feat(identify): immediately run identify protocol on new connections

protocols/identify/CHANGELOG.md

@@ -4,8 +4,12 @@
 - Raise MSRV to 1.65.
   See [PR 3715].
 
+- Reduce the initial delay before running the identify protocol to 0 and make the option deprecated.
+  See [PR 3545].
+
 [PR 3698]: https://github.com/libp2p/rust-libp2p/pull/3698
 [PR 3715]: https://github.com/libp2p/rust-libp2p/pull/3715
+[PR 3545]: https://github.com/libp2p/rust-libp2p/pull/3545
 
 ## 0.42.2
 

protocols/identify/src/behaviour.rs

@@ -88,7 +88,10 @@ pub struct Config {
     /// The initial delay before the first identification request
     /// is sent to a remote on a newly established connection.
     ///
-    /// Defaults to 500ms.
+    /// Defaults to 0ms.
+    #[deprecated(note = "The `initial_delay` is no longer necessary and will be
+                completely removed since a remote should be able to instantly
+                answer to an identify request")]
     pub initial_delay: Duration,
     /// The interval at which identification requests are sent to
     /// the remote on established connections after the first request,
@@ -117,12 +120,13 @@ pub struct Config {
 impl Config {
     /// Creates a new configuration for the identify [`Behaviour`] that
     /// advertises the given protocol version and public key.
+    #[allow(deprecated)]
     pub fn new(protocol_version: String, local_public_key: PublicKey) -> Self {
         Self {
             protocol_version,
             agent_version: format!("rust-libp2p/{}", env!("CARGO_PKG_VERSION")),
             local_public_key,
-            initial_delay: Duration::from_millis(500),
+            initial_delay: Duration::from_millis(0),
             interval: Duration::from_secs(5 * 60),
             push_listen_addr_updates: false,
             cache_size: 100,
@@ -137,6 +141,10 @@ impl Config {
 
     /// Configures the initial delay before the first identification
     /// request is sent on a newly established connection to a peer.
+    #[deprecated(note = "The `initial_delay` is no longer necessary and will be
+                completely removed since a remote should be able to instantly
+                answer to an identify request thus also this setter will be removed")]
+    #[allow(deprecated)]
     pub fn with_initial_delay(mut self, d: Duration) -> Self {
         self.initial_delay = d;
         self
@@ -239,6 +247,7 @@ impl NetworkBehaviour for Behaviour {
     type ConnectionHandler = Handler;
     type OutEvent = Event;
 
+    #[allow(deprecated)]
     fn handle_established_inbound_connection(
         &mut self,
         _: ConnectionId,
@@ -257,6 +266,7 @@ impl NetworkBehaviour for Behaviour {
         ))
     }
 
+    #[allow(deprecated)]
     fn handle_established_outbound_connection(
         &mut self,
         _: ConnectionId,
@@ -737,6 +747,7 @@ mod tests {
 
         let mut swarm1 = {
             let (pubkey, transport) = transport();
+            #[allow(deprecated)]
             let protocol = Behaviour::new(
                 Config::new("a".to_string(), pubkey.clone())
                     // `swarm1` will set `KeepAlive::No` once it identified `swarm2` and thus