Instead of messing with interceptors (since you are not dealing with
metadata) have you considered just using methods related to context(s)?
e.g. on the server side you can just restructure your existing stub code
and do something like
public void sayHello(HelloRequest req, StreamObserver<HelloReply>
responseObserver) {
String resource = req.getName();
MyCallable callable = new MyCallable(); // your server code is in MyCallable
result = Context.current().withValue(ResourceNameKey,
resource).wrap(callable);
responseObserver.onNext(result);
}
I think this is much easier than using an interceptor and/or delaying the
call etc. Or else you can have the client itself insert the resource name
in Metadata in which case the serverInterceptor can read that and add it to
the server context. Hopefully you know how to do that.
On Fri, Sep 23, 2022 at 8:15 AM 'Hans Wustrack' via grpc.io <
[email protected]> wrote:
> Hi all,
>
> I'm implementing a simple resource oriented API with a gRPC server. Every
> request message type will have a 'name' field (or similar) that specifies
> the resource to be operated on. I would like to add the value of that name
> field to the gRPC context on every request, so it can be used later in
> application code.
>
> As this is an action I'd like to perform on every request, a
> ServerInteceptor seemed like an appropriate place to add this bit of
> functionality. In implementing, I've taken inspiration from previous
> questions here and on the github repo:
> https://groups.google.com/g/grpc-io/c/_osH2D6L9Ck
> https://github.com/grpc/grpc-java/issues/5414
>
> Our server will only accept unary calls, so the pattern of delaying
> next.startCall() by setting a NOOP listener until we receive the first
> message seems okay for our use case. In OnMessage, we'll parse the request
> message and call Contexts.interceptCall with the necessary info from the
> request.
>
> I have a few questions about this approach:
>
> - We need to call call.request(1) to initiate the request for the first
> message (as discussed in grpc-io/c/_osH2D6L9Ck). Would this create issues
> if we need more than one ServerInterceptor of this type? I.e. we'd have
> multiple interceptors initially with NOOP listeners delaying the call and
> calling call.request(1).
>
> - I couldn't find many examples of implementing a ServerInterceptor that
> adds a piece of information from a request message to the context. Should
> we consider other ways of handling this like including the necessary values
> in Metadata or adding to context in the handlers?
>
> Thanks!
>
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