fix(iroh-net): use try_send rather than send so we dont block the local swarm discovery service

iroh-net/src/discovery.rs

@@ -158,6 +158,8 @@ pub trait Discovery: std::fmt::Debug + Send + Sync {
     /// until the stream is actually polled. To avoid missing discovered nodes,
     /// poll the stream as soon as possible.
     ///
+    /// If you do not regularly poll the stream, you may miss discovered nodes.
+    ///
     /// Any discovery systems that only discover when explicitly resolving a
     /// specific [`NodeId`] do not need to implement this method. Any nodes or
     /// addresses that are discovered by calling `resolve` should NOT be added

iroh-net/src/discovery/local_swarm_discovery.rs

@@ -47,7 +47,10 @@ use watchable::Watchable;
 
 use iroh_base::key::PublicKey;
 use swarm_discovery::{Discoverer, DropGuard, IpClass, Peer};
-use tokio::{sync::mpsc, task::JoinSet};
+use tokio::{
+    sync::mpsc::{self, error::TrySendError},
+    task::JoinSet,
+};
 use tokio_util::task::AbortOnDropHandle;
 
 use crate::{
@@ -107,8 +110,13 @@ impl Subscribers {
         let mut clean_up = vec![];
         for (i, subscriber) in self.0.iter().enumerate() {
             // assume subscriber was dropped
-            if (subscriber.send(item.clone()).await).is_err() {
-                clean_up.push(i);
+            if let Err(err) = subscriber.try_send(item.clone()) {
+                match err {
+                    TrySendError::Full(_) => {
+                        warn!("local swarm discovery subscriber {i} is blocked, dropping item {item:?}")
+                    }
+                    TrySendError::Closed(_) => clean_up.push(i),
+                }
             }
         }
         for i in clean_up.into_iter().rev() {