libasync: new stream.recv API

M-Labs/artiq-zynq#40 (comment)

experiments/src/main.rs

@@ -202,40 +202,8 @@ pub fn main_core0() {
     ps7_init::report_differences();
 
     Sockets::init(32);
-    /// `chargen`
-    const TCP_PORT: u16 = 19;
-    async fn handle_connection(stream: TcpStream) -> smoltcp::Result<()> {
-        stream.send("Enter your name: ".bytes()).await?;
-        let name = stream
-            .recv(|buf| {
-                for (i, b) in buf.iter().enumerate() {
-                    if *b == '\n' as u8 {
-                        return match core::str::from_utf8(&buf[0..i]) {
-                            Ok(name) => Poll::Ready((i + 1, Some(name.to_owned()))),
-                            Err(_) => Poll::Ready((i + 1, None)),
-                        };
-                    }
-                }
-                if buf.len() > 100 {
-                    // Too much input, consume all
-                    Poll::Ready((buf.len(), None))
-                } else {
-                    Poll::Pending
-                }
-            })
-            .await?;
-        match name {
-            Some(name) => stream.send(format!("Hello {}!\n", name).bytes()).await?,
-            None => {
-                stream
-                    .send("I had trouble reading your name.\n".bytes())
-                    .await?
-            }
-        }
-        let _ = stream.close().await;
-        Ok(())
-    }
 
+    const TCP_PORT: u16 = 19;
     // (rx, tx)
     let stats = alloc::rc::Rc::new(core::cell::RefCell::new((0, 0)));
     let stats_tx = stats.clone();
@@ -264,7 +232,7 @@ pub fn main_core0() {
             let stats_rx = stats_rx.clone();
             task::spawn(async move {
                 loop {
-                    match stream.recv(|buf| Poll::Ready((buf.len(), buf.len()))).await {
+                    match stream.recv(|buf| (buf.len(), buf.len())).await {
                         Ok(len) => stats_rx.borrow_mut().0 += len,
                         Err(e) => {
                             warn!("rx: {:?}", e);

libasync/src/smoltcp/tcp_stream.rs

@@ -103,21 +103,19 @@ impl TcpStream {
 
     /// Probe the receive buffer
     ///
-    /// Instead of handing you the data on the heap all at once,
-    /// smoltcp's read interface is wrapped so that your callback can
-    /// just return `Poll::Pending` if there is not enough data
-    /// yet. Likewise, return the amount of bytes consumed from the
-    /// buffer in the `Poll::Ready` result.
+    /// Your callback will only be called when there is some data available,
+    /// and it must consume at least one byte. It returns a tuple with the
+    /// number of bytes it consumed, and a user-defined return value of type R.
     pub async fn recv<F, R>(&self, f: F) -> Result<R>
     where
-        F: Fn(&[u8]) -> Poll<(usize, R)>,
+        F: Fn(&[u8]) -> (usize, R),
     {
-        struct Recv<'a, F: FnOnce(&[u8]) -> Poll<(usize, R)>, R> {
+        struct Recv<'a, F: FnOnce(&[u8]) -> (usize, R), R> {
             stream: &'a TcpStream,
             f: F,
         }
 
-        impl<'a, F: Fn(&[u8]) -> Poll<(usize, R)>, R> Future for Recv<'a, F, R> {
+        impl<'a, F: Fn(&[u8]) -> (usize, R), R> Future for Recv<'a, F, R> {
             type Output = Result<R>;
 
             fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
@@ -128,13 +126,8 @@ impl TcpStream {
 
                     socket.recv(|buf| {
                         if buf.len() > 0 {
-                            match (self.f)(buf) {
-                                Poll::Ready((amount, result)) =>
-                                    (amount, Poll::Ready(Ok(result))),
-                                Poll::Pending =>
-                                    // 0 bytes consumed
-                                    (0, Poll::Pending),
-                            }
+                            let (amount, result) = (self.f)(buf);
+                            (amount, Poll::Ready(Ok(result)))
                         } else {
                             (0, Poll::Pending)
                         }