feat: connection state

msg-common/Cargo.toml

@@ -15,3 +15,4 @@ repository.workspace = true
 [dependencies]
 futures.workspace = true
 tokio.workspace = true
+tokio-util.workspace = true

msg-common/src/lib.rs

@@ -1,13 +1,17 @@
 use futures::future::BoxFuture;
 use std::{
+    pin::Pin,
     task::{Context, Poll},
     time::SystemTime,
 };
+
+use futures::{Sink, SinkExt, Stream};
 use tokio::sync::mpsc::{
     self,
-    error::{SendError, TryRecvError, TrySendError},
-    Receiver, Sender,
+    error::{TryRecvError, TrySendError},
+    Receiver,
 };
+use tokio_util::sync::{PollSendError, PollSender};
 
 pub mod task;
 
@@ -36,8 +40,10 @@ pub mod constants {
 
 /// A bounded, bi-directional channel for sending and receiving messages.
 /// Relies on Tokio's [`mpsc`] channel.
+///
+/// Channel also implements the [`Stream`] and [`Sink`] traits for convenience.
 pub struct Channel<S, R> {
-    tx: Sender<S>,
+    tx: PollSender<S>,
     rx: Receiver<R>,
 }
 
@@ -49,14 +55,21 @@ pub struct Channel<S, R> {
 /// the tuple can be used to send messages of type `S` and receive messages of
 /// type `R`. The second channel can be used to send messages of type `R` and
 /// receive messages of type `S`.
-pub fn channel<S, R>(tx_buffer: usize, rx_buffer: usize) -> (Channel<S, R>, Channel<R, S>) {
+pub fn channel<S, R>(tx_buffer: usize, rx_buffer: usize) -> (Channel<S, R>, Channel<R, S>)
+where
+    S: Send,
+    R: Send,
+{
     let (tx1, rx1) = mpsc::channel(tx_buffer);
     let (tx2, rx2) = mpsc::channel(rx_buffer);
 
+    let tx1 = PollSender::new(tx1);
+    let tx2 = PollSender::new(tx2);
+
     (Channel { tx: tx1, rx: rx2 }, Channel { tx: tx2, rx: rx1 })
 }
 
-impl<S, R> Channel<S, R> {
+impl<S: Send + 'static, R> Channel<S, R> {
     /// Sends a value, waiting until there is capacity.
     ///
     /// A successful send occurs when it is determined that the other end of the
@@ -66,7 +79,7 @@ impl<S, R> Channel<S, R> {
     /// value of `Ok` does not mean that the data will be received. It is
     /// possible for the corresponding receiver to hang up immediately after
     /// this function returns `Ok`.
-    pub async fn send(&mut self, msg: S) -> Result<(), SendError<S>> {
+    pub async fn send(&mut self, msg: S) -> Result<(), PollSendError<S>> {
         self.tx.send(msg).await
     }
 
@@ -77,7 +90,11 @@ impl<S, R> Channel<S, R> {
     /// with [`send`], this function has two failure cases instead of one (one for
     /// disconnection, one for a full buffer).
     pub fn try_send(&mut self, msg: S) -> Result<(), TrySendError<S>> {
-        self.tx.try_send(msg)
+        if let Some(tx) = self.tx.get_ref() {
+            tx.try_send(msg)
+        } else {
+            Err(TrySendError::Closed(msg))
+        }
     }
 
     /// Receives the next value for this receiver.
@@ -135,3 +152,31 @@ impl<S, R> Channel<S, R> {
         self.rx.poll_recv(cx)
     }
 }
+
+impl<S, R> Stream for Channel<S, R> {
+    type Item = R;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        self.rx.poll_recv(cx)
+    }
+}
+
+impl<S: Send + 'static, R> Sink<S> for Channel<S, R> {
+    type Error = PollSendError<S>;
+
+    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.tx.poll_ready_unpin(cx)
+    }
+
+    fn start_send(mut self: Pin<&mut Self>, item: S) -> Result<(), Self::Error> {
+        self.tx.start_send_unpin(item)
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.tx.poll_flush_unpin(cx)
+    }
+
+    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.tx.poll_close_unpin(cx)
+    }
+}

msg-socket/src/backoff/mod.rs → msg-socket/src/connection/backoff.rs

@@ -2,6 +2,13 @@ use futures::{FutureExt, Stream};
 use std::{pin::Pin, task::Poll, time::Duration};
 use tokio::time::sleep;
 
+/// Helper trait alias for backoff streams.
+/// We define any stream that yields `Duration`s as a backoff
+pub trait Backoff: Stream<Item = Duration> + Unpin {}
+
+/// Blanket implementation of `Backoff` for any stream that yields `Duration`s.
+impl<T> Backoff for T where T: Stream<Item = Duration> + Unpin {}
+
 /// A stream that yields exponentially increasing backoff durations.
 pub struct ExponentialBackoff {
     /// Current number of retries.

msg-socket/src/connection/mod.rs

@@ -0,0 +1,5 @@
+pub mod state;
+pub use state::ConnectionState;
+
+pub mod backoff;
+pub use backoff::{Backoff, ExponentialBackoff};

msg-socket/src/connection/state.rs

@@ -0,0 +1,34 @@
+use std::net::SocketAddr;
+
+use super::Backoff;
+
+/// Abstraction to represent the state of a connection.
+///
+/// * `C` is the channel type, which is used to send and receive generic messages.
+/// * `B` is the backoff type, used to control the backoff state for inactive connections.
+pub enum ConnectionState<C, B> {
+    Active {
+        /// Channel to control the underlying connection. This is used to send
+        /// and receive any kind of message in any direction.
+        channel: C,
+    },
+    Inactive {
+        addr: SocketAddr,
+        /// The current backoff state for inactive connections.
+        backoff: B,
+    },
+}
+
+impl<C, B: Backoff> ConnectionState<C, B> {
+    /// Returns `true` if the connection is active.
+    #[allow(unused)]
+    pub fn is_active(&self) -> bool {
+        matches!(self, Self::Active { .. })
+    }
+
+    /// Returns `true` if the connection is inactive.
+    #[allow(unused)]
+    pub fn is_inactive(&self) -> bool {
+        matches!(self, Self::Inactive { .. })
+    }
+}

msg-socket/src/lib.rs

@@ -7,7 +7,7 @@ mod rep;
 mod req;
 mod sub;
 
-mod backoff;
+mod connection;
 
 use bytes::Bytes;
 pub use pubs::{PubError, PubOptions, PubSocket};

msg-socket/src/req/driver.rs

@@ -12,7 +12,10 @@ use std::{
 use tokio::sync::{mpsc, oneshot};
 use tokio_util::codec::Framed;
 
-use crate::req::SocketState;
+use crate::{
+    connection::{ConnectionState, ExponentialBackoff},
+    req::SocketState,
+};
 
 use super::{Command, ReqError, ReqOptions};
 use msg_wire::{
@@ -34,8 +37,9 @@ pub(crate) struct ReqDriver<T: Transport> {
     pub(crate) id_counter: u32,
     /// Commands from the socket.
     pub(crate) from_socket: mpsc::Receiver<Command>,
-    /// The actual [`Framed`] connection with the `Req`-specific codec.
-    pub(crate) conn: Framed<T::Io, reqrep::Codec>,
+    /// The transport controller, wrapped in a [`ConnectionState`] for backoff.
+    /// The [`Framed`] object can send and receive messages from the socket.
+    pub(crate) conn_state: ConnectionState<Framed<T::Io, reqrep::Codec>, ExponentialBackoff>,
     /// The outgoing message queue.
     pub(crate) egress_queue: VecDeque<reqrep::Message>,
     /// The currently pending requests, if any. Uses [`FxHashMap`] for performance.
@@ -138,63 +142,77 @@ where
         let this = self.get_mut();
 
         loop {
+            // Try to flush pending messages
             if this.should_flush(cx) {
-                if let Poll::Ready(Ok(_)) = this.conn.poll_flush_unpin(cx) {
-                    this.should_flush = false;
+                if let ConnectionState::Active { ref mut channel } = this.conn_state {
+                    if let Poll::Ready(Ok(_)) = channel.poll_flush_unpin(cx) {
+                        this.should_flush = false;
+                    }
                 }
+
+                // TODO: what to do with an inactive connection here?
             }
 
-            // Check for incoming messages from the socket
-            match this.conn.poll_next_unpin(cx) {
-                Poll::Ready(Some(Ok(msg))) => {
-                    this.on_message(msg);
+            match this.conn_state {
+                ConnectionState::Active { ref mut channel } => {
+                    // Check for incoming messages from the socket
+                    match channel.poll_next_unpin(cx) {
+                        Poll::Ready(Some(Ok(msg))) => {
+                            this.on_message(msg);
 
-                    continue;
-                }
-                Poll::Ready(Some(Err(e))) => {
-                    if let reqrep::Error::Io(e) = e {
-                        tracing::error!("Socket error: {:?}", e);
-                        if e.kind() == std::io::ErrorKind::Other {
-                            tracing::error!("Other error: {:?}", e);
+                            continue;
+                        }
+                        Poll::Ready(Some(Err(e))) => {
+                            if let reqrep::Error::Io(e) = e {
+                                tracing::error!("Socket error: {:?}", e);
+                                if e.kind() == std::io::ErrorKind::Other {
+                                    tracing::error!("Other error: {:?}", e);
+                                    return Poll::Ready(());
+                                }
+                            }
+
+                            continue;
+                        }
+                        Poll::Ready(None) => {
+                            tracing::debug!("Socket closed, shutting down backend");
                             return Poll::Ready(());
                         }
+                        Poll::Pending => {}
+                    }
+
+                    // Check for outgoing messages to the socket
+                    if channel.poll_ready_unpin(cx).is_ready() {
+                        // Drain the egress queue
+                        if let Some(msg) = this.egress_queue.pop_front() {
+                            // Generate the new message
+                            let size = msg.size();
+                            tracing::debug!("Sending msg {}", msg.id());
+                            match channel.start_send_unpin(msg) {
+                                Ok(_) => {
+                                    this.socket_state.stats.increment_tx(size);
+
+                                    this.should_flush = true;
+                                    // We might be able to send more queued messages
+                                    continue;
+                                }
+                                Err(e) => {
+                                    tracing::error!("Failed to send message to socket: {:?}", e);
+                                    return Poll::Ready(());
+                                }
+                            }
+                        }
                     }
-                    continue;
                 }
-                Poll::Ready(None) => {
-                    tracing::debug!("Socket closed, shutting down backend");
-                    return Poll::Ready(());
+                ConnectionState::Inactive { addr, ref backoff } => {
+                    // TODO: handle backoff in case of an inactive connection
                 }
-                Poll::Pending => {}
             }
 
             // Check for request timeouts
             while this.timeout_check_interval.poll_tick(cx).is_ready() {
                 this.check_timeouts();
             }
 
-            if this.conn.poll_ready_unpin(cx).is_ready() {
-                // Drain the egress queue
-                if let Some(msg) = this.egress_queue.pop_front() {
-                    // Generate the new message
-                    let size = msg.size();
-                    tracing::debug!("Sending msg {}", msg.id());
-                    match this.conn.start_send_unpin(msg) {
-                        Ok(_) => {
-                            this.socket_state.stats.increment_tx(size);
-
-                            this.should_flush = true;
-                            // We might be able to send more queued messages
-                            continue;
-                        }
-                        Err(e) => {
-                            tracing::error!("Failed to send message to socket: {:?}", e);
-                            return Poll::Ready(());
-                        }
-                    }
-                }
-            }
-
             // Check for outgoing messages from the socket handle
             match this.from_socket.poll_recv(cx) {
                 Poll::Ready(Some(Command::Send {
@@ -236,7 +254,13 @@ where
                     tracing::debug!(
                         "Socket dropped, shutting down backend and flushing connection"
                     );
-                    let _ = ready!(this.conn.poll_close_unpin(cx));
+
+                    if let ConnectionState::Active { ref mut channel } = this.conn_state {
+                        let _ = ready!(channel.poll_close_unpin(cx));
+                    }
+
+                    // TODO: handle inactive connection here?
+
                     return Poll::Ready(());
                 }
                 Poll::Pending => {}

msg-socket/src/req/socket.rs

@@ -12,7 +12,7 @@ use msg_transport::Transport;
 use msg_wire::{auth, reqrep};
 
 use super::{Command, ReqDriver, ReqError, ReqOptions, DEFAULT_BUFFER_SIZE};
-use crate::backoff::ExponentialBackoff;
+use crate::connection::{ConnectionState, ExponentialBackoff};
 use crate::ReqMessage;
 use crate::{req::stats::SocketStats, req::SocketState};
 
@@ -122,13 +122,14 @@ where
 
         let mut framed = Framed::new(stream, reqrep::Codec::new());
         framed.set_backpressure_boundary(self.options.backpressure_boundary);
+        let conn = ConnectionState::Active { channel: framed };
 
         // Create the socket backend
         let driver: ReqDriver<T> = ReqDriver {
             options: Arc::clone(&self.options),
             id_counter: 0,
             from_socket,
-            conn: framed,
+            conn_state: conn,
             egress_queue: VecDeque::new(),
             // TODO: we should limit the amount of active outgoing requests, and that should be the capacity.
             // If we do this, we'll never have to re-allocate.