Unable to handle Deserialization error

[cortopy]

Bug Report

Version

├── axum v0.2.8

Platform

Linux laptop 5.10.70-1-MANJARO #1 SMP PREEMPT Thu Sep 30 15:29:01 UTC 2021 x86_64 GNU/Linux

Crates

serde

Description

I'm using the JSON extractor to deserialize Body into a defined struct.

With the following code:

struct Foo { field1: String }

async fn handler(Json(payload): Json<Foo>) -> StatusCode {
    println!("payload = {:#?}", payload);

    StatusCode::NO_CONTENT
}

pub fn handle_error(error: BoxError) -> Result<impl IntoResponse, Infallible> {
    error!(?error, "Service error");
    
    // I'd like to be able to handle 400 errors here

    Ok((
        StatusCode::INTERNAL_SERVER_ERROR,
        Cow::from(format!("Unhandled internal error: {}", error)),
    ))
}

pub fn routes() -> Router<BoxRoute> {
    Router::new()
        .route("/healthz", get(|| async { "OK" }))
        .route("/", post(webhooks.layer(TraceLayer::new_for_http())))
        .handle_error(handle_error)
        .check_infallible()
        .boxed()
}

If I make the right request like

curl -X POST https://localhost
   -H 'Content-Type: application/json'
   -d '{"field1":"bar"}'

the handler gets called and all is fine.

However, if the request is not valid, like

curl -X POST https://localhost
   -H 'Content-Type: application/json'
   -d '{"random":"value"}'

the server will respond with a 400. This is to be expected, except handle_error does not get called

I expected handle_error to get the error so that I can handle the 400 response myself

[davidpdrsn]

A request not matching an extractor is not considered an error in axum, so handle_error doesn't apply.

This wasn't very well explained in axum 0.2's documentation but have been improved in 0.3, which I'm hoping to release today. I recommend you read through error handling and extractor which hopefully makes things more clear. While the docs are using 0.3 there should be very few differences in those areas between 0.2 and 0.3.

Let me know if you have more questions.

[cortopy]

All clear now. Thanks a lot @davidpdrsn