Grabbing unknown dc into unknown-dc.txt

src/config/mod.rs

@@ -54,6 +54,10 @@ fn default_metrics_whitelist() -> Vec<IpAddr> {
     vec!["127.0.0.1".parse().unwrap(), "::1".parse().unwrap()]
 }
 
+fn default_unknown_dc_log_path() -> Option<String> {
+    Some("unknown-dc.txt".to_string())
+}
+
 // ============= Custom Deserializers =============
 
 #[derive(Deserialize)]
@@ -242,6 +246,10 @@ pub struct GeneralConfig {
     #[serde(default)]
     pub stun_iface_mismatch_ignore: bool,
 
+    /// Log unknown (non-standard) DC requests to a file (default: unknown-dc.txt). Set to null to disable.
+    #[serde(default = "default_unknown_dc_log_path")]
+    pub unknown_dc_log_path: Option<String>,
+
     #[serde(default)]
     pub log_level: LogLevel,
 
@@ -263,6 +271,7 @@ impl Default for GeneralConfig {
             middle_proxy_nat_probe: false,
             middle_proxy_nat_stun: None,
             stun_iface_mismatch_ignore: false,
+            unknown_dc_log_path: default_unknown_dc_log_path(),
             log_level: LogLevel::Normal,
             disable_colors: false,
         }

src/proxy/direct_relay.rs

@@ -1,3 +1,5 @@
+use std::fs::OpenOptions;
+use std::io::Write;
 use std::net::SocketAddr;
 use std::sync::Arc;
 
@@ -113,6 +115,16 @@ fn get_dc_addr_static(dc_idx: i16, config: &ProxyConfig) -> Result<SocketAddr> {
         return Ok(SocketAddr::new(datacenters[abs_dc - 1], TG_DATACENTER_PORT));
     }
 
+    // Unknown DC requested by client without override: log and fall back.
+    if !config.dc_overrides.contains_key(&dc_key) {
+        warn!(dc_idx = dc_idx, "Requested non-standard DC with no override; falling back to default cluster");
+        if let Some(path) = &config.general.unknown_dc_log_path {
+            if let Ok(mut file) = OpenOptions::new().create(true).append(true).open(path) {
+                let _ = writeln!(file, "dc_idx={dc_idx}");
+            }
+        }
+    }
+
     let default_dc = config.default_dc.unwrap_or(2) as usize;
     let fallback_idx = if default_dc >= 1 && default_dc <= num_dcs {
         default_dc - 1