How to get error propagated back to caller with tide and glommio?

I am experimenting with tide and glommio using Rust. Consider following code:

use std::io::Result;
use glommio::prelude::*;

use tide::Request;
use tide::Response;
use tide::http::mime;
use tide::prelude::*;

#[async_std::main]
async fn main() -> Result<()> {
    let mut app = tide::new();
    app.at("/orders/shoes").post(order_shoes);
    let builder = LocalExecutorPoolBuilder::new(16);
    let handles = builder.on_all_shards(|| async move {
        app.listen("127.0.0.1:8080").await;
    }).unwrap();

    handles.join_all();
    Ok(())
}

#[derive(Debug, Deserialize)]
struct Animal {
    name: String,
    legs: u8,
}

pub async fn order_shoes(mut req: Request<()>) -> tide::Result {
    let Animal { name, legs } = req.body_json().await?;
    let res = Response::builder(203)
    .body("Hi")
    .header("custom-header", "value")
    .content_type(mime::HTML)
    .build();
    Ok(res)
}

Now in case the request has legs greater than 255 then it should respond with error but I am unable to figure out how to return that to caller.