Rust学习之Axum框架中间件链Stack实现

pub trait Layer<S> {
    /// The wrapped service
    type Service;

    /// Wrap the given service with the middleware, returning a new service
    /// that has been decorated with the middleware.
    fn layer(&self, inner: S) -> Self::Service;
}

/// Two middlewares chained together.
pub struct Stack<Inner, Outer> {
    inner: Inner,
    outer: Outer,
}

impl<S, Inner, Outer> Layer<S> for Stack<Inner, Outer>
where
    Inner: Layer<S>,
    Outer: Layer<Inner::Service>,
{
    type Service = Outer::Service;

    fn layer(&self, service: S) -> Self::Service {
        let inner = self.inner.layer(service);

        self.outer.layer(inner)
    }
}