Async client interceptors?

[acoutts]

I would like to perform an async operation within an interceptor. The problem is it has to return a ResponseFuture, not a Future, so I cannot mark the interceptUnary method as async and perform asynchronous code within it (like access the platform method channel).

Is there a way to work around this to perform async operations within the interceptor?

3.0.2

Repro steps

  @override
  ResponseFuture<R> interceptUnary<Q, R>(
    ClientMethod<Q, R> method,
    Q request,
    CallOptions options,
    ClientUnaryInvoker<Q, R> invoker,
  ) async { } // error

[esenmx]

There are many issues and pull requests for this. Waiting https://github.com/grpc/grpc-dart/pull/489 to be merged.

[lazicah]

Any Solution?

[EnesKaraosman]

Any update/workaround?

[mraleph]

@EnesKaraosman you should probably use this code as a solution

[EnesKaraosman]

@EnesKaraosman you should probably use this code as a solution

Tried this one but received syntax issues with dart 2.18.4

[mraleph]

Tried this one but received syntax issues with dart 2.18.4

Well, you most likely can fix them. The code should still work but needs to be updated.

[lazicah]

Hi thanks for this solutions, but how I can return an custom error in the interceptor?

[zs-dima]

@mraleph it is very useful to have Async interceptStreaming as well. For example we want retrive Firebase Token in the interceptor - it will affect interceptStreaming and interceptUnary

Ideally:

  @override
  Stream<R> interceptStreaming<Q, R>(
    ClientMethod<Q, R> method,
    Stream<Q> requests,
    CallOptions options,
    ClientStreamingInvoker<Q, R> invoker,
  ) async* {
    final token = await _getToken?.call();
    yield* invoker(method, requests, options.withToken(token));
  }

  @override
  FutureOr<R> interceptUnary<Q, R>(
    ClientMethod<Q, R> method,
    Q request,
    CallOptions options,
    ClientUnaryInvoker<Q, R> invoker,
  ) async {
    final token = await _getToken?.call();
    return invoker(method, request, options.withToken(token));
  }

[natebot13]

Came here looking for exactly the same need as @zs-dima . I would love to be able to just await in the intercept* methods. I've been trying to rework the workaround "retry" solution from @mraleph but I'm getting confused with the multiple layers of completers and futures.

[natebot13]

After a lot of experimentation and nearly modifying the package for my own needs, I discovered metadataProviders which does exactly what I needed to modify the call options metadata before the request is made. I remember reading that field a while ago, but somehow ignored it, thinking an interceptor is what I really needed.

It turned out to be very simple:

@override
ResponseFuture<R> interceptUnary<Q, R>(
  ClientMethod<Q, R> method,
  Q request,
  CallOptions options,
  ClientUnaryInvoker<Q, R> invoker,
) {
  addToken(Map<String, String> metadata, String _) async {
    final token = await FirebaseAuth.instance.currentUser?.getIdToken();
    metadata['auth'] = token ?? '';
  }

  return invoker(
    method,
    request,
    options.mergedWith(CallOptions(providers: [addToken])),
  );
}