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    use std::fmt;

    use serde::de;

    use crate::{AsResult, Error, Parse};

    /// The maximum per-worker concurrent TLS connection limit.
    ///
    /// All listeners will stop accepting connections when this limit is reached. It can be used to
    /// limit the global TLS CPU usage. By default max connections is set to a 256. Takes a string
    /// value: Either "default", or an integer N > 0 e.g. "6".
    #[derive(Debug, Clone, PartialEq, Eq, Hash)]
    pub enum MaxConnectionRate {
        /// The default connection limit. See struct docs.
        Default,

        /// A specific connection limit.
        Manual(usize),
    }

    impl Parse for MaxConnectionRate {
        fn parse(string: &str) -> AsResult<Self> {
            match string {
                "default" => Ok(MaxConnectionRate::Default),
                string => match string.parse::<usize>() {
                    Ok(val) => Ok(MaxConnectionRate::Manual(val)),
                    Err(_) => Err(InvalidValue! {
                        expected: "an integer > 0",
                        got: string,
                    }),
                },
            }
        }
    }

    impl<'de> de::Deserialize<'de> for MaxConnectionRate {
        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where
            D: de::Deserializer<'de>,
        {
            struct MaxConnectionRateVisitor;

            impl<'de> de::Visitor<'de> for MaxConnectionRateVisitor {
                type Value = MaxConnectionRate;

                fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                    let msg = "Either \"default\" or a string containing an integer > 0";
                    f.write_str(msg)
                }

                fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
                where
                    E: de::Error,
                {
                    match MaxConnectionRate::parse(value) {
                        Ok(max_connection_rate) => Ok(max_connection_rate),
                        Err(Error::InvalidValue { expected, got, .. }) => Err(
                            de::Error::invalid_value(de::Unexpected::Str(&got), &expected),
                        ),
                        Err(_) => unreachable!(),
                    }
                }
            }

            deserializer.deserialize_string(MaxConnectionRateVisitor)
        }
    }