extract::Query does not work with #[serde(flatten)]

[Mivik]

• I have looked for existing issues (including closed) about this

Bug Report

Version

├── axum v0.6.6
│   ├── axum-core v0.3.2

Platform

Ubuntu 22.04.1 LTS (x86_64)

Description

Using #[serde(flatten)] inside the Query parameter leads to the failure to deserialize the parameter, if fields inside the flattened struct are not String.

extern crate serde;
extern crate axum;
extern crate tokio;

use axum::extract::Query;
use serde::Deserialize;
use std::net::SocketAddr;

#[derive(Deserialize)]
struct Params1 {
    page: u32,
}

#[derive(Deserialize)]
struct InnerParam {
    page: u32,
}

#[derive(Deserialize)]
struct Params2 {
    #[serde(flatten)]
    inner: InnerParam,
}

#[tokio::main]
async fn main() {
    use axum::routing::*;
    let app = Router::new()
        .route("/p1", get(p1))
        .route("/p2", get(p2));

    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));

    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .await
        .unwrap()
}


async fn p1(Query(param): Query<Params1>) -> String {
    format!("page is {}", param.page)
}

async fn p2(Query(param): Query<Params2>) -> String {
    format!("page is {}", param.inner.page)
}

Theoretically, p1 and p2 should behaves exactly the same. However the result denies that:

> curl 'http://127.0.0.1:3000/p1?page=42'
> page is 42
> curl 'http://127.0.0.1:3000/p2?page=42'
> Failed to deserialize query string: invalid type: string "42", expected u32

[Mivik]

After investigation this seems to be a bug of serde_urlencoded (nox/serde_urlencoded#33).

[davidpdrsn]

Yep. Nothing axum can do about this.