From 1086efc8be8bc6abc06d1e3d38e8ebfdc933cdd7 Mon Sep 17 00:00:00 2001
From: James Pine <ijamespine@me.com>
Date: Fri, 17 Apr 2026 18:39:28 -0700
Subject: [PATCH] fall back to pkarr+DNS discovery when mDNS port is
 unavailable
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Iroh's endpoint.bind() fails wholesale if any configured discovery service
fails to initialize. MdnsDiscovery requires binding UDP :5353, which on
most Linux systems (including TrueNAS) is already owned by avahi-daemon.
Result: endpoint creation errors out with "Service 'mdns' error", the
event loop never starts, command_sender stays None, and protocol
registration fails — so sd-server has no working networking at all.

Make mDNS best-effort: on any error whose message mentions "mdns",
retry endpoint creation with only pkarr + DNS discovery. Local-network
auto-discovery is lost but remote pairing via node ID (which uses n0's
DNS infrastructure, not mDNS) continues to work normally.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 core/src/service/network/core/mod.rs | 98 +++++++++++++++++++---------
 1 file changed, 68 insertions(+), 30 deletions(-)

diff --git a/core/src/service/network/core/mod.rs b/core/src/service/network/core/mod.rs
index 5edae2bc2..7497ded37 100644
--- a/core/src/service/network/core/mod.rs
+++ b/core/src/service/network/core/mod.rs
@@ -213,40 +213,78 @@ impl NetworkingService {
 		// - mDNS for local network discovery
 		// - PkarrPublisher to publish our address to dns.iroh.link (enables remote discovery)
 		// - DnsDiscovery to resolve other nodes from dns.iroh.link
-		let endpoint = Endpoint::builder()
-			.secret_key(secret_key)
-			.alpns(vec![
-				PAIRING_ALPN.to_vec(),
-				FILE_TRANSFER_ALPN.to_vec(),
-				MESSAGING_ALPN.to_vec(),
-				SYNC_ALPN.to_vec(),
-				JOB_ACTIVITY_ALPN.to_vec(),
-			])
-			.relay_mode(iroh::RelayMode::Default)
-			.discovery(MdnsDiscovery::builder())
-			.discovery(PkarrPublisher::n0_dns())
-			.discovery(DnsDiscovery::n0_dns())
-			.bind_addr_v4(std::net::SocketAddrV4::new(
-				std::net::Ipv4Addr::UNSPECIFIED,
-				0,
-			))
-			.bind_addr_v6(std::net::SocketAddrV6::new(
-				std::net::Ipv6Addr::UNSPECIFIED,
-				0,
-				0,
-				0,
-			))
-			.bind()
-			.await
-			.map_err(|e| NetworkingError::Transport(format!("Failed to create endpoint: {}", e)))?;
+		//
+		// mDNS is best-effort: on hosts where another service (e.g. avahi-daemon
+		// on most Linux boxes / TrueNAS) already owns UDP :5353, Iroh's own mDNS
+		// service can't bind and endpoint creation fails wholesale. Fall back to
+		// pkarr + DNS-only discovery in that case — remote pairing via node ID
+		// continues to work, we just lose local-network auto-discovery.
+		let build_endpoint = |with_mdns: bool| {
+			let mut builder = Endpoint::builder()
+				.secret_key(secret_key.clone())
+				.alpns(vec![
+					PAIRING_ALPN.to_vec(),
+					FILE_TRANSFER_ALPN.to_vec(),
+					MESSAGING_ALPN.to_vec(),
+					SYNC_ALPN.to_vec(),
+					JOB_ACTIVITY_ALPN.to_vec(),
+				])
+				.relay_mode(iroh::RelayMode::Default)
+				.discovery(PkarrPublisher::n0_dns())
+				.discovery(DnsDiscovery::n0_dns())
+				.bind_addr_v4(std::net::SocketAddrV4::new(
+					std::net::Ipv4Addr::UNSPECIFIED,
+					0,
+				))
+				.bind_addr_v6(std::net::SocketAddrV6::new(
+					std::net::Ipv6Addr::UNSPECIFIED,
+					0,
+					0,
+					0,
+				));
+			if with_mdns {
+				builder = builder.discovery(MdnsDiscovery::builder());
+			}
+			builder.bind()
+		};
+
+		let endpoint = match build_endpoint(true).await {
+			Ok(ep) => {
+				self.logger
+					.info("Endpoint bound successfully with mDNS + pkarr discovery enabled")
+					.await;
+				ep
+			}
+			Err(e) => {
+				let err_str = e.to_string().to_lowercase();
+				if err_str.contains("mdns") {
+					self.logger
+						.warn(&format!(
+							"mDNS discovery unavailable ({}); retrying with pkarr + DNS only. \
+							 Local-network auto-discovery is disabled on this host, but remote \
+							 pairing via node ID will still work.",
+							e
+						))
+						.await;
+					let ep = build_endpoint(false).await.map_err(|e| {
+						NetworkingError::Transport(format!("Failed to create endpoint: {}", e))
+					})?;
+					self.logger
+						.info("Endpoint bound successfully without mDNS (pkarr + DNS only)")
+						.await;
+					ep
+				} else {
+					return Err(NetworkingError::Transport(format!(
+						"Failed to create endpoint: {}",
+						e
+					)));
+				}
+			}
+		};
 
 		// Store endpoint reference for other methods
 		self.endpoint = Some(endpoint.clone());
 
-		self.logger
-			.info("Endpoint bound successfully with mDNS + pkarr discovery enabled")
-			.await;
-
 		// Create and start event loop
 		let event_loop = NetworkingEventLoop::new(
 			endpoint,