Nested custom extractor with pair as rejection

[BratSinot]

Bug Report

Greeting!

I'm trying to make custom error response handlers and to do that, I started writing extractor wrappers like here: https://github.com/tokio-rs/axum/blob/main/examples/customize-extractor-error/src/main.rs

Version

➜  playground3 git:(master) ✗ cargo tree | grep axum
├── axum v0.5.13
│   ├── axum-core v0.2.7
│   ├── axum-macros v0.2.3 (proc-macro)

Description

I tried this code:

use axum::{
    body::HttpBody,
    extract::{
        rejection::ContentLengthLimitRejection, ContentLengthLimit, FromRequest, RequestParts,
    },
    http::StatusCode,
    BoxError, Json,
};
use serde::{de::DeserializeOwned, Deserialize, Serialize};
use serde_json::{json, Value as JsonValue};
use std::fmt;

struct ContentLengthLimitWrapper<T, const N: u64>(pub T);
struct JsonWrapper<T>(pub T);

#[async_trait::async_trait]
impl<T, B, const N: u64> FromRequest<B> for ContentLengthLimitWrapper<T, N>
where
    T: FromRequest<B>,
    ContentLengthLimitRejection<<T as FromRequest<B>>::Rejection>: fmt::Display,
    B: Send,
{
    type Rejection = (StatusCode, Json<JsonValue>);

    async fn from_request(req: &mut RequestParts<B>) -> Result<Self, Self::Rejection> {
        match ContentLengthLimit::<T, N>::from_request(req).await {
            Ok(ContentLengthLimit(data)) => Ok(Self(data)),
            Err(err) => Err((
                StatusCode::INTERNAL_SERVER_ERROR,
                Json(json!({"description": err.to_string()})),
            )),
        }
    }
}

#[async_trait::async_trait]
impl<T, B> FromRequest<B> for JsonWrapper<T>
where
    T: DeserializeOwned,
    B: HttpBody + Send,
    B::Data: Send,
    B::Error: Into<BoxError>,
{
    type Rejection = (StatusCode, Json<JsonValue>);

    async fn from_request(req: &mut RequestParts<B>) -> Result<Self, Self::Rejection> {
        match Json::<T>::from_request(req).await {
            Ok(Json(data)) => Ok(Self(data)),
            Err(err) => Err((
                StatusCode::INTERNAL_SERVER_ERROR,
                Json(json!({"description": err.to_string()})),
            )),
        }
    }
}

#[derive(Serialize, Deserialize)]
struct Parameters {
    name: Box<str>,
}

#[axum::debug_handler]
async fn handler(
    ContentLengthLimitWrapper(JsonWrapper(param)): ContentLengthLimitWrapper<
        JsonWrapper<Parameters>,
        10,
    >,
) -> Result<Json<JsonValue>, (StatusCode, Json<JsonValue>)> {
    Ok(Json(json!({
        "msg": "ok",
        "parameters": param,
    })))
}

fn main() {
    let _ = handler;
}

But got error:

error[E0277]: `(axum::http::StatusCode, axum::Json<serde_json::Value>)` doesn't implement `std::fmt::Display`
  --> src/main.rs:64:52
   |
64 |     ContentLengthLimitWrapper(JsonWrapper(param)): ContentLengthLimitWrapper<
   |                                                    ^^^^^^^^^^^^^^^^^^^^^^^^^ `(axum::http::StatusCode, axum::Json<serde_json::Value>)` cannot be formatted with the default formatter
   |
   = help: the trait `std::fmt::Display` is not implemented for `(axum::http::StatusCode, axum::Json<serde_json::Value>)`
   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
   = help: the trait `axum::extract::FromRequest<B>` is implemented for `ContentLengthLimitWrapper<T, N>`
   = note: required because of the requirements on the impl of `std::fmt::Display` for `axum::extract::rejection::ContentLengthLimitRejection<(axum::http::StatusCode, axum::Json<serde_json::Value>)>`
note: required because of the requirements on the impl of `axum::extract::FromRequest<axum::body::Body>` for `ContentLengthLimitWrapper<JsonWrapper<Parameters>, 10_u64>`
  --> src/main.rs:17:26
   |
17 | impl<T, B, const N: u64> FromRequest<B> for ContentLengthLimitWrapper<T, N>
   |                          ^^^^^^^^^^^^^^     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = help: see issue #48214

And I can't get from it comes from, because type Rejection have trait IntoResponse and both of them doesn't have fmt::Display trait.

[davidpdrsn]

With what you've written ContentLengthLimitWrapper requires the inner extractor's rejection to implement Display, which (StatusCode, Json<JsonValue>) does not. That is JsonWrapper<Parameters>'s rejection.

[BratSinot]

requires the inner extractor's rejection to implement Display

Can you please point place in source code where this requirement? Because I can't find it at all:

[davidpdrsn]

You require it in your code where you write ContentLengthLimitRejection<<T as FromRequest<B>>::Rejection>: fmt::Display,.

[BratSinot]

You require it in your code where you write ContentLengthLimitRejection<<T as FromRequest<B>>::Rejection>: fmt::Display,.

Ow.... I'm sorry, I feel myself so stupid....
It's been a long time since I've been lost in templates...

Many thanks and again I'm really sorry for spending your time!

[davidpdrsn]

No worries 😊