HTTP 103 Early Hints support

[junderw]

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

Feature Request

Motivation

https://developer.chrome.com/docs/web-platform/early-hints

Early Hints is a method for returning a list of resources to the client before actually sending back the actual response to their query.

This will help with performance on heavier SSR websites.

Proposal

enum EarlyHint {
    Preconnect(String),
    Script(String),
    Style(String),
}
async fn send_early_hint(hints: Vec<EarlyHint>) {
    // ... use tokio::spawn etc. to send off a HTTP 103 Early Hint Response
    // While the body of the handler function (after this await)
    // calls a billion databases to generate the HTML
}

// example
send_early_hint(vec![
    EarlyHint::Style("/main.css".into()),
    EarlyHint::Script("/main.js".into()),
    EarlyHint::Preconnect("https://fonts.google.com".into()),
]).await;

[junderw]

(This actually feels like something better suited for a proc macro on top of the handler... thoughts?)

[mladedav]

We'll need hyper support here. There's already some discussion here so you might want to check that out. axum cannot support this until hyper does.