Refuse to use a decorating `Client` and `Service` if `as()` or `serviceAdded()` is not overriden.

A common mistake a user makes when writing a decorator is:

ServerBuilder sb = new ServerBuilder();
sb.service("/svc", myService.decorate(delegate -> (ctx, req) -> {
    ...
    return delegate.serve(ctx, req);
}));

The above decorator is not correct because the returned service does not override the default as() and serviceAdded() implementation. A correct usage is:

sb.service("/svc", myService.decorate((delegate, ctx, req) -> {
    return delegate.serve(ctx, req);
});
// or
sb.service("/svc", myService.decorate(delegate -> new SimpleDecoratingService(delegate) {
    ...
    return delegate().serve(ctx, req);
    ...
}));

We can detect such a mistake by checking if the decorator overrides the default as() and serviceAdded() implementation using Java reflection API and raise an exception.

[trustin]

🤣 Yes, please!

[ikhoon]

I’m not trustin, but I could tell “Yes, please!” 😄