Validator

Showing how to use the validator crate to validate the values passed by the users.

Run

cargo run -p example-validator

Test

cargo test -p example-validator

Use

Field not supplied

$ curl -i http://localhost:3000/
HTTP/1.1 400 Bad Request
content-type: text/plain; charset=utf-8
content-length: 48
date: Wed, 19 Mar 2025 15:00:06 GMT

Failed to deserialize form: missing field `name`

Input too short

$ curl -i http://localhost:3000/?name=
HTTP/1.1 400 Bad Request
content-type: text/plain; charset=utf-8
content-length: 48
date: Wed, 19 Mar 2025 15:03:22 GMT

Input validation error: [name: Can not be empty]

Acceptable input

$ curl -i http://localhost:3000/?name=Jo
HTTP/1.1 200 OK
content-type: text/html; charset=utf-8
content-length: 19
date: Wed, 19 Mar 2025 15:03:52 GMT

<h1>Hello, Jo!</h1>$

[package]
edition = "2021"
name = "example-validator"
publish = false
version = "0.1.0"

[dependencies]
axum = { path = "../../axum" }
serde = { version = "1.0", features = ["derive"] }
thiserror = "1.0.29"
tokio = { version = "1.0", features = ["full"] }
tracing = "0.1"
tracing-subscriber = { version = "0.3", features = ["env-filter"] }
validator = { version = "0.18.1", features = ["derive"] }

[dev-dependencies]
http-body-util = "0.1.0"
tower = { version = "0.5.2", features = ["util"] }

//! Run with
//!
//! ```not_rust
//! cargo run -p example-validator
//!
//! curl '127.0.0.1:3000?name='
//! -> Input validation error: [name: Can not be empty]
//!
//! curl '127.0.0.1:3000?name=LT'
//! -> <h1>Hello, LT!</h1>
//! ```

use axum::{
    extract::{rejection::FormRejection, Form, FromRequest, Request},
    http::StatusCode,
    response::{Html, IntoResponse, Response},
    routing::get,
    Router,
};
use serde::{de::DeserializeOwned, Deserialize};
use thiserror::Error;
use tokio::net::TcpListener;
use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
use validator::Validate;

#[tokio::main]
async fn main() {
    tracing_subscriber::registry()
        .with(
            tracing_subscriber::EnvFilter::try_from_default_env()
                .unwrap_or_else(|_| format!("{}=debug", env!("CARGO_CRATE_NAME")).into()),
        )
        .with(tracing_subscriber::fmt::layer())
        .init();

    // build our application with a route
    let app = app();

    // run it
    let listener = TcpListener::bind("127.0.0.1:3000").await.unwrap();
    tracing::debug!("listening on {}", listener.local_addr().unwrap());
    axum::serve(listener, app).await.unwrap();
}

fn app() -> Router {
    Router::new().route("/", get(handler))
}

#[derive(Debug, Deserialize, Validate)]
pub struct NameInput {
    #[validate(length(min = 2, message = "Can not be empty"))]
    pub name: String,
}

async fn handler(ValidatedForm(input): ValidatedForm<NameInput>) -> Html<String> {
    Html(format!("<h1>Hello, {}!</h1>", input.name))
}

#[derive(Debug, Clone, Copy, Default)]
pub struct ValidatedForm<T>(pub T);

impl<T, S> FromRequest<S> for ValidatedForm<T>
where
    T: DeserializeOwned + Validate,
    S: Send + Sync,
    Form<T>: FromRequest<S, Rejection = FormRejection>,
{
    type Rejection = ServerError;

    async fn from_request(req: Request, state: &S) -> Result<Self, Self::Rejection> {
        let Form(value) = Form::<T>::from_request(req, state).await?;
        value.validate()?;
        Ok(ValidatedForm(value))
    }
}

#[derive(Debug, Error)]
pub enum ServerError {
    #[error(transparent)]
    ValidationError(#[from] validator::ValidationErrors),

    #[error(transparent)]
    AxumFormRejection(#[from] FormRejection),
}

impl IntoResponse for ServerError {
    fn into_response(self) -> Response {
        match self {
            ServerError::ValidationError(_) => {
                let message = format!("Input validation error: [{self}]").replace('\n', ", ");
                (StatusCode::BAD_REQUEST, message)
            }
            ServerError::AxumFormRejection(_) => (StatusCode::BAD_REQUEST, self.to_string()),
        }
        .into_response()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use axum::{
        body::Body,
        http::{Request, StatusCode},
    };
    use http_body_util::BodyExt;
    use tower::ServiceExt;

    async fn get_html(response: Response<Body>) -> String {
        let body = response.into_body();
        let bytes = body.collect().await.unwrap().to_bytes();
        String::from_utf8(bytes.to_vec()).unwrap()
    }

    #[tokio::test]
    async fn test_no_param() {
        let response = app()
            .oneshot(Request::builder().uri("/").body(Body::empty()).unwrap())
            .await
            .unwrap();

        assert_eq!(response.status(), StatusCode::BAD_REQUEST);
        let html = get_html(response).await;
        assert_eq!(html, "Failed to deserialize form: missing field `name`");
    }

    #[tokio::test]
    async fn test_with_param_without_value() {
        let response = app()
            .oneshot(
                Request::builder()
                    .uri("/?name=")
                    .body(Body::empty())
                    .unwrap(),
            )
            .await
            .unwrap();

        assert_eq!(response.status(), StatusCode::BAD_REQUEST);
        let html = get_html(response).await;
        assert_eq!(html, "Input validation error: [name: Can not be empty]");
    }

    #[tokio::test]
    async fn test_with_param_with_short_value() {
        let response = app()
            .oneshot(
                Request::builder()
                    .uri("/?name=X")
                    .body(Body::empty())
                    .unwrap(),
            )
            .await
            .unwrap();

        assert_eq!(response.status(), StatusCode::BAD_REQUEST);
        let html = get_html(response).await;
        assert_eq!(html, "Input validation error: [name: Can not be empty]");
    }

    #[tokio::test]
    async fn test_with_param_and_value() {
        let response = app()
            .oneshot(
                Request::builder()
                    .uri("/?name=LT")
                    .body(Body::empty())
                    .unwrap(),
            )
            .await
            .unwrap();

        assert_eq!(response.status(), StatusCode::OK);
        let html = get_html(response).await;
        assert_eq!(html, "<h1>Hello, LT!</h1>");
    }
}