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A handle trait for asynchronous context pipeline

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Handle

A handle trait for asynchronous context pipeline.

Example

use handle::{Handle, BoxFuture};
use futures::executor::block_on;
use std::{future::Future, pin::Pin, sync::Arc};
use anyhow::Error;

type Result = anyhow::Result<()>;
type Middleware = dyn for<'a> Handle<'a, Context, Result>;

struct Context {
    index: usize,
    middleware: Vec<Arc<Middleware>>,
}

impl Context {
    async fn next(&mut self) -> Result {
        if let Some(m) = self.middleware.pop() {
            m.call(self).await
        } else {
            Ok(())
        }
    }
}

async fn a(cx: &mut Context) -> Result {
    let size = cx.middleware.len();
    let repeat = "-".repeat(2 * size);

    println!("exec Fn a --{}>> {:>2}", repeat, cx.index);

    assert_eq!(cx.index, 0);
    cx.index += 1;
    assert_eq!(cx.index, 1);

    let fut = cx.next().await;

    assert_eq!(cx.index, 1);
    cx.index -= 1;
    assert_eq!(cx.index, 0);

    println!("exec Fn a --{}<< {:>2}", repeat, cx.index);

    fut
}

fn b<'a>(cx: &'a mut Context) -> BoxFuture<'a, Result> {
    let size = cx.middleware.len();
    let repeat = "-".repeat(2 * size);

    println!("exec Fn b --{}>> {:>2}", repeat, cx.index);

    assert_eq!(cx.index, 1);
    cx.index += 1;
    assert_eq!(cx.index, 2);

    Box::pin(async move {
        let fut = cx.next().await;

        assert_eq!(cx.index, 2);
        cx.index -= 1;
        assert_eq!(cx.index, 1);

        println!("exec Fn b --{}<< {:>2}", repeat, cx.index);

        fut
    })
}

fn c(cx: &mut Context) -> BoxFuture<'_, Result> {
    let size = cx.middleware.len();
    let repeat = "-".repeat(2 * size);

    println!("exec Fn c --{}>> {:>2}", repeat, cx.index);

    assert_eq!(cx.index, 2);
    cx.index += 1;
    assert_eq!(cx.index, 3);

    Box::pin(async move {
        let fut = cx.next().await;

        assert_eq!(cx.index, 3);
        cx.index -= 1;
        assert_eq!(cx.index, 2);

        println!("exec Fn c --{}<< {:>2}", repeat, cx.index);

        fut
    })
}

fn d<'a>(cx: &'a mut Context) -> impl Future<Output = Result> + 'a {
    let size = cx.middleware.len();
    let repeat = "-".repeat(2 * size);

    println!("exec Fn d --{}>> {:>2}", repeat, cx.index);

    assert_eq!(cx.index, 3);
    cx.index += 1;
    assert_eq!(cx.index, 4);

    async move {
        let fut = cx.next().await;

        assert_eq!(cx.index, 4);
        cx.index -= 1;
        assert_eq!(cx.index, 3);

        println!("exec Fn d --{}<< {:>2}", repeat, cx.index);

        fut
    }
}

fn e(cx: Pin<&mut Context>) -> impl Future<Output = Result> + '_ {
    let size = cx.middleware.len();
    let repeat = "-".repeat(2 * size);

    println!("exec Fn e --{}>> {:>2}", repeat, cx.index);

    assert_eq!(cx.index, 4);
    cx.index += 1;
    assert_eq!(cx.index, 5);

    async move {
        let fut = cx.next().await;

        assert_eq!(cx.index, 5);
        cx.index -= 1;
        assert_eq!(cx.index, 4);

        println!("exec Fn e --{}<< {:>2}", repeat, cx.index);

        fut
    }
}

async fn f(cx: &mut Context) -> Result {
    let size = cx.middleware.len();
    let repeat = "-".repeat(2 * size);

    println!("exec Fn f --{}>> {:>2}", repeat, cx.index);

    assert_eq!(cx.index, 5);
    cx.index += 1;
    assert_eq!(cx.index, 6);

    let fut = cx.next().await;

    assert_eq!(cx.index, 6);
    cx.index -= 1;
    assert_eq!(cx.index, 5);

    println!("exec Fn f --{}<< {:>2}", repeat, cx.index);

    fut
}

#[derive(Clone)]
struct A {
    index: usize,
}

impl<'a> Handle<'a, Context, Result> for A {
    fn call(&'a self, cx: &'a mut Context) -> BoxFuture<'a, Self::Output> {
        Box::pin(async move {
            let size = cx.middleware.len();
            let repeat = "-".repeat(2 * size);

            println!("exec St A --{}>> {:>2}", repeat, cx.index);

            assert_eq!(cx.index, 6);
            cx.index += self.index; // + 1
            assert_eq!(cx.index, 7);

            let fut = cx.next().await;

            assert_eq!(cx.index, 7);
            cx.index -= self.index; // - 1
            assert_eq!(cx.index, 6);

            println!("exec St A --{}<< {:>2}", repeat, cx.index);

            fut
        })
    }
}

struct B {
    index: usize,
}

impl<'a> Handle<'a, Context, Result> for B {
    fn call(&'a self, cx: &'a mut Context) -> BoxFuture<'a, Self::Output> {
        Box::pin(async move {
            let size = cx.middleware.len();
            let repeat = "-".repeat(2 * size);

            println!("exec St B --{}>> {:>2}", repeat, cx.index);

            assert_eq!(cx.index, 7);
            cx.index += self.index; // + 2
            assert_eq!(cx.index, 9);

            let fut = cx.next().await;

            assert_eq!(cx.index, 9);
            cx.index -= self.index; // - 2
            assert_eq!(cx.index, 7);

            println!("exec St B --{}<< {:>2}", repeat, cx.index);

            fut
        })
    }
}

struct C {
    index: usize,
}

impl<'a> Handle<'a, Context, Result> for C {
    fn call(&'a self, cx: &'a mut Context) -> BoxFuture<'a, Self::Output> {
        Box::pin(async move {
            let size = cx.middleware.len();
            let repeat = "-".repeat(2 * size);

            println!("exec St C --{}>> {:>2}", repeat, cx.index);

            assert_eq!(cx.index, 9);
            cx.index += self.index; // + 3
            assert_eq!(cx.index, 12);

            let fut = cx.next().await;

            assert_eq!(cx.index, 12);
            cx.index -= self.index; // - 3
            assert_eq!(cx.index, 9);

            println!("exec St C --{}<< {:>2}", repeat, cx.index);

            fut
        })
    }
}

fn main() {
    assert!(block_on(async move {
        let mut cx = Context {
            index: 0,
            middleware: Vec::new(),
        };

        let mut v: Vec<Box<Middleware>> = vec![
            Box::new(a),
            Box::new(b),
            Box::new(c),
            Box::new(d),
            Box::new(e),
            Box::new(f),
        ];

        let mut v: Vec<Arc<Middleware>> = vec![
            // Handled it!
            // A Closure cant use `cx.next()` in async block.
            Arc::new(|cx: &mut Context| {
                assert_eq!(cx.index, 12);

                println!("We handled it!");

                async move {
                    // assert_eq!(cx.index, 12); // compiled panic!
                    Ok(())
                }
            }),
            Arc::new(C { index: 3 }),
            Arc::new(B { index: 2 }),
            Arc::new(A { index: 1 }),
            Arc::new(f),
            Arc::new(e),
            Arc::new(d),
            Arc::new(c),
            Arc::new(b),
            Arc::new(a),
        ];

        cx.middleware = v.clone();
        println!("mw 0: {}", v.len());

        let result = cx.next().await?;
        assert_eq!(result, ());

        v.clear();

        v.insert(0, Arc::new(a));
        v.insert(0, Arc::new(b));
        v.insert(0, Arc::new(c));
        v.insert(0, Arc::new(d));
        v.insert(0, Arc::new(e));
        v.insert(0, Arc::new(f));
        v.insert(0, Arc::new(A { index: 1 }));
        v.insert(0, Arc::new(B { index: 2 }));
        v.insert(0, Arc::new(C { index: 3 }));
        // Handled it!
        async fn handler(cx: &mut Context) -> Result {
            assert_eq!(cx.index, 12);

            println!("We handled it!");

            Ok(())
        }
        v.insert(0, Arc::new(handler));

        println!("mw 1: {}", v.len());

        let result = cx.next().await?;
        assert_eq!(result, ());

        Ok::<_, Error>()
    }).is_ok());
}

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

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A handle trait for asynchronous context pipeline

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License

Apache-2.0, MIT licenses found

Licenses found

Apache-2.0
LICENSE-APACHE
MIT
LICENSE-MIT

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