feat: extend announce_ip to accept hostnames

Add new 'announce' field to ListenerConfig that accepts both IP addresses
and hostnames for proxy link generation. The old 'announce_ip' field is
deprecated but still supported via automatic migration.

Changes:
- Add 'announce: Option<String>' field to ListenerConfig
- Add migration logic: announce_ip → announce if announce not set
- Update main.rs to use announce field for link generation
- Support both hostnames (e.g., 'proxy.example.com') and IPs

Backward compatible: existing configs using announce_ip continue to work.

src/config/mod.rs

@@ -497,6 +497,12 @@ pub struct UpstreamConfig {
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ListenerConfig {
     pub ip: IpAddr,
+    /// IP address or hostname to announce in proxy links.
+    /// Takes precedence over `announce_ip` if both are set.
+    #[serde(default)]
+    pub announce: Option<String>,
+    /// Deprecated: Use `announce` instead. IP address to announce in proxy links.
+    /// Migrated to `announce` automatically if `announce` is not set.
     #[serde(default)]
     pub announce_ip: Option<IpAddr>,
 }
@@ -716,6 +722,7 @@ impl ProxyConfig {
             if let Ok(ipv4) = ipv4_str.parse::<IpAddr>() {
                 config.server.listeners.push(ListenerConfig {
                     ip: ipv4,
+                    announce: None,
                     announce_ip: None,
                 });
             }
@@ -723,12 +730,20 @@ impl ProxyConfig {
                 if let Ok(ipv6) = ipv6_str.parse::<IpAddr>() {
                     config.server.listeners.push(ListenerConfig {
                         ip: ipv6,
+                        announce: None,
                         announce_ip: None,
                     });
                 }
             }
         }
 
+        // Migration: announce_ip → announce for each listener
+        for listener in &mut config.server.listeners {
+            if listener.announce.is_none() && listener.announce_ip.is_some() {
+                listener.announce = Some(listener.announce_ip.unwrap().to_string());
+            }
+        }
+
         // Migration: show_link (top-level) → general.links.show
         if !config.show_link.is_empty() && config.general.links.show.is_empty() {
             config.general.links.show = config.show_link.clone();

src/main.rs

@@ -563,22 +563,28 @@ match crate::transport::middle_proxy::fetch_proxy_secret(proxy_secret_path).awai
                 let listener = TcpListener::from_std(socket.into())?;
                 info!("Listening on {}", addr);
 
-                let public_ip = if let Some(ip) = listener_conf.announce_ip {
-                    ip
+                // Resolve the public host for link generation
+                let public_host = if let Some(ref announce) = listener_conf.announce {
+                    announce.clone()  // Use announce (IP or hostname) if explicitly set
                 } else if listener_conf.ip.is_unspecified() {
+                    // Auto-detect for unspecified addresses
                     if listener_conf.ip.is_ipv4() {
-                        detected_ip.ipv4.unwrap_or(listener_conf.ip)
+                        detected_ip.ipv4
+                            .map(|ip| ip.to_string())
+                            .unwrap_or_else(|| listener_conf.ip.to_string())
                     } else {
-                        detected_ip.ipv6.unwrap_or(listener_conf.ip)
+                        detected_ip.ipv6
+                            .map(|ip| ip.to_string())
+                            .unwrap_or_else(|| listener_conf.ip.to_string())
                     }
                 } else {
-                    listener_conf.ip
+                    listener_conf.ip.to_string()
                 };
 
                 // Show per-listener proxy links only when public_host is not set
                 if config.general.links.public_host.is_none() && !config.general.links.show.is_empty() {
                     let link_port = config.general.links.public_port.unwrap_or(config.server.port);
-                    print_proxy_links(&public_ip.to_string(), link_port, &config);
+                    print_proxy_links(&public_host, link_port, &config);
                 }
 
                 listeners.push(listener);