Return impl Future instead of Pin<Box<dyn Future>>

Returning a boxed trait object requires specifying whether the returned
future is `Send`/`Sync`, which means we can't support both `Send` and
non-`Send` async HTTP clients. The `reqwest` client returns a `Send`
future when using versions of `hyper` >= 0.14.14 (see
hyperium/hyper#2653), except in WASM builds,
for which the future is non-`Send`.

With this change, each `request_async()` method now returns
`impl Future`, which may or may not be `Send` depending on the inputs.
This provides the flexibility to support all the necessary HTTP
clients, while providing the convenience of `Send` futures for the
built-in `reqwest` client in non-WASM builds.

BREAKING CHANGES:
 - Removed `TokenRequestFuture` and `DeviceAuthorizationRequestFuture`
   type aliases.
 - Added `Future` associated type to `AsyncHttpClient` trait and changed
   `call()` method to return `Self::Future` (which may or may not be
   `Send`/`Sync`).
 - Changed each `request_async()` method to return `impl Future` instead
   of `Pin<Box<dyn Future>>`.

Fixes #255 and #260.

src/devicecode.rs

@@ -5,7 +5,7 @@ use crate::{
     AsyncHttpClient, AuthType, Client, ClientId, ClientSecret, DeviceAuthorizationUrl, DeviceCode,
     EndUserVerificationUrl, EndpointState, ErrorResponse, ErrorResponseType, HttpRequest,
     HttpResponse, RequestTokenError, RevocableToken, Scope, StandardErrorResponse, SyncHttpClient,
-    TokenIntrospectionResponse, TokenRequestFuture, TokenResponse, TokenType, TokenUrl, UserCode,
+    TokenIntrospectionResponse, TokenResponse, TokenType, TokenUrl, UserCode,
 };
 
 use chrono::{DateTime, Utc};
@@ -18,7 +18,6 @@ use std::fmt::Error as FormatterError;
 use std::fmt::{Debug, Display, Formatter};
 use std::future::Future;
 use std::marker::PhantomData;
-use std::pin::Pin;
 use std::sync::Arc;
 use std::time::Duration;
 
@@ -98,10 +97,6 @@ where
     }
 }
 
-/// Future returned by [`DeviceAuthorizationRequest::request_async`].
-pub type DeviceAuthorizationRequestFuture<'c, C, EF, TE> =
-    TokenRequestFuture<'c, <C as AsyncHttpClient<'c>>::Error, TE, DeviceAuthorizationResponse<EF>>;
-
 /// The request for a set of verification codes from the authorization server.
 ///
 /// See <https://tools.ietf.org/html/rfc8628#section-3.1>.
@@ -193,7 +188,12 @@ where
     pub fn request_async<'c, C, EF>(
         self,
         http_client: &'c C,
-    ) -> Pin<Box<DeviceAuthorizationRequestFuture<'c, C, EF, TE>>>
+    ) -> impl Future<
+        Output = Result<
+            DeviceAuthorizationResponse<EF>,
+            RequestTokenError<<C as AsyncHttpClient<'c>>::Error, TE>,
+        >,
+    > + 'c
     where
         Self: 'c,
         C: AsyncHttpClient<'c>,
@@ -326,9 +326,12 @@ where
         http_client: &'c C,
         sleep_fn: S,
         timeout: Option<Duration>,
-    ) -> Pin<
-        Box<TokenRequestFuture<'c, <C as AsyncHttpClient<'c>>::Error, DeviceCodeErrorResponse, TR>>,
-    >
+    ) -> impl Future<
+        Output = Result<
+            TR,
+            RequestTokenError<<C as AsyncHttpClient<'c>>::Error, DeviceCodeErrorResponse>,
+        >,
+    > + 'c
     where
         Self: 'c,
         C: AsyncHttpClient<'c>,

src/endpoint.rs

@@ -11,7 +11,6 @@ use url::{form_urlencoded, Url};
 use std::borrow::Cow;
 use std::error::Error;
 use std::future::Future;
-use std::pin::Pin;
 
 /// An HTTP request.
 pub type HttpRequest = http::Request<Vec<u8>>;
@@ -24,11 +23,11 @@ pub trait AsyncHttpClient<'c> {
     /// Error type returned by HTTP client.
     type Error: Error + 'static;
 
+    /// Future type returned by HTTP client.
+    type Future: Future<Output = Result<HttpResponse, Self::Error>> + 'c;
+
     /// Perform a single HTTP request.
-    fn call(
-        &'c self,
-        request: HttpRequest,
-    ) -> Pin<Box<dyn Future<Output = Result<HttpResponse, Self::Error>> + 'c>>;
+    fn call(&'c self, request: HttpRequest) -> Self::Future;
 }
 impl<'c, E, F, T> AsyncHttpClient<'c> for T
 where
@@ -39,12 +38,10 @@ where
     T: Fn(HttpRequest) -> F,
 {
     type Error = E;
+    type Future = F;
 
-    fn call(
-        &'c self,
-        request: HttpRequest,
-    ) -> Pin<Box<dyn Future<Output = Result<HttpResponse, Self::Error>> + 'c>> {
-        Box::pin(self(request))
+    fn call(&'c self, request: HttpRequest) -> Self::Future {
+        self(request)
     }
 }
 

src/introspection.rs

@@ -2,7 +2,7 @@ use crate::endpoint::{endpoint_request, endpoint_response};
 use crate::{
     AccessToken, AsyncHttpClient, AuthType, Client, ClientId, ClientSecret, EndpointState,
     ErrorResponse, ExtraTokenFields, HttpRequest, IntrospectionUrl, RequestTokenError,
-    RevocableToken, Scope, SyncHttpClient, TokenRequestFuture, TokenResponse, TokenType,
+    RevocableToken, Scope, SyncHttpClient, TokenResponse, TokenType,
 };
 
 use chrono::serde::ts_seconds_option;
@@ -13,8 +13,8 @@ use serde::{Deserialize, Serialize};
 use std::borrow::Cow;
 use std::error::Error;
 use std::fmt::Debug;
+use std::future::Future;
 use std::marker::PhantomData;
-use std::pin::Pin;
 
 impl<
         TE,
@@ -180,7 +180,7 @@ where
     pub fn request_async<'c, C>(
         self,
         http_client: &'c C,
-    ) -> Pin<Box<TokenRequestFuture<'c, <C as AsyncHttpClient<'c>>::Error, TE, TIR>>>
+    ) -> impl Future<Output = Result<TIR, RequestTokenError<<C as AsyncHttpClient<'c>>::Error, TE>>> + 'c
     where
         Self: 'c,
         C: AsyncHttpClient<'c>,

src/lib.rs

@@ -524,10 +524,9 @@ pub use crate::code::AuthorizationRequest;
 #[cfg(all(feature = "curl", not(target_arch = "wasm32")))]
 pub use crate::curl_client::CurlHttpClient;
 pub use crate::devicecode::{
-    DeviceAccessTokenRequest, DeviceAuthorizationRequest, DeviceAuthorizationRequestFuture,
-    DeviceAuthorizationResponse, DeviceCodeErrorResponse, DeviceCodeErrorResponseType,
-    EmptyExtraDeviceAuthorizationFields, ExtraDeviceAuthorizationFields,
-    StandardDeviceAuthorizationResponse,
+    DeviceAccessTokenRequest, DeviceAuthorizationRequest, DeviceAuthorizationResponse,
+    DeviceCodeErrorResponse, DeviceCodeErrorResponseType, EmptyExtraDeviceAuthorizationFields,
+    ExtraDeviceAuthorizationFields, StandardDeviceAuthorizationResponse,
 };
 pub use crate::endpoint::{AsyncHttpClient, HttpRequest, HttpResponse, SyncHttpClient};
 pub use crate::error::{
@@ -541,8 +540,7 @@ pub use crate::revocation::{
 };
 pub use crate::token::{
     ClientCredentialsTokenRequest, CodeTokenRequest, EmptyExtraTokenFields, ExtraTokenFields,
-    PasswordTokenRequest, RefreshTokenRequest, StandardTokenResponse, TokenRequestFuture,
-    TokenResponse, TokenType,
+    PasswordTokenRequest, RefreshTokenRequest, StandardTokenResponse, TokenResponse, TokenType,
 };
 pub use crate::types::{
     AccessToken, AuthUrl, AuthorizationCode, ClientId, ClientSecret, CsrfToken,

src/reqwest_client.rs

@@ -6,10 +6,13 @@ use std::pin::Pin;
 impl<'c> AsyncHttpClient<'c> for reqwest::Client {
     type Error = HttpClientError<reqwest::Error>;
 
-    fn call(
-        &'c self,
-        request: HttpRequest,
-    ) -> Pin<Box<dyn Future<Output = Result<HttpResponse, Self::Error>> + 'c>> {
+    #[cfg(target_arch = "wasm32")]
+    type Future = Pin<Box<dyn Future<Output = Result<HttpResponse, Self::Error>> + 'c>>;
+    #[cfg(not(target_arch = "wasm32"))]
+    type Future =
+        Pin<Box<dyn Future<Output = Result<HttpResponse, Self::Error>> + Send + Sync + 'c>>;
+
+    fn call(&'c self, request: HttpRequest) -> Self::Future {
         Box::pin(async move {
             let response = self
                 .execute(request.try_into().map_err(Box::new)?)

src/revocation.rs

@@ -3,8 +3,7 @@ use crate::endpoint::{endpoint_request, endpoint_response, endpoint_response_sta
 use crate::{
     AccessToken, AsyncHttpClient, AuthType, Client, ClientId, ClientSecret, ConfigurationError,
     EndpointState, ErrorResponse, ErrorResponseType, HttpRequest, RefreshToken, RequestTokenError,
-    RevocationUrl, SyncHttpClient, TokenIntrospectionResponse, TokenRequestFuture, TokenResponse,
-    TokenType,
+    RevocationUrl, SyncHttpClient, TokenIntrospectionResponse, TokenResponse, TokenType,
 };
 
 use serde::{Deserialize, Serialize};
@@ -13,8 +12,8 @@ use std::borrow::Cow;
 use std::error::Error;
 use std::fmt::Error as FormatterError;
 use std::fmt::{Debug, Display, Formatter};
+use std::future::Future;
 use std::marker::PhantomData;
-use std::pin::Pin;
 
 impl<
         TE,
@@ -302,7 +301,7 @@ where
     pub fn request_async<'c, C>(
         self,
         http_client: &'c C,
-    ) -> Pin<Box<TokenRequestFuture<'c, <C as AsyncHttpClient<'c>>::Error, TE, ()>>>
+    ) -> impl Future<Output = Result<(), RequestTokenError<<C as AsyncHttpClient<'c>>::Error, TE>>> + 'c
     where
         Self: 'c,
         C: AsyncHttpClient<'c>,

src/token/mod.rs

@@ -14,7 +14,6 @@ use std::error::Error;
 use std::fmt::Debug;
 use std::future::Future;
 use std::marker::PhantomData;
-use std::pin::Pin;
 use std::time::Duration;
 
 #[cfg(test)]
@@ -129,10 +128,6 @@ where
     }
 }
 
-/// Future returned by `request_async` methods.
-pub type TokenRequestFuture<'c, RE, TE, TR> =
-    dyn Future<Output = Result<TR, RequestTokenError<RE, TE>>> + 'c;
-
 /// A request to exchange an authorization code for an access token.
 ///
 /// See <https://tools.ietf.org/html/rfc6749#section-4.1.3>.
@@ -237,7 +232,7 @@ where
     pub fn request_async<'c, C>(
         self,
         http_client: &'c C,
-    ) -> Pin<Box<TokenRequestFuture<'c, <C as AsyncHttpClient<'c>>::Error, TE, TR>>>
+    ) -> impl Future<Output = Result<TR, RequestTokenError<<C as AsyncHttpClient<'c>>::Error, TE>>> + 'c
     where
         Self: 'c,
         C: AsyncHttpClient<'c>,
@@ -322,7 +317,7 @@ where
     pub fn request_async<'c, C>(
         self,
         http_client: &'c C,
-    ) -> Pin<Box<TokenRequestFuture<'c, <C as AsyncHttpClient<'c>>::Error, TE, TR>>>
+    ) -> impl Future<Output = Result<TR, RequestTokenError<<C as AsyncHttpClient<'c>>::Error, TE>>> + 'c
     where
         Self: 'c,
         C: AsyncHttpClient<'c>,
@@ -429,7 +424,7 @@ where
     pub fn request_async<'c, C>(
         self,
         http_client: &'c C,
-    ) -> Pin<Box<TokenRequestFuture<'c, <C as AsyncHttpClient<'c>>::Error, TE, TR>>>
+    ) -> impl Future<Output = Result<TR, RequestTokenError<<C as AsyncHttpClient<'c>>::Error, TE>>> + 'c
     where
         Self: 'c,
         C: AsyncHttpClient<'c>,
@@ -535,7 +530,7 @@ where
     pub fn request_async<'c, C>(
         self,
         http_client: &'c C,
-    ) -> Pin<Box<TokenRequestFuture<'c, <C as AsyncHttpClient<'c>>::Error, TE, TR>>>
+    ) -> impl Future<Output = Result<TR, RequestTokenError<<C as AsyncHttpClient<'c>>::Error, TE>>> + 'c
     where
         Self: 'c,
         C: AsyncHttpClient<'c>,