME)
31class SecureStorageModule(reactContext: ReactApplicationContext) 
32  : NativeSecureStorageSpec(reactContext) {
33  
34  companion object {
35    const val NAME = "SecureStorage"
36  }
37  
38  private val prefs by lazy {
39    // EncryptedSharedPreferences for secure storage
40    EncryptedSharedPreferences.create(
41      "secure_prefs",
42      MasterKeys.getOrCreate(MasterKeys.AES256_GCM_SPEC),
43      reactApplicationContext,
44      EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
45      EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
46    )
47  }
48  
49  override fun getName() = NAME
50  
51  override fun setItem(key: String, value: String): Boolean {
52    return try {
53      prefs.edit().putString(key, value).commit()
54    } catch (e: Exception) {
55      false
56    }
57  }
58  
59  override fun getItem(key: String): String? {
60    return prefs.getString(key, null)
61  }
62  
63  override fun removeItem(key: String): Boolean {
64    return prefs.edit().remove(key).commit()
65  }
66  
67  override fun getAllKeys(): WritableArray {
68    val keys = Arguments.createArray()
69    prefs.all.keys.forEach { keys.pushString(it) }
70    return keys
71  }
72  
73  override fun clear(promise: Promise) {
74    try {
75      prefs.edit().clear().commit()
76      promise.resolve(null)
77    } catch (e: Exception) {
78      promise.reject("CLEAR_ERROR", e.message)
79    }
80  }
81}
82*/
83
84// 3. iOS Implementation (Swift)
85/*
86@objc(SecureStorage)
87class SecureStorage: NSObject, NativeSecureStorageSpec {
88  
89  @objc func setItem(_ key: String, value: String) -> Bool {
90    let data = value.data(using: .utf8)!
91    let query: [String: Any] = [
92      kSecClass as String: kSecClassGenericPassword,
93      kSecAttrAccount as String: key,
94      kSecValueData as String: data,
95    ]
96    SecItemDelete(query as CFDictionary) // Remove existing
97    let status = SecItemAdd(query as CFDictionary, nil)
98    return status == errSecSuccess
99  }
100  
101  @objc func getItem(_ key: String) -> String? {
102    let query: [String: Any] = [
103      kSecClass as String: kSecClassGenericPassword,
104      kSecAttrAccount as String: key,
105      kSecReturnData as String: true,
106    ]
107    var result: AnyObject?
108    let status = SecItemCopyMatching(query as CFDictionary, &result)
109    guard status == errSecSuccess, let data = result as? Data else { return nil }
110    return String(data: data, encoding: .utf8)
111  }
112}
113*/
114
115// 4. Usage in JS — same API regardless of platform
116import SecureStorage from './specs/NativeSecureStorage';
117
118// Synchronous access (JSI-powered)
119const token = SecureStorage.getItem('auth_token');
120if (token) {
121  api.setAuthHeader(token);
122}
123
124// Store new token
125const success = SecureStorage.setItem('auth_token', newToken);
126if (!success) {
127  ErrorReporter.report(new Error('Failed to store auth token'));
128}