Rewrite URI for sub-router

[vladkens]

Summary

Hi. I want to rewrite URI for sub-router. For example I have some api routes which can return .json or .xml format, and by default I have json.

So my routers can looks like:

/api/{something}/{name}
/api/{something}/{name}.json
/api/{something}/{name}.xml

I want to rewrite last two routes to pass .ext to query params as ?format=ext. This is not hard to do with middleware::map_request, but seems like path extractors works before map_request middleware applied, so in handler I receive {name}.{ext}. Handle example:

pub type Dict = HashMap<String, String>;

fn ext_to_qs<B>(mut req: Request<B>) -> Request<B> {
  let uri = req.uri().to_string();
  let re = Regex::new(r"^([^?]+?)(?:\.(xml|json))(\?.*)?$").unwrap();

  if let Some(caps) = re.captures(&uri) {
    let new_path = caps.get(1).unwrap().as_str().to_string();
    let ext = caps.get(2).unwrap().as_str();

    let new_query = match req.uri().query() {
      Some(existing_query) => format!("{}&format={}", existing_query, ext),
      None => format!("format={}", ext),
    };

    let new_uri = format!("{}?{}", new_path, new_query);
    *req.uri_mut() = new_uri.parse().unwrap();
  }

  req
}

fn handler(Path(name): Path<String>, Query(qs): Query<Dict>
) -> impl IntoResponse {
  println!(">> kind: {:?}, name: {}, qs: {:?}", kind, name, qs); // name still have ext, format added to qs
  println!(">> req: {:?}", req.uri()); // path without .ext here
  "hello".into_response()
}

In docs I found this guide to apply the layer around the whole Router, this working well for top level router:

let pages = Router::new()
  .route("/api/{name}", get(handler)) // and more api endpoinds
  .route("/", get(pages::index)); // and more page endpoinds
let middleware = tower::util::MapRequestLayer::new(ext_to_qs);
let app_with_middleware = middleware.layer(app);

let listener = tokio::net::TcpListener::bind("0.0.0.0:8080").await.unwrap();
axum::serve(listener, app_with_middleware.into_make_service()).await.unwrap();

But it not working if I want split apis and pages routes (like I want to rewrite path only for apis routes):

let pages = Router::new().route("/", get(pages::index));
let apis: Router<()> = Router::new().route("/api/{name}", get(handler));

let middleware = tower::util::MapRequestLayer::new(ext_to_qs);
let apis_with_muddleware = middleware.layer(apis);

let app: Router<()> = Router::new()
  .merge(pages) // ok
  .merge(apis_with_muddleware); // some long error here
  // or: .merge(apis_with_muddleware.into());


let listener = tokio::net::TcpListener::bind("0.0.0.0:8080").await.unwrap();
axum::serve(listener, app.into_make_service()).await.unwrap();

So final question is it possible to rewrite URI only for part of routes (sub-router), in order to extractors also respect to it?

axum version

0.8.1

[mladedav]

You can nest_service under /api which can be any service and doesn't have to be a Router.

[vladkens]

Thank you. So if I have multiple routes that need this behavior, I should use nest_service for all of them? For example, I'm working on a badges service and I have this routes, then I should wrap each specific endpoint that can return JSON / SVG depending on the endpoint in nest_service?

[mladedav]

If you want to rewrite the URL in this way, yeah.

Or you can rewrite the URL globally if that's something you're ok with.

[vladkens]

Thank you @mladedav. I implemented it with global handler (for reference), but it's also good to know about a separate service.