MCP: Fix stale state after server crash

vdavid · vdavid · commit 0369d219be52 · 2026-03-18T13:19:25.000+01:00
- Extract `is_port_available` and `find_available_port` into shared `net.rs` module, removing duplicate in `mcp/server.rs` and making `commands/settings.rs` a thin pass-through
- Use `MCP_ACTUAL_PORT` as the single source of truth for `is_mcp_running()` instead of checking handle existence (stale handles from crashed tasks returned false positives)
- Reset `MCP_ACTUAL_PORT` to 0 when the server task exits for any reason (crash or graceful shutdown), so the frontend always sees the correct state
diff --git a/apps/desktop/src-tauri/src/commands/settings.rs b/apps/desktop/src-tauri/src/commands/settings.rs
@@ -1,7 +1,5 @@
 //! Settings-related commands.
 
-use std::net::TcpListener;
-
 use tauri::{AppHandle, Manager};
 
 use crate::file_system::update_debounce_ms;
@@ -16,20 +14,14 @@ use crate::network::mdns_discovery::update_resolve_timeout;
 /// Check if a port is available for binding.
 #[tauri::command]
 pub fn check_port_available(port: u16) -> bool {
-    TcpListener::bind(("127.0.0.1", port)).is_ok()
+    crate::net::is_port_available(port)
 }
 
 /// Find an available port starting from the given port.
 /// Scans up to 100 ports from the start port.
 #[tauri::command]
 pub fn find_available_port(start_port: u16) -> Option<u16> {
-    for offset in 0..100 {
-        let port = start_port.saturating_add(offset);
-        if check_port_available(port) {
-            return Some(port);
-        }
-    }
-    None
+    crate::net::find_available_port(start_port)
 }
 
 /// Updates the file watcher debounce duration in milliseconds.
diff --git a/apps/desktop/src-tauri/src/lib.rs b/apps/desktop/src-tauri/src/lib.rs
@@ -94,6 +94,7 @@ mod linux_icons;
 mod macos_icons;
 mod mcp;
 mod menu;
+mod net;
 #[cfg(any(target_os = "macos", target_os = "linux"))]
 mod mtp;
 #[cfg(any(target_os = "macos", target_os = "linux"))]
diff --git a/apps/desktop/src-tauri/src/mcp/server.rs b/apps/desktop/src-tauri/src/mcp/server.rs
@@ -61,17 +61,6 @@ impl<R: Runtime> McpState<R> {
     }
 }
 
-/// Find an available port starting from `start_port`, scanning up to 100 ports.
-fn find_available_port(start_port: u16) -> Option<u16> {
-    for offset in 0..100 {
-        let port = start_port.saturating_add(offset);
-        if std::net::TcpListener::bind(("127.0.0.1", port)).is_ok() {
-            return Some(port);
-        }
-    }
-    None
-}
-
 /// Start the MCP server. Binds to the configured port and spawns the server task.
 /// If the configured port is taken, auto-probes upward to find the next available port.
 pub async fn start_mcp_server<R: Runtime + 'static>(app: AppHandle<R>, config: McpConfig) -> Result<(), String> {
@@ -89,7 +78,7 @@ pub async fn start_mcp_server<R: Runtime + 'static>(app: AppHandle<R>, config: M
     let configured_port = config.port;
 
     // Auto-probe: if the configured port is taken, find the next available one
-    let port = find_available_port(configured_port)
+    let port = crate::net::find_available_port(configured_port)
         .ok_or_else(|| format!("No available port found starting from {}.", configured_port))?;
     if port != configured_port {
         log::info!(
@@ -126,6 +115,9 @@ pub async fn start_mcp_server<R: Runtime + 'static>(app: AppHandle<R>, config: M
         if let Err(e) = axum::serve(listener, router).await {
             log::error!("MCP server crashed: {}", e);
         }
+        // Server exited (crash or graceful shutdown) — reset port so
+        // is_mcp_running() and get_mcp_actual_port() reflect reality.
+        MCP_ACTUAL_PORT.store(0, Ordering::Relaxed);
     });
 
     if let Ok(mut guard) = MCP_HANDLE.lock() {
@@ -157,8 +149,10 @@ pub fn stop_mcp_server() {
 }
 
 /// Returns whether the MCP server task is currently running.
+/// Uses `MCP_ACTUAL_PORT` as the source of truth — the spawned task resets it
+/// to 0 when it exits (crash or graceful shutdown), so a non-zero port means running.
 pub fn is_mcp_running() -> bool {
-    MCP_HANDLE.lock().ok().is_some_and(|guard| guard.is_some())
+    MCP_ACTUAL_PORT.load(Ordering::Relaxed) != 0
 }
 
 /// Returns the port the MCP server is actually listening on, or `None` if not running.
