can't merge or nest 2 routes with fallback

[Ludea]

• I have looked for existing issues (including closed) about this

Bug Report

Version

0.8.2

Platform

Ubuntu 24.04 x86_64

Crates

axum

Description

I created 3 routes:

• an http route with axum, wxith fallback_service to serve root and static file
• a tonic route which I use as axum::Router with into_axum_router() (Tonic add a fallback https://github.com/hyperium/tonic/blob/master/tonic/src/service/router.rs#L51)
• I created a third route, by merging or nesting the firs two, but get cannot merge rwo Router's that both have a fallback

One solution is to merge fallback between routes

[mladedav]

I think nesting should work.

But what would you expect to happen when you merge two routers that both define a fallback?

[Ludea]

let app = Router::new().nest("/", grpc).nest("/", http); give
Nesting at the root is no longer supported. Use merge instead ;

but I need to serve http at the root

[mladedav]

Nesting at root is explicitly not supported and I didn't get you're talking about nesting at the same path.

Anyway, what would you expect to have happened? You merge two routers with fallback, one fallback always returns 200, the other returns 404. What would you expect to happen when you call a non-existent route on the merged router?

[Ludea]

I modify to:

let app = Router::new().nest("/api", grpc).merge(http);

now I can reach static website at root, but not sub route (I use a js frontend lib)
If I use only one router, to create http route, with fallback_service, it works as expected.
The 2 routes I need to merge:

   let http = axum::Router::new()
        .fallback_service(serve_dir)
        .layer(TraceLayer::new_for_http());

    let mut routes = tonic::service::Routes::builder();
    routes.add_service(api);
    
  let grpc = routes
        .routes()
        .into_axum_router();

My goal is to do same thing as https://github.com/tokio-rs/axum/tree/axum-v0.6.20/examples/rest-grpc-multiplex

[mladedav]

But what would you expect to have happened when you call get("/this/path/does/not/exist/in/either/router")?

Would you expect the first router's fallback to run? Or the grpc one?

Having two fallbacks does not conceptually make sense, you need to get rid of one of them. I don't think you can do that currently though, we'll need to add a method on Router like remove_fallback.

[Ludea]

I would like only one fallback for both routes.

Another way is to not use fallback_service but route_service("/", ServeDir::new("static")) but get some issue with mime type

[Ludea]

removing fallback from another route is fine

[Ludea]

Another solution is to re enable nest routing with without_v07_checks()
Will you accept a PR to do that?

[mladedav]

So, the v07 checks exist so that people can move from 0.7 to 0.8 and have axum fail on startup if they use the old capture syntax. It's not intended to turn other features on or off.

Do you see an issue with merging after removing the fallback explicitly?

[jplatte]

axum v0.8.4 with Router::reset_fallback has been published :)