This is a plugin that lets you intercept the different requests and responses from Dart's http package. You can use to add headers, modify query params, or print a log of the response.

Quick Reference #

Include the package with the latest version available in your pubspec.yaml .

http_interceptor: any

import 'package:http_interceptor/http_interceptor.dart';

Building your own interceptor #

In order to implement http_interceptor you need to implement the InterceptorContract and create your own interceptor. This abstract class has two methods: interceptRequest , which triggers before the http request is called; and interceptResponse , which triggers after the request is called, it has a response attached to it which the corresponding to said request. You could use this to do logging, adding headers, error handling, or many other cool stuff. It is important to note that after you proccess the request/response objects you need to return them so that http can continue the execute.

Logging with interceptor:

class LoggingInterceptor implements InterceptorContract { @override Future<RequestData> interceptRequest({RequestData data}) async { print(data); return data; } @override Future<ResponseData> interceptResponse({ResponseData data}) async { print(data); return data; } }

Changing headers with interceptor:

class WeatherApiInterceptor implements InterceptorContract { @override Future<RequestData> interceptRequest({RequestData data}) async { try { data.params['appid'] = OPEN_WEATHER_API_KEY; data.params['units'] = 'metric'; data.headers["Content-Type"] = "application/json"; } catch (e) { print(e); } return data; } @override Future<ResponseData> interceptResponse({ResponseData data}) async => data; }

Using your interceptor #

Now that you actually have your interceptor implemented, now you need to use it. There are two general ways in which you can use them: by using the HttpWithInterceptor to do separate connections for different requests or using a HttpClientWithInterceptor for keeping a connection alive while making the different http calls. The ideal place to use them is in the service/provider class or the repository class (if you are not using services or providers); if you don't know about the repository pattern you can just google it and you'll know what I'm talking about. ;)

Using interceptors with Client

Normally, this approach is taken because of its ability to be tested and mocked.

Here is an example with a repository using the HttpClientWithInterceptor class.

class WeatherRepository { Client client = HttpClientWithInterceptor.build(interceptors: [ WeatherApiInterceptor(), ]); Future<Map<String, dynamic>> fetchCityWeather(int id) async { var parsedWeather; try { final response = await client.get("$baseUrl/weather", params: {'id': "$id"}); if (response.statusCode == 200) { parsedWeather = json.decode(response.body); } else { throw Exception("Error while fetching.

${response.body}"); } } catch (e) { print(e); } return parsedWeather; } }

Using interceptors without Client

This is mostly the straight forward approach for a one-and-only call that you might need intercepted.

Here is an example with a repository using the HttpWithInterceptor class.

class WeatherRepository { Future<Map<String, dynamic>> fetchCityWeather(int id) async { var parsedWeather; try { final response = await client.get("$baseUrl/weather", params: {'id': "$id"}); if (response.statusCode == 200) { parsedWeather = json.decode(response.body); } else { return Future.error( "Error while fetching.", StackTrace.fromString("${response.body}"), ); } } on SocketException { return Future.error('No Internet connection 😑'); } on FormatException { return Future.error('Bad response format 👎'); } on Exception { return Future.error('Unexpected error 😢'); } return parsedWeather; } }

Retrying requests #

(NEW 🎉) Sometimes you need to retry a request due to different circumstances, an expired token is a really good example. Here's how you could potentially implement an expired token retry policy with http_interceptor .

class ExpiredTokenRetryPolicy extends RetryPolicy { @override Future<bool> shouldAttemptRetryOnResponse(ResponseData response) async { if (response.statusCode == 401) { // Perform your token refresh here. return true; } return false; } }

You can also set the maximum amount of retry attempts with maxRetryAttempts property or override the shouldAttemptRetryOnException if you want to retry the request after it failed with an exception.

Using self signed certificates #

(EXPERIMENTAL ⚗️) This plugin allows you to override the default badCertificateCallback provided by Dart's io package, this is really useful when working with self-signed certificates in your server. This can be done by sending a the callback to the HttpInterceptor builder functions. This feature is marked as experimental and might be subject to change before release 1.0.0 comes.

class WeatherRepository { Future<Map<String, dynamic>> fetchCityWeather(int id) async { var parsedWeather; try { var response = await HttpWithInterceptor.build( interceptors: [WeatherApiInterceptor()], badCertificateCallback: (certificate, host, port) => true) .get("$baseUrl/weather", params: {'id': "$id"}); if (response.statusCode == 200) { parsedWeather = json.decode(response.body); } else { throw Exception("Error while fetching.

${response.body}"); } } catch (e) { print(e); } return parsedWeather; } }

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