Fix compiling for WASM with websockets disabled (#934)

* Fix compiling for WASM with websockets disabled

* Comment about usage

core/src/transport/dummy.rs

@@ -0,0 +1,110 @@
+// 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::transport::{Transport, TransportError};
+use multiaddr::Multiaddr;
+use std::{fmt, io, marker::PhantomData};
+
+/// Implementation of `Transport` that doesn't support any multiaddr.
+///
+/// Useful for testing purposes, or as a fallback implementation when no protocol is available.
+pub struct DummyTransport<TOut = DummyStream>(PhantomData<TOut>);
+
+impl<TOut> DummyTransport<TOut> {
+    /// Builds a new `DummyTransport`.
+    pub fn new() -> Self {
+        DummyTransport(PhantomData)
+    }
+}
+
+impl<TOut> Default for DummyTransport<TOut> {
+    fn default() -> Self {
+        DummyTransport::new()
+    }
+}
+
+impl<TOut> fmt::Debug for DummyTransport<TOut> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "DummyTransport")
+    }
+}
+
+impl<TOut> Clone for DummyTransport<TOut> {
+    fn clone(&self) -> Self {
+        DummyTransport(PhantomData)
+    }
+}
+
+impl<TOut> Transport for DummyTransport<TOut> {
+    type Output = TOut;
+    type Error = io::Error;
+    type Listener = futures::stream::Empty<(Self::ListenerUpgrade, Multiaddr), io::Error>;
+    type ListenerUpgrade = futures::future::Empty<Self::Output, io::Error>;
+    type Dial = futures::future::Empty<Self::Output, io::Error>;
+
+    #[inline]
+    fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), TransportError<Self::Error>> {
+        Err(TransportError::MultiaddrNotSupported(addr))
+    }
+
+    #[inline]
+    fn dial(self, addr: Multiaddr) -> Result<Self::Dial, TransportError<Self::Error>> {
+        Err(TransportError::MultiaddrNotSupported(addr))
+    }
+
+    #[inline]
+    fn nat_traversal(&self, _server: &Multiaddr, _observed: &Multiaddr) -> Option<Multiaddr> {
+        None
+    }
+}
+
+/// Implementation of `Read` and `Write`. Not meant to be instanciated.
+pub struct DummyStream(());
+
+impl fmt::Debug for DummyStream {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "DummyStream")
+    }
+}
+
+impl io::Read for DummyStream {
+    fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
+        Err(io::ErrorKind::Other.into())
+    }
+}
+
+impl io::Write for DummyStream {
+    fn write(&mut self, _: &[u8]) -> io::Result<usize> {
+        Err(io::ErrorKind::Other.into())
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        Err(io::ErrorKind::Other.into())
+    }
+}
+
+impl tokio_io::AsyncRead for DummyStream {
+}
+
+impl tokio_io::AsyncWrite for DummyStream {
+    fn shutdown(&mut self) -> futures::Poll<(), io::Error> {
+        Err(io::ErrorKind::Other.into())
+    }
+}

core/src/transport/mod.rs

@@ -36,6 +36,7 @@ use tokio_io::{AsyncRead, AsyncWrite};
 pub mod and_then;
 pub mod boxed;
 pub mod choice;
+pub mod dummy;
 pub mod map;
 pub mod map_err;
 pub mod memory;