Declaring Validators

Validators are regular Rust types that describe a validation rule. To define one, annotate the struct with #[validator] and implement Validate<T> for the input type you want to check. The #[koruma(value)] attribute marks the field that stores the actual input value used for error reporting.

For example, a generic range validator:

use koruma::{Validate, validator};
use std::fmt;

#[validator]
#[derive(Clone, Debug)]
pub struct NumberRangeValidation<T: PartialOrd + Copy + fmt::Display + Clone> {
    min: T,
    max: T,
    #[koruma(value)]
    pub actual: T,
}

impl<T: PartialOrd + Copy + fmt::Display> Validate<T> for NumberRangeValidation<T> {
    fn validate(&self, value: &T) -> bool {
        *value >= self.min && *value <= self.max
    }
}

impl<T: PartialOrd + Copy + fmt::Display + Clone> fmt::Display for NumberRangeValidation<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "value {} must be between {} and {}",
            self.actual, self.min, self.max
        )
    }
}

You can also write type-specific validators. For example, a validator for string length:

use koruma::{Validate, validator};
use std::fmt;

#[validator]
#[derive(Clone, Debug)]
pub struct StringLengthValidation {
    min: usize,
    max: usize,
    #[koruma(value)]
    pub input: String,
}

impl Validate<String> for StringLengthValidation {
    fn validate(&self, value: &String) -> bool {
        let len = value.len();
        len >= self.min && len <= self.max
    }
}

impl fmt::Display for StringLengthValidation {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "string length {} must be between {} and {} characters",
            self.input.len(),
            self.min,
            self.max
        )
    }
}

The core pattern stays the same: define any configuration fields you need, mark the validated value with #[koruma(value)], implement Validate<T>, and optionally implement Display for friendly error messages.