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Description:

http interceptor

http_interceptor #

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 #
Already using http_interceptor? Check out the 1.0.0 migration guide for quick reference on the changes made and how to migrate your code.

http_interceptor

Quick Reference
Installation
Features
Usage

Building your own interceptor
Using your interceptor

Using interceptors with Client
Using interceptors without Client

Retrying requests
Using self signed certificates
InterceptedClient
InterceptedHttp

Roadmap
Troubleshooting
Contributions

Contributors

Installation #
Include the package with the latest version available in your pubspec.yaml.
http_interceptor: <latest>
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Features #

🚦 Intercept & change unstreamed requests and responses.
✨ Retrying requests when an error occurs or when the response does not match the desired (useful for handling custom error responses).
👓 GET requests with separated parameters.
⚡️ Standard bodyBytes on ResponseData to encode or decode in the desired format.
🙌🏼 Array parameters on requests.
🖋 Supports self-signed certificates (except on Flutter Web).
🍦 Compatible with vanilla Dart projects or Flutter projects.
🎉 Null-safety.
⏲ Timeout configuration with duration and timeout functions.
⏳ Configure the delay for each retry attempt.

Usage #
import 'package:http_interceptor/http_interceptor.dart';
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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 LoggerInterceptor extends InterceptorContract {
@override
Future<BaseRequest> interceptRequest({
required BaseRequest request,
}) async {
print('----- Request -----');
print(request.toString());
print(request.headers.toString());
return request;
}

@override
Future<BaseResponse> interceptResponse({
required BaseResponse response,
}) async {
log('----- Response -----');
log('Code: ${response.statusCode}');
if (response is Response) {
log((response).body);
}
return response;
}
}
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Changing headers with interceptor:

class WeatherApiInterceptor implements InterceptorContract {
@override
Future<BaseRequest> interceptRequest({required BaseRequest request}) async {
try {
request.url.queryParameters['appid'] = OPEN_WEATHER_API_KEY;
request.url.queryParameters['units'] = 'metric';
request.headers[HttpHeaders.contentTypeHeader] = "application/json";
} catch (e) {
print(e);
}
return request;
}

@override
Future<BaseResponse> interceptResponse({required BaseResponse response}) async => response;
}
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You can also react to and modify specific types of requests and responses, such as StreamedRequest,StreamedResponse, or MultipartRequest :

class MultipartRequestInterceptor implements InterceptorContract {
@override
Future<BaseRequest> interceptRequest({required BaseRequest request}) async {
if(request is MultipartRequest){
request.fields['app_version'] = await PackageInfo.fromPlatform().version;
}
return request;
}

@override
Future<BaseResponse> interceptResponse({required BaseResponse response}) async {
if(response is StreamedResponse){
response.stream.asBroadcastStream().listen((data){
print(data);
});
}
return response;
}
}
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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 InterceptedHttp to do separate connections for different requests or using a InterceptedClient 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 InterceptedClient class.
class WeatherRepository {
Client client = InterceptedClient.build(interceptors: [
WeatherApiInterceptor(),
]);

Future<Map<String, dynamic>> fetchCityWeather(int id) async {
var parsedWeather;
try {
final response =
await client.get("$baseUrl/weather".toUri(), params: {'id': "$id"});
if (response.statusCode == 200) {
parsedWeather = json.decode(response.body);
} else {
throw Exception("Error while fetching. \n ${response.body}");
}
} catch (e) {
print(e);
}
return parsedWeather;
}

}
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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 InterceptedHttp class.
class WeatherRepository {

Future<Map<String, dynamic>> fetchCityWeather(int id) async {
var parsedWeather;
try {
final http = InterceptedHttp.build(interceptors: [
WeatherApiInterceptor(),
]);
final response =
await http.get("$baseUrl/weather".toUri(), params: {'id': "$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;
}

}
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Retrying requests #
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(BaseResponse response) async {
if (response.statusCode == 401) {
// Perform your token refresh here.

return true;
}

return false;
}
}
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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.
Sometimes it is helpful to have a cool-down phase between multiple requests. This delay could for example also differ between the first and the second retry attempt as shown in the following example.
class ExpiredTokenRetryPolicy extends RetryPolicy {
@override
Duration delayRetryAttemptOnResponse({required int retryAttempt}) {
return const Duration(milliseconds: 250) * math.pow(2.0, retryAttempt);
}
}
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Using self signed certificates #
You can achieve support for self-signed certificates by providing InterceptedHttp or InterceptedClient with the client parameter when using the build method on either of those, it should look something like this:
InterceptedClient #
Client client = InterceptedClient.build(
interceptors: [
WeatherApiInterceptor(),
],
client: IOClient(
HttpClient()
..badCertificateCallback = badCertificateCallback
..findProxy = findProxy,
);
);
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InterceptedHttp #
final http = InterceptedHttp.build(
interceptors: [
WeatherApiInterceptor(),
],
client: IOClient(
HttpClient()
..badCertificateCallback = badCertificateCallback
..findProxy = findProxy,
);
);
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Note: It is important to know that since both HttpClient and IOClient are part of dart:io package, this will not be a feature that you can perform on Flutter Web (due to BrowserClient and browser limitations).
Roadmap #
Check out our roadmap here.
We migrated our roadmap to better suit the needs for development since we use ClickUp as our task management tool.
Troubleshooting #
Open an issue and tell me, I will be happy to help you out as soon as I can.
Contributions #
Contributions are always welcomed and encouraged, we will always give you credit for your work on this section. If you are interested in maintaining the project on a regular basis drop me a line at me@codingale.dev.
Contributors #
Thanks to all the wonderful people contributing to improve this package. Check the Emoji Key for reference on what means what!

Alejandro Ulate Fallas💻 📖 ⚠️ 🤔 🚧
Konstantin Serov🤔
Virus1908🤔 💻 ⚠️
Wes Ehrlichman🤔 💻 ⚠️
Jan Lübeck🤔 💻 ⚠️
Lucas Alves🤔 💻 ⚠️
István Juhos🤔 💻 ⚠️

Scott Hyndman🤔
Islam Akhrarov🤔 ⚠️ 💻
Meysam📖
Martijn⚠️ 💻
MaciejZuk🐛
Lukas Kurz⚠️ 🤔 💻
Glenn Ruysschaert💻 ⚠️

Erick💻 ⚠️
javiermrz💻
nihar🤔
Ayush Yadav🤔