remove but inspired by tower

README.md

@@ -11,8 +11,8 @@ to allow for client middleware chains.
 This crate provides functionality for building and running middleware but no middleware
 implementations. This repository also contains a couple of useful concrete middleware crates:
 
-* [`reqwest-retry`](https://crates.io/crates/reqwest-retry): retry failed requests.
+- [`reqwest-retry`](https://crates.io/crates/reqwest-retry): retry failed requests.
-* [`reqwest-tracing`](https://crates.io/crates/reqwest-tracing):
+- [`reqwest-tracing`](https://crates.io/crates/reqwest-tracing):
   [`tracing`](https://crates.io/crates/tracing) integration, optional opentelemetry support.
 
 ## Overview
@@ -29,10 +29,12 @@ reqwest-middleware = "0.1.6"
 reqwest-retry = "0.1.5"
 reqwest-tracing = "0.2.3"
 tokio = { version = "1.12.0", features = ["macros", "rt-multi-thread"] }
+tower = "0.4"
 ```
 
 ```rust
-use reqwest_middleware::{ClientBuilder, ClientWithMiddleware};
+use reqwest::Response;
+use reqwest_middleware::{ClientBuilder, ClientWithMiddleware, Error, Layer, RequestInitialiser, ReqwestService, Service};
 use reqwest_retry::{RetryTransientMiddleware, policies::ExponentialBackoff};
 use reqwest_tracing::TracingMiddleware;
 
@@ -49,7 +51,12 @@ async fn main() {
     run(client).await;
 }
 
-async fn run(client: ClientWithMiddleware) {
+async fn run<M, I>(client: ClientWithMiddleware<M, I>)
+where
+    M: Layer<ReqwestService>,
+    M::Service: Service,
+    I: RequestInitialiser,
+{
     client
         .get("https://truelayer.com")
         .header("foo", "bar")

reqwest-middleware/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "reqwest-middleware"
-version = "0.2.0"
+version = "0.3.0"
 authors = ["Rodrigo Gryzinski <rodrigo.gryzinski@truelayer.com>"]
 edition = "2018"
 description = "Wrapper around reqwest to allow for client middleware chains."
@@ -18,6 +18,7 @@ reqwest = { version = "0.11", default-features = false, features = ["json", "mul
 serde = "1"
 task-local-extensions = "0.1.1"
 thiserror = "1"
+futures = "0.3"
 
 [dev-dependencies]
 reqwest = "0.11"

reqwest-middleware/src/client.rs

@@ -1,81 +1,67 @@
+use futures::future::BoxFuture;
+use futures::FutureExt;
 use reqwest::header::{HeaderMap, HeaderName, HeaderValue};
 use reqwest::multipart::Form;
 use reqwest::{Body, Client, IntoUrl, Method, Request, Response};
 use serde::Serialize;
 use std::convert::TryFrom;
 use std::fmt::{self, Display};
-use std::sync::Arc;
 use std::time::Duration;
 use task_local_extensions::Extensions;
+// use tower::{Layer, Service, ServiceBuilder, ServiceExt};
 
-use crate::error::Result;
+use crate::{Error, Identity, Layer, RequestInitialiser, RequestStack, Service, Stack};
-use crate::middleware::{Middleware, Next};
-use crate::RequestInitialiser;
 
 /// A `ClientBuilder` is used to build a [`ClientWithMiddleware`].
 ///
 /// [`ClientWithMiddleware`]: crate::ClientWithMiddleware
-pub struct ClientBuilder {
+pub struct ClientBuilder<M, I> {
     client: Client,
-    middleware_stack: Vec<Arc<dyn Middleware>>,
+    middleware_stack: M,
-    initialiser_stack: Vec<Arc<dyn RequestInitialiser>>,
+    initialiser_stack: I,
 }
 
-impl ClientBuilder {
+impl ClientBuilder<Identity, Identity> {
     pub fn new(client: Client) -> Self {
         ClientBuilder {
             client,
-            middleware_stack: Vec::new(),
+            middleware_stack: Identity,
-            initialiser_stack: Vec::new(),
+            initialiser_stack: Identity,
+        }
     }
 }
 
+impl<M, I> ClientBuilder<M, I> {
     /// Convenience method to attach middleware.
-    ///
+    pub fn with<T>(self, layer: T) -> ClientBuilder<Stack<T, M>, I> {
-    /// If you need to keep a reference to the middleware after attaching, use [`with_arc`].
+        ClientBuilder {
-    ///
+            client: self.client,
-    /// [`with_arc`]: Self::with_arc
+            middleware_stack: Stack {
-    pub fn with<M>(self, middleware: M) -> Self
+                inner: layer,
-    where
+                outer: self.middleware_stack,
-        M: Middleware,
+            },
-    {
+            initialiser_stack: self.initialiser_stack,
-        self.with_arc(Arc::new(middleware))
         }
-
-    /// Add middleware to the chain. [`with`] is more ergonomic if you don't need the `Arc`.
-    ///
-    /// [`with`]: Self::with
-    pub fn with_arc(mut self, middleware: Arc<dyn Middleware>) -> Self {
-        self.middleware_stack.push(middleware);
-        self
     }
 
     /// Convenience method to attach a request initialiser.
-    ///
+    pub fn with_init<T>(self, initialiser: T) -> ClientBuilder<M, RequestStack<T, I>> {
-    /// If you need to keep a reference to the initialiser after attaching, use [`with_arc_init`].
+        ClientBuilder {
-    ///
+            client: self.client,
-    /// [`with_arc_init`]: Self::with_arc_init
+            middleware_stack: self.middleware_stack,
-    pub fn with_init<I>(self, initialiser: I) -> Self
+            initialiser_stack: RequestStack {
-    where
+                inner: initialiser,
-        I: RequestInitialiser,
+                outer: self.initialiser_stack,
-    {
+            },
-        self.with_arc_init(Arc::new(initialiser))
         }
-
-    /// Add a request initialiser to the chain. [`with_init`] is more ergonomic if you don't need the `Arc`.
-    ///
-    /// [`with_init`]: Self::with_init
-    pub fn with_arc_init(mut self, initialiser: Arc<dyn RequestInitialiser>) -> Self {
-        self.initialiser_stack.push(initialiser);
-        self
     }
 
     /// Returns a `ClientWithMiddleware` using this builder configuration.
-    pub fn build(self) -> ClientWithMiddleware {
+    pub fn build(self) -> ClientWithMiddleware<M, I> {
         ClientWithMiddleware {
             inner: self.client,
-            middleware_stack: self.middleware_stack.into_boxed_slice(),
+            middleware_stack: self.middleware_stack,
-            initialiser_stack: self.initialiser_stack.into_boxed_slice(),
+            initialiser_stack: self.initialiser_stack,
         }
     }
 }
@@ -83,97 +69,68 @@ impl ClientBuilder {
 /// `ClientWithMiddleware` is a wrapper around [`reqwest::Client`] which runs middleware on every
 /// request.
 #[derive(Clone)]
-pub struct ClientWithMiddleware {
+pub struct ClientWithMiddleware<M, I> {
     inner: reqwest::Client,
-    middleware_stack: Box<[Arc<dyn Middleware>]>,
+    middleware_stack: M,
-    initialiser_stack: Box<[Arc<dyn RequestInitialiser>]>,
+    initialiser_stack: I,
-}
-
-impl ClientWithMiddleware {
-    /// See [`ClientBuilder`] for a more ergonomic way to build `ClientWithMiddleware` instances.
-    pub fn new<T>(client: Client, middleware_stack: T) -> Self
-    where
-        T: Into<Box<[Arc<dyn Middleware>]>>,
-    {
-        ClientWithMiddleware {
-            inner: client,
-            middleware_stack: middleware_stack.into(),
-            // TODO(conradludgate) - allow downstream code to control this manually if desired
-            initialiser_stack: Box::new([]),
-        }
 }
 
+impl<M: Layer<ReqwestService>, I: RequestInitialiser> ClientWithMiddleware<M, I> {
     /// See [`Client::get`]
-    pub fn get<U: IntoUrl>(&self, url: U) -> RequestBuilder {
+    pub fn get<U: IntoUrl>(&self, url: U) -> RequestBuilder<M, I> {
         self.request(Method::GET, url)
     }
 
     /// See [`Client::post`]
-    pub fn post<U: IntoUrl>(&self, url: U) -> RequestBuilder {
+    pub fn post<U: IntoUrl>(&self, url: U) -> RequestBuilder<M, I> {
         self.request(Method::POST, url)
     }
 
     /// See [`Client::put`]
-    pub fn put<U: IntoUrl>(&self, url: U) -> RequestBuilder {
+    pub fn put<U: IntoUrl>(&self, url: U) -> RequestBuilder<M, I> {
         self.request(Method::PUT, url)
     }
 
     /// See [`Client::patch`]
-    pub fn patch<U: IntoUrl>(&self, url: U) -> RequestBuilder {
+    pub fn patch<U: IntoUrl>(&self, url: U) -> RequestBuilder<M, I> {
         self.request(Method::PATCH, url)
     }
 
     /// See [`Client::delete`]
-    pub fn delete<U: IntoUrl>(&self, url: U) -> RequestBuilder {
+    pub fn delete<U: IntoUrl>(&self, url: U) -> RequestBuilder<M, I> {
         self.request(Method::DELETE, url)
     }
 
     /// See [`Client::head`]
-    pub fn head<U: IntoUrl>(&self, url: U) -> RequestBuilder {
+    pub fn head<U: IntoUrl>(&self, url: U) -> RequestBuilder<M, I> {
         self.request(Method::HEAD, url)
     }
 
     /// See [`Client::request`]
-    pub fn request<U: IntoUrl>(&self, method: Method, url: U) -> RequestBuilder {
+    pub fn request<U: IntoUrl>(&self, method: Method, url: U) -> RequestBuilder<'_, M, I> {
-        let req = RequestBuilder {
+        let mut extensions = Extensions::new();
-            inner: self.inner.request(method, url),
+        let request = self.inner.request(method, url);
-            client: self.clone(),
+        let request = self.initialiser_stack.init(request, &mut extensions);
-            extensions: Extensions::new(),
+        RequestBuilder {
-        };
+            inner: request,
-        self.initialiser_stack
+            client: self,
-            .iter()
+            extensions,
-            .fold(req, |req, i| i.init(req))
         }
-
-    /// See [`Client::execute`]
-    pub async fn execute(&self, req: Request) -> Result<Response> {
-        let mut ext = Extensions::new();
-        self.execute_with_extensions(req, &mut ext).await
-    }
-
-    /// Executes a request with initial [`Extensions`].
-    pub async fn execute_with_extensions(
-        &self,
-        req: Request,
-        ext: &mut Extensions,
-    ) -> Result<Response> {
-        let next = Next::new(&self.inner, &self.middleware_stack);
-        next.run(req, ext).await
     }
 }
 
 /// Create a `ClientWithMiddleware` without any middleware.
-impl From<Client> for ClientWithMiddleware {
+impl From<Client> for ClientWithMiddleware<Identity, Identity> {
     fn from(client: Client) -> Self {
         ClientWithMiddleware {
             inner: client,
-            middleware_stack: Box::new([]),
+            middleware_stack: Identity,
-            initialiser_stack: Box::new([]),
+            initialiser_stack: Identity,
         }
     }
 }
 
-impl fmt::Debug for ClientWithMiddleware {
+impl<M, I> fmt::Debug for ClientWithMiddleware<M, I> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         // skipping middleware_stack field for now
         f.debug_struct("ClientWithMiddleware")
@@ -184,13 +141,28 @@ impl fmt::Debug for ClientWithMiddleware {
 
 /// This is a wrapper around [`reqwest::RequestBuilder`] exposing the same API.
 #[must_use = "RequestBuilder does nothing until you 'send' it"]
-pub struct RequestBuilder {
+pub struct RequestBuilder<'client, M, I> {
     inner: reqwest::RequestBuilder,
-    client: ClientWithMiddleware,
+    client: &'client ClientWithMiddleware<M, I>,
     extensions: Extensions,
 }
 
-impl RequestBuilder {
+#[derive(Clone)]
+pub struct ReqwestService(Client);
+
+impl Service for ReqwestService {
+    type Future = BoxFuture<'static, Result<Response, Error>>;
+
+    fn call(&mut self, req: Request, _: &mut Extensions) -> Self::Future {
+        let fut = self.0.execute(req);
+        async { fut.await.map_err(Error::from) }.boxed()
+    }
+}
+
+impl<M: Layer<ReqwestService>, I: RequestInitialiser> RequestBuilder<'_, M, I>
+where
+    M::Service: Service,
+{
     pub fn header<K, V>(self, key: K, value: V) -> Self
     where
         HeaderName: TryFrom<K>,
@@ -289,14 +261,19 @@ impl RequestBuilder {
         &mut self.extensions
     }
 
-    pub async fn send(self) -> Result<Response> {
+    pub async fn send(self) -> Result<Response, Error> {
         let Self {
             inner,
             client,
             mut extensions,
         } = self;
         let req = inner.build()?;
-        client.execute_with_extensions(req, &mut extensions).await
+        let mut svc = client
+            .middleware_stack
+            .layer(ReqwestService(client.inner.clone()));
+        svc.call(req, &mut extensions).await
+
+        // client.execute_with_extensions(req, &mut extensions).await
     }
 
     /// Attempt to clone the RequestBuilder.
@@ -309,13 +286,13 @@ impl RequestBuilder {
     pub fn try_clone(&self) -> Option<Self> {
         self.inner.try_clone().map(|inner| RequestBuilder {
             inner,
-            client: self.client.clone(),
+            client: self.client,
             extensions: Extensions::new(),
         })
     }
 }
 
-impl fmt::Debug for RequestBuilder {
+impl<M, I> fmt::Debug for RequestBuilder<'_, M, I> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         // skipping middleware_stack field for now
         f.debug_struct("RequestBuilder")

reqwest-middleware/src/error.rs

@@ -1,7 +1,5 @@
 use thiserror::Error;
 
-pub type Result<T> = std::result::Result<T, Error>;
-
 #[derive(Error, Debug)]
 pub enum Error {
     /// There was an error running some middleware

reqwest-middleware/src/lib.rs

@@ -7,30 +7,44 @@
 //!
 //! ```
 //! use reqwest::{Client, Request, Response};
-//! use reqwest_middleware::{ClientBuilder, Middleware, Next, Result};
+//! use reqwest_middleware::{ClientBuilder, Error, Extension, Layer, Service};
 //! use task_local_extensions::Extensions;
+//! use futures::future::{BoxFuture, FutureExt};
+//! use std::task::{Context, Poll};
 //!
-//! struct LoggingMiddleware;
+//! struct LoggingLayer;
+//! struct LoggingService<S>(S);
 //!
-//! #[async_trait::async_trait]
+//! impl<S> Layer<S> for LoggingLayer {
-//! impl Middleware for LoggingMiddleware {
+//!     type Service = LoggingService<S>;
-//!     async fn handle(
+//!
-//!         &self,
+//!     fn layer(&self, inner: S) -> Self::Service {
-//!         req: Request,
+//!         LoggingService(inner)
-//!         extensions: &mut Extensions,
+//!     }
-//!         next: Next<'_>,
+//! }
-//!     ) -> Result<Response> {
+//!
-//!         println!("Request started {:?}", req);
+//! impl<S> Service for LoggingService<S>
-//!         let res = next.run(req, extensions).await;
+//! where
-//!         println!("Result: {:?}", res);
+//!     S: Service,
+//!     S::Future: Send + 'static,
+//! {
+//!     type Future = BoxFuture<'static, Result<Response, Error>>;
+//!     
+//!     fn call(&mut self, req: Request, ext: &mut Extensions) -> Self::Future {
+//!         println!("Request started {req:?}");
+//!         let fut = self.0.call(req, ext);
+//!         async {
+//!             let res = fut.await;
+//!             println!("Result: {res:?}");
 //!             res
+//!         }.boxed()
 //!     }
 //! }
 //!
 //! async fn run() {
 //!     let reqwest_client = Client::builder().build().unwrap();
 //!     let client = ClientBuilder::new(reqwest_client)
-//!         .with(LoggingMiddleware)
+//!         .with(LoggingLayer)
 //!         .build();
 //!     let resp = client.get("https://truelayer.com").send().await.unwrap();
 //!     println!("TrueLayer page HTML: {}", resp.text().await.unwrap());
@@ -51,10 +65,54 @@ pub struct ReadmeDoctests;
 
 mod client;
 mod error;
-mod middleware;
 mod req_init;
 
-pub use client::{ClientBuilder, ClientWithMiddleware, RequestBuilder};
+pub use client::{ClientBuilder, ClientWithMiddleware, RequestBuilder, ReqwestService};
-pub use error::{Error, Result};
+pub use error::Error;
-pub use middleware::{Middleware, Next};
+pub use req_init::{Extension, RequestInitialiser, RequestStack};
-pub use req_init::{Extension, RequestInitialiser};
+use reqwest::{Request, Response};
+use task_local_extensions::Extensions;
+
+/// Two [`RequestInitialiser`]s or [`Service`]s chained together.
+#[derive(Clone)]
+pub struct Stack<Inner, Outer> {
+    pub(crate) inner: Inner,
+    pub(crate) outer: Outer,
+}
+
+pub trait Service {
+    type Future: std::future::Future<Output = Result<Response, Error>>;
+    fn call(&mut self, req: Request, ext: &mut Extensions) -> Self::Future;
+}
+
+pub struct Identity;
+
+impl<S: Service> Layer<S> for Identity {
+    type Service = S;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        inner
+    }
+}
+
+pub trait Layer<S> {
+    /// The wrapped service
+    type Service;
+    /// Wrap the given service with the middleware, returning a new service
+    /// that has been decorated with the middleware.
+    fn layer(&self, inner: S) -> Self::Service;
+}
+
+impl<S, Inner, Outer> Layer<S> for Stack<Inner, Outer>
+where
+    Inner: Layer<S>,
+    Outer: Layer<Inner::Service>,
+{
+    type Service = Outer::Service;
+
+    fn layer(&self, service: S) -> Self::Service {
+        let inner = self.inner.layer(service);
+
+        self.outer.layer(inner)
+    }
+}

reqwest-middleware/src/middleware.rs

@@ -1,100 +0,0 @@
-use reqwest::{Client, Request, Response};
-use std::sync::Arc;
-use task_local_extensions::Extensions;
-
-use crate::error::{Error, Result};
-
-/// When attached to a [`ClientWithMiddleware`] (generally using [`with`]), middleware is run
-/// whenever the client issues a request, in the order it was attached.
-///
-/// # Example
-///
-/// ```
-/// use reqwest::{Client, Request, Response};
-/// use reqwest_middleware::{ClientBuilder, Middleware, Next, Result};
-/// use task_local_extensions::Extensions;
-///
-/// struct TransparentMiddleware;
-///
-/// #[async_trait::async_trait]
-/// impl Middleware for TransparentMiddleware {
-///     async fn handle(
-///         &self,
-///         req: Request,
-///         extensions: &mut Extensions,
-///         next: Next<'_>,
-///     ) -> Result<Response> {
-///         next.run(req, extensions).await
-///     }
-/// }
-/// ```
-///
-/// [`ClientWithMiddleware`]: crate::ClientWithMiddleware
-/// [`with`]: crate::ClientBuilder::with
-#[async_trait::async_trait]
-pub trait Middleware: 'static + Send + Sync {
-    /// Invoked with a request before sending it. If you want to continue processing the request,
-    /// you should explicitly call `next.run(req, extensions)`.
-    ///
-    /// If you need to forward data down the middleware stack, you can use the `extensions`
-    /// argument.
-    async fn handle(
-        &self,
-        req: Request,
-        extensions: &mut Extensions,
-        next: Next<'_>,
-    ) -> Result<Response>;
-}
-
-#[async_trait::async_trait]
-impl<F> Middleware for F
-where
-    F: Send
-        + Sync
-        + 'static
-        + for<'a> Fn(Request, &'a mut Extensions, Next<'a>) -> BoxFuture<'a, Result<Response>>,
-{
-    async fn handle(
-        &self,
-        req: Request,
-        extensions: &mut Extensions,
-        next: Next<'_>,
-    ) -> Result<Response> {
-        (self)(req, extensions, next).await
-    }
-}
-
-/// Next encapsulates the remaining middleware chain to run in [`Middleware::handle`]. You can
-/// forward the request down the chain with [`run`].
-///
-/// [`Middleware::handle`]: Middleware::handle
-/// [`run`]: Self::run
-#[derive(Clone)]
-pub struct Next<'a> {
-    client: &'a Client,
-    middlewares: &'a [Arc<dyn Middleware>],
-}
-
-pub type BoxFuture<'a, T> = std::pin::Pin<Box<dyn std::future::Future<Output = T> + Send + 'a>>;
-
-impl<'a> Next<'a> {
-    pub(crate) fn new(client: &'a Client, middlewares: &'a [Arc<dyn Middleware>]) -> Self {
-        Next {
-            client,
-            middlewares,
-        }
-    }
-
-    pub fn run(
-        mut self,
-        req: Request,
-        extensions: &'a mut Extensions,
-    ) -> BoxFuture<'a, Result<Response>> {
-        if let Some((current, rest)) = self.middlewares.split_first() {
-            self.middlewares = rest;
-            Box::pin(current.handle(req, extensions, self))
-        } else {
-            Box::pin(async move { self.client.execute(req).await.map_err(Error::from) })
-        }
-    }
-}

reqwest-middleware/src/req_init.rs

@@ -1,4 +1,7 @@
-use crate::RequestBuilder;
+use reqwest::RequestBuilder;
+use task_local_extensions::Extensions;
+
+use crate::Identity;
 
 /// When attached to a [`ClientWithMiddleware`] (generally using [`with_init`]), it is run
 /// whenever the client starts building a request, in the order it was attached.
@@ -6,12 +9,14 @@ use crate::RequestBuilder;
 /// # Example
 ///
 /// ```
-/// use reqwest_middleware::{RequestInitialiser, RequestBuilder};
+/// use reqwest::RequestBuilder;
+/// use reqwest_middleware::RequestInitialiser;
+/// use task_local_extensions::Extensions;
 ///
 /// struct AuthInit;
 ///
 /// impl RequestInitialiser for AuthInit {
-///     fn init(&self, req: RequestBuilder) -> RequestBuilder {
+///     fn init(&self, req: RequestBuilder, ext: &mut Extensions) -> RequestBuilder {
 ///         req.bearer_auth("my_auth_token")
 ///     }
 /// }
@@ -20,15 +25,30 @@ use crate::RequestBuilder;
 /// [`ClientWithMiddleware`]: crate::ClientWithMiddleware
 /// [`with_init`]: crate::ClientBuilder::with_init
 pub trait RequestInitialiser: 'static + Send + Sync {
-    fn init(&self, req: RequestBuilder) -> RequestBuilder;
+    fn init(&self, req: RequestBuilder, ext: &mut Extensions) -> RequestBuilder;
 }
 
-impl<F> RequestInitialiser for F
+impl RequestInitialiser for Identity {
+    fn init(&self, req: RequestBuilder, _: &mut Extensions) -> RequestBuilder {
+        req
+    }
+}
+
+/// Two [`RequestInitialiser`]s chained together.
+#[derive(Clone)]
+pub struct RequestStack<Inner, Outer> {
+    pub(crate) inner: Inner,
+    pub(crate) outer: Outer,
+}
+
+impl<I, O> RequestInitialiser for RequestStack<I, O>
 where
-    F: Send + Sync + 'static + Fn(RequestBuilder) -> RequestBuilder,
+    I: RequestInitialiser,
+    O: RequestInitialiser,
 {
-    fn init(&self, req: RequestBuilder) -> RequestBuilder {
+    fn init(&self, req: RequestBuilder, ext: &mut Extensions) -> RequestBuilder {
-        (self)(req)
+        let req = self.inner.init(req, ext);
+        self.outer.init(req, ext)
     }
 }
 
@@ -38,30 +58,45 @@ where
 ///
 /// ```
 /// use reqwest::{Client, Request, Response};
-/// use reqwest_middleware::{ClientBuilder, Middleware, Next, Result, Extension};
+/// use reqwest_middleware::{ClientBuilder, Error, Extension, Layer, Service};
 /// use task_local_extensions::Extensions;
+/// use futures::future::{BoxFuture, FutureExt};
+/// use std::task::{Context, Poll};
 ///
 /// #[derive(Clone)]
 /// struct LogName(&'static str);
-/// struct LoggingMiddleware;
 ///
-/// #[async_trait::async_trait]
+/// struct LoggingLayer;
-/// impl Middleware for LoggingMiddleware {
+/// struct LoggingService<S>(S);
-///     async fn handle(
+///
-///         &self,
+/// impl<S> Layer<S> for LoggingLayer {
-///         req: Request,
+///     type Service = LoggingService<S>;
-///         extensions: &mut Extensions,
+///
-///         next: Next<'_>,
+///     fn layer(&self, inner: S) -> Self::Service {
-///     ) -> Result<Response> {
+///         LoggingService(inner)
+///     }
+/// }
+///
+/// impl<S> Service for LoggingService<S>
+/// where
+///     S: Service,
+///     S::Future: Send + 'static,
+/// {
+///     type Future = BoxFuture<'static, Result<Response, Error>>;
+///     
+///     fn call(&mut self, req: Request, ext: &mut Extensions) -> Self::Future {
 ///         // get the log name or default to "unknown"
-///         let name = extensions
+///         let name = ext
 ///             .get()
 ///             .map(|&LogName(name)| name)
 ///             .unwrap_or("unknown");
 ///         println!("[{name}] Request started {req:?}");
-///         let res = next.run(req, extensions).await;
+///         let fut = self.0.call(req, ext);
+///         async move {
+///             let res = fut.await;
 ///             println!("[{name}] Result: {res:?}");
 ///             res
+///         }.boxed()
 ///     }
 /// }
 ///
@@ -69,7 +104,7 @@ where
 ///     let reqwest_client = Client::builder().build().unwrap();
 ///     let client = ClientBuilder::new(reqwest_client)
 ///         .with_init(Extension(LogName("my-client")))
-///         .with(LoggingMiddleware)
+///         .with(LoggingLayer)
 ///         .build();
 ///     let resp = client.get("https://truelayer.com").send().await.unwrap();
 ///     println!("TrueLayer page HTML: {}", resp.text().await.unwrap());
@@ -78,7 +113,8 @@ where
 pub struct Extension<T>(pub T);
 
 impl<T: Send + Sync + Clone + 'static> RequestInitialiser for Extension<T> {
-    fn init(&self, req: RequestBuilder) -> RequestBuilder {
+    fn init(&self, req: RequestBuilder, ext: &mut Extensions) -> RequestBuilder {
-        req.with_extension(self.0.clone())
+        ext.insert(self.0.clone());
+        req
     }
 }

reqwest-retry/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "reqwest-retry"
-version = "0.2.0"
+version = "0.3.0"
 authors = ["Rodrigo Gryzinski <rodrigo.gryzinski@truelayer.com>"]
 edition = "2018"
 description = "Retry middleware for reqwest."
@@ -10,7 +10,7 @@ keywords = ["reqwest", "http", "middleware", "retry"]
 categories = ["web-programming::http-client"]
 
 [dependencies]
-reqwest-middleware = { version = "0.2.0", path = "../reqwest-middleware" }
+reqwest-middleware = { version = "0.3.0", path = "../reqwest-middleware" }
 
 anyhow = "1"
 async-trait = "0.1.51"
@@ -23,6 +23,7 @@ retry-policies = "0.1"
 task-local-extensions = "0.1.1"
 tokio = { version = "1.6", features = ["time"] }
 tracing = "0.1.26"
+pin-project-lite = "0.2"
 
 [dev-dependencies]
 async-std = { version = "1.10"}

reqwest-retry/src/middleware.rs

@@ -1,15 +1,17 @@
 //! `RetryTransientMiddleware` implements retrying requests on transient errors.
 
+use std::pin::Pin;
+use std::task::{ready, Context, Poll};
+
 use crate::retryable::Retryable;
-use anyhow::anyhow;
 use chrono::Utc;
+use futures::Future;
+use pin_project_lite::pin_project;
 use reqwest::{Request, Response};
-use reqwest_middleware::{Error, Middleware, Next, Result};
+use reqwest_middleware::{Error, Layer, Service};
 use retry_policies::RetryPolicy;
 use task_local_extensions::Extensions;
-
+use tokio::time::Sleep;
-/// We limit the number of retries to a maximum of `10` to avoid stack-overflow issues due to the recursion.
-static MAXIMUM_NUMBER_OF_RETRIES: u32 = 10;
 
 /// `RetryTransientMiddleware` offers retry logic for requests that fail in a transient manner
 /// and can be safely executed again.
@@ -58,76 +60,253 @@ impl<T: RetryPolicy + Send + Sync> RetryTransientMiddleware<T> {
     }
 }
 
-#[async_trait::async_trait]
+impl<T, Svc> Layer<Svc> for RetryTransientMiddleware<T>
-impl<T: RetryPolicy + Send + Sync> Middleware for RetryTransientMiddleware<T> {
+where
-    async fn handle(
+    T: RetryPolicy + Clone + Send + Sync + 'static,
-        &self,
+{
-        req: Request,
+    type Service = Retry<TowerRetryPolicy<T>, Svc>;
-        extensions: &mut Extensions,
+
-        next: Next<'_>,
+    fn layer(&self, inner: Svc) -> Self::Service {
-    ) -> Result<Response> {
+        Retry {
-        // TODO: Ideally we should create a new instance of the `Extensions` map to pass
+            policy: TowerRetryPolicy {
-        // downstream. This will guard against previous retries poluting `Extensions`.
+                n_past_retries: 0,
-        // That is, we only return what's populated in the typemap for the last retry attempt
+                retry_policy: self.retry_policy.clone(),
-        // and copy those into the the `global` Extensions map.
+            },
-        self.execute_with_retry(req, next, extensions).await
+            service: inner,
+        }
     }
 }
 
-impl<T: RetryPolicy + Send + Sync> RetryTransientMiddleware<T> {
+#[derive(Clone)]
-    /// This function will try to execute the request, if it fails
+pub struct TowerRetryPolicy<T> {
-    /// with an error classified as transient it will call itself
+    n_past_retries: u32,
-    /// to retry the request.
+    retry_policy: T,
-    async fn execute_with_retry<'a>(
+}
-        &'a self,
-        req: Request,
-        next: Next<'a>,
-        ext: &'a mut Extensions,
-    ) -> Result<Response> {
-        let mut n_past_retries = 0;
-        loop {
-            // Cloning the request object before-the-fact is not ideal..
-            // However, if the body of the request is not static, e.g of type `Bytes`,
-            // the Clone operation should be of constant complexity and not O(N)
-            // since the byte abstraction is a shared pointer over a buffer.
-            let duplicate_request = req.try_clone().ok_or_else(|| {
-                Error::Middleware(anyhow!(
-                    "Request object is not clonable. Are you passing a streaming body?".to_string()
-                ))
-            })?;
 
-            let result = next.clone().run(duplicate_request, ext).await;
+pin_project! {
+    pub struct RetryFuture<T>
+    {
+        retry: Option<TowerRetryPolicy<T>>,
+        #[pin]
+        sleep: Sleep,
+    }
+}
 
+impl<T> Future for RetryFuture<T> {
+    type Output = TowerRetryPolicy<T>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = self.project();
+        ready!(this.sleep.poll(cx));
+        Poll::Ready(
+            this.retry
+                .take()
+                .expect("poll should not be called more than once"),
+        )
+    }
+}
+
+impl<T: RetryPolicy + Clone> Policy for TowerRetryPolicy<T> {
+    type Future = RetryFuture<T>;
+
+    fn retry(&self, _req: &Request, result: &Result<Response, Error>) -> Option<Self::Future> {
         // We classify the response which will return None if not
         // errors were returned.
-            break match Retryable::from_reqwest_response(&result) {
+        match Retryable::from_reqwest_response(result) {
-                Some(retryable)
+            Some(Retryable::Transient) => {
-                    if retryable == Retryable::Transient
-                        && n_past_retries < MAXIMUM_NUMBER_OF_RETRIES =>
-                {
                 // If the response failed and the error type was transient
                 // we can safely try to retry the request.
-                    let retry_decicion = self.retry_policy.should_retry(n_past_retries);
+                let retry_decicion = self.retry_policy.should_retry(self.n_past_retries);
                 if let retry_policies::RetryDecision::Retry { execute_after } = retry_decicion {
-                        let duration = (execute_after - Utc::now())
+                    let duration = (execute_after - Utc::now()).to_std().ok()?;
-                            .to_std()
-                            .map_err(Error::middleware)?;
                     // Sleep the requested amount before we try again.
                     tracing::warn!(
                         "Retry attempt #{}. Sleeping {:?} before the next attempt",
-                            n_past_retries,
+                        self.n_past_retries,
                         duration
                     );
-                        tokio::time::sleep(duration).await;
+                    let sleep = tokio::time::sleep(duration);
-
+                    Some(RetryFuture {
-                        n_past_retries += 1;
+                        retry: Some(TowerRetryPolicy {
-                        continue;
+                            n_past_retries: self.n_past_retries + 1,
+                            retry_policy: self.retry_policy.clone(),
+                        }),
+                        sleep,
+                    })
                 } else {
-                        result
+                    None
+                }
+            }
+            Some(_) | None => None,
+        }
+    }
+
+    fn clone_request(&self, req: &Request) -> Option<Request> {
+        req.try_clone()
+    }
+}
+
+pub trait Policy: Sized {
+    /// The [`Future`] type returned by [`Policy::retry`].
+    type Future: Future<Output = Self>;
+
+    /// Check the policy if a certain request should be retried.
+    ///
+    /// This method is passed a reference to the original request, and either
+    /// the [`Service::Response`] or [`Service::Error`] from the inner service.
+    ///
+    /// If the request should **not** be retried, return `None`.
+    ///
+    /// If the request *should* be retried, return `Some` future of a new
+    /// policy that would apply for the next request attempt.
+    ///
+    /// [`Service::Response`]: crate::Service::Response
+    /// [`Service::Error`]: crate::Service::Error
+    fn retry(&self, req: &Request, result: &Result<Response, Error>) -> Option<Self::Future>;
+
+    /// Tries to clone a request before being passed to the inner service.
+    ///
+    /// If the request cannot be cloned, return [`None`].
+    fn clone_request(&self, req: &Request) -> Option<Request>;
+}
+
+pin_project! {
+    /// Configure retrying requests of "failed" responses.
+    ///
+    /// A [`Policy`] classifies what is a "failed" response.
+    #[derive(Clone, Debug)]
+    pub struct Retry<P, S> {
+        #[pin]
+        policy: P,
+        service: S,
+    }
+}
+
+impl<P, S> Service for Retry<P, S>
+where
+    P: 'static + Policy + Clone,
+    S: 'static + Service + Clone,
+{
+    type Future = ResponseFuture<P, S>;
+
+    fn call(&mut self, request: Request, ext: &mut Extensions) -> Self::Future {
+        let cloned = self.policy.clone_request(&request);
+        let future = self.service.call(request, ext);
+
+        ResponseFuture::new(cloned, self.clone(), future)
+    }
+
+    // fn call(&mut self, request: Request) -> Self::Future {
+    //     let cloned = self.policy.clone_request(&request);
+    //     let future = self.service.call(request);
+
+    //     ResponseFuture::new(cloned, self.clone(), future)
+    // }
+}
+
+pin_project! {
+    /// The [`Future`] returned by a [`Retry`] service.
+    #[derive(Debug)]
+    pub struct ResponseFuture<P, S>
+    where
+        P: Policy,
+        S: Service,
+    {
+        request: Option<Request>,
+        #[pin]
+        retry: Retry<P, S>,
+        #[pin]
+        state: State<S::Future, P::Future>,
+    }
+}
+
+pin_project! {
+    #[project = StateProj]
+    #[derive(Debug)]
+    enum State<F, P> {
+        // Polling the future from [`Service::call`]
+        Called {
+            #[pin]
+            future: F
+        },
+        // Polling the future from [`Policy::retry`]
+        Checking {
+            #[pin]
+            checking: P
+        },
+        // Polling [`Service::poll_ready`] after [`Checking`] was OK.
+        Retrying,
+    }
+}
+
+impl<P, S> ResponseFuture<P, S>
+where
+    P: Policy,
+    S: Service,
+{
+    pub(crate) fn new(
+        request: Option<Request>,
+        retry: Retry<P, S>,
+        future: S::Future,
+    ) -> ResponseFuture<P, S> {
+        ResponseFuture {
+            request,
+            retry,
+            state: State::Called { future },
+        }
+    }
+}
+
+impl<P, S> Future for ResponseFuture<P, S>
+where
+    P: Policy + Clone,
+    S: Service + Clone,
+{
+    type Output = Result<Response, Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+
+        loop {
+            match this.state.as_mut().project() {
+                StateProj::Called { future } => {
+                    let result = ready!(future.poll(cx));
+                    if let Some(ref req) = this.request {
+                        match this.retry.policy.retry(req, &result) {
+                            Some(checking) => {
+                                this.state.set(State::Checking { checking });
+                            }
+                            None => return Poll::Ready(result),
+                        }
+                    } else {
+                        // request wasn't cloned, so no way to retry it
+                        return Poll::Ready(result);
+                    }
+                }
+                StateProj::Checking { checking } => {
+                    this.retry
+                        .as_mut()
+                        .project()
+                        .policy
+                        .set(ready!(checking.poll(cx)));
+                    this.state.set(State::Retrying);
+                }
+                StateProj::Retrying => {
+                    let req = this
+                        .request
+                        .take()
+                        .expect("retrying requires cloned request");
+                    *this.request = this.retry.policy.clone_request(&req);
+                    this.state.set(State::Called {
+                        future: this
+                            .retry
+                            .as_mut()
+                            .project()
+                            .service
+                            .call(req, &mut Extensions::new()),
+                    });
                 }
             }
-                Some(_) | None => result,
-            };
         }
     }
 }

reqwest-retry/tests/all/retry.rs

@@ -147,17 +147,6 @@ assert_retry_succeeds!(429, StatusCode::OK);
 assert_no_retry!(431, StatusCode::REQUEST_HEADER_FIELDS_TOO_LARGE);
 assert_no_retry!(451, StatusCode::UNAVAILABLE_FOR_LEGAL_REASONS);
 
-// We assert that we cap retries at 10, which means that we will
-// get 11 calls to the RetryResponder.
-assert_retry_succeeds_inner!(
-    500,
-    assert_maximum_retries_is_not_exceeded,
-    StatusCode::INTERNAL_SERVER_ERROR,
-    100,
-    11,
-    RetryResponder::new(100_u32, 500)
-);
-
 pub struct RetryTimeoutResponder(Arc<AtomicU32>, u32, std::time::Duration);
 
 impl RetryTimeoutResponder {

reqwest-tracing/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "reqwest-tracing"
-version = "0.4.0"
+version = "0.5.0"
 authors = ["Rodrigo Gryzinski <rodrigo.gryzinski@truelayer.com>"]
 edition = "2018"
 description = "Opentracing middleware for reqwest."
@@ -19,12 +19,13 @@ opentelemetry_0_18 = ["opentelemetry_0_18_pkg", "tracing-opentelemetry_0_18_pkg"
 
 
 [dependencies]
-reqwest-middleware = { version = "0.2.0", path = "../reqwest-middleware" }
+reqwest-middleware = { version = "0.3.0", path = "../reqwest-middleware" }
 
 async-trait = "0.1.51"
 reqwest = { version = "0.11", default-features = false }
 task-local-extensions = "0.1.1"
 tracing = "0.1.26"
+pin-project-lite = "0.2"
 
 opentelemetry_0_13_pkg = { package = "opentelemetry", version = "0.13", optional = true }
 opentelemetry_0_14_pkg = { package = "opentelemetry", version = "0.14", optional = true }

reqwest-tracing/src/lib.rs

@@ -4,11 +4,11 @@
 //!
 //! The simplest possible usage:
 //! ```no_run
-//! # use reqwest_middleware::Result;
+//! # use reqwest_middleware::Error;
 //! use reqwest_middleware::{ClientBuilder};
 //! use reqwest_tracing::TracingMiddleware;
 //!
-//! # async fn example() -> Result<()> {
+//! # async fn example() -> Result<(), Error> {
 //! let reqwest_client = reqwest::Client::builder().build().unwrap();
 //! let client = ClientBuilder::new(reqwest_client)
 //!    // Insert the tracing middleware
@@ -22,12 +22,12 @@
 //!
 //! To customise the span names use [`OtelName`].
 //! ```no_run
-//! # use reqwest_middleware::Result;
+//! # use reqwest_middleware::Error;
 //! use reqwest_middleware::{ClientBuilder, Extension};
 //! use reqwest_tracing::{
 //!     TracingMiddleware, OtelName
 //! };
-//! # async fn example() -> Result<()> {
+//! # async fn example() -> Result<(), Error> {
 //! let reqwest_client = reqwest::Client::builder().build().unwrap();
 //! let client = ClientBuilder::new(reqwest_client)
 //!    // Inserts the extension before the request is started
@@ -52,7 +52,7 @@
 //!
 //! Note that Opentelemetry tracks start and stop already, there is no need to have a custom builder like this.
 //! ```rust
-//! use reqwest_middleware::Result;
+//! use reqwest_middleware::Error;
 //! use task_local_extensions::Extensions;
 //! use reqwest::{Request, Response};
 //! use reqwest_middleware::ClientBuilder;
@@ -62,16 +62,17 @@
 //! use tracing::Span;
 //! use std::time::{Duration, Instant};
 //!
-//! pub struct TimeTrace;
+//! pub struct TimeTrace(Instant);
 //!
 //! impl ReqwestOtelSpanBackend for TimeTrace {
-//!     fn on_request_start(req: &Request, extension: &mut Extensions) -> Span {
+//!     fn on_request_start(req: &Request, _extension: &mut Extensions) -> (Self, Span) {
-//!         extension.insert(Instant::now());
+//!         let now = Self(Instant::now());
-//!         reqwest_otel_span!(name="example-request", req, time_elapsed = tracing::field::Empty)
+//!         let span = reqwest_otel_span!(name="example-request", req, time_elapsed = tracing::field::Empty);
+//!         (now, span)
 //!     }
 //!
-//!     fn on_request_end(span: &Span, outcome: &Result<Response>, extension: &mut Extensions) {
+//!     fn on_request_end(self, span: &Span, outcome: &Result<Response, Error>) {
-//!         let time_elapsed = extension.get::<Instant>().unwrap().elapsed().as_millis() as i64;
+//!         let time_elapsed = self.0.elapsed().as_millis() as i64;
 //!         default_on_request_end(span, outcome);
 //!         span.record("time_elapsed", &time_elapsed);
 //!     }

reqwest-tracing/src/middleware.rs

@@ -1,7 +1,14 @@
+use std::{
+    future::Future,
+    task::{ready, Context, Poll},
+};
+
+use pin_project_lite::pin_project;
 use reqwest::{Request, Response};
-use reqwest_middleware::{Middleware, Next, Result};
+use reqwest_middleware::{Error, Layer, Service};
 use task_local_extensions::Extensions;
-use tracing::Instrument;
+// use tower::{Layer, Service};
+use tracing::Span;
 
 use crate::{DefaultSpanBackend, ReqwestOtelSpanBackend};
 
@@ -10,6 +17,8 @@ pub struct TracingMiddleware<S: ReqwestOtelSpanBackend> {
     span_backend: std::marker::PhantomData<S>,
 }
 
+impl<S: ReqwestOtelSpanBackend> Copy for TracingMiddleware<S> {}
+
 impl<S: ReqwestOtelSpanBackend> TracingMiddleware<S> {
     pub fn new() -> TracingMiddleware<S> {
         TracingMiddleware {
@@ -30,20 +39,36 @@ impl Default for TracingMiddleware<DefaultSpanBackend> {
     }
 }
 
-#[async_trait::async_trait]
+impl<ReqwestOtelSpan, Svc> Layer<Svc> for TracingMiddleware<ReqwestOtelSpan>
-impl<ReqwestOtelSpan> Middleware for TracingMiddleware<ReqwestOtelSpan>
 where
     ReqwestOtelSpan: ReqwestOtelSpanBackend + Sync + Send + 'static,
+    Svc: Service,
 {
-    async fn handle(
+    type Service = TracingMiddlewareService<ReqwestOtelSpan, Svc>;
-        &self,
-        req: Request,
-        extensions: &mut Extensions,
-        next: Next<'_>,
-    ) -> Result<Response> {
-        let request_span = ReqwestOtelSpan::on_request_start(&req, extensions);
 
-        let outcome_future = async {
+    fn layer(&self, inner: Svc) -> Self::Service {
+        TracingMiddlewareService {
+            service: inner,
+            _layer: *self,
+        }
+    }
+}
+
+/// Middleware Service for tracing requests using the current Opentelemetry Context.
+pub struct TracingMiddlewareService<S: ReqwestOtelSpanBackend, Svc> {
+    _layer: TracingMiddleware<S>,
+    service: Svc,
+}
+
+impl<ReqwestOtelSpan, Svc> Service for TracingMiddlewareService<ReqwestOtelSpan, Svc>
+where
+    ReqwestOtelSpan: ReqwestOtelSpanBackend + Sync + Send + 'static,
+    Svc: Service,
+{
+    type Future = TracingMiddlewareFuture<ReqwestOtelSpan, Svc::Future>;
+
+    fn call(&mut self, req: Request, ext: &mut Extensions) -> Self::Future {
+        let (backend, span) = ReqwestOtelSpan::on_request_start(&req, ext);
         // Adds tracing headers to the given request to propagate the OpenTelemetry context to downstream revivers of the request.
         // Spans added by downstream consumers will be part of the same trace.
         #[cfg(any(
@@ -54,14 +79,42 @@ where
             feature = "opentelemetry_0_17",
             feature = "opentelemetry_0_18",
         ))]
-            let req = crate::otel::inject_opentelemetry_context_into_request(req);
+        let request = crate::otel::inject_opentelemetry_context_into_request(request);
 
-            // Run the request
+        let future = self.service.call(req, ext);
-            let outcome = next.run(req, extensions).await;
+
-            ReqwestOtelSpan::on_request_end(&request_span, &outcome, extensions);
+        TracingMiddlewareFuture {
-            outcome
+            span,
+            backend: Some(backend),
+            future,
+        }
+    }
+}
+
+pin_project!(
+    pub struct TracingMiddlewareFuture<S: ReqwestOtelSpanBackend, F> {
+        span: Span,
+        backend: Option<S>,
+        #[pin]
+        future: F,
+    }
+);
+
+impl<S: ReqwestOtelSpanBackend, F: Future<Output = Result<Response, Error>>> Future
+    for TracingMiddlewareFuture<S, F>
+{
+    type Output = F::Output;
+
+    fn poll(self: std::pin::Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = self.project();
+        let outcome = {
+            let _guard = this.span.enter();
+            ready!(this.future.poll(cx))
         };
-
+        this.backend
-        outcome_future.instrument(request_span.clone()).await
+            .take()
+            .expect("poll should not be called after completion")
+            .on_request_end(this.span, &outcome);
+        Poll::Ready(outcome)
     }
 }

reqwest-tracing/src/reqwest_otel_span_builder.rs

@@ -2,7 +2,7 @@ use std::borrow::Cow;
 
 use reqwest::header::{HeaderMap, HeaderValue};
 use reqwest::{Request, Response, StatusCode as RequestStatusCode, Url};
-use reqwest_middleware::{Error, Result};
+use reqwest_middleware::Error;
 use task_local_extensions::Extensions;
 use tracing::Span;
 
@@ -39,17 +39,17 @@ pub const HTTP_USER_AGENT: &str = "http.user_agent";
 /// Check out [`reqwest_otel_span`] documentation for examples.
 ///
 /// [`TracingMiddleware`]: crate::middleware::TracingMiddleware.
-pub trait ReqwestOtelSpanBackend {
+pub trait ReqwestOtelSpanBackend: Sized {
     /// Initalized a new span before the request is executed.
-    fn on_request_start(req: &Request, extension: &mut Extensions) -> Span;
+    fn on_request_start(req: &Request, extension: &mut Extensions) -> (Self, Span);
 
     /// Runs after the request call has executed.
-    fn on_request_end(span: &Span, outcome: &Result<Response>, extension: &mut Extensions);
+    fn on_request_end(self, span: &Span, outcome: &Result<Response, Error>);
 }
 
 /// Populates default success/failure fields for a given [`reqwest_otel_span!`] span.
 #[inline]
-pub fn default_on_request_end(span: &Span, outcome: &Result<Response>) {
+pub fn default_on_request_end(span: &Span, outcome: &Result<Response, Error>) {
     match outcome {
         Ok(res) => default_on_request_success(span, res),
         Err(err) => default_on_request_failure(span, err),
@@ -95,15 +95,15 @@ pub fn default_on_request_failure(span: &Span, e: &Error) {
 pub struct DefaultSpanBackend;
 
 impl ReqwestOtelSpanBackend for DefaultSpanBackend {
-    fn on_request_start(req: &Request, ext: &mut Extensions) -> Span {
+    fn on_request_start(req: &Request, ext: &mut Extensions) -> (DefaultSpanBackend, Span) {
         let name = ext
             .get::<OtelName>()
             .map(|on| on.0.as_ref())
             .unwrap_or("reqwest-http-client");
-        reqwest_otel_span!(name = name, req)
+        (Self, reqwest_otel_span!(name = name, req))
     }
 
-    fn on_request_end(span: &Span, outcome: &Result<Response>, _: &mut Extensions) {
+    fn on_request_end(self, span: &Span, outcome: &Result<Response, Error>) {
         default_on_request_end(span, outcome)
     }
 }
@@ -119,16 +119,19 @@ fn get_header_value(key: &str, headers: &HeaderMap) -> String {
 pub struct SpanBackendWithUrl;
 
 impl ReqwestOtelSpanBackend for SpanBackendWithUrl {
-    fn on_request_start(req: &Request, ext: &mut Extensions) -> Span {
+    fn on_request_start(req: &Request, ext: &mut Extensions) -> (Self, Span) {
         let name = ext
             .get::<OtelName>()
             .map(|on| on.0.as_ref())
             .unwrap_or("reqwest-http-client");
 
-        reqwest_otel_span!(name = name, req, http.url = %remove_credentials(req.url()))
+        (
+            Self,
+            reqwest_otel_span!(name = name, req, http.url = %remove_credentials(req.url())),
+        )
     }
 
-    fn on_request_end(span: &Span, outcome: &Result<Response>, _: &mut Extensions) {
+    fn on_request_end(self, span: &Span, outcome: &Result<Response, Error>) {
         default_on_request_end(span, outcome)
     }
 }
@@ -156,12 +159,12 @@ fn get_span_status(request_status: RequestStatusCode) -> Option<&'static str> {
 ///
 /// Usage:
 /// ```no_run
-/// # use reqwest_middleware::Result;
+/// # use reqwest_middleware::Error;
 /// use reqwest_middleware::{ClientBuilder, Extension};
 /// use reqwest_tracing::{
 ///     TracingMiddleware, OtelName
 /// };
-/// # async fn example() -> Result<()> {
+/// # async fn example() -> Result<(), Error> {
 /// let reqwest_client = reqwest::Client::builder().build().unwrap();
 /// let client = ClientBuilder::new(reqwest_client)
 ///     // Inserts the extension before the request is started

reqwest-tracing/src/reqwest_otel_span_macro.rs

@@ -30,7 +30,7 @@
 /// The second argument passed to [`reqwest_otel_span!`](crate::reqwest_otel_span) is a reference to an [`reqwest::Request`].
 ///
 /// ```rust
-/// use reqwest_middleware::Result;
+/// use reqwest_middleware::Error;
 /// use task_local_extensions::Extensions;
 /// use reqwest::{Request, Response};
 /// use reqwest_tracing::{
@@ -41,11 +41,11 @@
 /// pub struct CustomReqwestOtelSpanBackend;
 ///
 /// impl ReqwestOtelSpanBackend for CustomReqwestOtelSpanBackend {
-///     fn on_request_start(req: &Request, _extension: &mut Extensions) -> Span {
+///     fn on_request_start(req: &Request, _extension: &mut Extensions) -> (Self, Span) {
-///         reqwest_otel_span!(name = "reqwest-http-request", req)
+///         (Self, reqwest_otel_span!(name = "reqwest-http-request", req))
 ///     }
 ///
-///     fn on_request_end(span: &Span, outcome: &Result<Response>, _extension: &mut Extensions) {
+///     fn on_request_end(self, span: &Span, outcome: &Result<Response, Error>) {
 ///         default_on_request_end(span, outcome)
 ///     }
 /// }