Add OptionalPath extractor (#1889)

Co-authored-by: David Pedersen <[email protected]>

axum-extra/src/extract/mod.rs

@@ -1,6 +1,8 @@
 //! Additional extractors.
 
 mod cached;
+mod optional_path;
+mod with_rejection;
 
 #[cfg(feature = "form")]
 mod form;
@@ -14,9 +16,7 @@ mod query;
 #[cfg(feature = "multipart")]
 pub mod multipart;
 
-mod with_rejection;
-
-pub use self::cached::Cached;
+pub use self::{cached::Cached, optional_path::OptionalPath, with_rejection::WithRejection};
 
 #[cfg(feature = "cookie")]
 pub use self::cookie::CookieJar;
@@ -39,5 +39,3 @@ pub use self::multipart::Multipart;
 #[cfg(feature = "json-lines")]
 #[doc(no_inline)]
 pub use crate::json_lines::JsonLines;
-
-pub use self::with_rejection::WithRejection;

axum-extra/src/extract/optional_path.rs

@@ -0,0 +1,102 @@
+use axum::{
+    async_trait,
+    extract::{path::ErrorKind, rejection::PathRejection, FromRequestParts, Path},
+    RequestPartsExt,
+};
+use serde::de::DeserializeOwned;
+
+/// Extractor that extracts path arguments the same way as [`Path`], except if there aren't any.
+///
+/// This extractor can be used in place of `Path` when you have two routes that you want to handle
+/// in mostly the same way, where one has a path parameter and the other one doesn't.
+///
+/// # Example
+///
+/// ```
+/// use std::num::NonZeroU32;
+/// use axum::{
+///     response::IntoResponse,
+///     routing::get,
+///     Router,
+/// };
+/// use axum_extra::extract::OptionalPath;
+///
+/// async fn render_blog(OptionalPath(page): OptionalPath<NonZeroU32>) -> impl IntoResponse {
+///     // Convert to u32, default to page 1 if not specified
+///     let page = page.map_or(1, |param| param.get());
+///     // ...
+/// }
+///
+/// let app = Router::new()
+///     .route("/blog", get(render_blog))
+///     .route("/blog/:page", get(render_blog));
+/// # let app: Router = app;
+/// ```
+#[derive(Debug)]
+pub struct OptionalPath<T>(pub Option<T>);
+
+#[async_trait]
+impl<T, S> FromRequestParts<S> for OptionalPath<T>
+where
+    T: DeserializeOwned + Send + 'static,
+    S: Send + Sync,
+{
+    type Rejection = PathRejection;
+
+    async fn from_request_parts(
+        parts: &mut http::request::Parts,
+        _: &S,
+    ) -> Result<Self, Self::Rejection> {
+        match parts.extract::<Path<T>>().await {
+            Ok(Path(params)) => Ok(Self(Some(params))),
+            Err(PathRejection::FailedToDeserializePathParams(e))
+                if matches!(e.kind(), ErrorKind::WrongNumberOfParameters { got: 0, .. }) =>
+            {
+                Ok(Self(None))
+            }
+            Err(e) => Err(e),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::num::NonZeroU32;
+
+    use axum::{routing::get, Router};
+
+    use super::OptionalPath;
+    use crate::test_helpers::TestClient;
+
+    #[crate::test]
+    async fn supports_128_bit_numbers() {
+        async fn handle(OptionalPath(param): OptionalPath<NonZeroU32>) -> String {
+            let num = param.map_or(0, |p| p.get());
+            format!("Success: {num}")
+        }
+
+        let app = Router::new()
+            .route("/", get(handle))
+            .route("/:num", get(handle));
+
+        let client = TestClient::new(app);
+
+        let res = client.get("/").send().await;
+        assert_eq!(res.text().await, "Success: 0");
+
+        let res = client.get("/1").send().await;
+        assert_eq!(res.text().await, "Success: 1");
+
+        let res = client.get("/0").send().await;
+        assert_eq!(
+            res.text().await,
+            "Invalid URL: invalid value: integer `0`, expected a nonzero u32"
+        );
+
+        let res = client.get("/NaN").send().await;
+        assert_eq!(
+            res.text().await,
+            "Invalid URL: Cannot parse `\"NaN\"` to a `u32`"
+        );
+    }
+}