feat(tonic): add Interceptor trait (#713)

* Expose `Interceptor` trait.

* Revert changes to public API surface.

* Rename types, add deprecated alias for old names.

examples/src/tower/client.rs

@@ -15,7 +15,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 
     let channel = ServiceBuilder::new()
         // Interceptors can be also be applied as middleware
-        .layer(tonic::service::interceptor_fn(intercept))
+        .layer(tonic::service::interceptor(intercept))
         .layer_fn(AuthSvc::new)
         .service(channel);
 

examples/src/tower/server.rs

@@ -47,7 +47,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         // Apply our own middleware
         .layer(MyMiddlewareLayer::default())
         // Interceptors can be also be applied as middleware
-        .layer(tonic::service::interceptor_fn(intercept))
+        .layer(tonic::service::interceptor(intercept))
         .into_inner();
 
     Server::builder()

tonic-build/src/client.rs

@@ -68,7 +68,7 @@ pub fn generate<T: Service>(
 
                 pub fn with_interceptor<F>(inner: T, interceptor: F) -> #service_ident<InterceptedService<T, F>>
                 where
-                    F: FnMut(tonic::Request<()>) -> Result<tonic::Request<()>, tonic::Status>,
+                    F: tonic::service::Interceptor,
                     T: tonic::codegen::Service<
                         http::Request<tonic::body::BoxBody>,
                         Response = http::Response<<T as tonic::client::GrpcService<tonic::body::BoxBody>>::ResponseBody>

tonic-build/src/server.rs

@@ -104,7 +104,7 @@ pub fn generate<T: Service>(
 
                 pub fn with_interceptor<F>(inner: T, interceptor: F) -> InterceptedService<Self, F>
                 where
-                    F: FnMut(tonic::Request<()>) -> Result<tonic::Request<()>, tonic::Status>,
+                    F: tonic::service::Interceptor,
                 {
                     InterceptedService::new(Self::new(inner), interceptor)
                 }

tonic/src/extensions.rs

@@ -2,10 +2,10 @@ use std::fmt;
 
 /// A type map of protocol extensions.
 ///
-/// `Extensions` can be used by [`interceptor_fn`] and [`Request`] to store extra data derived from
+/// `Extensions` can be used by [`Interceptor`] and [`Request`] to store extra data derived from
 /// the underlying protocol.
 ///
-/// [`interceptor_fn`]: crate::service::interceptor_fn
+/// [`Interceptor`]: crate::service::Interceptor
 /// [`Request`]: crate::Request
 pub struct Extensions {
     inner: http::Extensions,

tonic/src/request.rs

@@ -300,13 +300,13 @@ impl<T> Request<T> {
     /// Extensions can be set in interceptors:
     ///
     /// ```no_run
-    /// use tonic::{Request, service::interceptor_fn};
+    /// use tonic::{Request, service::interceptor};
     ///
     /// struct MyExtension {
     ///     some_piece_of_data: String,
     /// }
     ///
-    /// interceptor_fn(|mut request: Request<()>| {
+    /// interceptor(|mut request: Request<()>| {
     ///     request.extensions_mut().insert(MyExtension {
     ///         some_piece_of_data: "foo".to_string(),
     ///     });

tonic/src/service/interceptor.rs

@@ -1,6 +1,6 @@
 //! gRPC interceptors which are a kind of middleware.
 //!
-//! See [`interceptor_fn`] for more details.
+//! See [`Interceptor`] for more details.
 
 use crate::{request::SanitizeHeaders, Status};
 use pin_project::pin_project;
@@ -13,12 +13,15 @@ use std::{
 use tower_layer::Layer;
 use tower_service::Service;
 
-/// Create a new interceptor from a function.
+/// A gRPC incerceptor.
 ///
 /// gRPC interceptors are similar to middleware but have less flexibility. An interceptor allows
 /// you to do two main things, one is to add/remove/check items in the `MetadataMap` of each
 /// request. Two, cancel a request with a `Status`.
 ///
+/// Any function that satisfies the bound `FnMut(Request<()>) -> Result<Request<()>, Status>` can be
+/// used as an `Interceptor`.
+///
 /// An interceptor can be used on both the server and client side through the `tonic-build` crate's
 /// generated structs.
 ///
@@ -35,24 +38,56 @@ use tower_service::Service;
 /// [tower]: https://crates.io/crates/tower
 /// [example]: https://github.com/hyperium/tonic/tree/master/examples/src/interceptor
 /// [tower-example]: https://github.com/hyperium/tonic/tree/master/examples/src/tower
-pub fn interceptor_fn<F>(f: F) -> InterceptorFn<F>
+pub trait Interceptor {
+    /// Intercept a request before it is sent, optionally cancelling it.
+    fn call(&mut self, request: crate::Request<()>) -> Result<crate::Request<()>, Status>;
+}
+
+impl<F> Interceptor for F
 where
     F: FnMut(crate::Request<()>) -> Result<crate::Request<()>, Status>,
 {
-    InterceptorFn { f }
+    fn call(&mut self, request: crate::Request<()>) -> Result<crate::Request<()>, Status> {
+        self(request)
+    }
 }
 
-/// An interceptor created from a function.
+/// Create a new interceptor layer.
 ///
-/// See [`interceptor_fn`] for more details.
+/// See [`Interceptor`] for more details.
+pub fn interceptor<F>(f: F) -> InterceptorLayer<F>
+where
+    F: Interceptor,
+{
+    InterceptorLayer { f }
+}
+
+#[deprecated(
+    since = "0.5.1",
+    note = "Please use the `interceptor` function instead"
+)]
+/// Create a new interceptor layer.
+///
+/// See [`Interceptor`] for more details.
+pub fn interceptor_fn<F>(f: F) -> InterceptorLayer<F>
+where
+    F: Interceptor,
+{
+    interceptor(f)
+}
+
+/// A gRPC interceptor that can be used as a [`Layer`],
+/// created by calling [`interceptor`].
+///
+/// See [`Interceptor`] for more details.
 #[derive(Debug, Clone, Copy)]
-pub struct InterceptorFn<F> {
+pub struct InterceptorLayer<F> {
     f: F,
 }
 
-impl<S, F> Layer<S> for InterceptorFn<F>
+impl<S, F> Layer<S> for InterceptorLayer<F>
 where
-    F: FnMut(crate::Request<()>) -> Result<crate::Request<()>, Status> + Clone,
+    F: Interceptor + Clone,
 {
     type Service = InterceptedService<S, F>;
 
@@ -61,9 +96,19 @@ where
     }
 }
 
+#[deprecated(
+    since = "0.5.1",
+    note = "Please use the `InterceptorLayer` type instead"
+)]
+/// A gRPC interceptor that can be used as a [`Layer`],
+/// created by calling [`interceptor`].
+///
+/// See [`Interceptor`] for more details.
+pub type InterceptorFn<F> = InterceptorLayer<F>;
+
 /// A service wrapped in an interceptor middleware.
 ///
-/// See [`interceptor_fn`] for more details.
+/// See [`Interceptor`] for more details.
 #[derive(Clone, Copy)]
 pub struct InterceptedService<S, F> {
     inner: S,
@@ -75,7 +120,7 @@ impl<S, F> InterceptedService<S, F> {
     /// function `F`.
     pub fn new(service: S, f: F) -> Self
     where
-        F: FnMut(crate::Request<()>) -> Result<crate::Request<()>, Status>,
+        F: Interceptor,
     {
         Self { inner: service, f }
     }
@@ -95,7 +140,7 @@ where
 
 impl<S, F, ReqBody, ResBody> Service<http::Request<ReqBody>> for InterceptedService<S, F>
 where
-    F: FnMut(crate::Request<()>) -> Result<crate::Request<()>, Status>,
+    F: Interceptor,
     S: Service<http::Request<ReqBody>, Response = http::Response<ResBody>>,
     S::Error: Into<crate::Error>,
 {
@@ -113,7 +158,10 @@ where
         let req = crate::Request::from_http(req);
         let (metadata, extensions, msg) = req.into_parts();
 
-        match (self.f)(crate::Request::from_parts(metadata, extensions, ())) {
+        match self
+            .f
+            .call(crate::Request::from_parts(metadata, extensions, ()))
+        {
             Ok(req) => {
                 let (metadata, extensions, _) = req.into_parts();
                 let req = crate::Request::from_parts(metadata, extensions, msg);

tonic/src/service/mod.rs

@@ -3,4 +3,5 @@
 pub mod interceptor;
 
 #[doc(inline)]
-pub use self::interceptor::interceptor_fn;
+#[allow(deprecated)]
+pub use self::interceptor::{interceptor, interceptor_fn, Interceptor};

tonic/src/transport/server/mod.rs

@@ -395,7 +395,7 @@ impl<L> Server<L> {
     /// # use tower_service::Service;
     /// use tower::ServiceBuilder;
     /// use std::time::Duration;
-    /// use tonic::{Request, Status, service::interceptor_fn};
+    /// use tonic::{Request, Status, service::interceptor};
     ///
     /// fn auth_interceptor(request: Request<()>) -> Result<Request<()>, Status> {
     ///     if valid_credentials(&request) {
@@ -417,8 +417,8 @@ impl<L> Server<L> {
     /// let layer = ServiceBuilder::new()
     ///     .load_shed()
     ///     .timeout(Duration::from_secs(30))
-    ///     .layer(interceptor_fn(auth_interceptor))
-    ///     .layer(interceptor_fn(some_other_interceptor))
+    ///     .layer(interceptor(auth_interceptor))
+    ///     .layer(interceptor(some_other_interceptor))
     ///     .into_inner();
     ///
     /// Server::builder().layer(layer);
@@ -428,7 +428,7 @@ impl<L> Server<L> {
     /// [`Layer`]: tower::layer::Layer
     /// [eco]: https://github.com/tower-rs
     /// [`ServiceBuilder`]: tower::ServiceBuilder
-    /// [interceptors]: crate::service::interceptor_fn
+    /// [interceptors]: crate::service::Interceptor
     pub fn layer<NewLayer>(self, new_layer: NewLayer) -> Server<NewLayer> {
         Server {
             layer: new_layer,