add config for disabling mdns

docker/sbtc/signer/signer-config.toml

@@ -231,3 +231,12 @@ listen_on = []
 # Required: false
 # Environment: SIGNER_SIGNER__P2P__PUBLIC_ENDPOINTS
 public_endpoints = []
+
+# Enables/disables mDNS (multicast DNS) discovery. mDNS allows sBTC signers
+# running on the same local network to discover each other without explicitly
+# providing them as seed nodes.
+#
+# Default: false
+# Required: false
+# Environment: SIGNER_SIGNER__P2P__ENABLE_MDNS
+enable_mdns = false

signer/src/config/default.toml

@@ -241,3 +241,12 @@ listen_on = ["tcp://0.0.0.0:4122", "quic-v1://0.0.0.0:4122"]
 # Required: false
 # Environment: SIGNER_SIGNER__P2P__PUBLIC_ENDPOINTS
 public_endpoints = []
+
+# Enables/disables mDNS (multicast DNS) discovery. mDNS allows sBTC signers
+# running on the same local network to discover each other without explicitly
+# providing them as seed nodes.
+#
+# Default: false
+# Required: false
+# Environment: SIGNER_SIGNER__P2P__ENABLE_MDNS
+enable_mdns = true

signer/src/config/mod.rs

@@ -129,6 +129,10 @@ pub struct P2PNetworkConfig {
     /// public endpoint(s).
     #[serde(deserialize_with = "p2p_multiaddr_deserializer_vec")]
     pub public_endpoints: Vec<Multiaddr>,
+    /// Enable mDNS discovery for the P2P network. This is useful for local
+    /// testing and development.
+    #[serde(default)]
+    pub enable_mdns: bool,
 }
 
 impl Validatable for P2PNetworkConfig {

signer/src/network/libp2p/event_loop.rs

@@ -304,6 +304,11 @@ fn handle_mdns_event(swarm: &mut Swarm<SignerBehavior>, ctx: &impl Context, even
         // so this will never be raised for WAN peers which must otherwise
         // be discovered via seed nodes.
         Event::Discovered(peers) => {
+            // If we have disabled mDNS, we should not process this event.
+            if !ctx.config().signer.p2p.enable_mdns {
+                return;
+            }
+
             for (peer_id, addr) in peers {
                 if !ctx.state().current_signer_set().is_allowed_peer(&peer_id) {
                     tracing::warn!(%peer_id, %addr, "Discovered peer via mDNS, however it is not a known signer; ignoring");
@@ -320,6 +325,10 @@ fn handle_mdns_event(swarm: &mut Swarm<SignerBehavior>, ctx: &impl Context, even
         Event::Expired(peers) => {
             for (peer_id, addr) in peers {
                 tracing::info!(%peer_id, %addr, "Expired peer via mDNS");
+                swarm
+                    .behaviour_mut()
+                    .gossipsub
+                    .remove_explicit_peer(&peer_id);
             }
         }
     }