swarm/src/lib: Refactor trait usage (#2182)

- Removes the `Swarm` type alias, renaming `ExpandedSwarm` to `Swarm`.
- Remove `TInEvent`, `TOutEvent` and `THandler` trait parameters on
`Swarm`, instead deriving them through `TBehaviour`. Move derive logic
to separate type aliases.
- Simplify trait bounds on `Swarm` main `impl` and `Stream` `impl`.

swarm/CHANGELOG.md

@@ -6,7 +6,12 @@
   except for `new_handler`, `inject_event` and `poll`.
   This should make it easier to create new implementations. See [PR 2150].
 
+- Remove `Swarm` type alias and rename `ExpandedSwarm` to `Swarm`. Reduce direct
+  trait parameters on `Swarm` (previously `ExpandedSwarm`), deriving parameters
+  through associated types on `TBehaviour`. See [PR 2182].
+
 [PR 2150]: https://github.com/libp2p/rust-libp2p/pull/2150/
+[PR 2182]: https://github.com/libp2p/rust-libp2p/pull/2182
 
 # 0.30.0 [2021-07-12]
 

swarm/src/lib.rs

@@ -120,25 +120,34 @@ use std::collections::HashSet;
 use std::num::{NonZeroU32, NonZeroUsize};
 use upgrade::UpgradeInfoSend as _;
 
-/// Contains the state of the network, plus the way it should behave.
-pub type Swarm<TBehaviour> = ExpandedSwarm<
-    TBehaviour,
-    <<<TBehaviour as NetworkBehaviour>::ProtocolsHandler as IntoProtocolsHandler>::Handler as ProtocolsHandler>::InEvent,
-    <<<TBehaviour as NetworkBehaviour>::ProtocolsHandler as IntoProtocolsHandler>::Handler as ProtocolsHandler>::OutEvent,
-    <TBehaviour as NetworkBehaviour>::ProtocolsHandler,
->;
-
 /// Substream for which a protocol has been chosen.
 ///
 /// Implements the [`AsyncRead`](futures::io::AsyncRead) and
 /// [`AsyncWrite`](futures::io::AsyncWrite) traits.
 pub type NegotiatedSubstream = Negotiated<Substream<StreamMuxerBox>>;
 
+/// Event generated by the [`NetworkBehaviour`] that the swarm will report back.
+type TBehaviourOutEvent<TBehaviour> = <TBehaviour as NetworkBehaviour>::OutEvent;
+
+/// [`ProtocolsHandler`] of the [`NetworkBehaviour`] for all the protocols the [`NetworkBehaviour`]
+/// supports.
+type THandler<TBehaviour> = <TBehaviour as NetworkBehaviour>::ProtocolsHandler;
+
+/// Custom event that can be received by the [`ProtocolsHandler`] of the
+/// [`NetworkBehaviour`].
+type THandlerInEvent<TBehaviour> = <<THandler<TBehaviour> as IntoProtocolsHandler>::Handler as ProtocolsHandler>::InEvent;
+
+/// Custom event that can be produced by the [`ProtocolsHandler`] of the [`NetworkBehaviour`].
+type THandlerOutEvent<TBehaviour> = <<THandler<TBehaviour> as IntoProtocolsHandler>::Handler as ProtocolsHandler>::OutEvent;
+
+/// Custom error that can be produced by the [`ProtocolsHandler`] of the [`NetworkBehaviour`].
+type THandlerErr<TBehaviour> = <<THandler<TBehaviour> as IntoProtocolsHandler>::Handler as ProtocolsHandler>::Error;
+
 /// Event generated by the `Swarm`.
 #[derive(Debug)]
-pub enum SwarmEvent<TBvEv, THandleErr> {
+pub enum SwarmEvent<TBehaviourOutEvent, THandlerErr> {
     /// Event generated by the `NetworkBehaviour`.
-    Behaviour(TBvEv),
+    Behaviour(TBehaviourOutEvent),
     /// A connection to the given peer has been opened.
     ConnectionEstablished {
         /// Identity of the peer that we have connected to.
@@ -160,7 +169,7 @@ pub enum SwarmEvent<TBvEv, THandleErr> {
         num_established: u32,
         /// Reason for the disconnection, if it was not a successful
         /// active close.
-        cause: Option<ConnectionError<NodeHandlerWrapperError<THandleErr>>>,
+        cause: Option<ConnectionError<NodeHandlerWrapperError<THandlerErr>>>,
     },
     /// A new connection arrived on a listener and is in the process of protocol negotiation.
     ///
@@ -261,17 +270,17 @@ pub enum SwarmEvent<TBvEv, THandleErr> {
 
 /// Contains the state of the network, plus the way it should behave.
 ///
-/// Note: Needs to be polled via `<ExpandedSwarm as Stream>` in order to make
+/// Note: Needs to be polled via `<Swarm as Stream>` in order to make
 /// progress.
-pub struct ExpandedSwarm<TBehaviour, TInEvent, TOutEvent, THandler>
+pub struct Swarm<TBehaviour>
 where
-    THandler: IntoProtocolsHandler,
+    TBehaviour: NetworkBehaviour,
 {
     network: Network<
         transport::Boxed<(PeerId, StreamMuxerBox)>,
-        TInEvent,
+        THandlerInEvent<TBehaviour>,
-        TOutEvent,
+        THandlerOutEvent<TBehaviour>,
-        NodeHandlerWrapperBuilder<THandler>,
+        NodeHandlerWrapperBuilder<THandler<TBehaviour>>,
     >,
 
     /// Handles which nodes to connect to and how to handle the events sent back by the protocol
@@ -294,27 +303,21 @@ where
     /// Pending event to be delivered to connection handlers
     /// (or dropped if the peer disconnected) before the `behaviour`
     /// can be polled again.
-    pending_event: Option<(PeerId, PendingNotifyHandler, TInEvent)>,
+    pending_event: Option<(PeerId, PendingNotifyHandler, THandlerInEvent<TBehaviour>)>,
 
     /// The configured override for substream protocol upgrades, if any.
     substream_upgrade_protocol_override: Option<libp2p_core::upgrade::Version>,
 }
 
-impl<TBehaviour, TInEvent, TOutEvent, THandler> Unpin for
+impl<TBehaviour> Unpin for Swarm<TBehaviour>
-    ExpandedSwarm<TBehaviour, TInEvent, TOutEvent, THandler>
 where
-    THandler: IntoProtocolsHandler,
+    TBehaviour: NetworkBehaviour,
 {
 }
 
-impl<TBehaviour, TInEvent, TOutEvent, THandler, THandleErr>
+impl<TBehaviour> Swarm<TBehaviour>
-    ExpandedSwarm<TBehaviour, TInEvent, TOutEvent, THandler>
+where
-where TBehaviour: NetworkBehaviour<ProtocolsHandler = THandler>,
+    TBehaviour: NetworkBehaviour,
-      TInEvent: Send + 'static,
-      TOutEvent: Send + 'static,
-      THandler: IntoProtocolsHandler + Send + 'static,
-      THandler::Handler: ProtocolsHandler<InEvent = TInEvent, OutEvent = TOutEvent, Error = THandleErr>,
-      THandleErr: error::Error + Send + 'static,
 {
     /// Builds a new `Swarm`.
     pub fn new(
@@ -438,7 +441,7 @@ where TBehaviour: NetworkBehaviour<ProtocolsHandler = THandler>,
     }
 
     /// Removes an external address of the local node, regardless of
-    /// its current score. See [`ExpandedSwarm::add_external_address`]
+    /// its current score. See [`Swarm::add_external_address`]
     /// for details.
     ///
     /// Returns `true` if the address existed and was removed, `false`
@@ -473,7 +476,7 @@ where TBehaviour: NetworkBehaviour<ProtocolsHandler = THandler>,
     ///
     /// Returns `Ok(())` if there was one or more established connections to the peer.
     ///
-    /// Note: Closing a connection via [`ExpandedSwarm::disconnect_peer_id`] does
+    /// Note: Closing a connection via [`Swarm::disconnect_peer_id`] does
     /// not inform the corresponding [`ProtocolsHandler`].
     /// Closing a connection via a [`ProtocolsHandler`] can be done either in a
     /// collaborative manner across [`ProtocolsHandler`]s
@@ -507,7 +510,7 @@ where TBehaviour: NetworkBehaviour<ProtocolsHandler = THandler>,
     ///
     /// Polls the `Swarm` for the next event.
     fn poll_next_event(mut self: Pin<&mut Self>, cx: &mut Context<'_>)
-        -> Poll<SwarmEvent<TBehaviour::OutEvent, THandleErr>>
+        -> Poll<SwarmEvent<TBehaviour::OutEvent, THandlerErr<TBehaviour>>>
     {
         // We use a `this` variable because the compiler can't mutably borrow multiple times
         // across a `Deref`.
@@ -708,7 +711,7 @@ where TBehaviour: NetworkBehaviour<ProtocolsHandler = THandler>,
                     return Poll::Ready(SwarmEvent::Behaviour(event))
                 },
                 Poll::Ready(NetworkBehaviourAction::DialAddress { address }) => {
-                    let _ = ExpandedSwarm::dial_addr(&mut *this, address);
+                    let _ = Swarm::dial_addr(&mut *this, address);
                 },
                 Poll::Ready(NetworkBehaviourAction::DialPeer { peer_id, condition }) => {
                     if this.banned_peers.contains(&peer_id) {
@@ -720,7 +723,7 @@ where TBehaviour: NetworkBehaviour<ProtocolsHandler = THandler>,
                             DialPeerCondition::Always => true,
                         };
                         if condition_matched {
-                            if ExpandedSwarm::dial(this, &peer_id).is_ok() {
+                            if Swarm::dial(this, &peer_id).is_ok() {
                                 return Poll::Ready(SwarmEvent::Dialing(peer_id))
                             }
                         } else {
@@ -808,11 +811,11 @@ enum PendingNotifyHandler {
 ///
 /// Returns `None` if the connection is closing or the event has been
 /// successfully sent, in either case the event is consumed.
-fn notify_one<'a, TInEvent>(
+fn notify_one<'a, THandlerInEvent>(
-    conn: &mut EstablishedConnection<'a, TInEvent>,
+    conn: &mut EstablishedConnection<'a, THandlerInEvent>,
-    event: TInEvent,
+    event: THandlerInEvent,
     cx: &mut Context<'_>,
-) -> Option<TInEvent>
+) -> Option<THandlerInEvent>
 {
     match conn.poll_ready_notify_handler(cx) {
         Poll::Pending => Some(event),
@@ -835,12 +838,12 @@ fn notify_one<'a, TInEvent>(
 ///
 /// Returns `None` if either all connections are closing or the event
 /// was successfully sent to a handler, in either case the event is consumed.
-fn notify_any<'a, TTrans, TInEvent, TOutEvent, THandler>(
+fn notify_any<'a, TTrans, THandlerInEvent, THandlerOutEvent, THandler>(
     ids: SmallVec<[ConnectionId; 10]>,
-    peer: &mut ConnectedPeer<'a, TTrans, TInEvent, TOutEvent, THandler>,
+    peer: &mut ConnectedPeer<'a, TTrans, THandlerInEvent, THandlerOutEvent, THandler>,
-    event: TInEvent,
+    event: THandlerInEvent,
     cx: &mut Context<'_>,
-) -> Option<(TInEvent, SmallVec<[ConnectionId; 10]>)>
+) -> Option<(THandlerInEvent, SmallVec<[ConnectionId; 10]>)>
 where
     TTrans: Transport,
     THandler: IntoConnectionHandler,
@@ -872,24 +875,18 @@ where
         })
 }
 
-/// Stream of events returned by [`ExpandedSwarm`].
+/// Stream of events returned by [`Swarm`].
 ///
 /// Includes events from the [`NetworkBehaviour`] as well as events about
 /// connection and listener status. See [`SwarmEvent`] for details.
 ///
 /// Note: This stream is infinite and it is guaranteed that
 /// [`Stream::poll_next`] will never return `Poll::Ready(None)`.
-impl<TBehaviour, TInEvent, TOutEvent, THandler, THandleErr> Stream for
+impl<TBehaviour> Stream for Swarm<TBehaviour>
-    ExpandedSwarm<TBehaviour, TInEvent, TOutEvent, THandler>
+where
-where TBehaviour: NetworkBehaviour<ProtocolsHandler = THandler>,
+    TBehaviour: NetworkBehaviour,
-      THandler: IntoProtocolsHandler + Send + 'static,
-      TInEvent: Send + 'static,
-      TOutEvent: Send + 'static,
-      THandler::Handler:
-        ProtocolsHandler<InEvent = TInEvent, OutEvent = TOutEvent, Error = THandleErr>,
-      THandleErr: error::Error + Send + 'static,
 {
-    type Item = SwarmEvent<TBehaviour::OutEvent, THandleErr>;
+    type Item = SwarmEvent<TBehaviourOutEvent<TBehaviour>, THandlerErr<TBehaviour>>;
 
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
         self.as_mut()
@@ -899,13 +896,9 @@ where TBehaviour: NetworkBehaviour<ProtocolsHandler = THandler>,
 }
 
 /// The stream of swarm events never terminates, so we can implement fused for it.
-impl<TBehaviour, TInEvent, TOutEvent, THandler> FusedStream for
+impl<TBehaviour> FusedStream for Swarm<TBehaviour>
-    ExpandedSwarm<TBehaviour, TInEvent, TOutEvent, THandler>
+where
-where TBehaviour: NetworkBehaviour<ProtocolsHandler = THandler>,
+    TBehaviour: NetworkBehaviour,
-      THandler: IntoProtocolsHandler + Send + 'static,
-      TInEvent: Send + 'static,
-      TOutEvent: Send + 'static,
-      THandler::Handler: ProtocolsHandler<InEvent = TInEvent, OutEvent = TOutEvent>,
 {
     fn is_terminated(&self) -> bool {
         false
@@ -954,7 +947,8 @@ pub struct SwarmBuilder<TBehaviour> {
 }
 
 impl<TBehaviour> SwarmBuilder<TBehaviour>
-where TBehaviour: NetworkBehaviour,
+where
+    TBehaviour: NetworkBehaviour,
 {
     /// Creates a new `SwarmBuilder` from the given transport, behaviour and
     /// local peer ID. The `Swarm` with its underlying `Network` is obtained
@@ -1073,7 +1067,7 @@ where TBehaviour: NetworkBehaviour,
 
         let network = Network::new(self.transport, self.local_peer_id, network_cfg);
 
-        ExpandedSwarm {
+        Swarm {
             network,
             behaviour: self.behaviour,
             supported_protocols,
@@ -1086,7 +1080,7 @@ where TBehaviour: NetworkBehaviour,
     }
 }
 
-/// The possible failures of [`ExpandedSwarm::dial`].
+/// The possible failures of [`Swarm::dial`].
 #[derive(Debug)]
 pub enum DialError {
     /// The peer is currently banned.
@@ -1346,7 +1340,7 @@ mod tests {
     }
 
     /// Establishes multiple connections between two peers,
-    /// after which one peer disconnects the other using [`ExpandedSwarm::disconnect_peer_id`].
+    /// after which one peer disconnects the other using [`Swarm::disconnect_peer_id`].
     ///
     /// The test expects both behaviours to be notified via pairs of
     /// inject_connected / inject_disconnected as well as