axum/examples/customize-path-rejection/src/main.rs

//! Run with
//!
//! ```not_rust
//! cargo run -p example-customize-path-rejection
//! ```

use axum::{
    extract::{path::ErrorKind, rejection::PathRejection, FromRequestParts},
    http::{request::Parts, StatusCode},
    response::IntoResponse,
    routing::get,
    Router,
};
use serde::{de::DeserializeOwned, Deserialize, Serialize};
use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};

#[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 = Router::new().route("/users/{user_id}/teams/{team_id}", get(handler));

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

async fn handler(Path(params): Path<Params>) -> impl IntoResponse {
    axum::Json(params)
}

#[derive(Debug, Deserialize, Serialize)]
struct Params {
    user_id: u32,
    team_id: u32,
}

// We define our own `Path` extractor that customizes the error from `axum::extract::Path`
struct Path<T>(T);

impl<S, T> FromRequestParts<S> for Path<T>
where
    // these trait bounds are copied from `impl FromRequest for axum::extract::path::Path`
    T: DeserializeOwned + Send,
    S: Send + Sync,
{
    type Rejection = (StatusCode, axum::Json<PathError>);

    async fn from_request_parts(parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
        match axum::extract::Path::<T>::from_request_parts(parts, state).await {
            Ok(value) => Ok(Self(value.0)),
            Err(rejection) => {
                let (status, body) = match rejection {
                    PathRejection::FailedToDeserializePathParams(inner) => {
                        let mut status = StatusCode::BAD_REQUEST;

                        let kind = inner.into_kind();
                        let body = match &kind {
                            ErrorKind::WrongNumberOfParameters { .. } => PathError {
                                message: kind.to_string(),
                                location: None,
                            },

                            ErrorKind::ParseErrorAtKey { key, .. } => PathError {
                                message: kind.to_string(),
                                location: Some(key.clone()),
                            },

                            ErrorKind::ParseErrorAtIndex { index, .. } => PathError {
                                message: kind.to_string(),
                                location: Some(index.to_string()),
                            },

                            ErrorKind::ParseError { .. } => PathError {
                                message: kind.to_string(),
                                location: None,
                            },

                            ErrorKind::InvalidUtf8InPathParam { key } => PathError {
                                message: kind.to_string(),
                                location: Some(key.clone()),
                            },

                            ErrorKind::UnsupportedType { .. } => {
                                // this error is caused by the programmer using an unsupported type
                                // (such as nested maps) so respond with `500` instead
                                status = StatusCode::INTERNAL_SERVER_ERROR;
                                PathError {
                                    message: kind.to_string(),
                                    location: None,
                                }
                            }

                            ErrorKind::Message(msg) => PathError {
                                message: msg.clone(),
                                location: None,
                            },

                            _ => PathError {
                                message: format!("Unhandled deserialization error: {kind}"),
                                location: None,
                            },
                        };

                        (status, body)
                    }
                    PathRejection::MissingPathParams(error) => (
                        StatusCode::INTERNAL_SERVER_ERROR,
                        PathError {
                            message: error.to_string(),
                            location: None,
                        },
                    ),
                    _ => (
                        StatusCode::INTERNAL_SERVER_ERROR,
                        PathError {
                            message: format!("Unhandled path rejection: {rejection}"),
                            location: None,
                        },
                    ),
                };

                Err((status, axum::Json(body)))
            }
        }
    }
}

#[derive(Serialize)]
struct PathError {
    message: String,
    location: Option<String>,
}