Response middleware?

[ThomasCartier]

Hi,
using the latest hyper, I would like to create a middleware that comes after the service, to check the presence of some headers, and possibly modify them.

Middlewares before the service (requests) are handled but I can't reuse the middleware strategy for the response because it expects a request type.

How to do it? I don't wan't to clutter my service with this because it's a fragile approach (we can forget it or whatever reason); I have multiple servers and code reuse is important.
Something like

let svc = hyper::service::service_fn(hello);
let svc = ServiceBuilder::new().layer_fn(Logger::new).service(svc).layer_fn(PostService::new);

would be nice.

Thanks!

[seanmonstar]

The Service trait allows for handling the request and the response. For instance, if using a closure:

service_fn(|req| {
    let inner_fut = inner.call(req);
    async move {
        let resp = inner_fut.await?;
        Ok(transform_resp(resp))
    }
});

You can do similarly with impl<Req> Service<Req>, or with Layer.

There's several examples, such as in tower-http, here's just one of many: https://docs.rs/tower-http/latest/tower_http/map_response_body/index.html

[ThomasCartier]

You are right, didn't dig enough before asking. Thanks!