Flutter Dio

Networking with Dio

• Use Dio as the primary HTTP client package.
• Use type-safe model classes with fromJson / toJson factories for all request/response bodies.
• Handle all HTTP status codes appropriately with typed exceptions (e.g., ServerException, NetworkException, UnauthorizedException).
• Use proper request timeouts (connectTimeout, receiveTimeout, sendTimeout).

Dio Interceptors

• Use interceptors for cross-cutting concerns:
  • Auth Interceptor: Attach access tokens to headers, handle token refresh on 401.
  • Logging Interceptor: Log requests/responses in debug mode via AppLogger.
  • Error Interceptor: Transform DioException into domain-specific Failure types.
• Register interceptors centrally via injectable for consistent behavior across all API calls.

Repository Pattern

• DataSources contain only raw Dio API calls: no business logic or mapping
• Repositories orchestrate between remote DataSources and local cache for network data

Retry & Resilience

• Implement retry logic with exponential backoff for transient failures (e.g., 500, timeout).
• Set a maximum retry count (default: 3 retries).
• Cache responses when appropriate to reduce network calls and improve offline UX.

Performance

• Parse JSON in background isolates for large responses (> 1MB) using compute()
• Do NOT block the UI thread with synchronous network operations

Security

• Store tokens via flutter_secure_storage: never in source code or SharedPreferences
• All API communication MUST use HTTPS

Alternative: http Package

For simple REST calls that don't need interceptors, caching, or retry logic, use http instead of Dio.

Dio vs http

Use http for prototypes and simple fetch-and-display. Use Dio for production API clients that need auth, retry, and caching.

Basic http Patterns

import 'dart:convert';
import 'package:http/http.dart' as http;

// GET request
Future<Map<String, dynamic>> fetchData(http.Client client) async {
  final response = await client.get(
    Uri.parse('https://api.example.com/data'),
    headers: {'Accept': 'application/json'},
  );

  if (response.statusCode == 200) {
    return jsonDecode(response.body) as Map<String, dynamic>;
  } else {
    throw Exception('Failed to fetch: ${response.statusCode}');
  }
}

// POST request
Future<void> createItem(http.Client client, Map<String, dynamic> body) async {
  final response = await client.post(
    Uri.parse('https://api.example.com/items'),
    headers: {'Content-Type': 'application/json'},
    body: jsonEncode(body),
  );

  if (response.statusCode != 201) {
    throw Exception('Failed to create: ${response.statusCode}');
  }
}

Testing: Always accept http.Client as a parameter (not http.get() directly) to enable mock injection in tests.