概览

Motore 是一个使用了 GAT 和 TAIT 特性的中间件抽象层。

基于 Motore，我们编写了一些模块化并且可复用的，用来编写 client 和 server 的组件。

Motore 深受Tower 启发。

Motore 使用 GAT 和 TAIT 来减轻编写异步代码的精神负担，尤其是为了避免 Box 的开销而导致的负担，以减少使用者的焦虑。

Motore 最核心的抽象是 Service trait：

pub trait Service<Cx, Request> {
    /// Responses given by the service.
    type Response;
    /// Errors produced by the service.
    type Error;
    /// The future response value.
    type Future<'cx>: Future<Output = Result<Self::Response, Self::Error>> + Send + 'cx
    where
        Cx: 'cx,
        Self: 'cx;
    /// Process the request and return the response asynchronously.
    fn call<'cx, 's>(&'s mut self, cx: &'cx mut Cx, req: Request) -> Self::Future<'cx>
    where
        's: 'cx;
}

快速上手

通过将 GAT 和 TAIT 组合在一起，我们可以以非常简洁易读的方式编写异步代码：

pub struct Timeout<S> {
    inner: S,
    duration: Duration,
}
impl<Cx, Req, S> Service<Cx, Req> for Timeout<S>
where
    Req: 'static + Send,
    S: Service<Cx, Req> + 'static + Send,
    Cx: 'static + Send,
    S::Error: Send + Sync + Into<BoxError>,
{
    type Response = S::Response;
    type Error = BoxError;
    type Future<'cx> = impl Future<Output = Result<S::Response, Self::Error>> + 'cx;
    fn call<'cx, 's>(&'s mut self, cx: &'cx mut Cx, req: Req) -> Self::Future<'cx>
    where
        's: 'cx,
    {
        async move {
            let sleep = tokio::time::sleep(self.duration);
            tokio::select! {
                r = self.inner.call(cx, req) => {
                    r.map_err(Into::into)
                },
                _ = sleep => Err(std::io::Error::new(std::io::ErrorKind::TimedOut, "service time out").into()),
            }
        }
    }
}

我们还提供了#[motore::service]宏以使编写 Service 更加像编写原生异步 Rust：

use motore::service;
pub struct S<I> {
    inner: I,
}
#[service]
impl<Cx, Req, I> Service<Cx, Req> for S<I>
where
   Req: Send + 'static,
   I: Service<Cx, Req> + Send + 'static,
   Cx: Send + 'static,
{
    async fn call(&mut self, cx: &mut Cx, req: Req) -> Result<I::Response, I::Error> {
        self.inner.call(cx, req).await
    }
}

最后修改 July 30, 2023 : fix type error (#735) (50c91bf)