17. Network Resilience Layer: Dio Interceptors, Refresh Token Auto-Retry & Offline Cache Interceptor • Flutter & Dart Mobile Systems Architecture • Rishabh Ki Kaksha

Flutter & Dart Mobile Systems Architecture › 17. Network Resilience Layer: Dio Interceptors, Refresh Token Auto-Retry & Offline Cache Interceptor

45 mins

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Course Syllabus

Module 1: Dart 3+ Language Internals, Sound Null Safety & Concurrency (Isolates)

01. Dart 3+ Evolution: Sound Null Safety, Records, Pattern Matching & Sealed Classes 02. Dart Concurrency: Event Loops, Microtask Queue, Futures, Streams & Isolates (Spawn/Compute) 03. Dart Memory Management: Generational Garbage Collection & Object Pool Allocation

Part 1: Dart Mastery & Widget Tree Engine

Module 2: Flutter Rendering Pipeline: 3 Trees Architecture & Impeller Engine

04. Flutter Rendering Architecture: The 3 Trees (Widget Tree, Element Tree & RenderObject Tree) 05. The Impeller Rendering Engine: Vulkan/Metal Pre-compiled Shaders & Zero Junk Architecture 06. Custom RenderObjects & CustomPainter: Building High-Performance 60FPS Charts & UI Effects

Part 2: Platform Channels, Canvas & App Deployment

Module 3: Advanced State Management: Bloc, Cubit, Riverpod 2 & Signals

07. State Management Overview: Ephemeral vs App State & InheritedWidget Internals 08. BLoC (Business Logic Component) & Cubit Architecture with Reactive Streams 09. Riverpod 2.0 Masterclass: Auto-Dispose, Family Providers & Code Generation (riverpod_generator)

Module 4: Declarative Routing, Deep Linking with GoRouter & Micro-Apps

10. Declarative Navigation with GoRouter: URL-based Routing, Nested ShellRoutes & Redirect Guards 11. Deep Linking Architecture on Android & iOS with GoRouter Integration 12. Micro-App Architecture & Modularization in Enterprise Flutter Codebases

Module 5: Native Platform Channels, FFI (Foreign Function Interface) & SQLite (Drift)

13. Platform Channels: MethodChannel, EventChannel & BasicMessageChannel for Swift/Kotlin Interop 14. Dart FFI (Foreign Function Interface): Calling High-Performance C/C++ & Rust Native Libraries 15. High-Speed Local Persistence: Hive, Isar & Type-Safe SQLite with Drift (Moor)

Module 6: Flutter Clean Architecture, Testing & Multi-Platform Deployment (iOS, Android, Web)

16. Enterprise Clean Architecture: Domain, Data & Presentation Layers Separation 17. Network Resilience Layer: Dio Interceptors, Refresh Token Auto-Retry & Offline Cache Interceptor 18. Comprehensive Testing Suite: Unit Tests, Widget Tests & Integration Tests with Mockito/Mocktail 19. Flutter Web & Desktop Optimization: Responsive Layouts, Wasm Compilation & SEO Strategies 20. Automated CI/CD Pipelines with GitHub Actions, Fastlane & Codemagic for App Store Distribution

Interactive Lesson Studio

# 17. Network Resilience Layer: Dio Interceptors, Refresh Token Auto-Retry & Offline Cache Interceptor

> Flutter & Dart Notes by Rishabh - Topic 17

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### 1. The Production Dio Interceptor Architecture 🌐

1. **Auth Interceptor:** Har outgoing request me `Authorization: Bearer <token>` attach karta hai.
2. **Auto Refresh Token Queue (401 Interceptor):** JWT expire hone par request pause hoti hai, background me naya access token fetch hota hai, aur failed requests **auto-retry** ho jaati hain!

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### 2. Auto-Retry JWT Refresh Token Interceptor

```dart
class AuthInterceptor extends QueuedInterceptor {
    final Dio dio;
    AuthInterceptor(this.dio);

@override
    void onError(DioException err, ErrorInterceptorHandler handler) async {
        if (err.response?.statusCode == 401) {
            try {
                // Request new token using Refresh Token:
                final newToken = await AuthManager.refreshToken();
                // Update original request headers with new token:
                err.requestOptions.headers['Authorization'] = 'Bearer $newToken';
                // Retry original request:
                final response = await dio.fetch(err.requestOptions);
                return handler.resolve(response);
            } catch (refreshErr) {
                AuthManager.forceLogout();
                return handler.reject(err);
            }
        }
        return handler.next(err);
    }
}
```

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### 3. Master Comparison Matrix

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### 4. Interview Ke 3 Sawal Is Topic Se

1. **`QueuedInterceptor` standard `Interceptor` se kyu safer hota hai token refresh me?** -> Agar 5 parallel requests ek sath 401 fail hon, toh `QueuedInterceptor` unhe lock karke sirf 1 baar refresh token API call karta hai aur baaki 4 requests ko naye token ke sath replay karta hai.
2. **`CancelToken` screen dispose hone par network bandwidth kaise bachata hai?** -> User screen leave karte hi pending HTTP request ko abort kar deta hai.
3. **Exponential Backoff retry policy Dio me kaise implement hoti hai?** -> `dio_smart_retry` plugin use karke ($1\text{s}, 2\text{s}, 4\text{s}, 8\text{s}$ delays on network socket drops).

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**Next Topic:** 18. Comprehensive Testing Suite: Unit Tests, Widget Tests & Integration Tests with Mockito/Mocktail

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Rishabh Gehlot

PHP 8+ & Laravel 11 Master Track