feat(swarm): allow configuration to idle connection timeout

Previously, a connection would be shut down immediately as soon as its `ConnectionHandler` reports `KeepAlive::No`. As we have gained experience with libp2p, it turned out that this isn't ideal.

For one, tests often need to keep connections alive longer than the configured protocols require. Plus, some usecases require connections to be kept alive in general.

Both of these needs are currently served by the `keep_alive::Behaviour`. That one does essentially nothing other than statically returning `KeepAlive::Yes` from its `ConnectionHandler`.

It makes much more sense to deprecate `keep_alive::Behaviour` and instead allow users to globally configure an `idle_conncetion_timeout` on the `Swarm`. This timeout comes into effect once a `ConnectionHandler` reports `KeepAlive::No`. To start with, this timeout is 0. Together with https://github.com/libp2p/rust-libp2p/issues/3844, this will allow us to move towards a much more aggressive closing of idle connections, together with a more ergonomic way of opting out of this behaviour.

Fixes #4121.

Pull-Request: #4161.

examples/browser-webrtc/src/main.rs

@@ -13,11 +13,12 @@ use libp2p::{
     identity,
     multiaddr::{Multiaddr, Protocol},
     ping,
-    swarm::{keep_alive, NetworkBehaviour, SwarmBuilder, SwarmEvent},
+    swarm::{SwarmBuilder, SwarmEvent},
 };
 use libp2p_webrtc as webrtc;
 use rand::thread_rng;
 use std::net::{Ipv4Addr, SocketAddr};
+use std::time::Duration;
 use tower_http::cors::{Any, CorsLayer};
 
 #[tokio::main]
@@ -36,12 +37,10 @@ async fn main() -> anyhow::Result<()> {
     .map(|(peer_id, conn), _| (peer_id, StreamMuxerBox::new(conn)))
     .boxed();
 
-    let behaviour = Behaviour {
-        ping: ping::Behaviour::new(ping::Config::new()),
-        keep_alive: keep_alive::Behaviour,
-    };
-
-    let mut swarm = SwarmBuilder::with_tokio_executor(transport, behaviour, local_peer_id).build();
+    let mut swarm =
+        SwarmBuilder::with_tokio_executor(transport, ping::Behaviour::default(), local_peer_id)
+            .idle_connection_timeout(Duration::from_secs(30)) // Allows us to observe the pings.
+            .build();
 
     let address_webrtc = Multiaddr::from(Ipv4Addr::UNSPECIFIED)
         .with(Protocol::Udp(0))
@@ -84,12 +83,6 @@ async fn main() -> anyhow::Result<()> {
     Ok(())
 }
 
-#[derive(NetworkBehaviour)]
-struct Behaviour {
-    ping: ping::Behaviour,
-    keep_alive: keep_alive::Behaviour,
-}
-
 #[derive(rust_embed::RustEmbed)]
 #[folder = "$CARGO_MANIFEST_DIR/static"]
 struct StaticFiles;