add GuardContext::header (#2569)

CHANGES.md

@@ -1,10 +1,14 @@
 # Changes
 
 ## Unreleased - 2021-xx-xx
+### Added
+- `GuardContext::header` [#2569]
+
 ### Changed
-- `HttpResponse` can now be used as a `Responder` with any body type.
+- `HttpResponse` can now be used as a `Responder` with any body type. [#2567]
 
-[#2501]: https://github.com/actix/actix-web/pull/2501
+[#2567]: https://github.com/actix/actix-web/pull/2567
+[#2569]: https://github.com/actix/actix-web/pull/2569
 
 
 ## 4.0.0-beta.19 - 2022-01-04

src/guard.rs

@@ -54,7 +54,7 @@ use std::{
 
 use actix_http::{header, uri::Uri, Extensions, Method as HttpMethod, RequestHead};
 
-use crate::service::ServiceRequest;
+use crate::{http::header::Header, service::ServiceRequest};
 
 /// Provides access to request parts that are useful during routing.
 #[derive(Debug)]
@@ -80,6 +80,26 @@ impl<'a> GuardContext<'a> {
     pub fn req_data_mut(&self) -> RefMut<'a, Extensions> {
         self.req.req_data_mut()
     }
+
+    /// Extracts a typed header from the request.
+    ///
+    /// Returns `None` if parsing `H` fails.
+    ///
+    /// # Examples
+    /// ```
+    /// use actix_web::{guard::fn_guard, http::header};
+    ///
+    /// let image_accept_guard = fn_guard(|ctx| {
+    ///     match ctx.header::<header::Accept>() {
+    ///         Some(hdr) => hdr.preference() == "image/*",
+    ///         None => false,
+    ///     }
+    /// });
+    /// ```
+    #[inline]
+    pub fn header<H: Header>(&self) -> Option<H> {
+        H::parse(self.req).ok()
+    }
 }
 
 /// Interface for routing guards.

src/http/header/accept.rs

@@ -2,10 +2,10 @@ use std::cmp::Ordering;
 
 use mime::Mime;
 
-use super::QualityItem;
+use super::{common_header, QualityItem};
 use crate::http::header;
 
-crate::http::header::common_header! {
+common_header! {
     /// `Accept` header, defined
     /// in [RFC 7231 §5.3.2](https://datatracker.ietf.org/doc/html/rfc7231#section-5.3.2)
     ///