feat(swarm): rename associated types for message passing

Previously, the associated types on `NetworkBehaviour` and `ConnectionHandler` carried generic names like `InEvent` and `OutEvent`. These names are _correct_ in that `OutEvent`s are passed out and `InEvent`s are passed in but they don't help users understand how these types are used.

In theory, a `ConnectionHandler` could be used separately from `NetworkBehaviour`s but that is highly unlikely. Thus, we rename these associated types to indicate, where the message is going to be sent to:

- `NetworkBehaviour::OutEvent` is renamed to `ToSwarm`: It describes the message(s) a `NetworkBehaviour` can emit to the `Swarm`. The user is going to receive those in `SwarmEvent::Behaviour`.
- `ConnectionHandler::InEvent` is renamed to `FromBehaviour`: It describes the message(s) a `ConnectionHandler` can receive from its behaviour via `ConnectionHandler::on_swarm_event`. The `NetworkBehaviour` can send it via the `ToSwarm::NotifyHandler` command.
- `ConnectionHandler::OutEvent` is renamed to `ToBehaviour`: It describes the message(s) a `ConnectionHandler` can send back to the behaviour via the now also renamed `ConnectionHandlerEvent::NotifyBehaviour` (previously `ConnectionHandlerEvent::Custom`)

Resolves: #2854.

Pull-Request: #3848.

protocols/relay/src/behaviour.rs

@@ -249,7 +249,7 @@ impl Behaviour {
 
 impl NetworkBehaviour for Behaviour {
     type ConnectionHandler = Either<Handler, dummy::ConnectionHandler>;
-    type OutEvent = Event;
+    type ToSwarm = Event;
 
     fn handle_established_inbound_connection(
         &mut self,
@@ -671,7 +671,7 @@ impl NetworkBehaviour for Behaviour {
         &mut self,
         _cx: &mut Context<'_>,
         _: &mut impl PollParameters,
-    ) -> Poll<ToSwarm<Self::OutEvent, THandlerInEvent<Self>>> {
+    ) -> Poll<ToSwarm<Self::ToSwarm, THandlerInEvent<Self>>> {
         if let Some(action) = self.queued_actions.pop_front() {
             return Poll::Ready(action.build(self.local_peer_id, &self.external_addresses));
         }

protocols/relay/src/behaviour/handler.rs

@@ -340,7 +340,7 @@ pub struct Handler {
         ConnectionHandlerEvent<
             <Self as ConnectionHandler>::OutboundProtocol,
             <Self as ConnectionHandler>::OutboundOpenInfo,
-            <Self as ConnectionHandler>::OutEvent,
+            <Self as ConnectionHandler>::ToBehaviour,
             <Self as ConnectionHandler>::Error,
         >,
     >,
@@ -546,8 +546,8 @@ enum ReservationRequestFuture {
 type Futures<T> = FuturesUnordered<BoxFuture<'static, T>>;
 
 impl ConnectionHandler for Handler {
-    type InEvent = In;
-    type OutEvent = Event;
+    type FromBehaviour = In;
+    type ToBehaviour = Event;
     type Error = StreamUpgradeError<
         Either<inbound_hop::FatalUpgradeError, outbound_stop::FatalUpgradeError>,
     >;
@@ -567,7 +567,7 @@ impl ConnectionHandler for Handler {
         )
     }
 
-    fn on_behaviour_event(&mut self, event: Self::InEvent) {
+    fn on_behaviour_event(&mut self, event: Self::FromBehaviour) {
         match event {
             In::AcceptReservationReq {
                 inbound_reservation_req,
@@ -671,7 +671,7 @@ impl ConnectionHandler for Handler {
         ConnectionHandlerEvent<
             Self::OutboundProtocol,
             Self::OutboundOpenInfo,
-            Self::OutEvent,
+            Self::ToBehaviour,
             Self::Error,
         >,
     > {

protocols/relay/src/priv_client.rs

@@ -156,7 +156,7 @@ impl Behaviour {
 
 impl NetworkBehaviour for Behaviour {
     type ConnectionHandler = Either<Handler, dummy::ConnectionHandler>;
-    type OutEvent = Event;
+    type ToSwarm = Event;
 
     fn handle_established_inbound_connection(
         &mut self,
@@ -293,7 +293,7 @@ impl NetworkBehaviour for Behaviour {
         &mut self,
         cx: &mut Context<'_>,
         _poll_parameters: &mut impl PollParameters,
-    ) -> Poll<ToSwarm<Self::OutEvent, THandlerInEvent<Self>>> {
+    ) -> Poll<ToSwarm<Self::ToSwarm, THandlerInEvent<Self>>> {
         if let Some(action) = self.queued_actions.pop_front() {
             return Poll::Ready(action);
         }

protocols/relay/src/priv_client/handler.rs

@@ -123,7 +123,7 @@ pub struct Handler {
         ConnectionHandlerEvent<
             <Self as ConnectionHandler>::OutboundProtocol,
             <Self as ConnectionHandler>::OutboundOpenInfo,
-            <Self as ConnectionHandler>::OutEvent,
+            <Self as ConnectionHandler>::ToBehaviour,
             <Self as ConnectionHandler>::Error,
         >,
     >,
@@ -393,8 +393,8 @@ impl Handler {
 }
 
 impl ConnectionHandler for Handler {
-    type InEvent = In;
-    type OutEvent = Event;
+    type FromBehaviour = In;
+    type ToBehaviour = Event;
     type Error = StreamUpgradeError<
         Either<inbound_stop::FatalUpgradeError, outbound_hop::FatalUpgradeError>,
     >;
@@ -407,7 +407,7 @@ impl ConnectionHandler for Handler {
         SubstreamProtocol::new(inbound_stop::Upgrade {}, ())
     }
 
-    fn on_behaviour_event(&mut self, event: Self::InEvent) {
+    fn on_behaviour_event(&mut self, event: Self::FromBehaviour) {
         match event {
             In::Reserve { to_listener } => {
                 self.queued_events
@@ -444,7 +444,7 @@ impl ConnectionHandler for Handler {
         ConnectionHandlerEvent<
             Self::OutboundProtocol,
             Self::OutboundOpenInfo,
-            Self::OutEvent,
+            Self::ToBehaviour,
             Self::Error,
         >,
     > {