single_threaded.rs

#![deny(warnings)]

use std::cell::Cell;
use std::rc::Rc;
use tokio::sync::oneshot;

use hyper::body::{Bytes, HttpBody};
use hyper::header::{HeaderMap, HeaderValue};
use hyper::service::{make_service_fn, service_fn};
use hyper::{Error, Response, Server};
use std::marker::PhantomData;
use std::pin::Pin;
use std::task::{Context, Poll};

struct Body {
    // Our Body type is !Send and !Sync:
    _marker: PhantomData<*const ()>,
    data: Option<Bytes>,
}

impl From<String> for Body {
    fn from(a: String) -> Self {
        Body {
            _marker: PhantomData,
            data: Some(a.into()),
        }
    }
}

impl HttpBody for Body {
    type Data = Bytes;
    type Error = Error;

    fn poll_data(
        self: Pin<&mut Self>,
        _: &mut Context<'_>,
    ) -> Poll<Option<Result<Self::Data, Self::Error>>> {
        Poll::Ready(self.get_mut().data.take().map(Ok))
    }

    fn poll_trailers(
        self: Pin<&mut Self>,
        _: &mut Context<'_>,
    ) -> Poll<Result<Option<HeaderMap<HeaderValue>>, Self::Error>> {
        Poll::Ready(Ok(None))
    }
}

fn main() {
    pretty_env_logger::init();

    // Configure a runtime that runs everything on the current thread
    let rt = tokio::runtime::Builder::new_current_thread()
        .enable_all()
        .build()
        .expect("build runtime");

    // Combine it with a `LocalSet,  which means it can spawn !Send futures...
    let local = tokio::task::LocalSet::new();
    local.block_on(&rt, run());
}

async fn run() {
    let addr = ([127, 0, 0, 1], 3000).into();

    // Using a !Send request counter is fine on 1 thread...
    let counter = Rc::new(Cell::new(0));

    let make_service = make_service_fn(move |_| {
        // For each connection, clone the counter to use in our service...
        let cnt = counter.clone();

        async move {
            Ok::<_, Error>(service_fn(move |_| {
                let prev = cnt.get();
                cnt.set(prev + 1);
                let value = cnt.get();
                async move { Ok::<_, Error>(Response::new(Body::from(format!("Request #{}", value)))) }
            }))
        }
    });

    let server = Server::bind(&addr).executor(LocalExec).serve(make_service);

    // Just shows that with_graceful_shutdown compiles with !Send,
    // !Sync HttpBody.
    let (_tx, rx) = oneshot::channel::<()>();
    let server = server.with_graceful_shutdown(async move {
        rx.await.ok();
    });

    println!("Listening on http://{}", addr);

    // The server would block on current thread to await !Send futures.
    if let Err(e) = server.await {
        eprintln!("server error: {}", e);
    }
}

// Since the Server needs to spawn some background tasks, we needed
// to configure an Executor that can spawn !Send futures...
#[derive(Clone, Copy, Debug)]
struct LocalExec;

impl<F> hyper::rt::Executor<F> for LocalExec
where
    F: std::future::Future + 'static, // not requiring `Send`
{
    fn execute(&self, fut: F) {
        // This will spawn into the currently running `LocalSet`.
        tokio::task::spawn_local(fut);
    }
}