Add `MatchedPath` extractor (#412)

Fixes #386

CHANGELOG.md

@@ -136,6 +136,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
       without trailing a slash.
 - **breaking:** `EmptyRouter` has been renamed to `MethodNotAllowed` as its only
   used in method routers and not in path routers (`Router`)
+- **added:** Add `extract::MatchedPath` for accessing path in router that
+  matched request ([#412])
 
 [#339]: https://github.com/tokio-rs/axum/pull/339
 [#286]: https://github.com/tokio-rs/axum/pull/286
@@ -147,6 +149,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 [#404]: https://github.com/tokio-rs/axum/pull/404
 [#405]: https://github.com/tokio-rs/axum/pull/405
 [#408]: https://github.com/tokio-rs/axum/pull/408
+[#412]: https://github.com/tokio-rs/axum/pull/412
 
 # 0.2.8 (07. October, 2021)
 

Cargo.toml

@@ -60,6 +60,7 @@ serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 tokio = { version = "1.6.1", features = ["macros", "rt", "rt-multi-thread", "net"] }
 tokio-stream = "0.1"
+tracing = "0.1"
 uuid = { version = "0.8", features = ["serde", "v4"] }
 
 [dev-dependencies.tower]

src/extract/matched_path.rs

@@ -0,0 +1,86 @@
+use super::{rejection::*, FromRequest, RequestParts};
+use async_trait::async_trait;
+use std::sync::Arc;
+
+/// Access the path in the router that matches the request.
+///
+/// ```
+/// use axum::{
+///     Router,
+///     extract::MatchedPath,
+///     routing::get,
+/// };
+///
+/// let app = Router::new().route(
+///     "/users/:id",
+///     get(|path: MatchedPath| async move {
+///         let path = path.as_str();
+///         // `path` will be "/users/:id"
+///     })
+/// );
+/// # async {
+/// # axum::Server::bind(&"".parse().unwrap()).serve(app.into_make_service()).await.unwrap();
+/// # };
+/// ```
+///
+/// `MatchedPath` can also be accessed from middleware via request extensions.
+/// This is useful for example with [`Trace`](tower_http::trace::Trace) to
+/// create a span that contains the matched path:
+///
+/// ```
+/// use axum::{
+///     Router,
+///     extract::MatchedPath,
+///     http::Request,
+///     routing::get,
+/// };
+/// use tower_http::trace::TraceLayer;
+///
+/// let app = Router::new()
+///     .route("/users/:id", get(|| async { /* ... */ }))
+///     .layer(
+///         TraceLayer::new_for_http().make_span_with(|req: &Request<_>| {
+///             let path = if let Some(path) = req.extensions().get::<MatchedPath>() {
+///                 path.as_str()
+///             } else {
+///                 req.uri().path()
+///             };
+///             tracing::info_span!("http-request", %path)
+///         }),
+///     );
+/// # async {
+/// # axum::Server::bind(&"".parse().unwrap()).serve(app.into_make_service()).await.unwrap();
+/// # };
+/// ```
+#[derive(Clone, Debug)]
+pub struct MatchedPath(pub(crate) Arc<str>);
+
+impl MatchedPath {
+    /// Returns a `str` representation of the path.
+    pub fn as_str(&self) -> &str {
+        &*self.0
+    }
+}
+
+#[async_trait]
+impl<B> FromRequest<B> for MatchedPath
+where
+    B: Send,
+{
+    type Rejection = MatchedPathRejection;
+
+    async fn from_request(req: &mut RequestParts<B>) -> Result<Self, Self::Rejection> {
+        let extensions =
+            req.extensions()
+                .ok_or(MatchedPathRejection::ExtensionsAlreadyExtracted(
+                    ExtensionsAlreadyExtracted,
+                ))?;
+
+        let matched_path = extensions
+            .get::<Self>()
+            .ok_or(MatchedPathRejection::MatchedPathMissing(MatchedPathMissing))?
+            .clone();
+
+        Ok(matched_path)
+    }
+}

src/extract/mod.rs

@@ -172,6 +172,7 @@ pub mod ws;
 mod content_length_limit;
 mod extension;
 mod form;
+mod matched_path;
 mod path;
 mod query;
 mod raw_query;
@@ -186,6 +187,7 @@ pub use self::{
     extension::Extension,
     extractor_middleware::extractor_middleware,
     form::Form,
+    matched_path::MatchedPath,
     path::Path,
     query::Query,
     raw_query::RawQuery,

src/extract/rejection.rs

@@ -273,6 +273,23 @@ composite_rejection! {
     }
 }
 
+define_rejection! {
+    #[status = INTERNAL_SERVER_ERROR]
+    #[body = "No matched path found"]
+    /// Rejection if no matched path could be found.
+    ///
+    /// See [`MatchedPath`](super::MatchedPath) for more details.
+    pub struct MatchedPathMissing;
+}
+
+composite_rejection! {
+    /// Rejection used for [`MatchedPath`](super::MatchedPath).
+    pub enum MatchedPathRejection {
+        ExtensionsAlreadyExtracted,
+        MatchedPathMissing,
+    }
+}
+
 /// Rejection used for [`ContentLengthLimit`](super::ContentLengthLimit).
 ///
 /// Contains one variant for each way the

src/routing/mod.rs

@@ -738,6 +738,11 @@ where
         let id = *match_.value;
         req.extensions_mut().insert(id);
 
+        if let Some(matched_path) = self.node.paths.get(&id) {
+            req.extensions_mut()
+                .insert(crate::extract::MatchedPath(matched_path.clone()));
+        }
+
         let params = match_
             .params
             .iter()
@@ -1059,7 +1064,7 @@ impl<B> Service<Request<B>> for Route<B> {
 #[derive(Clone, Default)]
 struct Node {
     inner: matchit::Node<RouteId>,
-    paths: Vec<(Arc<str>, RouteId)>,
+    paths: HashMap<RouteId, Arc<str>>,
 }
 
 impl Node {
@@ -1070,12 +1075,12 @@ impl Node {
     ) -> Result<(), matchit::InsertError> {
         let path = path.into();
         self.inner.insert(&path, val)?;
-        self.paths.push((path.into(), val));
+        self.paths.insert(val, path.into());
         Ok(())
     }
 
     fn merge(&mut self, other: Node) -> Result<(), matchit::InsertError> {
-        for (path, id) in other.paths {
+        for (id, path) in other.paths {
             self.insert(&*path, id)?;
         }
         Ok(())

src/tests/mod.rs

@@ -1,6 +1,7 @@
 #![allow(clippy::blacklisted_name)]
 
 use crate::error_handling::HandleErrorLayer;
+use crate::extract::MatchedPath;
 use crate::BoxError;
 use crate::{
     extract::{self, Path},
@@ -27,6 +28,7 @@ use std::{
 };
 use tower::{service_fn, timeout::TimeoutLayer, ServiceBuilder};
 use tower_http::auth::RequireAuthorizationLayer;
+use tower_http::trace::TraceLayer;
 use tower_service::Service;
 
 pub(crate) use helpers::*;
@@ -618,6 +620,26 @@ async fn with_and_without_trailing_slash() {
     assert_eq!(res.text().await, "without tsr");
 }
 
+#[tokio::test]
+async fn access_matched_path() {
+    let app = Router::new()
+        .route(
+            "/:key",
+            get(|path: MatchedPath| async move { path.as_str().to_string() }),
+        )
+        .layer(
+            TraceLayer::new_for_http().make_span_with(|req: &Request<_>| {
+                let path = req.extensions().get::<MatchedPath>().unwrap().as_str();
+                tracing::info_span!("http-request", %path)
+            }),
+        );
+
+    let client = TestClient::new(app);
+
+    let res = client.get("/foo").send().await;
+    assert_eq!(res.text().await, "/:key");
+}
+
 pub(crate) fn assert_send<T: Send>() {}
 pub(crate) fn assert_sync<T: Sync>() {}
 pub(crate) fn assert_unpin<T: Unpin>() {}