refactor: expose and use THandlerOutEvent type alias (#3368)

Previously, we used the full reference to the `OutEvent` of the `ConnectionHandler` in all implementations of `NetworkBehaviour`. Not only is this very verbose, it is also more brittle to changes. With the current implementation plan for #2824, we will be removing the `IntoConnectionHandler` abstraction. Using a type-alias to refer to the `OutEvent` makes the migration much easier.

protocols/autonat/src/behaviour.rs

@@ -37,8 +37,8 @@ use libp2p_swarm::{
         AddressChange, ConnectionClosed, ConnectionEstablished, DialFailure, ExpiredExternalAddr,
         ExpiredListenAddr, FromSwarm,
     },
-    ConnectionHandler, ConnectionId, ExternalAddresses, IntoConnectionHandler, ListenAddresses,
-    NetworkBehaviour, NetworkBehaviourAction, PollParameters,
+    ConnectionId, ExternalAddresses, ListenAddresses, NetworkBehaviour, NetworkBehaviourAction,
+    PollParameters, THandlerOutEvent,
 };
 use std::{
     collections::{HashMap, VecDeque},
@@ -553,8 +553,7 @@ impl NetworkBehaviour for Behaviour {
         &mut self,
         peer_id: PeerId,
         connection_id: ConnectionId,
-        event:  <<Self::ConnectionHandler as IntoConnectionHandler>::Handler as
-    ConnectionHandler>::OutEvent,
+        event: THandlerOutEvent<Self>,
     ) {
         self.inner
             .on_connection_handler_event(peer_id, connection_id, event)

protocols/dcutr/src/behaviour_impl.rs

@@ -27,11 +27,11 @@ use libp2p_core::multiaddr::Protocol;
 use libp2p_core::{Multiaddr, PeerId};
 use libp2p_swarm::behaviour::{ConnectionClosed, ConnectionEstablished, DialFailure, FromSwarm};
 use libp2p_swarm::dial_opts::{self, DialOpts};
-use libp2p_swarm::ConnectionId;
 use libp2p_swarm::{
-    ConnectionHandler, ConnectionHandlerUpgrErr, ExternalAddresses, IntoConnectionHandler,
-    NetworkBehaviour, NetworkBehaviourAction, NotifyHandler, PollParameters,
+    ConnectionHandlerUpgrErr, ExternalAddresses, NetworkBehaviour, NetworkBehaviourAction,
+    NotifyHandler, PollParameters,
 };
+use libp2p_swarm::{ConnectionId, THandlerOutEvent};
 use std::collections::{HashMap, HashSet, VecDeque};
 use std::task::{Context, Poll};
 use thiserror::Error;
@@ -222,8 +222,7 @@ impl NetworkBehaviour for Behaviour {
         &mut self,
         event_source: PeerId,
         connection: ConnectionId,
-        handler_event: <<Self::ConnectionHandler as IntoConnectionHandler>::Handler as
-            ConnectionHandler>::OutEvent,
+        handler_event: THandlerOutEvent<Self>,
     ) {
         match handler_event {
             Either::Left(handler::relayed::Event::InboundConnectRequest {

protocols/floodsub/src/layer.rs

@@ -30,9 +30,8 @@ use libp2p_core::PeerId;
 use libp2p_swarm::behaviour::{ConnectionClosed, ConnectionEstablished, FromSwarm};
 use libp2p_swarm::{
     dial_opts::DialOpts, ConnectionId, NetworkBehaviour, NetworkBehaviourAction, NotifyHandler,
-    OneShotHandler, PollParameters,
+    OneShotHandler, PollParameters, THandlerOutEvent,
 };
-use libp2p_swarm::{ConnectionHandler, IntoConnectionHandler};
 use log::warn;
 use smallvec::SmallVec;
 use std::collections::hash_map::{DefaultHasher, HashMap};
@@ -352,8 +351,7 @@ impl NetworkBehaviour for Floodsub {
         &mut self,
         propagation_source: PeerId,
         _connection_id: ConnectionId,
-        event: <<Self::ConnectionHandler as IntoConnectionHandler>::Handler as
-            ConnectionHandler>::OutEvent,
+        event: THandlerOutEvent<Self>,
     ) {
         // We ignore successful sends or timeouts.
         let event = match event {

protocols/gossipsub/src/behaviour.rs

@@ -41,8 +41,8 @@ use libp2p_core::{
 use libp2p_swarm::{
     behaviour::{AddressChange, ConnectionClosed, ConnectionEstablished, FromSwarm},
     dial_opts::DialOpts,
-    ConnectionHandler, ConnectionId, IntoConnectionHandler, NetworkBehaviour,
-    NetworkBehaviourAction, NotifyHandler, PollParameters,
+    ConnectionId, NetworkBehaviour, NetworkBehaviourAction, NotifyHandler, PollParameters,
+    THandlerOutEvent,
 };
 use wasm_timer::Instant;
 
@@ -3313,8 +3313,7 @@ where
         &mut self,
         propagation_source: PeerId,
         _connection_id: ConnectionId,
-        handler_event: <<Self::ConnectionHandler as IntoConnectionHandler>::Handler as
-            ConnectionHandler>::OutEvent,
+        handler_event: THandlerOutEvent<Self>,
     ) {
         match handler_event {
             HandlerEvent::PeerKind(kind) => {

protocols/identify/src/behaviour.rs

@@ -21,12 +21,12 @@
 use crate::handler::{self, InEvent, Proto};
 use crate::protocol::{Info, Protocol, UpgradeError};
 use libp2p_core::{multiaddr, ConnectedPoint, Multiaddr, PeerId, PublicKey};
-use libp2p_swarm::behaviour::{ConnectionClosed, ConnectionEstablished, DialFailure, FromSwarm};
-use libp2p_swarm::ConnectionId;
 use libp2p_swarm::{
-    dial_opts::DialOpts, AddressScore, ConnectionHandler, ConnectionHandlerUpgrErr, DialError,
-    ExternalAddresses, IntoConnectionHandler, ListenAddresses, NetworkBehaviour,
-    NetworkBehaviourAction, NotifyHandler, PollParameters,
+    behaviour::{ConnectionClosed, ConnectionEstablished, DialFailure, FromSwarm},
+    dial_opts::DialOpts,
+    AddressScore, ConnectionHandlerUpgrErr, ConnectionId, DialError, ExternalAddresses,
+    ListenAddresses, NetworkBehaviour, NetworkBehaviourAction, NotifyHandler, PollParameters,
+    THandlerOutEvent,
 };
 use lru::LruCache;
 use std::num::NonZeroUsize;
@@ -253,7 +253,7 @@ impl NetworkBehaviour for Behaviour {
         &mut self,
         peer_id: PeerId,
         connection_id: ConnectionId,
-        event: <<Self::ConnectionHandler as IntoConnectionHandler>::Handler as ConnectionHandler>::OutEvent,
+        event: THandlerOutEvent<Self>,
     ) {
         match event {
             handler::Event::Identified(mut info) => {

protocols/kad/src/behaviour.rs

@@ -46,7 +46,7 @@ use libp2p_swarm::behaviour::{
 use libp2p_swarm::{
     dial_opts::{self, DialOpts},
     ConnectionId, DialError, ExternalAddresses, ListenAddresses, NetworkBehaviour,
-    NetworkBehaviourAction, NotifyHandler, PollParameters,
+    NetworkBehaviourAction, NotifyHandler, PollParameters, THandlerOutEvent,
 };
 use log::{debug, info, warn};
 use smallvec::SmallVec;
@@ -2025,7 +2025,7 @@ where
         &mut self,
         source: PeerId,
         connection: ConnectionId,
-        event: KademliaHandlerEvent<QueryId>,
+        event: THandlerOutEvent<Self>,
     ) {
         match event {
             KademliaHandlerEvent::ProtocolConfirmed { endpoint } => {

protocols/mdns/src/behaviour.rs

@@ -30,8 +30,8 @@ use if_watch::IfEvent;
 use libp2p_core::{Multiaddr, PeerId};
 use libp2p_swarm::behaviour::{ConnectionClosed, FromSwarm};
 use libp2p_swarm::{
-    dummy, ConnectionHandler, ListenAddresses, NetworkBehaviour, NetworkBehaviourAction,
-    PollParameters,
+    dummy, ListenAddresses, NetworkBehaviour, NetworkBehaviourAction, PollParameters,
+    THandlerOutEvent,
 };
 use smallvec::SmallVec;
 use std::collections::hash_map::{Entry, HashMap};
@@ -190,7 +190,7 @@ where
         &mut self,
         _: PeerId,
         _: libp2p_swarm::ConnectionId,
-        ev: <Self::ConnectionHandler as ConnectionHandler>::OutEvent,
+        ev: THandlerOutEvent<Self>,
     ) {
         void::unreachable(ev)
     }

protocols/ping/src/lib.rs

@@ -50,6 +50,7 @@ pub use handler::{Config, Failure, Success};
 use libp2p_core::PeerId;
 use libp2p_swarm::{
     behaviour::FromSwarm, ConnectionId, NetworkBehaviour, NetworkBehaviourAction, PollParameters,
+    THandlerOutEvent,
 };
 use std::{
     collections::VecDeque,
@@ -123,7 +124,12 @@ impl NetworkBehaviour for Behaviour {
         Handler::new(self.config.clone())
     }
 
-    fn on_connection_handler_event(&mut self, peer: PeerId, _: ConnectionId, result: Result) {
+    fn on_connection_handler_event(
+        &mut self,
+        peer: PeerId,
+        _: ConnectionId,
+        result: THandlerOutEvent<Self>,
+    ) {
         self.events.push_front(Event { peer, result })
     }
 

protocols/relay/src/behaviour.rs

@@ -32,7 +32,7 @@ use libp2p_core::PeerId;
 use libp2p_swarm::behaviour::{ConnectionClosed, FromSwarm};
 use libp2p_swarm::{
     ConnectionHandlerUpgrErr, ConnectionId, ExternalAddresses, NetworkBehaviour,
-    NetworkBehaviourAction, NotifyHandler, PollParameters,
+    NetworkBehaviourAction, NotifyHandler, PollParameters, THandlerOutEvent,
 };
 use std::collections::{hash_map, HashMap, HashSet, VecDeque};
 use std::num::NonZeroU32;
@@ -287,7 +287,7 @@ impl NetworkBehaviour for Behaviour {
         &mut self,
         event_source: PeerId,
         connection: ConnectionId,
-        event: Either<handler::Event, void::Void>,
+        event: THandlerOutEvent<Self>,
     ) {
         let event = match event {
             Either::Left(e) => e,

protocols/relay/src/priv_client.rs

@@ -37,7 +37,7 @@ use libp2p_swarm::behaviour::{ConnectionClosed, ConnectionEstablished, FromSwarm
 use libp2p_swarm::dial_opts::DialOpts;
 use libp2p_swarm::{
     ConnectionHandlerUpgrErr, ConnectionId, NegotiatedSubstream, NetworkBehaviour,
-    NetworkBehaviourAction, NotifyHandler, PollParameters,
+    NetworkBehaviourAction, NotifyHandler, PollParameters, THandlerOutEvent,
 };
 use std::collections::{hash_map, HashMap, VecDeque};
 use std::io::{Error, ErrorKind, IoSlice};
@@ -194,7 +194,7 @@ impl NetworkBehaviour for Behaviour {
         &mut self,
         event_source: PeerId,
         _connection: ConnectionId,
-        handler_event: Either<handler::Event, void::Void>,
+        handler_event: THandlerOutEvent<Self>,
     ) {
         let handler_event = match handler_event {
             Either::Left(e) => e,

protocols/rendezvous/src/client.rs

@@ -34,7 +34,7 @@ use libp2p_core::{Multiaddr, PeerId, PeerRecord};
 use libp2p_swarm::behaviour::FromSwarm;
 use libp2p_swarm::{
     CloseConnection, ConnectionId, ExternalAddresses, NetworkBehaviour, NetworkBehaviourAction,
-    NotifyHandler, PollParameters,
+    NotifyHandler, PollParameters, THandlerOutEvent,
 };
 use std::collections::{HashMap, VecDeque};
 use std::iter::FromIterator;
@@ -191,7 +191,7 @@ impl NetworkBehaviour for Behaviour {
         &mut self,
         peer_id: PeerId,
         connection_id: ConnectionId,
-        event: handler::OutboundOutEvent,
+        event: THandlerOutEvent<Self>,
     ) {
         let new_events = match event {
             handler::OutboundOutEvent::InboundEvent { message, .. } => void::unreachable(message),

protocols/rendezvous/src/server.rs

@@ -31,7 +31,7 @@ use libp2p_core::PeerId;
 use libp2p_swarm::behaviour::FromSwarm;
 use libp2p_swarm::{
     CloseConnection, ConnectionId, NetworkBehaviour, NetworkBehaviourAction, NotifyHandler,
-    PollParameters,
+    PollParameters, THandlerOutEvent,
 };
 use std::collections::{HashMap, HashSet, VecDeque};
 use std::iter::FromIterator;
@@ -123,7 +123,7 @@ impl NetworkBehaviour for Behaviour {
         &mut self,
         peer_id: PeerId,
         connection: ConnectionId,
-        event: handler::InboundOutEvent,
+        event: THandlerOutEvent<Self>,
     ) {
         let new_events = match event {
             handler::InboundOutEvent::InboundEvent { id, message } => {

protocols/request-response/src/lib.rs

@@ -74,8 +74,8 @@ use libp2p_core::{ConnectedPoint, Multiaddr, PeerId};
 use libp2p_swarm::{
     behaviour::{AddressChange, ConnectionClosed, ConnectionEstablished, DialFailure, FromSwarm},
     dial_opts::DialOpts,
-    ConnectionId, IntoConnectionHandler, NetworkBehaviour, NetworkBehaviourAction, NotifyHandler,
-    PollParameters,
+    ConnectionId, NetworkBehaviour, NetworkBehaviourAction, NotifyHandler, PollParameters,
+    THandlerOutEvent,
 };
 use smallvec::SmallVec;
 use std::{
@@ -776,8 +776,7 @@ where
         &mut self,
         peer: PeerId,
         connection: ConnectionId,
-        event: <<Self::ConnectionHandler as IntoConnectionHandler>::Handler as
-            libp2p_swarm::ConnectionHandler>::OutEvent,
+        event: THandlerOutEvent<Self>,
     ) {
         match event {
             handler::Event::Response {

swarm/src/behaviour.rs

@@ -29,7 +29,7 @@ pub use listen_addresses::ListenAddresses;
 use crate::connection::ConnectionId;
 use crate::dial_opts::DialOpts;
 use crate::handler::{ConnectionHandler, IntoConnectionHandler};
-use crate::{AddressRecord, AddressScore, DialError};
+use crate::{AddressRecord, AddressScore, DialError, THandlerOutEvent};
 use libp2p_core::{transport::ListenerId, ConnectedPoint, Multiaddr, PeerId};
 use std::{task::Context, task::Poll};
 
@@ -37,9 +37,6 @@ use std::{task::Context, task::Poll};
 pub(crate) type THandlerInEvent<THandler> =
     <<THandler as IntoConnectionHandler>::Handler as ConnectionHandler>::InEvent;
 
-pub(crate) type THandlerOutEvent<THandler> =
-    <<THandler as IntoConnectionHandler>::Handler as ConnectionHandler>::OutEvent;
-
 /// A [`NetworkBehaviour`] defines the behaviour of the local node on the network.
 ///
 /// In contrast to [`Transport`](libp2p_core::Transport) which defines **how** to send bytes on the
@@ -170,8 +167,7 @@ pub trait NetworkBehaviour: 'static {
         &mut self,
         _peer_id: PeerId,
         _connection_id: ConnectionId,
-        _event: <<Self::ConnectionHandler as IntoConnectionHandler>::Handler as
-        ConnectionHandler>::OutEvent,
+        _event: THandlerOutEvent<Self>,
     );
 
     /// Polls for things that swarm should do.
@@ -264,7 +260,7 @@ pub enum NetworkBehaviourAction<
     /// # use libp2p_plaintext::PlainText2Config;
     /// # use libp2p_swarm::{
     /// #     ConnectionId, DialError, IntoConnectionHandler, KeepAlive, NegotiatedSubstream,
-    /// #     FromSwarm, DialFailure,
+    /// #     FromSwarm, DialFailure, THandlerOutEvent,
     /// #     NetworkBehaviour, NetworkBehaviourAction, PollParameters, ConnectionHandler,
     /// #     ConnectionHandlerEvent, ConnectionHandlerUpgrErr, SubstreamProtocol, Swarm, SwarmEvent,
     /// # };
@@ -334,7 +330,7 @@ pub enum NetworkBehaviourAction<
     ///     #     &mut self,
     ///     #     _: PeerId,
     ///     #     _: ConnectionId,
-    ///     #     _: <<Self::ConnectionHandler as IntoConnectionHandler>::Handler as ConnectionHandler>::OutEvent,
+    ///     #     _: THandlerOutEvent<Self>,
     ///     # ) {
     ///     #     unreachable!();
     ///     # }

swarm/src/behaviour/either.rs

@@ -21,6 +21,7 @@
 use crate::behaviour::{self, NetworkBehaviour, NetworkBehaviourAction, PollParameters};
 use crate::connection::ConnectionId;
 use crate::handler::either::IntoEitherHandler;
+use crate::THandlerOutEvent;
 use either::Either;
 use libp2p_core::{Multiaddr, PeerId};
 use std::{task::Context, task::Poll};
@@ -71,7 +72,7 @@ where
         &mut self,
         peer_id: PeerId,
         connection_id: ConnectionId,
-        event: crate::THandlerOutEvent<Self>,
+        event: THandlerOutEvent<Self>,
     ) {
         match (self, event) {
             (Either::Left(left), Either::Left(event)) => {

swarm/src/behaviour/toggle.rs

@@ -26,7 +26,7 @@ use crate::handler::{
     IntoConnectionHandler, KeepAlive, ListenUpgradeError, SubstreamProtocol,
 };
 use crate::upgrade::SendWrapper;
-use crate::{NetworkBehaviour, NetworkBehaviourAction, PollParameters};
+use crate::{NetworkBehaviour, NetworkBehaviourAction, PollParameters, THandlerOutEvent};
 use either::Either;
 use futures::future;
 use libp2p_core::{upgrade::DeniedUpgrade, ConnectedPoint, Multiaddr, PeerId};
@@ -94,7 +94,7 @@ where
         &mut self,
         peer_id: PeerId,
         connection_id: ConnectionId,
-        event: crate::THandlerOutEvent<Self>,
+        event: THandlerOutEvent<Self>,
     ) {
         if let Some(behaviour) = &mut self.inner {
             behaviour.on_connection_handler_event(peer_id, connection_id, event)

swarm/src/connection/pool.rs

@@ -21,7 +21,7 @@
 
 use crate::connection::{Connection, ConnectionId, PendingPoint};
 use crate::{
-    behaviour::{THandlerInEvent, THandlerOutEvent},
+    behaviour::THandlerInEvent,
     connection::{
         Connected, ConnectionError, ConnectionLimit, IncomingInfo, PendingConnectionError,
         PendingInboundConnectionError, PendingOutboundConnectionError,
@@ -294,7 +294,7 @@ pub enum PoolEvent<THandler: IntoConnectionHandler> {
         id: ConnectionId,
         peer_id: PeerId,
         /// The produced event.
-        event: THandlerOutEvent<THandler>,
+        event: <<THandler as IntoConnectionHandler>::Handler as ConnectionHandler>::OutEvent,
     },
 
     /// The connection to a node has changed its address.

swarm/src/dummy.rs

@@ -3,7 +3,10 @@ use crate::connection::ConnectionId;
 use crate::handler::{
     ConnectionEvent, DialUpgradeError, FullyNegotiatedInbound, FullyNegotiatedOutbound,
 };
-use crate::{ConnectionHandlerEvent, ConnectionHandlerUpgrErr, KeepAlive, SubstreamProtocol};
+use crate::{
+    ConnectionHandlerEvent, ConnectionHandlerUpgrErr, KeepAlive, SubstreamProtocol,
+    THandlerOutEvent,
+};
 use libp2p_core::upgrade::DeniedUpgrade;
 use libp2p_core::PeerId;
 use libp2p_core::UpgradeError;
@@ -21,7 +24,12 @@ impl NetworkBehaviour for Behaviour {
         ConnectionHandler
     }
 
-    fn on_connection_handler_event(&mut self, _: PeerId, _: ConnectionId, event: Void) {
+    fn on_connection_handler_event(
+        &mut self,
+        _: PeerId,
+        _: ConnectionId,
+        event: THandlerOutEvent<Self>,
+    ) {
         void::unreachable(event)
     }
 

swarm/src/keep_alive.rs

@@ -4,6 +4,7 @@ use crate::handler::{
     ConnectionEvent, ConnectionHandlerEvent, FullyNegotiatedInbound, FullyNegotiatedOutbound,
     KeepAlive, SubstreamProtocol,
 };
+use crate::THandlerOutEvent;
 use libp2p_core::upgrade::DeniedUpgrade;
 use libp2p_core::PeerId;
 use std::task::{Context, Poll};
@@ -26,7 +27,12 @@ impl NetworkBehaviour for Behaviour {
         ConnectionHandler
     }
 
-    fn on_connection_handler_event(&mut self, _: PeerId, _: ConnectionId, event: Void) {
+    fn on_connection_handler_event(
+        &mut self,
+        _: PeerId,
+        _: ConnectionId,
+        event: THandlerOutEvent<Self>,
+    ) {
         void::unreachable(event)
     }
 

swarm/src/lib.rs

@@ -166,7 +166,7 @@ type THandlerInEvent<TBehaviour> =
     <<THandler<TBehaviour> as IntoConnectionHandler>::Handler as ConnectionHandler>::InEvent;
 
 /// Custom event that can be produced by the [`ConnectionHandler`] of the [`NetworkBehaviour`].
-type THandlerOutEvent<TBehaviour> =
+pub type THandlerOutEvent<TBehaviour> =
     <<THandler<TBehaviour> as IntoConnectionHandler>::Handler as ConnectionHandler>::OutEvent;
 
 /// Custom error that can be produced by the [`ConnectionHandler`] of the [`NetworkBehaviour`].

swarm/src/test.rs

@@ -24,7 +24,7 @@ use crate::behaviour::{
 };
 use crate::{
     ConnectionHandler, ConnectionId, IntoConnectionHandler, NetworkBehaviour,
-    NetworkBehaviourAction, PollParameters,
+    NetworkBehaviourAction, PollParameters, THandlerOutEvent,
 };
 use libp2p_core::{multiaddr::Multiaddr, transport::ListenerId, ConnectedPoint, PeerId};
 use std::collections::HashMap;
@@ -107,8 +107,7 @@ where
         &mut self,
         _peer_id: PeerId,
         _connection_id: ConnectionId,
-        _event: <<Self::ConnectionHandler as IntoConnectionHandler>::Handler as
-            ConnectionHandler>::OutEvent,
+        _event: THandlerOutEvent<Self>,
     ) {
     }
 }
@@ -455,7 +454,7 @@ where
         &mut self,
         p: PeerId,
         c: ConnectionId,
-        e: <<Self::ConnectionHandler as IntoConnectionHandler>::Handler as ConnectionHandler>::OutEvent,
+        e: THandlerOutEvent<Self>,
     ) {
         assert!(
             self.on_connection_established

swarm/tests/swarm_derive.rs

@@ -21,7 +21,7 @@
 use futures::StreamExt;
 use libp2p_identify as identify;
 use libp2p_ping as ping;
-use libp2p_swarm::{behaviour::FromSwarm, dummy, NetworkBehaviour, SwarmEvent};
+use libp2p_swarm::{behaviour::FromSwarm, dummy, NetworkBehaviour, SwarmEvent, THandlerOutEvent};
 use std::fmt::Debug;
 
 /// Small utility to check that a type implements `NetworkBehaviour`.
@@ -369,10 +369,7 @@ fn generated_out_event_derive_debug() {
 #[test]
 fn custom_out_event_no_type_parameters() {
     use libp2p_core::PeerId;
-    use libp2p_swarm::{
-        ConnectionHandler, ConnectionId, IntoConnectionHandler, NetworkBehaviourAction,
-        PollParameters,
-    };
+    use libp2p_swarm::{ConnectionId, NetworkBehaviourAction, PollParameters};
     use std::task::Context;
     use std::task::Poll;
 
@@ -392,7 +389,7 @@ fn custom_out_event_no_type_parameters() {
             &mut self,
             _peer: PeerId,
             _connection: ConnectionId,
-            message: <<Self::ConnectionHandler as IntoConnectionHandler>::Handler as ConnectionHandler>::OutEvent,
+            message: THandlerOutEvent<Self>,
         ) {
             void::unreachable(message);
         }