Add axum::Error (#150)

Replace `BoxStdError` and supports downcasting

src/body.rs

@@ -1,8 +1,8 @@
 //! HTTP body utilities.
 
+use crate::Error;
 use bytes::Bytes;
 use http_body::Body as _;
-use std::{error::Error as StdError, fmt};
 use tower::BoxError;
 
 #[doc(no_inline)]
@@ -12,7 +12,7 @@ pub use hyper::body::Body;
 ///
 /// This is used in axum as the response body type for applications. Its
 /// necessary to unify multiple response bodies types into one.
-pub type BoxBody = http_body::combinators::BoxBody<Bytes, BoxStdError>;
+pub type BoxBody = http_body::combinators::BoxBody<Bytes, Error>;
 
 /// Convert a [`http_body::Body`] into a [`BoxBody`].
 pub fn box_body<B>(body: B) -> BoxBody
@@ -20,28 +20,9 @@ where
     B: http_body::Body<Data = Bytes> + Send + Sync + 'static,
     B::Error: Into<BoxError>,
 {
-    body.map_err(|err| BoxStdError(err.into())).boxed()
+    body.map_err(Error::new).boxed()
 }
 
 pub(crate) fn empty() -> BoxBody {
     box_body(http_body::Empty::new())
 }
-
-/// A boxed error trait object that implements [`std::error::Error`].
-///
-/// This is necessary for compatibility with middleware that changes the error
-/// type of the response body.
-#[derive(Debug)]
-pub struct BoxStdError(pub(crate) tower::BoxError);
-
-impl StdError for BoxStdError {
-    fn source(&self) -> std::option::Option<&(dyn StdError + 'static)> {
-        self.0.source()
-    }
-}
-
-impl fmt::Display for BoxStdError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        self.0.fmt(f)
-    }
-}