chore: remove WindowUpdateMode::OnReceive

Follow up to previous deprecation libp2p#177.

Fixes libp2p#175.

CHANGELOG.md

@@ -1,3 +1,9 @@
+# 0.13.0
+
+- Remove `WindowUpdateMode`.
+  Behavior will always be `WindowUpdateMode::OnRead`, thus enabling flow-control and enforcing backpressure.
+  See [PR 178](https://github.com/libp2p/rust-yamux/pull/178).
+
 # 0.12.0
 
 - Remove `Control` and `ControlledConnection`.

yamux/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "yamux"
-version = "0.12.0"
+version = "0.13.0"
 authors = ["Parity Technologies <admin@parity.io>"]
 license = "Apache-2.0 OR MIT"
 description = "Multiplexer over reliable, ordered connections"
@@ -19,4 +19,5 @@ static_assertions = "1"
 pin-project = "1.1.0"
 
 [dev-dependencies]
+futures = { version = "0.3.12", default-features = false, features = ["executor"] }
 quickcheck = "1.0"

yamux/src/connection.rs

@@ -21,7 +21,7 @@ use crate::{
     error::ConnectionError,
     frame::header::{self, Data, GoAway, Header, Ping, StreamId, Tag, WindowUpdate, CONNECTION_ID},
     frame::{self, Frame},
-    Config, WindowUpdateMode, DEFAULT_CREDIT,
+    Config, DEFAULT_CREDIT,
 };
 use crate::{Result, MAX_ACK_BACKLOG};
 use cleanup::Cleanup;
@@ -304,9 +304,7 @@ enum Action {
     /// Nothing to be done.
     None,
     /// A new stream has been opened by the remote.
-    New(Stream, Option<Frame<WindowUpdate>>),
-    /// A window update should be sent to the remote.
-    Update(Frame<WindowUpdate>),
+    New(Stream),
     /// A ping should be answered.
     Ping(Frame<Ping>),
     /// A stream should be reset.
@@ -504,23 +502,13 @@ impl<T: AsyncRead + AsyncWrite + Unpin> Active<T> {
                 // The remote may be out of credit though and blocked on
                 // writing more data. We may need to reset the stream.
                 State::SendClosed => {
-                    if self.config.window_update_mode == WindowUpdateMode::OnRead
-                        && shared.window == 0
-                    {
-                        // The remote may be waiting for a window update
-                        // which we will never send, so reset the stream now.
-                        let mut header = Header::data(stream_id, 0);
-                        header.rst();
-                        Some(Frame::new(header))
-                    } else {
-                        // The remote has either still credit or will be given more
-                        // (due to an enqueued window update or because the update
-                        // mode is `OnReceive`) or we already have inbound frames in
-                        // the socket buffer which will be processed later. In any
-                        // case we will reply with an RST in `Connection::on_data`
-                        // because the stream will no longer be known.
-                        None
-                    }
+                    // The remote has either still credit or will be given more
+                    // (due to an enqueued window update or because the update
+                    // mode is `OnReceive`) or we already have inbound frames in
+                    // the socket buffer which will be processed later. In any
+                    // case we will reply with an RST in `Connection::on_data`
+                    // because the stream will no longer be known.
+                    None
                 }
                 // The stream was properly closed. We already have sent our FIN frame. The
                 // remote end has already done so in the past.
@@ -569,18 +557,10 @@ impl<T: AsyncRead + AsyncWrite + Unpin> Active<T> {
         };
         match action {
             Action::None => {}
-            Action::New(stream, update) => {
+            Action::New(stream) => {
                 log::trace!("{}: new inbound {} of {}", self.id, stream, self);
-                if let Some(f) = update {
-                    log::trace!("{}/{}: sending update", self.id, f.header().stream_id());
-                    self.pending_frames.push_back(f.into());
-                }
                 return Ok(Some(stream));
             }
-            Action::Update(f) => {
-                log::trace!("{}: sending update: {:?}", self.id, f.header());
-                self.pending_frames.push_back(f.into());
-            }
             Action::Ping(f) => {
                 log::trace!("{}/{}: pong", self.id, f.header().stream_id());
                 self.pending_frames.push_back(f.into());
@@ -641,29 +621,17 @@ impl<T: AsyncRead + AsyncWrite + Unpin> Active<T> {
                 return Action::Terminate(Frame::internal_error());
             }
             let mut stream = self.make_new_inbound_stream(stream_id, DEFAULT_CREDIT);
-            let mut window_update = None;
             {
                 let mut shared = stream.shared();
                 if is_finish {
                     shared.update_state(self.id, stream_id, State::RecvClosed);
                 }
                 shared.window = shared.window.saturating_sub(frame.body_len());
                 shared.buffer.push(frame.into_body());
-
-                if matches!(self.config.window_update_mode, WindowUpdateMode::OnReceive) {
-                    if let Some(credit) = shared.next_window_update() {
-                        shared.window += credit;
-                        let mut frame = Frame::window_update(stream_id, credit);
-                        frame.header_mut().ack();
-                        window_update = Some(frame)
-                    }
-                }
-            }
-            if window_update.is_none() {
-                stream.set_flag(stream::Flag::Ack)
             }
+            stream.set_flag(stream::Flag::Ack);
             self.streams.insert(stream_id, stream.clone_shared());
-            return Action::New(stream, window_update);
+            return Action::New(stream);
         }
 
         if let Some(s) = self.streams.get_mut(&stream_id) {
@@ -695,13 +663,6 @@ impl<T: AsyncRead + AsyncWrite + Unpin> Active<T> {
             if let Some(w) = shared.reader.take() {
                 w.wake()
             }
-            if matches!(self.config.window_update_mode, WindowUpdateMode::OnReceive) {
-                if let Some(credit) = shared.next_window_update() {
-                    shared.window += credit;
-                    let frame = Frame::window_update(stream_id, credit);
-                    return Action::Update(frame);
-                }
-            }
         } else {
             log::trace!(
                 "{}/{}: data frame for unknown stream, possibly dropped earlier: {:?}",
@@ -766,7 +727,7 @@ impl<T: AsyncRead + AsyncWrite + Unpin> Active<T> {
                     .update_state(self.id, stream_id, State::RecvClosed);
             }
             self.streams.insert(stream_id, stream.clone_shared());
-            return Action::New(stream, None);
+            return Action::New(stream);
         }
 
         if let Some(s) = self.streams.get_mut(&stream_id) {

yamux/src/connection/stream.rs

@@ -16,7 +16,7 @@ use crate::{
         header::{Data, Header, StreamId, WindowUpdate},
         Frame,
     },
-    Config, WindowUpdateMode, DEFAULT_CREDIT,
+    Config, DEFAULT_CREDIT,
 };
 use futures::{
     channel::mpsc,
@@ -200,12 +200,6 @@ impl Stream {
     /// Send new credit to the sending side via a window update message if
     /// permitted.
     fn send_window_update(&mut self, cx: &mut Context) -> Poll<io::Result<()>> {
-        // When using [`WindowUpdateMode::OnReceive`] window update messages are
-        // send early on data receival (see [`crate::Connection::on_frame`]).
-        if matches!(self.config.window_update_mode, WindowUpdateMode::OnReceive) {
-            return Poll::Ready(Ok(()));
-        }
-
         let mut shared = self.shared.lock();
 
         if let Some(credit) = shared.next_window_update() {
@@ -487,6 +481,7 @@ impl Shared {
         current // Return the previous stream state for informational purposes.
     }
 
+    // TODO: This does not need to live in shared any longer.
     /// Calculate the number of additional window bytes the receiving side
     /// should grant the sending side via a window update message.
     ///
@@ -499,19 +494,12 @@ impl Shared {
             return None;
         }
 
-        let new_credit = match self.config.window_update_mode {
-            WindowUpdateMode::OnReceive => {
-                debug_assert!(self.config.receive_window >= self.window);
+        let new_credit = {
+            debug_assert!(self.config.receive_window >= self.window);
+            let bytes_received = self.config.receive_window.saturating_sub(self.window);
+            let buffer_len: u32 = self.buffer.len().try_into().unwrap_or(std::u32::MAX);
 
-                self.config.receive_window.saturating_sub(self.window)
-            }
-            WindowUpdateMode::OnRead => {
-                debug_assert!(self.config.receive_window >= self.window);
-                let bytes_received = self.config.receive_window.saturating_sub(self.window);
-                let buffer_len: u32 = self.buffer.len().try_into().unwrap_or(std::u32::MAX);
-
-                bytes_received.saturating_sub(buffer_len)
-            }
+            bytes_received.saturating_sub(buffer_len)
         };
 
         // Send WindowUpdate message when half or more of the configured receive

yamux/src/lib.rs

@@ -63,32 +63,6 @@ const MAX_ACK_BACKLOG: usize = 256;
 /// https://github.com/paritytech/yamux/issues/100.
 const DEFAULT_SPLIT_SEND_SIZE: usize = 16 * 1024;
 
-/// Specifies when window update frames are sent.
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub enum WindowUpdateMode {
-    /// Send window updates as soon as a [`Stream`]'s receive window drops to 0.
-    ///
-    /// This ensures that the sender can resume sending more data as soon as possible
-    /// but a slow reader on the receiving side may be overwhelmed, i.e. it accumulates
-    /// data in its buffer which may reach its limit (see `set_max_buffer_size`).
-    /// In this mode, window updates merely prevent head of line blocking but do not
-    /// effectively exercise back pressure on senders.
-    OnReceive,
-
-    /// Send window updates only when data is read on the receiving end.
-    ///
-    /// This ensures that senders do not overwhelm receivers and keeps buffer usage
-    /// low. However, depending on the protocol, there is a risk of deadlock, namely
-    /// if both endpoints want to send data larger than the receivers window and they
-    /// do not read before finishing their writes. Use this mode only if you are sure
-    /// that this will never happen, i.e. if
-    ///
-    /// - Endpoints *A* and *B* never write at the same time, *or*
-    /// - Endpoints *A* and *B* write at most *n* frames concurrently such that the sum
-    ///   of the frame lengths is less or equal to the available credit of *A* and *B*
-    ///   respectively.
-    OnRead,
-}
 
 /// Yamux configuration.
 ///
@@ -105,7 +79,6 @@ pub struct Config {
     receive_window: u32,
     max_buffer_size: usize,
     max_num_streams: usize,
-    window_update_mode: WindowUpdateMode,
     read_after_close: bool,
     split_send_size: usize,
 }
@@ -116,7 +89,6 @@ impl Default for Config {
             receive_window: DEFAULT_CREDIT,
             max_buffer_size: 1024 * 1024,
             max_num_streams: 8192,
-            window_update_mode: WindowUpdateMode::OnRead,
             read_after_close: true,
             split_send_size: DEFAULT_SPLIT_SEND_SIZE,
         }
@@ -147,12 +119,6 @@ impl Config {
         self
     }
 
-    /// Set the window update mode to use.
-    pub fn set_window_update_mode(&mut self, m: WindowUpdateMode) -> &mut Self {
-        self.window_update_mode = m;
-        self
-    }
-
     /// Allow or disallow streams to read from buffered data after
     /// the connection has been closed.
     pub fn set_read_after_close(&mut self, b: bool) -> &mut Self {