add on_close to abstract and simplify ws_client socket closing

backend/common/src/ws_client/connect.rs

@@ -19,6 +19,7 @@ use soketto::handshake::{Client, ServerResponse};
 use tokio::net::TcpStream;
 use tokio_util::compat::TokioAsyncReadCompatExt;
 use std::sync::Arc;
+use super::on_close::OnClose;
 
 use super::{
     receiver::{Receiver, RecvMessage},
@@ -67,10 +68,9 @@ impl Connection {
         // and recv channels that we hand out are dropped. Notably, we allow either recv or
         // send alone to be dropped and still keep the socket open (we may only care about
         // one way communication).
-        let (tx_closed, mut rx_closed1) = tokio::sync::broadcast::channel::<()>(1);
-        let tx_closed1 = tx_closed.clone();
-        let tx_closed2 = tx_closed.clone();
-        let mut rx_closed2 = tx_closed.subscribe();
+        let (tx_closed1, mut rx_closed1) = tokio::sync::broadcast::channel::<()>(1);
+        let tx_closed2 = tx_closed1.clone();
+        let mut rx_closed2 = tx_closed1.subscribe();
 
         // Receive messages from the socket and post them out:
         let (mut tx_to_external, rx_from_ws) = mpsc::unbounded();
@@ -90,7 +90,7 @@ impl Connection {
                         // The socket had an error, so notify interested parties that we should
                         // shut the connection down and bail out of this receive loop.
                         log::error!("Shutting down websocket connection: Failed to receive data: {}", e);
-                        let _ = tx_closed.send(());
+                        let _ = tx_closed1.send(());
                         break;
                     }
                     Ok(data) => data,
@@ -193,18 +193,16 @@ impl Connection {
         });
 
         // Keep track of whether one of sender or received have
-        // been dropped. If both have, close the socket connection.
-        let counter = Arc::new(());
+        // been dropped. If both have, we close the socket connection.
+        let on_close = Arc::new(OnClose(tx_closed2));
 
         (Sender {
             inner: tx_to_ws,
-            closer: tx_closed1,
-            count: Arc::clone(&counter),
+            closer: Arc::clone(&on_close),
         },
         Receiver {
-            inner: rx_from_ws ,
-            closer: tx_closed2,
-            count: counter,
+            inner: rx_from_ws,
+            _closer: on_close,
         })
     }
 }

backend/common/src/ws_client/mod.rs

@@ -20,6 +20,8 @@ mod connect;
 mod receiver;
 /// The channel based send interface
 mod sender;
+/// A close helper that we use in sender/receiver.
+mod on_close;
 
 pub use connect::{connect, ConnectError, Connection, RawReceiver, RawSender};
 pub use receiver::{Receiver, RecvError, RecvMessage};

backend/common/src/ws_client/on_close.rs

@@ -0,0 +1,26 @@
+// Source code for the Substrate Telemetry Server.
+// Copyright (C) 2021 Parity Technologies (UK) Ltd.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+use tokio::sync::broadcast;
+
+/// A small helper to fire the "close" channel when it's dropped.
+pub struct OnClose(pub broadcast::Sender<()>);
+
+impl Drop for OnClose {
+    fn drop(&mut self) {
+        let _ = self.0.send(());
+    }
+}

backend/common/src/ws_client/receiver.rs

@@ -16,22 +16,13 @@
 
 use futures::channel::mpsc;
 use futures::{Stream, StreamExt};
+use std::sync::Arc;
+use super::on_close::OnClose;
 
 /// Receive messages out of a connection
 pub struct Receiver {
     pub(super) inner: mpsc::UnboundedReceiver<Result<RecvMessage, RecvError>>,
-    pub(super) closer: tokio::sync::broadcast::Sender<()>,
-    pub(super) count: std::sync::Arc<()>,
-}
-
-impl Drop for Receiver {
-    fn drop(&mut self) {
-        // Close the socket connection if this is the last half
-        // of the channel (ie the sender has been dropped already).
-        if std::sync::Arc::strong_count(&self.count) == 1 {
-            let _ = self.closer.send(());
-        }
-    }
+    pub(super) _closer: Arc<OnClose>,
 }
 
 #[derive(thiserror::Error, Debug)]

backend/common/src/ws_client/sender.rs

@@ -16,6 +16,8 @@
 
 use futures::channel::mpsc;
 use futures::{Sink, SinkExt};
+use std::sync::Arc;
+use super::on_close::OnClose;
 
 /// A message that can be sent into the channel interface
 #[derive(Debug, Clone)]
@@ -47,24 +49,16 @@ pub(super) enum SentMessageInternal {
 #[derive(Clone)]
 pub struct Sender {
     pub(super) inner: mpsc::UnboundedSender<SentMessageInternal>,
-    pub(super) closer: tokio::sync::broadcast::Sender<()>,
-    pub(super) count: std::sync::Arc<()>,
-}
-
-impl Drop for Sender {
-    fn drop(&mut self) {
-        // Close the socket connection if this is the last half
-        // of the channel (ie the receiver has been dropped already).
-        if std::sync::Arc::strong_count(&self.count) == 1 {
-            let _ = self.closer.send(());
-        }
-    }
+    pub(super) closer: Arc<OnClose>,
 }
 
 impl Sender {
     /// Ask the underlying Websocket connection to close.
     pub async fn close(&mut self) -> Result<(), SendError> {
         self.inner.send(SentMessageInternal::Close).await?;
+        // fire the "proper" close handler (this shouldn't really be necessary
+        // since the above will cascade closing to both sides anyway).
+        let _ = self.closer.0.send(());
         Ok(())
     }
     /// Returns whether this channel is closed.