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    use std::borrow::Cow;
    use std::fmt;
    use std::str;

    use actix_web::http::header::{HeaderValue, InvalidHeaderValue, TryIntoHeaderValue};
    use actix_web::web::{BufMut, Bytes, BytesMut};

    use super::super::Challenge;
    use super::{BearerBuilder, Error};
    use crate::utils;

    /// Challenge for [`WWW-Authenticate`] header with HTTP Bearer auth scheme,
    /// described in [RFC 6750](https://tools.ietf.org/html/rfc6750#section-3)
    ///
    /// ## Example
    ///
    /// ```
    /// # use actix_web::{web, App, HttpRequest, HttpResponse, HttpServer};
    /// use actix_web_httpauth::headers::www_authenticate::bearer::{
    ///     Bearer, Error,
    /// };
    /// use actix_web_httpauth::headers::www_authenticate::WwwAuthenticate;
    ///
    /// fn index(_req: HttpRequest) -> HttpResponse {
    ///     let challenge = Bearer::build()
    ///         .realm("example")
    ///         .scope("openid profile email")
    ///         .error(Error::InvalidToken)
    ///         .error_description("The access token expired")
    ///         .error_uri("http://example.org")
    ///         .finish();
    ///
    ///     HttpResponse::Unauthorized()
    ///         .insert_header(WwwAuthenticate(challenge))
    ///         .finish()
    /// }
    /// ```
    ///
    /// [`WWW-Authenticate`]: ../struct.WwwAuthenticate.html
    #[derive(Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Default, Clone)]
    pub struct Bearer {
        pub(crate) scope: Option<Cow<'static, str>>,
        pub(crate) realm: Option<Cow<'static, str>>,
        pub(crate) error: Option<Error>,
        pub(crate) error_description: Option<Cow<'static, str>>,
        pub(crate) error_uri: Option<Cow<'static, str>>,
    }

    impl Bearer {
        /// Creates the builder for `Bearer` challenge.
        ///
        /// ## Example
        ///
        /// ```
        /// # use actix_web_httpauth::headers::www_authenticate::bearer::{Bearer};
        /// let challenge = Bearer::build()
        ///     .realm("Restricted area")
        ///     .scope("openid profile email")
        ///     .finish();
        /// ```
        pub fn build() -> BearerBuilder {
            BearerBuilder::default()
        }
    }

    #[doc(hidden)]
    impl Challenge for Bearer {
        fn to_bytes(&self) -> Bytes {
            let desc_uri_required = self
                .error_description
                .as_ref()
                .map_or(0, |desc| desc.len() + 20)
                + self.error_uri.as_ref().map_or(0, |url| url.len() + 12);
            let capacity = 6
                + self.realm.as_ref().map_or(0, |realm| realm.len() + 9)
                + self.scope.as_ref().map_or(0, |scope| scope.len() + 9)
                + desc_uri_required;
            let mut buffer = BytesMut::with_capacity(capacity);
            buffer.put(&b"Bearer"[..]);

            if let Some(ref realm) = self.realm {
                buffer.put(&b" realm=\""[..]);
                utils::put_quoted(&mut buffer, realm);
                buffer.put_u8(b'"');
            }

            if let Some(ref scope) = self.scope {
                buffer.put(&b" scope=\""[..]);
                utils::put_quoted(&mut buffer, scope);
                buffer.put_u8(b'"');
            }

            if let Some(ref error) = self.error {
                let error_repr = error.as_str();
                let remaining = buffer.remaining_mut();
                let required = desc_uri_required + error_repr.len() + 9; // 9 is for `" error=\"\""`
                if remaining < required {
                    buffer.reserve(required);
                }
                buffer.put(&b" error=\""[..]);
                utils::put_quoted(&mut buffer, error_repr);
                buffer.put_u8(b'"')
            }

            if let Some(ref error_description) = self.error_description {
                buffer.put(&b" error_description=\""[..]);
                utils::put_quoted(&mut buffer, error_description);
                buffer.put_u8(b'"');
            }

            if let Some(ref error_uri) = self.error_uri {
                buffer.put(&b" error_uri=\""[..]);
                utils::put_quoted(&mut buffer, error_uri);
                buffer.put_u8(b'"');
            }

            buffer.freeze()
        }
    }

    impl fmt::Display for Bearer {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
            let bytes = self.to_bytes();
            let repr = str::from_utf8(&bytes)
                // Should not happen since challenges are crafted manually
                // from `&'static str`'s and Strings
                .map_err(|_| fmt::Error)?;

            f.write_str(repr)
        }
    }

    impl TryIntoHeaderValue for Bearer {
        type Error = InvalidHeaderValue;

        fn try_into_value(self) -> Result<HeaderValue, Self::Error> {
            HeaderValue::from_maybe_shared(self.to_bytes())
        }
    }