feat(core): remove SingletonMuxer

This is effectively dead code as nothing within `rust-libp2p` uses it. Users should provide it themselves if they need it.

Pull-Request: #3883.

core/CHANGELOG.md

@@ -13,8 +13,12 @@
   We delete the `ProtocolName` trait and replace it with a requirement for `AsRef<str>`.
   See [PR 3746]
 
+- Remove `SingletonMuxer`.
+  See [PR 3883].
+
 [spec]: https://github.com/libp2p/specs/blob/master/connections/README.md#multistream-select
 [PR 3746]: https://github.com/libp2p/rust-libp2p/pull/3746
+[PR 3883]: https://github.com/libp2p/rust-libp2p/pull/3883
 
 ## 0.39.2
 

core/src/muxing.rs

@@ -57,10 +57,8 @@ use std::pin::Pin;
 
 pub use self::boxed::StreamMuxerBox;
 pub use self::boxed::SubstreamBox;
-pub use self::singleton::SingletonMuxer;
 
 mod boxed;
-mod singleton;
 
 /// Provides multiplexing for a connection by allowing users to open substreams.
 ///

core/src/muxing/singleton.rs

@@ -1,101 +0,0 @@
-// Copyright 2019 Parity Technologies (UK) Ltd.
-//
-// Permission is hereby granted, free of charge, to any person obtaining a
-// copy of this software and associated documentation files (the "Software"),
-// to deal in the Software without restriction, including without limitation
-// the rights to use, copy, modify, merge, publish, distribute, sublicense,
-// and/or sell copies of the Software, and to permit persons to whom the
-// Software is furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in
-// all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
-// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
-// DEALINGS IN THE SOFTWARE.
-
-use crate::connection::Endpoint;
-use crate::muxing::{StreamMuxer, StreamMuxerEvent};
-
-use futures::prelude::*;
-use std::cell::Cell;
-use std::pin::Pin;
-use std::{io, task::Context, task::Poll};
-
-/// Implementation of `StreamMuxer` that allows only one substream on top of a connection,
-/// yielding the connection itself.
-///
-/// Applying this muxer on a connection doesn't read or write any data on the connection itself.
-/// Most notably, no protocol is negotiated.
-pub struct SingletonMuxer<TSocket> {
-    /// The inner connection.
-    inner: Cell<Option<TSocket>>,
-    /// Our local endpoint. Always the same value as was passed to `new`.
-    endpoint: Endpoint,
-}
-
-impl<TSocket> SingletonMuxer<TSocket> {
-    /// Creates a new `SingletonMuxer`.
-    ///
-    /// If `endpoint` is `Dialer`, then only one outbound substream will be permitted.
-    /// If `endpoint` is `Listener`, then only one inbound substream will be permitted.
-    pub fn new(inner: TSocket, endpoint: Endpoint) -> Self {
-        SingletonMuxer {
-            inner: Cell::new(Some(inner)),
-            endpoint,
-        }
-    }
-}
-
-impl<TSocket> StreamMuxer for SingletonMuxer<TSocket>
-where
-    TSocket: AsyncRead + AsyncWrite + Unpin,
-{
-    type Substream = TSocket;
-    type Error = io::Error;
-
-    fn poll_inbound(
-        self: Pin<&mut Self>,
-        _: &mut Context<'_>,
-    ) -> Poll<Result<Self::Substream, Self::Error>> {
-        let this = self.get_mut();
-
-        match this.endpoint {
-            Endpoint::Dialer => Poll::Pending,
-            Endpoint::Listener => match this.inner.replace(None) {
-                None => Poll::Pending,
-                Some(stream) => Poll::Ready(Ok(stream)),
-            },
-        }
-    }
-
-    fn poll_outbound(
-        self: Pin<&mut Self>,
-        _: &mut Context<'_>,
-    ) -> Poll<Result<Self::Substream, Self::Error>> {
-        let this = self.get_mut();
-
-        match this.endpoint {
-            Endpoint::Listener => Poll::Pending,
-            Endpoint::Dialer => match this.inner.replace(None) {
-                None => Poll::Pending,
-                Some(stream) => Poll::Ready(Ok(stream)),
-            },
-        }
-    }
-
-    fn poll_close(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
-        Poll::Ready(Ok(()))
-    }
-
-    fn poll(
-        self: Pin<&mut Self>,
-        _: &mut Context<'_>,
-    ) -> Poll<Result<StreamMuxerEvent, Self::Error>> {
-        Poll::Pending
-    }
-}