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/dcutr/src/behaviour_impl.rs

@@ -237,7 +237,7 @@ impl NetworkBehaviour for Behaviour {
         handler::relayed::Handler,
         Either<handler::direct::Handler, dummy::ConnectionHandler>,
     >;
-    type OutEvent = Event;
+    type ToSwarm = Event;
 
     fn handle_established_inbound_connection(
         &mut self,
@@ -415,7 +415,7 @@ 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(event) = self.queued_events.pop_front() {
             return Poll::Ready(event);
         }

protocols/dcutr/src/handler/direct.rs

@@ -39,8 +39,8 @@ pub struct Handler {
 }
 
 impl ConnectionHandler for Handler {
-    type InEvent = void::Void;
-    type OutEvent = Event;
+    type FromBehaviour = void::Void;
+    type ToBehaviour = Event;
     type Error = StreamUpgradeError<std::io::Error>;
     type InboundProtocol = DeniedUpgrade;
     type OutboundProtocol = DeniedUpgrade;
@@ -51,7 +51,7 @@ impl ConnectionHandler for Handler {
         SubstreamProtocol::new(DeniedUpgrade, ())
     }
 
-    fn on_behaviour_event(&mut self, _: Self::InEvent) {}
+    fn on_behaviour_event(&mut self, _: Self::FromBehaviour) {}
 
     fn connection_keep_alive(&self) -> KeepAlive {
         KeepAlive::No
@@ -64,7 +64,7 @@ impl ConnectionHandler for Handler {
         ConnectionHandlerEvent<
             Self::OutboundProtocol,
             Self::OutboundOpenInfo,
-            Self::OutEvent,
+            Self::ToBehaviour,
             Self::Error,
         >,
     > {

protocols/dcutr/src/handler/relayed.rs

@@ -135,7 +135,7 @@ pub struct Handler {
         ConnectionHandlerEvent<
             <Self as ConnectionHandler>::OutboundProtocol,
             <Self as ConnectionHandler>::OutboundOpenInfo,
-            <Self as ConnectionHandler>::OutEvent,
+            <Self as ConnectionHandler>::ToBehaviour,
             <Self as ConnectionHandler>::Error,
         >,
     >,
@@ -254,8 +254,8 @@ impl Handler {
 }
 
 impl ConnectionHandler for Handler {
-    type InEvent = Command;
-    type OutEvent = Event;
+    type FromBehaviour = Command;
+    type ToBehaviour = Event;
     type Error = StreamUpgradeError<
         Either<protocol::inbound::UpgradeError, protocol::outbound::UpgradeError>,
     >;
@@ -280,7 +280,7 @@ impl ConnectionHandler for Handler {
         }
     }
 
-    fn on_behaviour_event(&mut self, event: Self::InEvent) {
+    fn on_behaviour_event(&mut self, event: Self::FromBehaviour) {
         match event {
             Command::Connect { obs_addrs } => {
                 self.queued_events
@@ -323,7 +323,7 @@ impl ConnectionHandler for Handler {
         ConnectionHandlerEvent<
             Self::OutboundProtocol,
             Self::OutboundOpenInfo,
-            Self::OutEvent,
+            Self::ToBehaviour,
             Self::Error,
         >,
     > {