Flutter Chopper 401 renew & retry interceptor

Question

I'm using Chopper in my flutter app and what I need to do is, when I get 401 response status code (unauthorized) from my API, I must call another endpoint that will refresh my token and save it into secured storage, when all of this is done, I need to retry the request instantly (so that user cannot notice that his token expired). Is this dooable with Chopper only, or I have to use some other package?

Answer 1

It is possible. You need to use the authenticator field on the Chopper client, e.g.

 final ChopperClient client = ChopperClient(
  baseUrl: backendUrl,
  interceptors: [HeaderInterceptor()],
  services: <ChopperService>[
    _$UserApiService(),
  ],
  converter: converter,
  authenticator: MyAuthenticator(),
);

And your authenticator class, should look something like this:

class MyAuthenticator extends Authenticator {
  @override
  FutureOr<Request?> authenticate(
   Request request, Response<dynamic> response) async {
   if (response.statusCode == 401) {
     String? newToken = await refreshToken();

      final Map<String, String> updatedHeaders =
         Map<String, String>.of(request.headers);

        if (newToken != null) {
          newToken = 'Bearer $newToken';
          updatedHeaders.update('Authorization', (String _) => newToken!,
           ifAbsent: () => newToken!);
         return request.copyWith(headers: updatedHeaders);
        }
      }
    return null;
 }

Admittedly, it wasn't that easy to find/understand (though it is the first property of the chopper client mentioned in their docs), but it is precisely what this property is for. I was going to move to dio myself, but I still had the same issue with type conversion on a retry.

EDIT: You will probably want to keep a retry count somewhere so you don't end up in a loop.