smartmta/rust/crates/mailer-smtp/src/client/error.rs

//! SMTP client error types.

use serde::Serialize;

/// Errors that can occur during SMTP client operations.
#[derive(Debug, thiserror::Error, Serialize)]
pub enum SmtpClientError {
    #[error("Connection error: {message}")]
    ConnectionError { message: String },

    #[error("Timeout: {message}")]
    TimeoutError { message: String },

    #[error("TLS error: {message}")]
    TlsError { message: String },

    #[error("Authentication failed: {message}")]
    AuthenticationError { message: String },

    #[error("Protocol error ({code}): {message}")]
    ProtocolError { code: u16, message: String },

    #[error("Pool exhausted: {message}")]
    PoolExhausted { message: String },

    #[error("Invalid configuration: {message}")]
    ConfigError { message: String },
}

impl SmtpClientError {
    /// Whether this error is retryable (temporary failure).
    /// Permanent failures (5xx, auth failures) are not retryable.
    pub fn is_retryable(&self) -> bool {
        match self {
            SmtpClientError::ConnectionError { .. } => true,
            SmtpClientError::TimeoutError { .. } => true,
            SmtpClientError::TlsError { .. } => false,
            SmtpClientError::AuthenticationError { .. } => false,
            SmtpClientError::ProtocolError { code, .. } => *code >= 400 && *code < 500,
            SmtpClientError::PoolExhausted { .. } => true,
            SmtpClientError::ConfigError { .. } => false,
        }
    }

    /// The error type as a string for IPC serialization.
    pub fn error_type(&self) -> &'static str {
        match self {
            SmtpClientError::ConnectionError { .. } => "connection",
            SmtpClientError::TimeoutError { .. } => "timeout",
            SmtpClientError::TlsError { .. } => "tls",
            SmtpClientError::AuthenticationError { .. } => "authentication",
            SmtpClientError::ProtocolError { .. } => "protocol",
            SmtpClientError::PoolExhausted { .. } => "pool_exhausted",
            SmtpClientError::ConfigError { .. } => "config",
        }
    }

    /// The SMTP code if this is a protocol error.
    pub fn smtp_code(&self) -> Option<u16> {
        match self {
            SmtpClientError::ProtocolError { code, .. } => Some(*code),
            _ => None,
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_retryable_errors() {
        assert!(SmtpClientError::ConnectionError {
            message: "refused".into()
        }
        .is_retryable());
        assert!(SmtpClientError::TimeoutError {
            message: "timed out".into()
        }
        .is_retryable());
        assert!(SmtpClientError::PoolExhausted {
            message: "full".into()
        }
        .is_retryable());
        assert!(SmtpClientError::ProtocolError {
            code: 421,
            message: "try later".into()
        }
        .is_retryable());
        assert!(SmtpClientError::ProtocolError {
            code: 450,
            message: "mailbox busy".into()
        }
        .is_retryable());
    }

    #[test]
    fn test_non_retryable_errors() {
        assert!(!SmtpClientError::AuthenticationError {
            message: "bad creds".into()
        }
        .is_retryable());
        assert!(!SmtpClientError::TlsError {
            message: "cert invalid".into()
        }
        .is_retryable());
        assert!(!SmtpClientError::ProtocolError {
            code: 550,
            message: "no such user".into()
        }
        .is_retryable());
        assert!(!SmtpClientError::ProtocolError {
            code: 554,
            message: "rejected".into()
        }
        .is_retryable());
        assert!(!SmtpClientError::ConfigError {
            message: "bad config".into()
        }
        .is_retryable());
    }

    #[test]
    fn test_error_type_strings() {
        assert_eq!(
            SmtpClientError::ConnectionError {
                message: "x".into()
            }
            .error_type(),
            "connection"
        );
        assert_eq!(
            SmtpClientError::ProtocolError {
                code: 550,
                message: "x".into()
            }
            .error_type(),
            "protocol"
        );
    }

    #[test]
    fn test_smtp_code() {
        assert_eq!(
            SmtpClientError::ProtocolError {
                code: 550,
                message: "x".into()
            }
            .smtp_code(),
            Some(550)
        );
        assert_eq!(
            SmtpClientError::ConnectionError {
                message: "x".into()
            }
            .smtp_code(),
            None
        );
    }
}