added example

exemples/coroutines_better/Cargo.lock

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exemples/coroutines_better/Cargo.toml

+[package]
+name = "coroutines_better"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+mio = { version = "1.0.3", features = ["net", "os-poll"] }

exemples/coroutines_better/src/future.rs

+// Future trait looks like standard Future except for the missing context
+// pub trait Future {
+//    type Output;
+//    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>;
+//}
+pub trait Future {
+    type Output;
+
+    fn poll(&mut self) -> PollState<Self::Output>;
+}
+
+// Similar to the Poll #[derive(Debug)]
+// pub enum Poll<T> {
+//     Ready(T),
+//     Pending,
+// }
+pub enum PollState<T> {
+    Ready(T),
+    NotReady,
+}

exemples/coroutines_better/src/http.rs

+use mio::{Interest, Token};
+
+use crate::future::{Future, PollState};
+use crate::runtime;
+use std::io::{ErrorKind, Read, Write};
+
+fn get_req(path: &str) -> String {
+    format!(
+        "GET {path} HTTP/1.1\r\n\
+        Host: localhost\r\n\
+        Connection: close\r\n\
+        \r\n"
+    )
+}
+
+pub struct Http;
+
+impl Http {
+    pub fn get(path: &str) -> impl Future<Output = String> {
+        HttpGetFuture::new(path)
+    }
+}
+
+struct HttpGetFuture {
+    stream: Option<mio::net::TcpStream>,
+    buffer: Vec<u8>,
+    path: String,
+}
+
+impl HttpGetFuture {
+    fn new(path: &str) -> Self {
+        Self {
+            stream: None,
+            buffer: vec![],
+            path: String::from(path),
+        }
+    }
+
+    fn write_request(&mut self) {
+        let stream = std::net::TcpStream::connect("localhost:8080").unwrap();
+        stream.set_nonblocking(true).unwrap();
+        let mut stream = mio::net::TcpStream::from_std(stream);
+        stream.write_all(get_req(&self.path).as_bytes()).unwrap();
+        self.stream = Some(stream);
+    }
+}
+
+impl Future for HttpGetFuture {
+    type Output = String;
+
+    fn poll(&mut self) -> PollState<Self::Output> {
+        if self.stream.is_none() {
+            println!("First poll - start operation");
+            self.write_request();
+            // 1. Registering the Tcp stream as a source of events in the poll instance
+            // 2. On retourne pas encore NotReady mais on essaie de lire le stream directement
+        }
+        let mut buf = vec![0u8; 4096];
+        loop {
+            match self.stream.as_mut().unwrap().read(&mut buf) {
+                Ok(0) => {
+                    let s = String::from_utf8_lossy(&self.buffer);
+                    break PollState::Ready(String::from(s));
+                }
+                Ok(n) => {
+                    self.buffer.extend(&buf[0..n]);
+                    continue;
+                }
+                Err(e) if e.kind() == ErrorKind::WouldBlock => {
+                    println!("Data not ready");
+                    break PollState::NotReady;
+                }
+                Err(e) if e.kind() == ErrorKind::Interrupted => {
+                    continue;
+                }
+                Err(e) => panic!("{e:?}"),
+            }
+        }
+    }
+}

exemples/coroutines_better/src/main.rs

+mod future;
+mod http;
+mod runtime;
+
+use future::{Future, PollState};
+use http::Http;
+use runtime::Runtime;
+
+fn main() {
+    let future = async_main();
+    let mut runtime = Runtime::new();
+    runtime.block_on(future);
+}
+
+// =================================
+// We rewrite this:
+// =================================
+// coroutine fn async_main() -> impl Future<Output = String> {
+//     println!("Program starting");
+//     let txt = Http::get("/600/HelloAsyncAwait").wait;
+//     println!("{txt}");
+//     let txt = Http::get("/400/HelloAsyncAwait").wait;
+//     println!("{txt}");
+// }
+
+// =================================
+// Into this:
+// =================================
+
+fn async_main() -> impl Future<Output = String> {
+    Coroutine::new()
+}
+
+enum State {
+    Start,
+    Wait1(Box<dyn Future<Output = String>>),
+    Wait2(Box<dyn Future<Output = String>>),
+    Resolved,
+}
+
+struct Coroutine {
+    state: State,
+}
+
+impl Coroutine {
+    fn new() -> Self {
+        Self {
+            state: State::Start,
+        }
+    }
+}
+
+impl Future for Coroutine {
+    type Output = String;
+
+    fn poll(&mut self) -> PollState<Self::Output> {
+        loop {
+            match self.state {
+                State::Start => {
+                    println!("Program starting");
+                    let fut1 = Box::new(Http::get("/600/HelloAsyncAwait"));
+                    self.state = State::Wait1(fut1);
+                }
+
+                State::Wait1(ref mut future) => match future.poll() {
+                    PollState::Ready(txt) => {
+                        println!("{txt}");
+                        let fut2 = Box::new(Http::get("/400/HelloAsyncAwait"));
+                        self.state = State::Wait2(fut2);
+                    }
+                    PollState::NotReady => break PollState::NotReady,
+                },
+
+                State::Wait2(ref mut future) => match future.poll() {
+                    PollState::Ready(txt) => {
+                        println!("{txt}");
+                        self.state = State::Resolved;
+                        break PollState::Ready(String::new());
+                    }
+                    PollState::NotReady => break PollState::NotReady,
+                },
+
+                State::Resolved => panic!("Polled a resolved future"),
+            }
+        }
+    }
+}

exemples/coroutines_better/src/runtime.rs

+use std::sync::OnceLock;
+
+use mio::{Events, Poll, Registry};
+
+use crate::future::{Future, PollState};
+
+static REGISTRY: OnceLock<Registry> = OnceLock::new();
+pub fn registry() -> &'static Registry {
+    REGISTRY.get().expect("Called outside a runtime context")
+}
+
+pub struct Runtime {
+    poll: Poll,
+}
+
+impl Runtime {
+    pub fn new() -> Self {
+        // 1. creation d'une nouvelle instance de Poll
+        // 2. try_clone() du registry associé pour pouvoir ajouter une source plus tard
+        // 3. set() le registry au REGISTRY
+        // 4. return d'une nouvelle install avec le poll associé
+        unimplemented!()
+    }
+
+    pub fn block_on<F>(&mut self, future: F)
+    where
+        F: Future<Output = String>,
+    {
+        // 1. future -> mut future
+        // 2. tant que future.poll() n'est pas Ready poll.poll() un mut Event
+        // 3. Voilà
+        unimplemented!()
+    }
+}