async_interceptor.rs

use hello_world::greeter_server::{Greeter, GreeterServer};
use hello_world::{HelloReply, HelloRequest};
use tonic::{transport::Server, Request, Response, Status};

pub mod hello_world {
    tonic::include_proto!("helloworld");
}

#[derive(Default)]
pub struct MyGreeter {}

#[tonic::async_trait]
impl Greeter for MyGreeter {
    async fn say_hello(
        &self,
        request: Request<HelloRequest>,
    ) -> Result<Response<HelloReply>, Status> {
        let reply = hello_world::HelloReply {
            message: format!("Hello {}!", request.into_inner().name),
        };
        Ok(Response::new(reply))
    }
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let addr = "[::1]:50051".parse().unwrap();
    let greeter = MyGreeter::default();

    let svc = GreeterServer::new(greeter);

    println!("GreeterServer listening on {}", addr);

    Server::builder()
        .layer(async_interceptor::async_interceptor(|request| async move {
            println!("async!");
            Ok(request)
            // Err(Status::unauthenticated("bad auth"))
        }))
        .add_service(svc)
        .serve(addr)
        .await?;

    Ok(())
}

mod async_interceptor {
    use std::future::Future;
    use std::task::{Context, Poll};

    use tonic::Status;
    use tower::Service;

    pub fn async_interceptor<R, S, F>(
        f: impl Fn(R) -> F + Clone + Send + Sync + 'static,
    ) -> impl tower::layer::Layer<
        S,
        Service = impl Service<
            R,
            Response = S::Response,
            Future = impl Future<Output = Result<S::Response, S::Error>> + Send,
            Error = S::Error,
        > + Clone
                      + Send
                      + Sync,
    > + Clone
    where
        R: Send + Sync + 'static,
        S: Service<R> + Clone + Send + Sync + 'static,
        <S as Service<R>>::Future: Send,
        <S as Service<R>>::Error: From<Status> + Send + Sync,
        F: std::future::Future<Output = Result<R, Status>> + Send,
    {
        tower::layer::layer_fn({
            move |inner: S| {
                let f = f.clone();
                AsyncInterceptor { inner, f }
            }
        })
    }

    #[derive(Clone)]
    struct AsyncInterceptor<S, F> {
        inner: S,
        f: F,
    }

    impl<S, F, Fut, Request> Service<Request> for AsyncInterceptor<S, F>
    where
        Request: Send + 'static,
        S: Service<Request> + Clone + Send + Sync + 'static,
        <S as Service<Request>>::Future: Send,
        <S as Service<Request>>::Error: From<Status> + Send,
        F: (Fn(Request) -> Fut) + Clone + Send + Sync + 'static,
        Fut: std::future::Future<Output = Result<Request, Status>> + Send,
    {
        type Response = S::Response;
        type Error = S::Error;
        type Future = futures::future::BoxFuture<'static, Result<Self::Response, Self::Error>>;

        fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
            self.inner.poll_ready(cx)
        }

        fn call(&mut self, request: Request) -> Self::Future {
            let f = self.f.clone();
            let mut inner = self.inner.clone();
            Box::pin(async move {
                match f(request).await {
                    Ok(request) => inner.call(request).await,
                    Err(err) => Err(err.into()),
                }
            })
        }
    }
}