Nat hole punching for discv5.2

src/error.rs

@@ -1,4 +1,7 @@
-use crate::{handler::Challenge, node_info::NonContactable};
+use crate::{
+    handler::Challenge,
+    node_info::{NodeAddress, NonContactable},
+};
 use derive_more::From;
 use rlp::DecoderError;
 use std::fmt;
@@ -33,6 +36,8 @@ pub enum Discv5Error {
     ServiceAlreadyStarted,
     /// A session could not be established with the remote.
     SessionNotEstablished,
+    /// A session to the given peer is already established.
+    SessionAlreadyEstablished(NodeAddress),
     /// An RLP decoding error occurred.
     RLPError(DecoderError),
     /// Failed to encrypt a message.

src/handler/mod.rs

@@ -559,6 +559,11 @@ impl Handler {
                     .on_request_time_out::<P>(relay, local_enr, nonce, target)
                     .await
                 {
+                    Err(NatError::Initiator(Discv5Error::SessionAlreadyEstablished(
+                        node_address,
+                    ))) => {
+                        debug!("Session to peer already established, aborting hole punch attempt. Peer: {node_address}");
+                    }
                     Err(e) => {
                         warn!("Failed to start hole punching. Error: {:?}", e);
                     }
@@ -1608,7 +1613,9 @@ impl Handler {
     ) -> Result<(), NatError> {
         // Another hole punch process with this target may have just completed.
         if self.sessions.get(&target_node_address).is_some() {
-            return Ok(());
+            return Err(NatError::Initiator(Discv5Error::SessionAlreadyEstablished(
+                target_node_address,
+            )));
         }
         if let Some(session) = self.sessions.get_mut(&relay) {
             let relay_init_notif =