Clean up RequestParts API

In http-body 0.4.3 `BoxBody` implements `Default`. This allows us to
clean up the API of `RequestParts` quite a bit.

CHANGELOG.md

@@ -30,6 +30,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Removed `extract::UrlParams` and `extract::UrlParamsMap`. Use `extract::Path` instead
 - `EmptyRouter` now requires the response body to implement `Send + Sync + 'static'` ([#108](https://github.com/tokio-rs/axum/pull/108))
 - `ServiceExt` has been removed and its methods have been moved to `RoutingDsl` ([#160](https://github.com/tokio-rs/axum/pull/160))
+- `extractor_middleware` now requires `RequestBody: Default` ([#167](https://github.com/tokio-rs/axum/pull/167))
+- Convert `RequestAlreadyExtracted` to an enum with each possible error variant ([#167](https://github.com/tokio-rs/axum/pull/167))
 - These future types have been moved
     - `extract::extractor_middleware::ExtractorMiddlewareResponseFuture` moved
       to `extract::extractor_middleware::future::ResponseFuture` ([#133](https://github.com/tokio-rs/axum/pull/133))

Cargo.toml

@@ -22,7 +22,7 @@ bitflags = "1.0"
 bytes = "1.0"
 futures-util = "0.3"
 http = "0.2"
-http-body = "0.4.2"
+http-body = "0.4.3"
 hyper = { version = "0.14", features = ["server", "tcp", "http1", "stream"] }
 pin-project-lite = "0.2.7"
 regex = "1.5"

src/error.rs

@@ -13,6 +13,16 @@ impl Error {
             inner: error.into(),
         }
     }
+
+    pub(crate) fn downcast<T>(self) -> Result<T, Self>
+    where
+        T: StdError + 'static,
+    {
+        match self.inner.downcast::<T>() {
+            Ok(t) => Ok(*t),
+            Err(err) => Err(*err.downcast().unwrap()),
+        }
+    }
 }
 
 impl fmt::Display for Error {

src/extract/extractor_middleware.rs

@@ -152,7 +152,7 @@ where
 impl<S, E, ReqBody, ResBody> Service<Request<ReqBody>> for ExtractorMiddleware<S, E>
 where
     E: FromRequest<ReqBody> + 'static,
-    ReqBody: Send + 'static,
+    ReqBody: Default + Send + 'static,
     S: Service<Request<ReqBody>, Response = Response<ResBody>> + Clone,
     ResBody: http_body::Body<Data = Bytes> + Send + Sync + 'static,
     ResBody::Error: Into<BoxError>,
@@ -212,6 +212,7 @@ impl<ReqBody, S, E, ResBody> Future for ResponseFuture<ReqBody, S, E>
 where
     E: FromRequest<ReqBody>,
     S: Service<Request<ReqBody>, Response = Response<ResBody>>,
+    ReqBody: Default,
     ResBody: http_body::Body<Data = Bytes> + Send + Sync + 'static,
     ResBody::Error: Into<BoxError>,
 {
@@ -223,12 +224,13 @@ where
 
             let new_state = match this.state.as_mut().project() {
                 StateProj::Extracting { future } => {
-                    let (mut req, extracted) = ready!(future.as_mut().poll(cx));
+                    let (req, extracted) = ready!(future.as_mut().poll(cx));
 
                     match extracted {
                         Ok(_) => {
                             let mut svc = this.svc.take().expect("future polled after completion");
-                            let future = svc.call(req.into_request());
+                            let req = req.try_into_request().unwrap_or_default();
+                            let future = svc.call(req);
                             State::Call { future }
                         }
                         Err(err) => {

src/extract/mod.rs

@@ -244,7 +244,7 @@
 //!
 //! [`body::Body`]: crate::body::Body
 
-use crate::response::IntoResponse;
+use crate::{response::IntoResponse, Error};
 use async_trait::async_trait;
 use http::{header, Extensions, HeaderMap, Method, Request, Uri, Version};
 use rejection::*;
@@ -397,32 +397,45 @@ impl<B> RequestParts<B> {
         }
     }
 
-    #[allow(clippy::wrong_self_convention)]
-    pub(crate) fn into_request(&mut self) -> Request<B> {
+    pub(crate) fn try_into_request(self) -> Result<Request<B>, Error> {
         let Self {
             method,
             uri,
             version,
-            headers,
-            extensions,
-            body,
+            mut headers,
+            mut extensions,
+            mut body,
         } = self;
 
-        let mut req = Request::new(body.take().expect("body already extracted"));
+        let mut req = if let Some(body) = body.take() {
+            Request::new(body)
+        } else {
+            return Err(Error::new(RequestAlreadyExtracted::BodyAlreadyExtracted(
+                BodyAlreadyExtracted,
+            )));
+        };
 
-        *req.method_mut() = method.clone();
-        *req.uri_mut() = uri.clone();
-        *req.version_mut() = *version;
+        *req.method_mut() = method;
+        *req.uri_mut() = uri;
+        *req.version_mut() = version;
 
         if let Some(headers) = headers.take() {
             *req.headers_mut() = headers;
+        } else {
+            return Err(Error::new(
+                RequestAlreadyExtracted::HeadersAlreadyExtracted(HeadersAlreadyExtracted),
+            ));
         }
 
         if let Some(extensions) = extensions.take() {
             *req.extensions_mut() = extensions;
+        } else {
+            return Err(Error::new(
+                RequestAlreadyExtracted::ExtensionsAlreadyExtracted(ExtensionsAlreadyExtracted),
+            ));
         }
 
-        req
+        Ok(req)
     }
 
     /// Gets a reference the request method.

src/extract/rejection.rs

@@ -13,14 +13,15 @@ use tower::BoxError;
 define_rejection! {
     #[status = INTERNAL_SERVER_ERROR]
     #[body = "Extensions taken by other extractor"]
-    /// Rejection used if the method has been taken by another extractor.
+    /// Rejection used if the request extension has been taken by another
+    /// extractor.
     pub struct ExtensionsAlreadyExtracted;
 }
 
 define_rejection! {
     #[status = INTERNAL_SERVER_ERROR]
     #[body = "Headers taken by other extractor"]
-    /// Rejection used if the URI has been taken by another extractor.
+    /// Rejection used if the headers has been taken by another extractor.
     pub struct HeadersAlreadyExtracted;
 }
 
@@ -94,13 +95,6 @@ define_rejection! {
     pub struct BodyAlreadyExtracted;
 }
 
-define_rejection! {
-    #[status = INTERNAL_SERVER_ERROR]
-    #[body = "Cannot have two `Request<_>` extractors for a single handler"]
-    /// Rejection type used if you try and extract the request more than once.
-    pub struct RequestAlreadyExtracted;
-}
-
 define_rejection! {
     #[status = BAD_REQUEST]
     #[body = "Form requests must have `Content-Type: x-www-form-urlencoded`"]
@@ -272,6 +266,19 @@ composite_rejection! {
     }
 }
 
+composite_rejection! {
+    /// Rejection used for [`Request<_>`].
+    ///
+    /// Contains one variant for each way the [`Request<_>`] extractor can fail.
+    ///
+    /// [`Request<_>`]: http::Request
+    pub enum RequestAlreadyExtracted {
+        BodyAlreadyExtracted,
+        HeadersAlreadyExtracted,
+        ExtensionsAlreadyExtracted,
+    }
+}
+
 /// Rejection used for [`ContentLengthLimit`](super::ContentLengthLimit).
 ///
 /// Contains one variant for each way the

src/extract/request_parts.rs

@@ -18,21 +18,29 @@ where
     type Rejection = RequestAlreadyExtracted;
 
     async fn from_request(req: &mut RequestParts<B>) -> Result<Self, Self::Rejection> {
-        let RequestParts {
-            method: _,
-            uri: _,
-            version: _,
-            headers,
-            extensions,
-            body,
-        } = req;
-
-        let all_parts = extensions.as_ref().zip(body.as_ref()).zip(headers.as_ref());
-
-        if all_parts.is_some() {
-            Ok(req.into_request())
-        } else {
-            Err(RequestAlreadyExtracted)
+        let req = std::mem::replace(
+            req,
+            RequestParts {
+                method: req.method.clone(),
+                version: req.version,
+                uri: req.uri.clone(),
+                headers: None,
+                extensions: None,
+                body: None,
+            },
+        );
+
+        let err = match req.try_into_request() {
+            Ok(req) => return Ok(req),
+            Err(err) => err,
+        };
+
+        match err.downcast::<RequestAlreadyExtracted>() {
+            Ok(err) => return Err(err),
+            Err(err) => unreachable!(
+                "Unexpected error type from `try_into_request`: `{:?}`. This is a bug in axum, please file an issue",
+                err,
+            ),
         }
     }
 }
@@ -251,3 +259,33 @@ where
         Ok(string)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{body::Body, prelude::*, tests::*};
+    use http::StatusCode;
+
+    #[tokio::test]
+    async fn multiple_request_extractors() {
+        async fn handler(_: Request<Body>, _: Request<Body>) {}
+
+        let app = route("/", post(handler));
+
+        let addr = run_in_background(app).await;
+
+        let client = reqwest::Client::new();
+
+        let res = client
+            .post(format!("http://{}", addr))
+            .body("hi there")
+            .send()
+            .await
+            .unwrap();
+        assert_eq!(res.status(), StatusCode::INTERNAL_SERVER_ERROR);
+        assert_eq!(
+            res.text().await.unwrap(),
+            "Cannot have two request body extractors for a single handler"
+        );
+    }
+}

src/tests/mod.rs

@@ -605,7 +605,7 @@ async fn wrong_method_service() {
 }
 
 /// Run a `tower::Service` in the background and get a URI for it.
-async fn run_in_background<S, ResBody>(svc: S) -> SocketAddr
+pub(crate) async fn run_in_background<S, ResBody>(svc: S) -> SocketAddr
 where
     S: Service<Request<Body>, Response = Response<ResBody>> + Clone + Send + 'static,
     ResBody: http_body::Body + Send + 'static,