feat(swarm)!: allow NetworkBehaviours to manage connections

Previously, a `ConnectionHandler` was immediately requested from the `NetworkBehaviour` as soon as a new dial was initiated or a new incoming connection accepted.

With this patch, we delay the creation of the handler until the connection is actually established and fully upgraded, i.e authenticated and multiplexed.

As a consequence, `NetworkBehaviour::new_handler` is now deprecated in favor of a new set of callbacks:

- `NetworkBehaviour::handle_pending_inbound_connection`
- `NetworkBehaviour::handle_pending_outbound_connection`
- `NetworkBehaviour::handle_established_inbound_connection`
- `NetworkBehaviour::handle_established_outbound_connection`

All callbacks are fallible, allowing the `NetworkBehaviour` to abort the connection either immediately or after it is fully established. All callbacks also receive a `ConnectionId` parameter which uniquely identifies the connection. For example, in case a `NetworkBehaviour` issues a dial via `NetworkBehaviourAction::Dial`, it can unambiguously detect this dial in these lifecycle callbacks via the `ConnectionId`.

Finally, `NetworkBehaviour::handle_pending_outbound_connection` also replaces `NetworkBehaviour::addresses_of_peer` by allowing the behaviour to return more addresses to be used for the dial.

Resolves libp2p#2824.

Pull-Request: libp2p#3254.

src/behaviour.rs

@@ -37,8 +37,8 @@ use libp2p_swarm::{
         AddressChange, ConnectionClosed, ConnectionEstablished, DialFailure, ExpiredExternalAddr,
         ExpiredListenAddr, FromSwarm,
     },
-    ConnectionId, ExternalAddresses, ListenAddresses, NetworkBehaviour, NetworkBehaviourAction,
-    PollParameters, THandlerInEvent, THandlerOutEvent,
+    ConnectionDenied, ConnectionId, ExternalAddresses, ListenAddresses, NetworkBehaviour,
+    NetworkBehaviourAction, PollParameters, THandler, THandlerInEvent, THandlerOutEvent,
 };
 use std::{
     collections::{HashMap, VecDeque},
@@ -485,12 +485,55 @@ impl NetworkBehaviour for Behaviour {
         }
     }
 
-    fn new_handler(&mut self) -> Self::ConnectionHandler {
-        self.inner.new_handler()
+    fn handle_pending_inbound_connection(
+        &mut self,
+        connection_id: ConnectionId,
+        local_addr: &Multiaddr,
+        remote_addr: &Multiaddr,
+    ) -> Result<(), ConnectionDenied> {
+        self.inner
+            .handle_pending_inbound_connection(connection_id, local_addr, remote_addr)
+    }
+
+    fn handle_established_inbound_connection(
+        &mut self,
+        _connection_id: ConnectionId,
+        peer: PeerId,
+        local_addr: &Multiaddr,
+        remote_addr: &Multiaddr,
+    ) -> Result<THandler<Self>, ConnectionDenied> {
+        self.inner.handle_established_inbound_connection(
+            _connection_id,
+            peer,
+            local_addr,
+            remote_addr,
+        )
     }
 
-    fn addresses_of_peer(&mut self, peer: &PeerId) -> Vec<Multiaddr> {
-        self.inner.addresses_of_peer(peer)
+    fn handle_pending_outbound_connection(
+        &mut self,
+        _connection_id: ConnectionId,
+        maybe_peer: Option<PeerId>,
+        _addresses: &[Multiaddr],
+        _effective_role: Endpoint,
+    ) -> Result<Vec<Multiaddr>, ConnectionDenied> {
+        self.inner.handle_pending_outbound_connection(
+            _connection_id,
+            maybe_peer,
+            _addresses,
+            _effective_role,
+        )
+    }
+
+    fn handle_established_outbound_connection(
+        &mut self,
+        _connection_id: ConnectionId,
+        peer: PeerId,
+        addr: &Multiaddr,
+        role_override: Endpoint,
+    ) -> Result<THandler<Self>, ConnectionDenied> {
+        self.inner
+            .handle_established_outbound_connection(_connection_id, peer, addr, role_override)
     }
 
     fn on_swarm_event(&mut self, event: FromSwarm<Self::ConnectionHandler>) {