PoC of introducing FromSpoofableRequestParts and Spoofable

[bengsparks]

Motivation

PoC to check which solution to pick for #2998.
Attempts to come as close to the original idea of extractors as possible, without increasing implementation complexity.

Solution

Add a new trait FromSpoofableRequestParts that is private to axum-extra.
This trait is only to be implemented by extractors that read from spoofable portions of HTTP requests.
No extractor should ever implement both FromSpoofableRequestParts and FromRequestsParts.

A blanket implementation of FromRequestsParts is provided by Spoofable for all extractors that implement FromSpoofableRequestParts, so that reading via destructuring i.e. Spoofable(Extractor(inner)) can continue to be used in handlers.

use axum::{routing::get, Router};
use axum_extra::extract::{Scheme, Spoofable};
use tokio::net::TcpListener;

#[tokio::main]
async fn main() {
    let app = Router::new().route("/", get(f));

    let listener = TcpListener::bind("127.0.0.1:3000").await.unwrap();
    axum::serve(listener, app).await.unwrap();
}

async fn f(Spoofable(Scheme(scheme)): Spoofable<Scheme>) -> String {
    scheme
}

See examples/spoofable-scheme for a short demonstration.

[yanns]

Thanks!
How would we force Host and Schema to use this? We would remove the FromRequestParts for them right?

[bengsparks]

The traits share the same function signatures and bounds, so simply exchanging the trait name within the impl block is sufficient.