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/// `tokio-listener`-specific bind errors, to be packed in [`std::io::Error::other`].
#[derive(Debug, Clone)]
#[allow(missing_docs)]
#[non_exhaustive]
pub enum BindError {
    /// Binding failed because of support of specified address type was not enabled at compile time.
    MissingCompileTimeFeature {
        reason: &'static str,
        feature: &'static str,
    },

    /// Binding failed because of support of specified address type is not available on this platform
    MissingPlatformSupport {
        reason: &'static str,
        feature: &'static str,
    },

    /// Inspecion of current process environment variable to serve `sd-listen` failed because of missing or malformed value
    EvnVarError {
        reason: &'static str,
        var: &'static str,
        fault: &'static str,
    },

    /// Attempt to use [`crate::Listener::bind_multiple`] with empty slice of addresses
    MultiBindWithoutAddresses,

    /// There is some invalid value in [`crate::UserOptions`]
    InvalidUserOption { name: &'static str },
}

impl std::error::Error for BindError {}

impl std::fmt::Display for BindError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            BindError::MissingCompileTimeFeature { reason, feature } => write!(f, "tokio-listener: cannot {reason} because of {feature} was not enabled at compile time"),
            BindError::MissingPlatformSupport { reason, feature } => write!(f, "tokio-listener: cannot {reason} because of it is not a {feature}"),
            BindError::EvnVarError { var, fault, reason } => write!(f, "tokio-listener: cannot {reason} due to problem with environment variable {var}: {fault}"),
            BindError::MultiBindWithoutAddresses => write!(f, "tokio-listener: no addresses specified to bind to"),
            BindError::InvalidUserOption { name } => write!(f, "tokio-listener: invalid value for user option {name}"),
        }
    }
}

impl BindError {
    pub(crate) fn ioerr<T>(self) -> Result<T, std::io::Error> {
        Err(std::io::Error::new(std::io::ErrorKind::Other, self))
    }
}

#[allow(dead_code)]
pub(crate) fn get_envvar(
    reason: &'static str,
    var: &'static str,
) -> Result<String, std::io::Error> {
    match std::env::var(var) {
        Ok(x) => Ok(x),
        Err(e) => match e {
            std::env::VarError::NotPresent => BindError::EvnVarError {
                reason,
                var,
                fault: "not present",
            }
            .ioerr(),
            std::env::VarError::NotUnicode(..) => BindError::EvnVarError {
                reason,
                var,
                fault: "not unicode",
            }
            .ioerr(),
        },
    }
}

/// `tokio-listener`-specific accept errors, to be packed in [`std::io::Error::other`].
#[derive(Debug, Clone)]
#[allow(missing_docs)]
#[non_exhaustive]
pub enum AcceptError {
    /// In inetd mode we have already accepted and served one connection.
    ///
    /// It is not possible to serve another connection, hence this error is used to bubble up from
    /// accept loop and exit process.
    ///
    /// `tokio-listener` takes care not to trigger this error prematurely, when the first connection is still being served.
    InetdPseudosocketAlreadyTaken,
}

impl std::error::Error for AcceptError {}

impl std::fmt::Display for AcceptError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            AcceptError::InetdPseudosocketAlreadyTaken => write!(
                f,
                "tokio-listener: Cannot serve a second connection in inetd mode"
            ),
        }
    }
}