keyfork/crates/daemon/keyforkd/src/middleware.rs

use std::{future::Future, marker::PhantomData, pin::Pin};

use bincode::{deserialize, serialize};
use serde::{de::DeserializeOwned, Serialize};
use thiserror::Error;
use tower::{Layer, Service};

/// Layer a [`BincodeService`] upon another Service.
pub struct BincodeLayer<'a, Request> {
    phantom: PhantomData<&'a ()>,
    phantom_request: PhantomData<&'a Request>,
}

impl<'a, Request> BincodeLayer<'a, Request> {
    /// Create a new [`BincodeLayer`].
    pub fn new() -> Self {
        Self {
            phantom: PhantomData,
            phantom_request: PhantomData,
        }
    }
}

impl<'a, Request> Default for BincodeLayer<'a, Request> {
    fn default() -> Self {
        Self::new()
    }
}

impl<'a, S: 'a, Request> Layer<S> for BincodeLayer<'a, Request> {
    type Service = BincodeService<S, Request>;

    fn layer(&self, service: S) -> Self::Service {
        BincodeService {
            service,
            phantom_request: PhantomData,
        }
    }
}

/// Transform a Bincode-serialized type to a Rust type.
#[derive(Clone)]
pub struct BincodeService<S, Request> {
    service: S,
    phantom_request: PhantomData<Request>,
}

/// An error encountered either while transforming data or against the interior Service.
#[derive(Debug, Error)]
pub enum BincodeServiceError {
    /// An error occurred while polling the internal service.
    #[error("Error while polling: {0}")]
    Poll(String),

    /// An error occurred while calling the internal service.
    #[error("Error while calling: {0}")]
    Call(String),

    /// An error occurred while converting to or from bincode.
    #[error("Error while converting: {0}")]
    Convert(String),
}

impl<S, Request> Service<Vec<u8>> for BincodeService<S, Request>
where
    S: Service<Request>,
    Request: DeserializeOwned,
    <S as Service<Request>>::Response: Serialize,
    <S as Service<Request>>::Error: std::error::Error + Serialize,
    <S as Service<Request>>::Future: Send + 'static,
{
    type Response = Vec<u8>;
    type Error = BincodeServiceError;
    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;

    fn poll_ready(
        &mut self,
        cx: &mut std::task::Context<'_>,
    ) -> std::task::Poll<Result<(), Self::Error>> {
        self.service
            .poll_ready(cx)
            .map_err(|e| BincodeServiceError::Poll(e.to_string()))
    }

    fn call(&mut self, req: Vec<u8>) -> Self::Future {
        let request: Request = match deserialize(&req) {
            Ok(r) => r,
            Err(e) => {
                return Box::pin(async move { Err(BincodeServiceError::Convert(e.to_string())) })
            }
        };

        let response = self.service.call(request);

        Box::pin(async move {
            let response = response.await;
            #[cfg(feature = "tracing")]
            if let Err(e) = &response {
                tracing::error!("Error performing derivation: {e}");
            }
            serialize(&response).map_err(|e| BincodeServiceError::Convert(e.to_string()))
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use serde::{Deserialize, Serialize};
    use std::{future::Future, pin::Pin, task::Poll};
    use tower::{ServiceBuilder, ServiceExt};

    #[derive(Serialize, Deserialize)]
    struct Test {
        field: String,
    }

    impl Test {
        fn new() -> Self {
            Self {
                field: "hello world!".to_string(),
            }
        }
    }

    struct App;

    #[derive(Debug, thiserror::Error, Serialize)]
    enum Infallible {}

    impl Service<Test> for App {
        type Response = Test;
        type Error = Infallible;
        type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;

        fn poll_ready(
            &mut self,
            _cx: &mut std::task::Context<'_>,
        ) -> std::task::Poll<Result<(), Self::Error>> {
            Poll::Ready(Ok(()))
        }

        fn call(&mut self, req: Test) -> Self::Future {
            Box::pin(async {
                assert_eq!(req.field, Test::new().field);
                Ok(req)
            })
        }
    }

    #[tokio::test]
    async fn can_serde_responses() {
        let test = Test::new();
        let content = serialize(&test).unwrap();
        let mut service = ServiceBuilder::new()
            .layer(BincodeLayer::<Test>::default())
            .service(App);
        let result = service
            .ready()
            .await
            .unwrap()
            .call(content.clone())
            .await
            .unwrap();
        assert_eq!(result, serialize(&Result::<Test, Infallible>::Ok(test)).unwrap());
    }
}