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HTTP Interceptor para solicitudes de API en Flutter

Alejandro Carrazana


HTTP Interceptor diagram
HTTP Interceptors

HTTP interceptors are components that allow manipulating and customizing HTTP requests and responses before they enter or exit the application. Having HTTP interceptors in an application can address several questions and issues, including:

  1. How to add authentication headers to HTTP requests?

  2. How to handle network errors and return a customized response?

  3. How to monitor and log network activity in the application?

  4. How to reduce the number of required requests by using caching?

  5. How to improve network speed by compressing HTTP responses?

These are just some examples of tasks that HTTP interceptors can perform in an application. Implementing interceptors enables developers to have greater control over how network communication is carried out in the application, which can improve security, efficiency, and user experience.


What are HTTP interceptors?


HTTP interceptors are a programming concept used in web and mobile applications. An interceptor is a function that is automatically invoked each time an HTTP request or response is made.


These interceptors are used to perform common tasks on all or many requests or responses, such as adding headers to the request, manipulating the response before returning it to the application, etc. HTTP interceptors are a useful tool for developing web and mobile applications.


Types of popular HTTP interceptor packages for Flutter


In Flutter, interceptors can be implemented using HTTP client libraries or packages. These packages allow developers to define and customize interceptors to meet their specific needs.


In Flutter, some of the most popular HTTP interceptor packages include:

  1. Dio: a highly customizable and flexible HTTP client library that supports interceptors.

  2. Http: a simple and easy-to-use HTTP client library that supports interceptors.

  3. Chopper: a Dart-based HTTP client library that uses interceptors to facilitate network customization and handling.

  4. Http Interceptor: a Flutter package that allows developers to implement and compose custom interceptors.

  5. Retrofit: an HTTP client library that allows developers to define and customize HTTP requests and responses using a syntax similar to Retrofit for Android.

These are just some of the most popular HTTP interceptor packages for Flutter. There are many other options available, so it's important to choose the one that best suits your project's needs.


Implementation of an HTTP Interceptor for a Flutter app


In the following example, we will discuss the implementation of the http_interceptor package to control HTTP requests and responses in a Flutter application.


First, we create the interceptor_client.dart file which contains the InterceptorClient class. This class implements the InterceptorContract class, allowing it to manipulate HTTP requests and responses with the interceptRequest and interceptResponse methods respectively, as shown below:

import 'package:http_interceptor/http_interceptor.dart';

class InterceptorClient implements InterceptorContract {
 @override
 Future<RequestData> interceptRequest({required RequestData data}) async {
   return data;
 }

 @override
 Future<ResponseData> interceptResponse({required ResponseData data}) async {
   switch (data.statusCode) {
     case 200:
       break;
     case 400:
       break;
     case 401:
       break;
     case 403:
       break;
     case 404:
       break;
     case 422:
       break;
     case 500:
       break;
     case 501:
       break;
     case 502:
       break;
     case 503:
       break;
     default:
       break;
   }
   return data;
 }
}

In addition, it is necessary to create an object of type InterceptedClient that receives the previously created interceptor as configuration.

class InterceptorService {
 static InterceptedClient client = InterceptedClient.build(interceptors: [
   InterceptorClient(),
 ]);
}

This way, the interceptor can be used to control HTTP requests and responses: get, post, put, delete head, patch, read, send, readBytes.

InterceptorService.client.get(...);
InterceptorService.client.post(...);
InterceptorService.client.put(...);

For more information about this package, you can visit the official documentation on GitHub.


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