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    use std::error::Error as StdError;

    use crate::body::HttpBody;
    use crate::common::{task, Future, Poll};
    use crate::{Request, Response};

    /// An asynchronous function from `Request` to `Response`.
    pub trait HttpService<ReqBody>: sealed::Sealed<ReqBody> {
        /// The `HttpBody` body of the `http::Response`.
        type ResBody: HttpBody;

        /// The error type that can occur within this `Service`.
        ///
        /// Note: Returning an `Error` to a hyper server will cause the connection
        /// to be abruptly aborted. In most cases, it is better to return a `Response`
        /// with a 4xx or 5xx status code.
        type Error: Into<Box<dyn StdError + Send + Sync>>;

        /// The `Future` returned by this `Service`.
        type Future: Future<Output = Result<Response<Self::ResBody>, Self::Error>>;

        #[doc(hidden)]
        fn poll_ready(&mut self, cx: &mut task::Context<'_>) -> Poll<Result<(), Self::Error>>;

        #[doc(hidden)]
        fn call(&mut self, req: Request<ReqBody>) -> Self::Future;
    }

    impl<T, B1, B2> HttpService<B1> for T
    where
        T: tower_service::Service<Request<B1>, Response = Response<B2>>,
        B2: HttpBody,
        T::Error: Into<Box<dyn StdError + Send + Sync>>,
    {
        type ResBody = B2;

        type Error = T::Error;
        type Future = T::Future;

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

        fn call(&mut self, req: Request<B1>) -> Self::Future {
            tower_service::Service::call(self, req)
        }
    }

    impl<T, B1, B2> sealed::Sealed<B1> for T
    where
        T: tower_service::Service<Request<B1>, Response = Response<B2>>,
        B2: HttpBody,
    {
    }

    mod sealed {
        pub trait Sealed<T> {}
    }