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    use std::{collections::HashSet, rc::Rc};

    use actix_utils::future::ok;
    use actix_web::{
        body::{EitherBody, MessageBody},
        dev::{forward_ready, Service, ServiceRequest, ServiceResponse},
        http::{
            header::{self, HeaderValue},
            Method,
        },
        Error, HttpResponse, Result,
    };
    use futures_util::future::{FutureExt as _, LocalBoxFuture};
    use log::debug;

    use crate::{
        builder::intersperse_header_values,
        inner::{add_vary_header, header_value_try_into_method},
        AllOrSome, CorsError, Inner,
    };

    /// Service wrapper for Cross-Origin Resource Sharing support.
    ///
    /// This struct contains the settings for CORS requests to be validated and for responses to
    /// be generated.
    #[doc(hidden)]
    #[derive(Debug, Clone)]
    pub struct CorsMiddleware<S> {
        pub(crate) service: S,
        pub(crate) inner: Rc<Inner>,
    }

    impl<S> CorsMiddleware<S> {
        /// Returns true if request is `OPTIONS` and contains an `Access-Control-Request-Method` header.
        fn is_request_preflight(req: &ServiceRequest) -> bool {
            // check request method is OPTIONS
            if req.method() != Method::OPTIONS {
                return false;
            }

            // check follow-up request method is present and valid
            if req
                .headers()
                .get(header::ACCESS_CONTROL_REQUEST_METHOD)
                .and_then(header_value_try_into_method)
                .is_none()
            {
                return false;
            }

            true
        }

        /// Validates preflight request headers against configuration and constructs preflight response.
        ///
        /// Checks:
        /// - `Origin` header is acceptable;
        /// - `Access-Control-Request-Method` header is acceptable;
        /// - `Access-Control-Request-Headers` header is acceptable.
        fn handle_preflight(&self, req: ServiceRequest) -> ServiceResponse {
            let inner = Rc::clone(&self.inner);

            match inner.validate_origin(req.head()) {
                Ok(true) => {}
                Ok(false) => return req.error_response(CorsError::OriginNotAllowed),
                Err(err) => return req.error_response(err),
            };

            if let Err(err) = inner
                .validate_allowed_method(req.head())
                .and_then(|_| inner.validate_allowed_headers(req.head()))
            {
                return req.error_response(err);
            }

            let mut res = HttpResponse::Ok();

            if let Some(origin) = inner.access_control_allow_origin(req.head()) {
                res.insert_header((header::ACCESS_CONTROL_ALLOW_ORIGIN, origin));
            }

            if let Some(ref allowed_methods) = inner.allowed_methods_baked {
                res.insert_header((
                    header::ACCESS_CONTROL_ALLOW_METHODS,
                    allowed_methods.clone(),
                ));
            }

            if let Some(ref headers) = inner.allowed_headers_baked {
                res.insert_header((header::ACCESS_CONTROL_ALLOW_HEADERS, headers.clone()));
            } else if let Some(headers) = req.headers().get(header::ACCESS_CONTROL_REQUEST_HEADERS) {
                // all headers allowed, return
                res.insert_header((header::ACCESS_CONTROL_ALLOW_HEADERS, headers.clone()));
            }

            #[cfg(feature = "draft-private-network-access")]
            if inner.allow_private_network_access
                && req
                    .headers()
                    .contains_key("access-control-request-private-network")
            {
                res.insert_header((
                    header::HeaderName::from_static("access-control-allow-private-network"),
                    HeaderValue::from_static("true"),
                ));
            }

            if inner.supports_credentials {
                res.insert_header((
                    header::ACCESS_CONTROL_ALLOW_CREDENTIALS,
                    HeaderValue::from_static("true"),
                ));
            }

            if let Some(max_age) = inner.max_age {
                res.insert_header((header::ACCESS_CONTROL_MAX_AGE, max_age.to_string()));
            }

            let mut res = res.finish();

            if inner.vary_header {
                add_vary_header(res.headers_mut());
            }

            req.into_response(res)
        }

        fn augment_response<B>(
            inner: &Inner,
            origin_allowed: bool,
            mut res: ServiceResponse<B>,
        ) -> ServiceResponse<B> {
            if origin_allowed {
                if let Some(origin) = inner.access_control_allow_origin(res.request().head()) {
                    res.headers_mut()
                        .insert(header::ACCESS_CONTROL_ALLOW_ORIGIN, origin);
                };
            }

            if let Some(ref expose) = inner.expose_headers_baked {
                log::trace!("exposing selected headers: {:?}", expose);

                res.headers_mut()
                    .insert(header::ACCESS_CONTROL_EXPOSE_HEADERS, expose.clone());
            } else if matches!(inner.expose_headers, AllOrSome::All) {
                // intersperse_header_values requires that argument is non-empty
                if !res.headers().is_empty() {
                    // extract header names from request
                    let expose_all_request_headers = res
                        .headers()
                        .keys()
                        .map(|name| name.as_str())
                        .collect::<HashSet<_>>();

                    // create comma separated string of header names
                    let expose_headers_value = intersperse_header_values(&expose_all_request_headers);

                    log::trace!(
                        "exposing all headers from request: {:?}",
                        expose_headers_value
                    );

                    // add header names to expose response header
                    res.headers_mut()
                        .insert(header::ACCESS_CONTROL_EXPOSE_HEADERS, expose_headers_value);
                }
            }

            if inner.supports_credentials {
                res.headers_mut().insert(
                    header::ACCESS_CONTROL_ALLOW_CREDENTIALS,
                    HeaderValue::from_static("true"),
                );
            }

            #[cfg(feature = "draft-private-network-access")]
            if inner.allow_private_network_access
                && res
                    .request()
                    .headers()
                    .contains_key("access-control-request-private-network")
            {
                res.headers_mut().insert(
                    header::HeaderName::from_static("access-control-allow-private-network"),
                    HeaderValue::from_static("true"),
                );
            }

            if inner.vary_header {
                add_vary_header(res.headers_mut());
            }

            res
        }
    }

    impl<S, B> Service<ServiceRequest> for CorsMiddleware<S>
    where
        S: Service<ServiceRequest, Response = ServiceResponse<B>, Error = Error>,
        S::Future: 'static,

        B: MessageBody + 'static,
    {
        type Response = ServiceResponse<EitherBody<B>>;
        type Error = Error;
        type Future = LocalBoxFuture<'static, Result<ServiceResponse<EitherBody<B>>, Error>>;

        forward_ready!(service);

        fn call(&self, req: ServiceRequest) -> Self::Future {
            let origin = req.headers().get(header::ORIGIN);

            // handle preflight requests
            if self.inner.preflight && Self::is_request_preflight(&req) {
                let res = self.handle_preflight(req);
                return ok(res.map_into_right_body()).boxed_local();
            }

            // only check actual requests with a origin header
            let origin_allowed = match (origin, self.inner.validate_origin(req.head())) {
                (None, _) => false,
                (_, Ok(origin_allowed)) => origin_allowed,
                (_, Err(err)) => {
                    debug!("origin validation failed; inner service is not called");
                    let mut res = req.error_response(err);

                    if self.inner.vary_header {
                        add_vary_header(res.headers_mut());
                    }

                    return ok(res.map_into_right_body()).boxed_local();
                }
            };

            let inner = Rc::clone(&self.inner);
            let fut = self.service.call(req);

            Box::pin(async move {
                let res = fut.await;
                Ok(Self::augment_response(&inner, origin_allowed, res?).map_into_left_body())
            })
        }
    }

    #[cfg(test)]
    mod tests {
        use actix_web::{
            dev::Transform,
            middleware::Compat,
            test::{self, TestRequest},
            App,
        };

        use super::*;
        use crate::Cors;

        #[test]
        fn compat_compat() {
            let _ = App::new().wrap(Compat::new(Cors::default()));
        }

        #[actix_web::test]
        async fn test_options_no_origin() {
            // Tests case where allowed_origins is All but there are validate functions to run incase.
            // In this case, origins are only allowed when the DNT header is sent.

            let cors = Cors::default()
                .allow_any_origin()
                .allowed_origin_fn(|origin, req_head| {
                    assert_eq!(&origin, req_head.headers.get(header::ORIGIN).unwrap());
                    req_head.headers().contains_key(header::DNT)
                })
                .new_transform(test::ok_service())
                .await
                .unwrap();

            let req = TestRequest::get()
                .insert_header((header::ORIGIN, "http://example.com"))
                .to_srv_request();
            let res = cors.call(req).await.unwrap();
            assert_eq!(
                None,
                res.headers()
                    .get(header::ACCESS_CONTROL_ALLOW_ORIGIN)
                    .map(HeaderValue::as_bytes)
            );

            let req = TestRequest::get()
                .insert_header((header::ORIGIN, "http://example.com"))
                .insert_header((header::DNT, "1"))
                .to_srv_request();
            let res = cors.call(req).await.unwrap();
            assert_eq!(
                Some(&b"http://example.com"[..]),
                res.headers()
                    .get(header::ACCESS_CONTROL_ALLOW_ORIGIN)
                    .map(HeaderValue::as_bytes)
            );
        }
    }