How to build an HttpInterceptor Service in Angular Dart? - dart

Question

I am trying to port the code of an Angular 2 app to Angular Dart, so that I can reuse the business logic in Flutter.
My app makes use of HttpInterceptors for Error handling and server authorization.
In typescript I would inject a simple service :
#Injectable({
providedIn: 'root'
})
export class InterceptorService implements HttpInterceptor {
intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
return;
}
constructor(private auth: AuthService) { }
intercept(
req: HttpRequest<any>,
next: HttpHandler
): Observable<HttpEvent<any>> {}
}
But the Dart API does not seem to have an HttpInterceptor class. Does one have to extend the HttpClient class in order to do so ?
I have looked at this S.O question but it dates back from 5 years ago, the way to do it has probably changed quite a bit in the meantime.

Answer 1

Turns out there are a couple ways you can achieve this in Angular Dart / Flutter.
Some third party libraries built on top of dart http provide convenience methods for Http interception (DIO, Http Interceptor). However, both handle interception at the client level.
I decided to go with the Dart Http library, using the recommended method :
class UserAgentClient extends http.BaseClient {
final String userAgent;
final http.Client _inner;
UserAgentClient(this.userAgent, this._inner);
Future<StreamedResponse> send(BaseRequest request) {
request.headers['user-agent'] = userAgent;
return _inner.send(request);
}
}