Fix trim trailing slash middleware

The axum docs point out that any middleware that should affect routing must wrap
the Router. In 0.6.12 we rely on a bug in axum routing that allows the
trailing slash middleware to work on nested paths (but fails on root
paths). In 0.6.13 onwards this bug is no longer present, so we lose the
trailing slash removal.

This change fixes the issue.

tokio-rs/axum#1978
https://docs.rs/axum/0.6.18/axum/middleware/index.html#rewriting-request-uri-in-middleware

Author: markgoddard

Cargo.lock

@@ -33,6 +33,7 @@ thiserror = "1.0"
 tokio = { version = "1.28", features = ["full"] }
 tower = "0.4"
 tower-http = { version = "0.4", features = ["normalize-path", "trace", "validate-request"] }
+tower-service = "0.3"
 tokio-stream = "0.1"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }

Cargo.toml

@@ -19,6 +19,7 @@ use axum::{
     Router, TypedHeader,
 };
 
+use tower::Layer;
 use tower::ServiceBuilder;
 use tower_http::normalize_path::NormalizePathLayer;
 use tower_http::trace::TraceLayer;
@@ -54,9 +55,7 @@ impl IntoResponse for models::Response {
 /// * a [tower_http::trace::TraceLayer] for tracing requests and responses
 /// * a [tower_http::validate_request::ValidateRequestHeaderLayer] for validating authorisation
 ///   headers
-/// * a [tower_http::normalize_path::NormalizePathLayer] for trimming trailing slashes from
-///   requests
-pub fn router() -> Router {
+fn router() -> Router {
     fn v1() -> Router {
         Router::new()
             .route("/count", post(operation_handler::<operations::Count>))
@@ -85,7 +84,25 @@ pub fn router() -> Router {
     Router::new()
         .route("/.well-known/s3-active-storage-schema", get(schema))
         .nest("/v1", v1())
-        .layer(NormalizePathLayer::trim_trailing_slash())
+}
+
+/// Returns a [tower_service::Service] for the Active Storage server API
+///
+/// The service is populated with all routes as well as the following middleware:
+///
+/// * a [tower_http::trace::TraceLayer] for tracing requests and responses
+/// * a [tower_http::validate_request::ValidateRequestHeaderLayer] for validating authorisation
+///   headers
+/// * a [tower_http::normalize_path::NormalizePathLayer] for trimming trailing slashes from
+///   requests
+pub fn service() -> tower_http::normalize_path::NormalizePath<Router> {
+    // FIXME: The return type should be some form of tower_service::Service, but couldn't find the
+    // necessary trait bounds.
+
+    // Note that any middleware that should affect routing must wrap the router.
+    // See
+    // https://docs.rs/axum/0.6.18/axum/middleware/index.html#rewriting-request-uri-in-middleware.
+    NormalizePathLayer::trim_trailing_slash().layer(router())
 }
 
 /// TODO: Return an OpenAPI schema

src/app.rs

@@ -24,6 +24,7 @@
 
 use std::{net::SocketAddr, process::exit, str::FromStr, time::Duration};
 
+use axum::ServiceExt;
 use axum_server::{tls_rustls::RustlsConfig, Handle};
 use clap::Parser;
 use expanduser::expanduser;
@@ -77,7 +78,7 @@ async fn main() {
 
     init_tracing();
 
-    let router = app::router();
+    let service = app::service();
     let addr = SocketAddr::from_str(&format!("{}:{}", args.host, args.port))
         .expect("invalid host name, IP address or port number");
 
@@ -120,14 +121,14 @@ async fn main() {
         // run HTTPS server with hyper
         axum_server::bind_rustls(addr, tls_config)
             .handle(handle)
-            .serve(router.into_make_service())
+            .serve(service.into_make_service())
             .await
             .unwrap();
     } else {
         // run HTTP server with hyper
         axum_server::bind(addr)
             .handle(handle)
-            .serve(router.into_make_service())
+            .serve(service.into_make_service())
             .await
             .unwrap();
     }