Add !Send server example

Cargo.toml

@@ -79,3 +79,7 @@ required-features = ["client-legacy", "http1", "tokio"]
 [[example]]
 name = "server"
 required-features = ["server", "http1", "tokio"]
+
+[[example]]
+name = "single_threaded_server"
+required-features = ["server", "http1", "http2", "tokio"]

examples/single_threaded_server.rs

@@ -0,0 +1,149 @@
+//! This example runs a server that responds to any request with "Hello, world!".
+//! Unlike it's server.rs counter part, it demonstrates using a !Send executor (i.e. gloomio,
+//! monoio).
+
+use std::{convert::Infallible, error::Error};
+
+use std::marker::PhantomData;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::thread;
+
+use bytes::Bytes;
+use http::{header::CONTENT_TYPE, Request, Response};
+use http_body_util::{combinators::BoxBody, BodyExt, Full};
+use hyper::{body::Incoming, service::service_fn};
+use hyper_util::{
+    rt::{TokioExecutor, TokioIo},
+    server::conn::auto::Builder,
+};
+use tokio::{net::TcpListener, net::TcpStream, task::JoinSet};
+
+/// Function from an incoming request to an outgoing response
+///
+/// This function gets turned into a [`hyper::service::Service`] later via
+/// [`service_fn`]. Instead of doing this, you could also write a type that
+/// implements [`hyper::service::Service`] directly and pass that in place of
+/// writing a function like this and calling [`service_fn`].
+async fn handle_request(_request: Request<Incoming>) -> Result<Response<Full<Bytes>>, Infallible> {
+    let response = Response::builder()
+        .header(CONTENT_TYPE, "text/plain")
+        .body(Full::new(Bytes::from("Hello, world!\n")))
+        .expect("values provided to the builder should be valid");
+
+    Ok(response)
+}
+
+async fn upgradable_server() -> Result<(), Box<dyn Error + 'static>> {
+    let listen_addr = "127.0.0.1:8000";
+    let tcp_listener = TcpListener::bind(listen_addr).await?;
+    println!("listening on http://{listen_addr}");
+
+    loop {
+        let (stream, addr) = match tcp_listener.accept().await {
+            Ok(x) => x,
+            Err(e) => {
+                eprintln!("failed to accept connection: {e}");
+                continue;
+            }
+        };
+
+        let serve_connection = async move {
+            println!("handling a request from {addr}");
+
+            let result = Builder::new(LocalExec)
+                .serve_connection(TokioIo::new(stream), service_fn(handle_request))
+                .await;
+
+            if let Err(e) = result {
+                eprintln!("error serving {addr}: {e}");
+            }
+
+            println!("handled a request from {addr}");
+        };
+
+        tokio::task::spawn_local(serve_connection);
+    }
+}
+
+#[tokio::main(flavor = "current_thread")]
+async fn main() {
+    let server_http2 = thread::spawn(move || {
+        // Configure a runtime for the server 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, upgradable_server()).unwrap();
+    });
+
+    server_http2.join().unwrap()
+}
+
+// NOTE: This part is only needed for HTTP/2. HTTP/1 doesn't need an executor.
+//
+// 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);
+    }
+}
+
+struct IOTypeNotSend {
+    _marker: PhantomData<*const ()>,
+    stream: TokioIo<TcpStream>,
+}
+
+impl IOTypeNotSend {
+    fn new(stream: TokioIo<TcpStream>) -> Self {
+        Self {
+            _marker: PhantomData,
+            stream,
+        }
+    }
+}
+
+impl hyper::rt::Write for IOTypeNotSend {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<Result<usize, std::io::Error>> {
+        Pin::new(&mut self.stream).poll_write(cx, buf)
+    }
+
+    fn poll_flush(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), std::io::Error>> {
+        Pin::new(&mut self.stream).poll_flush(cx)
+    }
+
+    fn poll_shutdown(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), std::io::Error>> {
+        Pin::new(&mut self.stream).poll_shutdown(cx)
+    }
+}
+
+impl hyper::rt::Read for IOTypeNotSend {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: hyper::rt::ReadBufCursor<'_>,
+    ) -> Poll<std::io::Result<()>> {
+        Pin::new(&mut self.stream).poll_read(cx, buf)
+    }
+}