fix(agent-tunnel): bind QUIC sockets dual-stack

Both the gateway listener and the agent client socket previously bound
to 0.0.0.0 (IPv4 only). When the agent's DNS resolution for the
gateway endpoint returns an IPv6 address first — the default for
`localhost` on modern Windows/Linux, and common for any name with a
AAAA record — quinn refuses to send to that peer over a v4 socket and
the tunnel never connects. Bind to `[::]` instead so both ends accept
v4 and v6.

Author: irvingoujAtDevolution

devolutions-agent/src/tunnel.rs

@@ -337,8 +337,11 @@ async fn run_single_connection(
 
     // -- Connect --
 
+    // Bind to the IPv6 unspecified address so the client socket is dual-stack.
+    // A v4-only socket (0.0.0.0:0) cannot reach a peer resolved to an IPv6 address,
+    // which is the default `localhost`/AAAA-record case on modern systems.
     let mut endpoint =
-        quinn::Endpoint::client("0.0.0.0:0".parse().context("parse bind address")?).context("create QUIC endpoint")?;
+        quinn::Endpoint::client("[::]:0".parse().context("parse bind address")?).context("create QUIC endpoint")?;
     endpoint.set_default_client_config(client_config);
 
     let connection = endpoint

devolutions-gateway/src/service.rs

@@ -283,7 +283,10 @@ async fn spawn_tasks(conf_handle: ConfHandle) -> anyhow::Result<Tasks> {
         let ca_manager = agent_tunnel::cert::CaManager::load_or_generate(&data_dir)
             .context("failed to initialize agent tunnel CA")?;
 
-        let listen_addr = std::net::SocketAddr::from((std::net::Ipv4Addr::UNSPECIFIED, conf.agent_tunnel.listen_port));
+        // Bind to the IPv6 unspecified address so the listener is dual-stack and
+        // accepts both IPv4 and IPv6 agent connections (matters when an agent's DNS
+        // resolution returns an IPv6 address for the configured gateway endpoint).
+        let listen_addr = std::net::SocketAddr::from((std::net::Ipv6Addr::UNSPECIFIED, conf.agent_tunnel.listen_port));
 
         let (listener, handle) =
             agent_tunnel::AgentTunnelListener::bind(listen_addr, Arc::clone(&ca_manager), hostname)