fix: don't use extra STUN nine server for fallback

just fallback to turn.delta.chat
which also answers STUN "what is my IP address" requests.

src/calls.rs

@@ -42,7 +42,7 @@ const RINGING_SECONDS: i64 = 120;
 const CALL_ACCEPTED_TIMESTAMP: Param = Param::Arg;
 const CALL_ENDED_TIMESTAMP: Param = Param::Arg4;
 
-const STUN_PORT: u16 = 3478;
+const TURN_PORT: u16 = 3478;
 
 /// Set if incoming call was ended explicitly
 /// by the other side before we accepted it.
@@ -658,12 +658,9 @@ pub(crate) async fn create_ice_servers_from_metadata(
     Ok((expiration_timestamp, ice_servers))
 }
 
-/// STUN or TURN server with unresolved DNS name.
+/// TURN server with unresolved DNS name.
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
 pub(crate) enum UnresolvedIceServer {
-    /// STUN server.
-    Stun { hostname: String, port: u16 },
-
     /// TURN server with the username and password.
     Turn {
         hostname: String,
@@ -688,28 +685,6 @@ pub(crate) async fn resolve_ice_servers(
 
     for unresolved_ice_server in unresolved_ice_servers {
         match unresolved_ice_server {
-            UnresolvedIceServer::Stun { hostname, port } => {
-                match lookup_host_with_cache(context, &hostname, port, "", load_cache).await {
-                    Ok(addrs) => {
-                        let urls: Vec<String> = addrs
-                            .into_iter()
-                            .map(|addr| format!("stun:{addr}"))
-                            .collect();
-                        let stun_server = IceServer {
-                            urls,
-                            username: None,
-                            credential: None,
-                        };
-                        result.push(stun_server);
-                    }
-                    Err(err) => {
-                        warn!(
-                            context,
-                            "Failed to resolve STUN {hostname}:{port}: {err:#}."
-                        );
-                    }
-                }
-            }
             UnresolvedIceServer::Turn {
                 hostname,
                 port,
@@ -742,25 +717,17 @@ pub(crate) async fn resolve_ice_servers(
 
 /// Creates JSON with ICE servers when no TURN servers are known.
 pub(crate) fn create_fallback_ice_servers() -> Vec<UnresolvedIceServer> {
-    // Do not use public STUN server from https://stunprotocol.org/.
-    // It changes the hostname every year
-    // (e.g. stunserver2025.stunprotocol.org
-    // which was previously stunserver2024.stunprotocol.org)
-    // because of bandwidth costs:
-    // <https://github.com/jselbie/stunserver/issues/50>
-
-    vec![
-        UnresolvedIceServer::Stun {
-            hostname: "nine.testrun.org".to_string(),
-            port: STUN_PORT,
-        },
-        UnresolvedIceServer::Turn {
-            hostname: "turn.delta.chat".to_string(),
-            port: STUN_PORT,
-            username: "public".to_string(),
-            credential: "o4tR7yG4rG2slhXqRUf9zgmHz".to_string(),
-        },
-    ]
+    // As long as we can't rely on most chat profiles
+    // having a multi-relay setup and offering TURN servers,
+    // fall back to a service run by Delta Chat developers
+    // which ensures that no IP addresses or other metadata is
+    // persistently logged.
+    vec![UnresolvedIceServer::Turn {
+        hostname: "turn.delta.chat".to_string(),
+        port: TURN_PORT,
+        username: "public".to_string(),
+        credential: "o4tR7yG4rG2slhXqRUf9zgmHz".to_string(),
+    }]
 }
 
 /// Returns JSON with ICE servers.

src/calls/calls_tests.rs

@@ -779,3 +779,13 @@ async fn test_end_text_call() -> Result<()> {
 
     Ok(())
 }
+
+/// Tests that fallback ice servers just carry the Turn one
+#[test]
+fn test_fallback_ice_servers() {
+    let hostnames: Vec<String> = create_fallback_ice_servers()
+        .into_iter()
+        .map(|UnresolvedIceServer::Turn { hostname, .. }| hostname)
+        .collect();
+    assert_eq!(hostnames, ["turn.delta.chat"]);
+}