Update middleware.md - existing documentation doesn't compile

[CrypticError]

I ran into an issue following the documentation trying to implement a uri-rewrite middleware.

Found https://users.rust-lang.org/t/rewrite-request-uri-in-middleware-for-axum/104619 - which fixed this issue, so updating the doc to reflect this

Motivation

Solution

[mladedav]

When I copy the original code from docs it compiles for me. CI also fails on the changes you made because that documentation example does not seem to compile.

The issue you linked also seems to have been caused by an incorrect signature of the middleware.

Can you try providing a full example of what regarding this example does not compile for you?

[CrypticError]

Hmm, this code errors for me with some very unhelpful error messages.

pub async fn api_versioning_middleware<B>(mut req: Request<B>) -> Request<B> {
    let path = req.uri().path();

    let version = API_VERSIONING_PATTERN
        .captures(path)
        .and_then(|x| x.get(1).map(|m| ApiVersion::from_str(m.as_str())))
        .unwrap_or_else(|| Ok(ApiVersion::latest()))
        .unwrap_or(ApiVersion::latest());

    let new_path = API_VERSIONING_PATTERN.replace(path, "/").to_string();
    let new_uri = Builder::new().path_and_query(new_path).build().unwrap();
    *req.uri_mut() = new_uri;

    req.extensions_mut().insert(version);
    req
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
    // this can be any `tower::Layer`
    let middleware = tower::util::MapRequestLayer::new(api_versioning_middleware);

    let app = Router::new();

    // apply the layer around the whole `Router`
    // this way the middleware will run before `Router` receives the request
    let app_with_middleware = middleware.layer(app);

    let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
    axum::serve(listener, app_with_middleware.into_make_service())
        .await
        .unwrap();
    Ok(())
}

error[E0599]: the method `into_make_service` exists for struct `MapRequest<Router<_>, ...>`, but its trait bounds were not satisfied
  --> app\api-backend\src\main.rs:83:47
   |
83 |     axum::serve(listener, app_with_middleware.into_make_service())
   |                                               ^^^^^^^^^^^^^^^^^ method cannot be called on `MapRequest<Router<_>, ...>` due to unsatisfied trait bounds
   |
  ::: C:\Users\user\.cargo\registry\src\index.crates.io-6f17d22bba15001f\tower-0.5.2\src\util\map_request.rs:10:1
   |
10 | pub struct MapRequest<S, F> {
   | --------------------------- doesn't satisfy `_: Service<_>` or `_: ServiceExt<_>`
   |
   = note: the full type name has been written to 'C:\Users\user\RustroverProjects\apex-monorepo\target\debug\deps\api_backend.long-type-10123062717469459164.txt'
   = note: consider using `--verbose` to print the full type name to the console
   = note: the following trait bounds were not satisfied:
           `tower::util::MapRequest<Router<_>, fn(axum::http::Request<_>) -> impl Future<Output = axum::http::Request<_>> {api_versioning_middleware::<_>}>: Service<_>`
           which is required by `tower::util::MapRequest<Router<_>, fn(axum::http::Request<_>) -> impl Future<Output = axum::http::Request<_>> {api_versioning_middleware::<_>}>: axum::ServiceExt<_>`
           `&tower::util::MapRequest<Router<_>, fn(axum::http::Request<_>) -> impl Future<Output = axum::http::Request<_>> {api_versioning_middleware::<_>}>: Service<_>`
           which is required by `&tower::util::MapRequest<Router<_>, fn(axum::http::Request<_>) -> impl Future<Output = axum::http::Request<_>> {api_versioning_middleware::<_>}>: axum::ServiceExt<_>`
           `&mut tower::util::MapRequest<Router<_>, fn(axum::http::Request<_>) -> impl Future<Output = axum::http::Request<_>> {api_versioning_middleware::<_>}>: Service<_>`
           which is required by `&mut tower::util::MapRequest<Router<_>, fn(axum::http::Request<_>) -> impl Future<Output = axum::http::Request<_>> {api_versioning_middleware::<_>}>: axum::ServiceExt<_>`

Cargo.toml dependencies

[dependencies]
anyhow = "1.0"
indexmap = { version = "2.7", features = ["serde"] }
serde = { version = "1.0", features = ["derive"] }
sqlx = { version = "0.8", features = ["postgres", "runtime-tokio", "tls-rustls"] }
toml = "0.8"
tokio = { version = "1.43", features = ["full"] }
axum = "0.8"
tower = { version = "0.5", features = ["util"] }
serde_json = "1.0"
regex = "1.11"
rand = "0.9"
base64 = "0.22"
argon2 = "0.5"
axum-macros = "0.5.0"
zxcvbn = "3.1.0"
validator = { version = "0.20.0", features = ["derive"] }
lazy_static = "1.5.0"

Sorry I am very new to rust, so it could be some horrible oversight on my part, but assume it was just outdated documentation due to the linked changes working.

[CrypticError]

I just noticed that my signature differs from the one in the doc, as I am taking a mutable reference.

It seems like axom::middleware::map_request is already documented on this change difference.

Create a middleware from an async function that transforms a request.
This differs from tower::util::MapRequest in that it allows you to easily run axum-specific extractors

I guess the thing that I actually want is better error messages, but that is clearly out of scope.

Thanks for your time looking into this, and sorry for the inconvenience.