Add Transport::map_err (#317)

* Add Transport::map_err

core/src/transport/map_err.rs

@@ -0,0 +1,114 @@
+// Copyright 2018 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 futures::prelude::*;
+use multiaddr::Multiaddr;
+use std::io::Error as IoError;
+use transport::{MuxedTransport, Transport};
+
+/// See `Transport::map_err`.
+#[derive(Debug, Copy, Clone)]
+pub struct MapErr<T, F> {
+    transport: T,
+    map: F,
+}
+
+impl<T, F> MapErr<T, F> {
+    /// Internal function that builds a `MapErr`.
+    #[inline]
+    pub(crate) fn new(transport: T, map: F) -> MapErr<T, F> {
+        MapErr { transport, map }
+    }
+}
+
+impl<T, F> Transport for MapErr<T, F>
+where
+    T: Transport + 'static,                          // TODO: 'static :-/
+    F: FnOnce(IoError) -> IoError + Clone + 'static, // TODO: 'static :-/
+{
+    type Output = T::Output;
+    type MultiaddrFuture = T::MultiaddrFuture;
+    type Listener = Box<Stream<Item = Self::ListenerUpgrade, Error = IoError>>;
+    type ListenerUpgrade =
+        Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+    type Dial = Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+
+    fn listen_on(self, addr: Multiaddr) -> Result<(Self::Listener, Multiaddr), (Self, Multiaddr)> {
+        let map = self.map;
+
+        match self.transport.listen_on(addr) {
+            Ok((stream, listen_addr)) => {
+                let map2 = map.clone();
+                let stream = stream
+                    .map(move |future| {
+                        let map = map.clone();
+                        let future = future.into_future().map_err(move |err| map(err));
+                        Box::new(future) as Box<_>
+                    })
+                    .map_err(move |err| {
+                        let map = map2.clone();
+                        map(err)
+                    });
+                Ok((Box::new(stream), listen_addr))
+            }
+            Err((transport, addr)) => Err((MapErr { transport, map }, addr)),
+        }
+    }
+
+    fn dial(self, addr: Multiaddr) -> Result<Self::Dial, (Self, Multiaddr)> {
+        let map = self.map;
+
+        match self.transport.dial(addr) {
+            Ok(future) => {
+                let future = future.into_future().map_err(move |err| map(err));
+                Ok(Box::new(future))
+            }
+            Err((transport, addr)) => Err((MapErr { transport, map }, addr)),
+        }
+    }
+
+    #[inline]
+    fn nat_traversal(&self, server: &Multiaddr, observed: &Multiaddr) -> Option<Multiaddr> {
+        self.transport.nat_traversal(server, observed)
+    }
+}
+
+impl<T, F> MuxedTransport for MapErr<T, F>
+where
+    T: MuxedTransport + 'static,                     // TODO: 'static :-/
+    F: FnOnce(IoError) -> IoError + Clone + 'static, // TODO: 'static :-/
+{
+    type Incoming = Box<Future<Item = Self::IncomingUpgrade, Error = IoError>>;
+    type IncomingUpgrade =
+        Box<Future<Item = (Self::Output, Self::MultiaddrFuture), Error = IoError>>;
+
+    fn next_incoming(self) -> Self::Incoming {
+        let map = self.map;
+        let map2 = map.clone();
+        let future = self.transport
+            .next_incoming()
+            .map(move |upgrade| {
+                let future = upgrade.map_err(map);
+                Box::new(future) as Box<_>
+            })
+            .map_err(map2);
+        Box::new(future)
+    }
+}

core/src/transport/mod.rs

@@ -40,6 +40,7 @@ pub mod choice;
 pub mod denied;
 pub mod dummy;
 pub mod map;
+pub mod map_err;
 pub mod memory;
 pub mod muxed;
 pub mod upgrade;
@@ -126,6 +127,16 @@ pub trait Transport {
         map::Map::new(self, map)
     }
 
+    /// Applies a function on the errors generated by the futures of the `Transport`.
+    #[inline]
+    fn map_err<F>(self, map_err: F) -> map_err::MapErr<Self, F>
+    where
+        Self: Sized,
+        F: FnOnce(IoError) -> IoError + Clone + 'static,        // TODO: 'static :-/
+    {
+        map_err::MapErr::new(self, map_err)
+    }
+
     /// Builds a new struct that implements `Transport` that contains both `self` and `other`.
     ///
     /// The returned object will redirect its calls to `self`, except that if `listen_on` or `dial`