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

Criteria	http	Dio
Interceptors	No	Yes, full chain
Retry logic	Manual	Built-in with backoff
Response caching	Manual	Plugin available
FormData / Multipart	Manual	Built-in
Cancel requests	No	Yes, CancelToken
Dependencies	Minimal (1 package)	Heavier
Use case	Simple CRUD APIs	Production API clients

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.