fix(net): Fix off-by-one error in DNS seed peer retries, and clarify logs

zebra-network/src/config.rs

@@ -1,3 +1,5 @@
+//! Configuration for Zebra's network communication.
+
 use std::{
     collections::HashSet,
     net::{IpAddr, SocketAddr},
@@ -24,7 +26,14 @@ mod tests;
 
 /// The number of times Zebra will retry each initial peer's DNS resolution,
 /// before checking if any other initial peers have returned addresses.
-const MAX_SINGLE_PEER_RETRIES: usize = 1;
+///
+/// After doing this number of retries of a failed single peer, Zebra will
+/// check if it has enough peer addresses from other seed peers. If it has
+/// enough addresses, it won't retry this peer again.
+///
+/// If the number of retries is `0`, other peers are checked after every successful
+/// or failed DNS attempt.
+const MAX_SINGLE_SEED_PEER_DNS_RETRIES: usize = 0;
 
 /// Configuration for networking code.
 #[derive(Clone, Debug, Serialize)]
@@ -164,7 +173,7 @@ impl Config {
             // address peers. Individual retries avoid this issue.
             let peer_addresses = peers
                 .iter()
-                .map(|s| Config::resolve_host(s, MAX_SINGLE_PEER_RETRIES))
+                .map(|s| Config::resolve_host(s, MAX_SINGLE_SEED_PEER_DNS_RETRIES))
                 .collect::<futures::stream::FuturesUnordered<_>>()
                 .concat()
                 .await;
@@ -188,12 +197,25 @@ impl Config {
     ///
     /// If DNS continues to fail, returns an empty list of addresses.
     async fn resolve_host(host: &str, max_retries: usize) -> HashSet<SocketAddr> {
-        for retry_count in 1..=max_retries {
-            match Config::resolve_host_once(host).await {
-                Ok(addresses) => return addresses,
-                Err(_) => tracing::info!(?host, ?retry_count, "Retrying peer DNS resolution"),
-            };
-            tokio::time::sleep(DNS_LOOKUP_TIMEOUT).await;
+        for retries in 0..=max_retries {
+            if let Ok(addresses) = Config::resolve_host_once(host).await {
+                return addresses;
+            }
+
+            if retries < max_retries {
+                tracing::info!(
+                    ?host,
+                    previous_attempts = ?(retries + 1),
+                    "Waiting {DNS_LOOKUP_TIMEOUT:?} to retry seed peer DNS resolution",
+                );
+                tokio::time::sleep(DNS_LOOKUP_TIMEOUT).await;
+            } else {
+                tracing::info!(
+                    ?host,
+                    attempts = ?(retries + 1),
+                    "Seed peer DNS resolution failed, checking for addresses from other seed peers",
+                );
+            }
         }
 
         HashSet::new()