Type Definition roa_core::Next

type Next = ResultFuture<'static, ()>;

Type of the second parameter in a middleware.

Next is usually a closure capturing the next middleware, context and the next Next.

Developer of middleware can jump to next middleware by calling next.await.

Example

use roa_core::App;
use roa_core::http::StatusCode;

let mut app = App::new(());
app.gate_fn(|mut ctx, next| async move {
    ctx.store("id", "1".to_string());
    next.await?;
    assert_eq!("5", &*ctx.load::<String>("id").unwrap());
    Ok(())
});
app.gate_fn(|mut ctx, next| async move {
    assert_eq!("1", &*ctx.load::<String>("id").unwrap());
    ctx.store("id", "2".to_string());
    next.await?;
    assert_eq!("4", &*ctx.load::<String>("id").unwrap());
    ctx.store("id", "5".to_string());
    Ok(())
});
app.gate_fn(|mut ctx, next| async move {
    assert_eq!("2", &*ctx.load::<String>("id").unwrap());
    ctx.store("id", "3".to_string());
    next.await?; // next is none; do nothing
    assert_eq!("3", &*ctx.load::<String>("id").unwrap());
    ctx.store("id", "4".to_string());
    Ok(())
});

Error Handling

You can catch or straightly throw a Error returned by next.

use roa_core::{App, throw};
use roa_core::http::StatusCode;

let mut app = App::new(());
app.gate_fn(|ctx, next| async move {
    // catch
    if let Err(err) = next.await {
        // teapot is ok
        if err.status_code != StatusCode::IM_A_TEAPOT {
            return Err(err);
        }
    }
    Ok(())
});
app.gate_fn(|ctx, next| async move {
    next.await?; // just throw
    unreachable!()
});
app.gate_fn(|_ctx, _next| async move {
    throw!(StatusCode::IM_A_TEAPOT, "I'm a teapot!")
});