How to Validate Data in Rust (validator crate)

Add the validator crate to your Cargo.toml and use the #[derive(Validate)] macro with field attributes to enforce rules at runtime.

[dependencies]
validator = { version = "0.19", features = ["derive"] }

use validator::Validate;

#[derive(Validate)]
struct User {
    #[validate(length(min = 3, message = "Username must be at least 3 characters"))]
    username: String,
    #[validate(email(message = "Invalid email address"))]
    email: String,
}

fn main() {
    let user = User {
        username: "ab".to_string(),
        email: "not-an-email".to_string(),
    };
    
    match user.validate() {
        Ok(_) => println!("Valid!"),
        Err(e) => println!("Validation failed: {:?}", e),
    }
}

The validator crate lets you define rules for your data structures using simple tags on your code. When you run your program, it checks if the data follows these rules and tells you exactly what is wrong if it doesn't. Think of it like a bouncer at a club who checks IDs against a list of requirements before letting anyone in.