Rework the transport upgrade API.

ALthough transport upgrades must follow a specific pattern
in order fot the resulting transport to be usable with a
`Network` or `Swarm`, that pattern is currently not well
reflected in the transport upgrade API. Rather, transport
upgrades are rather laborious and involve non-trivial code
duplication.

This commit introduces a `transport::upgrade::Builder` that is
obtained from `Transport::upgrade`. The `Builder` encodes the
previously implicit rules for transport upgrades:

  1. Authentication upgrades must happen first.
  2. Any number of upgrades may follow.
  3. A multiplexer upgrade must happen last.

Since multiplexing is the last (regular) transport upgrade (because
that upgrade yields a `StreamMuxer` which is no longer a `AsyncRead`
/ `AsyncWrite` resource, which the upgrade process is based on),
the upgrade starts with `Transport::upgrade` and ends with
`Builder::multiplex`, which drops back down to the `Transport`,
providing a fluent API.

Authentication and multiplexer upgrades must furthermore adhere
to a minimal contract w.r.t their outputs:

  1. An authentication upgrade is given an (async) I/O resource `C`
     and must produce a pair `(I, D)` where `I: ConnectionInfo` and
     `D` is a new (async) I/O resource `D`.
  2. A multiplexer upgrade is given an (async) I/O resource `C`
     and must produce a `M: StreamMuxer`.

core/src/lib.rs

@@ -60,6 +60,7 @@ pub use identity::PublicKey;
 pub use transport::Transport;
 pub use translation::address_translation;
 pub use upgrade::{InboundUpgrade, OutboundUpgrade, UpgradeInfo, UpgradeError, ProtocolName};
+pub use nodes::ConnectionInfo;
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Endpoint {

core/src/nodes/network.rs

@@ -782,9 +782,8 @@ where
         TTrans: Transport<Output = (TConnInfo, TMuxer)>,
         TTrans::Error: Send + 'static,
         TTrans::Dial: Send + 'static,
-        TMuxer: StreamMuxer + Send + Sync + 'static,
+        TMuxer: Send + Sync + 'static,
         TMuxer::OutboundSubstream: Send,
-        TMuxer::Substream: Send,
         TInEvent: Send + 'static,
         TOutEvent: Send + 'static,
         TConnInfo: Send + 'static,
@@ -937,12 +936,10 @@ where
         TTrans: Transport<Output = (TConnInfo, TMuxer)>,
         TTrans::Dial: Send + 'static,
         TTrans::Error: Send + 'static,
-        TMuxer: StreamMuxer + Send + Sync + 'static,
+        TMuxer: Send + Sync + 'static,
         TMuxer::OutboundSubstream: Send,
-        TMuxer::Substream: Send,
         TInEvent: Send + 'static,
         TOutEvent: Send + 'static,
-        TConnInfo: Send + 'static,
         TPeerId: Send + 'static,
     {
         let reach_id = match self.transport().clone().dial(first.clone()) {
@@ -985,14 +982,12 @@ where
         TTrans::Error: Send + 'static,
         TTrans::Dial: Send + 'static,
         TTrans::ListenerUpgrade: Send + 'static,
-        TMuxer: StreamMuxer + Send + Sync + 'static,
+        TMuxer: Send + Sync + 'static,
         TMuxer::OutboundSubstream: Send,
-        TMuxer::Substream: Send,
         TInEvent: Send + 'static,
         TOutEvent: Send + 'static,
         THandler: IntoNodeHandler<(TConnInfo, ConnectedPoint)> + Send + 'static,
         THandler::Handler: NodeHandler<Substream = Substream<TMuxer>, InEvent = TInEvent, OutEvent = TOutEvent, Error = THandlerErr> + Send + 'static,
-        <THandler::Handler as NodeHandler>::OutboundOpenInfo: Send + 'static, // TODO: shouldn't be necessary
         THandlerErr: error::Error + Send + 'static,
         TConnInfo: Clone,
         TPeerId: AsRef<[u8]> + Send + 'static,
@@ -1151,7 +1146,6 @@ where
     TTrans: Transport<Output = (TConnInfo, TMuxer)> + Clone,
     TMuxer: StreamMuxer + Send + Sync + 'static,
     TMuxer::OutboundSubstream: Send,
-    TMuxer::Substream: Send,
     TInEvent: Send + 'static,
     TOutEvent: Send + 'static,
     TConnInfo: ConnectionInfo<PeerId = TPeerId> + Clone + Send + 'static,

core/src/transport/mod.rs

@@ -25,12 +25,11 @@
 //! any desired protocols. The rest of the module defines combinators for
 //! modifying a transport through composition with other transports or protocol upgrades.
 
-use crate::{InboundUpgrade, OutboundUpgrade, ConnectedPoint};
+use crate::ConnectedPoint;
 use futures::prelude::*;
 use multiaddr::Multiaddr;
-use std::{error, fmt};
+use std::{error::Error, fmt};
 use std::time::Duration;
-use tokio_io::{AsyncRead, AsyncWrite};
 
 pub mod and_then;
 pub mod boxed;
@@ -69,11 +68,7 @@ pub use self::upgrade::Upgrade;
 ///
 /// Additional protocols can be layered on top of the connections established
 /// by a [`Transport`] through an upgrade mechanism that is initiated via
-/// [`with_upgrade`](Transport::with_upgrade) and optionally followed by further upgrades
-/// through chaining calls to [`with_upgrade`](Transport::with_upgrade) and
-/// [`and_then`](Transport::and_then). Thereby every upgrade yields a new [`Transport`]
-/// whose connection setup incorporates all earlier upgrades followed by the new upgrade,
-/// i.e. the order of the upgrades is significant.
+/// [`upgrade`](Transport::upgrade).
 ///
 /// > **Note**: The methods of this trait use `self` and not `&self` or `&mut self`. In other
 /// >           words, listening or dialing consumes the transport object. This has been designed
@@ -88,7 +83,7 @@ pub trait Transport {
     type Output;
 
     /// An error that occurred during connection setup.
-    type Error: error::Error;
+    type Error: Error;
 
     /// A stream of [`Output`](Transport::Output)s for inbound connections.
     ///
@@ -127,104 +122,101 @@ pub trait Transport {
     where
         Self: Sized;
 
-    /// Turns this `Transport` into an abstract boxed transport.
-    fn boxed(self) -> boxed::Boxed<Self::Output, Self::Error>
-    where Self: Sized + Clone + Send + Sync + 'static,
-          Self::Dial: Send + 'static,
-          Self::Listener: Send + 'static,
-          Self::ListenerUpgrade: Send + 'static,
-    {
-        boxed::boxed(self)
-    }
-
     /// Applies a function on the connections created by the transport.
-    fn map<F, O>(self, map: F) -> map::Map<Self, F>
+    fn map<F, O>(self, f: F) -> map::Map<Self, F>
     where
         Self: Sized,
         F: FnOnce(Self::Output, ConnectedPoint) -> O + Clone
     {
-        map::Map::new(self, map)
+        map::Map::new(self, f)
     }
 
     /// Applies a function on the errors generated by the futures of the transport.
-    fn map_err<F, TNewErr>(self, map_err: F) -> map_err::MapErr<Self, F>
+    fn map_err<F, E>(self, f: F) -> map_err::MapErr<Self, F>
     where
         Self: Sized,
-        F: FnOnce(Self::Error) -> TNewErr + Clone
+        E: Error + 'static,
+        F: FnOnce(Self::Error) -> E + Clone
     {
-        map_err::MapErr::new(self, map_err)
+        map_err::MapErr::new(self, f)
     }
 
-    /// Builds a new transport that falls back to another transport when
-    /// encountering errors on dialing or listening for connections.
+    /// Applies a function producing an asynchronous result to every connection
+    /// created by this transport.
     ///
-    /// The returned transport will act like `self`, except that if `listen_on` or `dial`
-    /// return an error then `other` will be tried.
-    fn or_transport<T>(self, other: T) -> OrTransport<Self, T>
+    /// This function can be used for ad-hoc protocol upgrades or
+    /// for processing or adapting the output for following configurations.
+    ///
+    /// For the high-level transport upgrade procedure, see [`Transport::upgrade`].
+    fn and_then<C, F, O>(self, f: C) -> and_then::AndThen<Self, C>
     where
         Self: Sized,
+        C: FnOnce(Self::Output, ConnectedPoint) -> F + Clone,
+        F: IntoFuture<Item = O>,
+        <F as IntoFuture>::Error: Error + 'static
     {
-        OrTransport::new(self, other)
+        and_then::AndThen::new(self, f)
     }
 
-    /// Wraps this transport inside an [`Upgrade`].
-    ///
-    /// Whenever an inbound or outbound connection is established by this
-    /// transport, the upgrade is applied on the current state of the
-    /// connection (which may have already gone through previous upgrades)
-    /// as an [`upgrade::InboundUpgrade`] or [`upgrade::OutboundUpgrade`],
-    /// respectively.
-    fn with_upgrade<U, O, E>(self, upgrade: U) -> Upgrade<Self, U>
-    where
-        Self: Sized,
-        Self::Output: AsyncRead + AsyncWrite,
-        U: InboundUpgrade<Self::Output, Output = O, Error = E>,
-        U: OutboundUpgrade<Self::Output, Output = O, Error = E>
+    /// Turns the transport into an abstract boxed (i.e. heap-allocated) transport.
+    fn boxed(self) -> boxed::Boxed<Self::Output, Self::Error>
+    where Self: Sized + Clone + Send + Sync + 'static,
+          Self::Dial: Send + 'static,
+          Self::Listener: Send + 'static,
+          Self::ListenerUpgrade: Send + 'static,
     {
-        Upgrade::new(self, upgrade)
+        boxed::boxed(self)
     }
 
-    /// Applies a function producing an asynchronous result to every connection
-    /// created by this transport.
+    /// Adds a fallback transport that is used when encountering errors
+    /// while establishing inbound or outbound connections.
     ///
-    /// This function can be used for ad-hoc protocol upgrades on a transport or
-    /// for processing or adapting the output of an earlier upgrade before
-    /// applying the next upgrade.
-    fn and_then<C, F, O>(self, upgrade: C) -> and_then::AndThen<Self, C>
+    /// The returned transport will act like `self`, except that if `listen_on` or `dial`
+    /// return an error then `other` will be tried.
+    fn or_transport<U>(self, other: U) -> OrTransport<Self, U>
     where
         Self: Sized,
-        C: FnOnce(Self::Output, ConnectedPoint) -> F + Clone,
-        F: IntoFuture<Item = O>
+        U: Transport,
+        <U as Transport>::Error: 'static
     {
-        and_then::AndThen::new(self, upgrade)
+        OrTransport::new(self, other)
     }
 
-    /// Adds a timeout to the connection setup (including upgrades) for all inbound
-    /// and outbound connection attempts.
-    fn with_timeout(self, timeout: Duration) -> timeout::TransportTimeout<Self>
+    /// Adds a timeout to the connection setup (including upgrades) for all
+    /// inbound and outbound connections established through the transport.
+    fn timeout(self, timeout: Duration) -> timeout::TransportTimeout<Self>
     where
-        Self: Sized,
+        Self: Sized
     {
         timeout::TransportTimeout::new(self, timeout)
     }
 
     /// Adds a timeout to the connection setup (including upgrades) for all outbound
-    /// connection attempts.
-    fn with_outbound_timeout(self, timeout: Duration) -> timeout::TransportTimeout<Self>
+    /// connections established through the transport.
+    fn outbound_timeout(self, timeout: Duration) -> timeout::TransportTimeout<Self>
     where
-        Self: Sized,
+        Self: Sized
     {
         timeout::TransportTimeout::with_outgoing_timeout(self, timeout)
     }
 
     /// Adds a timeout to the connection setup (including upgrades) for all inbound
-    /// connection attempts.
-    fn with_inbound_timeout(self, timeout: Duration) -> timeout::TransportTimeout<Self>
+    /// connections established through the transport.
+    fn inbound_timeout(self, timeout: Duration) -> timeout::TransportTimeout<Self>
     where
-        Self: Sized,
+        Self: Sized
     {
         timeout::TransportTimeout::with_ingoing_timeout(self, timeout)
     }
+
+    /// Begins a series of protocol upgrades via an [`upgrade::Builder`].
+    fn upgrade(self) -> upgrade::Builder<Self>
+    where
+        Self: Sized,
+        Self::Error: 'static
+    {
+        upgrade::Builder::new(self)
+    }
 }
 
 /// Event produced by [`Transport::Listener`]s.
@@ -362,10 +354,10 @@ where TErr: fmt::Display,
     }
 }
 
-impl<TErr> error::Error for TransportError<TErr>
-where TErr: error::Error + 'static,
+impl<TErr> Error for TransportError<TErr>
+where TErr: Error + 'static,
 {
-    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
         match self {
             TransportError::MultiaddrNotSupported(_) => None,
             TransportError::Other(err) => Some(err),