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    use std::convert::TryFrom;

    use derive_more::{Display, From};

    /// A session key, the string stored in a client-side cookie to associate a user with its session
    /// state on the backend.
    ///
    /// # Validation
    /// Session keys are stored as cookies, therefore they cannot be arbitrary long. Session keys are
    /// required to be smaller than 4064 bytes.
    ///
    /// ```rust
    /// # use std::convert::TryInto;
    /// use actix_session::storage::SessionKey;
    ///
    /// let key: String = std::iter::repeat('a').take(4065).collect();
    /// let session_key: Result<SessionKey, _> = key.try_into();
    /// assert!(session_key.is_err());
    /// ```
    #[derive(Debug, PartialEq, Eq)]
    pub struct SessionKey(String);

    impl TryFrom<String> for SessionKey {
        type Error = InvalidSessionKeyError;

        fn try_from(val: String) -> Result<Self, Self::Error> {
            if val.len() > 4064 {
                return Err(anyhow::anyhow!(
                    "The session key is bigger than 4064 bytes, the upper limit on cookie content."
                )
                .into());
            }

            Ok(SessionKey(val))
        }
    }

    impl AsRef<str> for SessionKey {
        fn as_ref(&self) -> &str {
            &self.0
        }
    }

    impl From<SessionKey> for String {
        fn from(key: SessionKey) -> Self {
            key.0
        }
    }

    #[derive(Debug, Display, From)]
    #[display(fmt = "The provided string is not a valid session key")]
    pub struct InvalidSessionKeyError(anyhow::Error);

    impl std::error::Error for InvalidSessionKeyError {
        fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
            Some(self.0.as_ref())
        }
    }