Add types for channel dynamic dispatch

* Add internal DynamicChannel trait implemented by Channel that allows
  polling for internal state in a lock safe manner and does not require
  knowing the channel size.
* Existing usage of Sender and Receiver is preserved and does not use
  dynamic dispatch.
* Add DynamicSender and DynamicReceiver types that references the
  channel using the DynamicChannel trait and does not require the const
  generic channel size parameter.

embassy/src/channel/channel.rs

@@ -66,6 +66,57 @@ where
     }
 }
 
+/// Send-only access to a [`Channel`] without knowing channel size.
+#[derive(Copy)]
+pub struct DynamicSender<'ch, M, T>
+where
+    M: RawMutex,
+{
+    channel: &'ch dyn DynamicChannel<M, T>,
+}
+
+impl<'ch, M, T> Clone for DynamicSender<'ch, M, T>
+where
+    M: RawMutex,
+{
+    fn clone(&self) -> Self {
+        DynamicSender {
+            channel: self.channel,
+        }
+    }
+}
+
+impl<'ch, M, T, const N: usize> From<Sender<'ch, M, T, N>> for DynamicSender<'ch, M, T>
+where
+    M: RawMutex,
+{
+    fn from(s: Sender<'ch, M, T, N>) -> Self {
+        Self { channel: s.channel }
+    }
+}
+
+impl<'ch, M, T> DynamicSender<'ch, M, T>
+where
+    M: RawMutex,
+{
+    /// Sends a value.
+    ///
+    /// See [`Channel::send()`]
+    pub fn send(&self, message: T) -> DynamicSendFuture<'ch, M, T> {
+        DynamicSendFuture {
+            channel: self.channel,
+            message: Some(message),
+        }
+    }
+
+    /// Attempt to immediately send a message.
+    ///
+    /// See [`Channel::send()`]
+    pub fn try_send(&self, message: T) -> Result<(), TrySendError<T>> {
+        self.channel.try_send_with_context(message, None)
+    }
+}
+
 /// Receive-only access to a [`Channel`].
 #[derive(Copy)]
 pub struct Receiver<'ch, M, T, const N: usize>
@@ -105,6 +156,56 @@ where
     }
 }
 
+/// Receive-only access to a [`Channel`] without knowing channel size.
+#[derive(Copy)]
+pub struct DynamicReceiver<'ch, M, T>
+where
+    M: RawMutex,
+{
+    channel: &'ch dyn DynamicChannel<M, T>,
+}
+
+impl<'ch, M, T> Clone for DynamicReceiver<'ch, M, T>
+where
+    M: RawMutex,
+{
+    fn clone(&self) -> Self {
+        DynamicReceiver {
+            channel: self.channel,
+        }
+    }
+}
+
+impl<'ch, M, T> DynamicReceiver<'ch, M, T>
+where
+    M: RawMutex,
+{
+    /// Receive the next value.
+    ///
+    /// See [`Channel::recv()`].
+    pub fn recv(&self) -> DynamicRecvFuture<'_, M, T> {
+        DynamicRecvFuture {
+            channel: self.channel,
+        }
+    }
+
+    /// Attempt to immediately receive the next value.
+    ///
+    /// See [`Channel::try_recv()`]
+    pub fn try_recv(&self) -> Result<T, TryRecvError> {
+        self.channel.try_recv_with_context(None)
+    }
+}
+
+impl<'ch, M, T, const N: usize> From<Receiver<'ch, M, T, N>> for DynamicReceiver<'ch, M, T>
+where
+    M: RawMutex,
+{
+    fn from(s: Receiver<'ch, M, T, N>) -> Self {
+        Self { channel: s.channel }
+    }
+}
+
 pub struct RecvFuture<'ch, M, T, const N: usize>
 where
     M: RawMutex,
@@ -119,11 +220,31 @@ where
     type Output = T;
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
-        self.channel
-            .lock(|c| match c.try_recv_with_context(Some(cx)) {
+        match self.channel.try_recv_with_context(Some(cx)) {
             Ok(v) => Poll::Ready(v),
             Err(TryRecvError::Empty) => Poll::Pending,
-            })
+        }
+    }
+}
+
+pub struct DynamicRecvFuture<'ch, M, T>
+where
+    M: RawMutex,
+{
+    channel: &'ch dyn DynamicChannel<M, T>,
+}
+
+impl<'ch, M, T> Future for DynamicRecvFuture<'ch, M, T>
+where
+    M: RawMutex,
+{
+    type Output = T;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
+        match self.channel.try_recv_with_context(Some(cx)) {
+            Ok(v) => Poll::Ready(v),
+            Err(TryRecvError::Empty) => Poll::Pending,
+        }
     }
 }
 
@@ -143,7 +264,7 @@ where
 
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
         match self.message.take() {
-            Some(m) => match self.channel.lock(|c| c.try_send_with_context(m, Some(cx))) {
+            Some(m) => match self.channel.try_send_with_context(m, Some(cx)) {
                 Ok(..) => Poll::Ready(()),
                 Err(TrySendError::Full(m)) => {
                     self.message = Some(m);
@@ -157,6 +278,49 @@ where
 
 impl<'ch, M, T, const N: usize> Unpin for SendFuture<'ch, M, T, N> where M: RawMutex {}
 
+pub struct DynamicSendFuture<'ch, M, T>
+where
+    M: RawMutex,
+{
+    channel: &'ch dyn DynamicChannel<M, T>,
+    message: Option<T>,
+}
+
+impl<'ch, M, T> Future for DynamicSendFuture<'ch, M, T>
+where
+    M: RawMutex,
+{
+    type Output = ();
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.message.take() {
+            Some(m) => match self.channel.try_send_with_context(m, Some(cx)) {
+                Ok(..) => Poll::Ready(()),
+                Err(TrySendError::Full(m)) => {
+                    self.message = Some(m);
+                    Poll::Pending
+                }
+            },
+            None => panic!("Message cannot be None"),
+        }
+    }
+}
+
+impl<'ch, M, T> Unpin for DynamicSendFuture<'ch, M, T> where M: RawMutex {}
+
+trait DynamicChannel<M, T>
+where
+    M: RawMutex,
+{
+    fn try_send_with_context(
+        &self,
+        message: T,
+        cx: Option<&mut Context<'_>>,
+    ) -> Result<(), TrySendError<T>>;
+
+    fn try_recv_with_context(&self, cx: Option<&mut Context<'_>>) -> Result<T, TryRecvError>;
+}
+
 /// Error returned by [`try_recv`](Channel::try_recv).
 #[derive(PartialEq, Eq, Clone, Copy, Debug)]
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
@@ -287,6 +451,18 @@ where
         self.inner.lock(|rc| f(&mut *rc.borrow_mut()))
     }
 
+    fn try_recv_with_context(&self, cx: Option<&mut Context<'_>>) -> Result<T, TryRecvError> {
+        self.lock(|c| c.try_recv_with_context(cx))
+    }
+
+    fn try_send_with_context(
+        &self,
+        m: T,
+        cx: Option<&mut Context<'_>>,
+    ) -> Result<(), TrySendError<T>> {
+        self.lock(|c| c.try_send_with_context(m, cx))
+    }
+
     /// Get a sender for this channel.
     pub fn sender(&self) -> Sender<'_, M, T, N> {
         Sender { channel: self }
@@ -339,6 +515,25 @@ where
     }
 }
 
+/// Implements the DynamicChannel to allow creating types that are unaware of the queue size with the
+/// tradeoff cost of dynamic dispatch.
+impl<M, T, const N: usize> DynamicChannel<M, T> for Channel<M, T, N>
+where
+    M: RawMutex,
+{
+    fn try_send_with_context(
+        &self,
+        m: T,
+        cx: Option<&mut Context<'_>>,
+    ) -> Result<(), TrySendError<T>> {
+        Channel::try_send_with_context(self, m, cx)
+    }
+
+    fn try_recv_with_context(&self, cx: Option<&mut Context<'_>>) -> Result<T, TryRecvError> {
+        Channel::try_recv_with_context(self, cx)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use core::time::Duration;
@@ -411,6 +606,16 @@ mod tests {
         let _ = s1.clone();
     }
 
+    #[test]
+    fn dynamic_dispatch() {
+        let c = Channel::<NoopRawMutex, u32, 3>::new();
+        let s: DynamicSender<'_, NoopRawMutex, u32> = c.sender().into();
+        let r: DynamicReceiver<'_, NoopRawMutex, u32> = c.receiver().into();
+
+        assert!(s.try_send(1).is_ok());
+        assert_eq!(r.try_recv().unwrap(), 1);
+    }
+
     #[futures_test::test]
     async fn receiver_receives_given_try_send_async() {
         let executor = ThreadPool::new().unwrap();