Add ServiceRequest::extract (#2647)

Co-authored-by: Rob Ede <robjtede@icloud.com>

actix-web/CHANGES.md

@@ -1,6 +1,9 @@
 # Changelog
 
 ## Unreleased - 2021-xx-xx
+- Add `ServiceRequest::extract` to make it easier to use extractors when writing middlewares. [#2647]
+
+[#2647]: https://github.com/actix/actix-web/pull/2647
 
 
 ## 4.0.1 - 2022-02-25

actix-web/src/extract.rs

@@ -18,9 +18,11 @@ use crate::{dev::Payload, Error, HttpRequest};
 /// A type that implements [`FromRequest`] is called an **extractor** and can extract data from
 /// the request. Some types that implement this trait are: [`Json`], [`Header`], and [`Path`].
 ///
+/// Check out [`ServiceRequest::extract`](crate::dev::ServiceRequest::extract) if you want to
+/// leverage extractors when implementing middlewares.
+///
 /// # Configuration
 /// An extractor can be customized by injecting the corresponding configuration with one of:
-///
 /// - [`App::app_data()`][crate::App::app_data]
 /// - [`Scope::app_data()`][crate::Scope::app_data]
 /// - [`Resource::app_data()`][crate::Resource::app_data]

actix-web/src/service.rs

@@ -24,7 +24,7 @@ use crate::{
     guard::{Guard, GuardContext},
     info::ConnectionInfo,
     rmap::ResourceMap,
-    Error, HttpRequest, HttpResponse,
+    Error, FromRequest, HttpRequest, HttpResponse,
 };
 
 pub(crate) type BoxedHttpService = BoxService<ServiceRequest, ServiceResponse<BoxBody>, Error>;
@@ -95,6 +95,31 @@ impl ServiceRequest {
         (&mut self.req, &mut self.payload)
     }
 
+    /// Derives a type from this request using an [extractor](crate::FromRequest).
+    ///
+    /// Returns the `T` extractor's `Future` type which can be `await`ed. This is particularly handy
+    /// when you want to use an extractor in a middleware implementation.
+    ///
+    /// # Examples
+    /// ```
+    /// use actix_web::{
+    ///     dev::{ServiceRequest, ServiceResponse},
+    ///     web::Path, Error
+    /// };
+    ///
+    /// async fn my_helper(mut srv_req: ServiceRequest) -> Result<ServiceResponse, Error> {
+    ///     let path = srv_req.extract::<Path<(String, u32)>>().await?;
+    ///     // [...]
+    /// #   todo!()
+    /// }
+    /// ```
+    pub fn extract<T>(&mut self) -> <T as FromRequest>::Future
+    where
+        T: FromRequest,
+    {
+        T::from_request(&self.req, &mut self.payload)
+    }
+
     /// Construct request from parts.
     pub fn from_parts(req: HttpRequest, payload: Payload) -> Self {
         #[cfg(debug_assertions)]