Api Interceptor For Network Layer

api_interceptor.dart

import 'package:dio/dio.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

// Providers
import '../../../features/all_providers.dart';

/// A class that holds intercepting logic for API related requests. This is
/// the first interceptor in case of both request and response.
///
/// Primary purpose is to handle token injection and response success validation
///
/// Since this interceptor isn't responsible for error handling, if an exception
/// occurs it is passed on the next [Interceptor] or to [Dio].
class ApiInterceptor extends Interceptor {
  late final Ref _ref;

  ApiInterceptor(this._ref) : super();

  /// This method intercepts an out-going request before it reaches the
  /// destination.
  ///
  /// [options] contains http request information and configuration.
  /// [handler] is used to forward, resolve, or reject requests.
  ///
  /// This method is used to inject any token/API keys in the request.
  ///
  /// The [RequestInterceptorHandler] in each method controls the what will
  /// happen to the intercepted request. It has 3 possible options:
  ///
  /// - [handler.next]/[super.onRequest], if you want to forward the request.
  /// - [handler.resolve]/[super.onResponse], if you want to resolve the
  /// request with your custom [Response]. All ** request ** interceptors are ignored.
  /// - [handler.reject]/[super.onError], if you want to fail the request
  /// with your custom [DioError].
  @override
  Future<void> onRequest(
    RequestOptions options,
    RequestInterceptorHandler handler,
  ) async {
    if (options.extra.containsKey('requiresAuthToken')) {
      if (options.extra['requiresAuthToken'] == true) {
        final token =
            await _ref.watch(keyValueStorageServiceProvider).getAuthToken();
        options.headers.addAll(
          <String, Object?>{'Authorization': 'Bearer $token'},
        );
      }

      options.extra.remove('requiresAuthToken');
    }
    return handler.next(options);
  }

  /// This method intercepts an incoming response before it reaches Dio.
  ///
  /// [response] contains http [Response] info.
  /// [handler] is used to forward, resolve, or reject responses.
  ///
  /// This method is used to check the success of the response by verifying
  /// its headers.
  ///
  /// If response is successful, it is simply passed on. It may again be
  /// intercepted if there are any after it. If none, it is passed to [Dio].
  ///
  /// Else if response indicates failure, a [DioError] is thrown with the
  /// response and original request's options.
  ///
  /// ** The success criteria is dependant on the API and may not always be
  /// the same. It might need changing according to your own API. **
  ///
  /// The [RequestInterceptorHandler] in each method controls the what will
  /// happen to the intercepted response. It has 3 possible options:
  ///
  /// - [handler.next]/[super.onRequest], if you want to forward the [Response].
  /// - [handler.resolve]/[super.onResponse], if you want to resolve the
  /// [Response] with your custom data. All ** response ** interceptors are ignored.
  /// - [handler.reject]/[super.onError], if you want to fail the response
  /// with your custom [DioError].
  @override
  void onResponse(
    Response response,
    ResponseInterceptorHandler handler,
  ) {
    final success = response.data['headers']['error'] == 0;

    if (success) return handler.next(response);

    //Reject all error codes from server except 402 and 200 OK
    return handler.reject(
      DioError(
        requestOptions: response.requestOptions,
        response: response,
      ),
    );
  }
}