Custom layers on *nested* router isn't getting called

[bryanburgers]

Bug Report

I created a service to do some custom routing that isn't supported by axum::Router. When I add it to a root-level router, it works fine. However, when I add it to a router and then nest that router, it doesn't ever seem to be called.

// This seems to work
let my_custom_router = ...;
let app = Router::new().layer(my_custom_router);

// This compiles, but my custom router never gets calls to `Service::call`
let my_custom_router = ...;
let nested = Router::new().layer(my_custom_router);
let app = Router::new().nest("/nested", nested);

Version

axum-nest-repro v0.1.0 (/Users/bryan/personal/axum-nest-repro)
├── axum v0.5.15
│   ├── axum-core v0.2.7

Platform

Darwin Bryans-MacBook-Pro.local 20.6.0 Darwin Kernel Version 20.6.0: Tue Feb 22 21:10:41 PST 2022; root:xnu-7195.141.26~1/RELEASE_X86_64 x86_64

Crates

• axum

Description

As mentioned above, it seems like when calling Router::nest with another Router as the target, my custom layer gets lost.

However, if I turn my custom layer into a service without using another Router and nest that, it seems to work fine (but then I lose the ability to do other additional routing).

Summary:

• 🥰 Custom layer at root level
• 🥰 Custom layer when turned into its own service and nested
• 🤬 Custom layer added to another Router, then nested in root Router

Reproduction is here: https://github.com/bryanburgers/axum-nest-repro.

To try it out, you can do cargo run in one terminal to start the server on 0.0.0.0:3000 and cargo test in another terminal.

Ultimately, the code that I would like to work looks like this

pub fn create_app(context: Context) -> Router {
    let odata_layer = odata_router::Router::new()
        .get("Property", get_property)    // GET /odata/Property('12345')
        .list("Property", list_property); // GET /odata/Property?$query=... 
    let odata_router = Router::new().layer(odata_layer);

    let api_router = Router::new()
        .route("/properties", get(list_own_properties).post(post_new_property))
        .route("/properties/:id", get(get_own_property).patch(patch_own_property))
        .route("/properties/:id/validate", post(validate_own_property));

    Router::new()
        .nest("/api", api_router)
        .nest("/odata", odata_router)
        .layer(Extension(context))

but once I try to nest odata_router instead of putting .layer(odata_layer) on the root, I can no longer get the odata_layer to handle requests.

[davidpdrsn]

Router::new().layer(odata_layer); only adds the layer to the fallback which is then discarded when you nest the router. Axum 0.5 doesn't support nested fallbacks.

A workaround is to box the nested service Router::new().layer(odata_layer).boxed_clone() using ServiceExt::boxed_clone.