custom-domain-errors

Custom Domain Errors Example

Demonstrates creating domain-specific custom error types using masterror's derive macro for a payment processing system.

Features

• Payment Processing Errors - Domain errors for payment operations
• Authentication Errors - User authentication and authorization failures
• Validation Errors - Input validation with detailed field information
• External Service Errors - Third-party API integration errors
• Derive Macro Usage - Full use of #[derive(Error)]

Running

cd examples/custom-domain-errors
cargo run

Error Domains

Payment Domain

#[derive(Debug, Error, Clone)]
pub enum PaymentError {
    #[error("insufficient funds: balance={balance}, required={required}")]
    InsufficientFunds { balance: u64, required: u64 },

    #[error("payment method declined")]
    PaymentDeclined,

    #[error("invalid amount: {0}")]
    InvalidAmount(String),
}

Authentication Domain

#[derive(Debug, Error, Clone)]
pub enum AuthError {
    #[error("invalid credentials")]
    InvalidCredentials,

    #[error("session expired")]
    SessionExpired,

    #[error("insufficient permissions")]
    Forbidden,
}

Validation Domain

#[derive(Debug, Error, Clone)]
pub enum ValidationError {
    #[error("field '{field}' is required")]
    RequiredField { field: String },

    #[error("field '{field}' has invalid format: {reason}")]
    InvalidFormat { field: String, reason: String },
}

Converting to AppError

impl From<PaymentError> for AppError {
    fn from(err: PaymentError) -> Self {
        match err {
            PaymentError::InsufficientFunds { .. } => {
                AppError::bad_request(err.to_string())
            }
            PaymentError::PaymentDeclined => {
                AppError::bad_request(err.to_string())
            }
            PaymentError::InvalidAmount(_) => {
                AppError::validation(err.to_string())
            }
        }
    }
}

Testing

cargo test

Key Concepts

• Domain Separation - Each domain (payment, auth, validation) has its own error enum
• Derive Macro - Using #[derive(Error)] for automatic Display and Error trait implementation
• Conversion - Clean conversion from domain errors to AppError with appropriate HTTP status codes
• Error Context - Rich error information with structured data

License

MIT