Clean up race condition in initial watch on Windows

[netwatcher] / src / watch_win.rs

diff --git a/src/watch_win.rs b/src/watch_win.rs
index e495e9a4467c809cc29ffe918fc6bbf97e9d0125..67e0d4c88fc27d3216a5760a2d7ddc13afb294bb 100644 (file)
--- a/src/watch_win.rs
+++ b/src/watch_win.rs
@@ -1,8 +1,102 @@
-use crate::Update;\r
-\r
-pub struct WatchHandle;\r
-\r
-pub fn watch_interfaces<F: FnMut(Update)>(callback: F) -> WatchHandle {\r
-    drop(callback);\r
-    WatchHandle\r
-}\r
+use std::ffi::c_void;
+use std::pin::Pin;
+use std::sync::Mutex;
+
+use windows::Win32::Foundation::ERROR_INVALID_HANDLE;
+use windows::Win32::Foundation::ERROR_INVALID_PARAMETER;
+use windows::Win32::Foundation::ERROR_NOT_ENOUGH_MEMORY;
+use windows::Win32::Foundation::NO_ERROR;
+use windows::Win32::NetworkManagement::IpHelper::CancelMibChangeNotify2;
+use windows::Win32::NetworkManagement::IpHelper::MIB_NOTIFICATION_TYPE;
+use windows::Win32::NetworkManagement::IpHelper::MIB_UNICASTIPADDRESS_ROW;
+use windows::Win32::{
+    Foundation::{BOOLEAN, HANDLE},
+    NetworkManagement::IpHelper::NotifyUnicastIpAddressChange,
+    Networking::WinSock::AF_UNSPEC,
+};
+
+use crate::Error;
+use crate::List;
+use crate::Update;
+
+pub struct WatchState {
+    /// The last result that we captured, for diffing
+    prev_list: List,
+    /// User's callback
+    cb: Box<dyn FnMut(Update) + 'static>,
+}
+
+pub struct WatchHandle {
+    hnd: HANDLE,
+    _state: Pin<Box<Mutex<WatchState>>>,
+}
+
+impl Drop for WatchHandle {
+    fn drop(&mut self) {
+        unsafe {
+            let _ = CancelMibChangeNotify2(self.hnd);
+        }
+    }
+}
+
+pub(crate) fn watch_interfaces<F: FnMut(Update) + 'static>(
+    callback: F,
+) -> Result<WatchHandle, Error> {
+    let state = Box::pin(Mutex::new(WatchState {
+        prev_list: List::default(),
+        cb: Box::new(callback),
+    }));
+    let state_ctx = &*state.as_ref() as *const _ as *const c_void;
+
+    let mut hnd = HANDLE::default();
+    let res = unsafe {
+        NotifyUnicastIpAddressChange(
+            AF_UNSPEC,
+            Some(notif),
+            Some(state_ctx),
+            BOOLEAN(0),
+            &mut hnd,
+        )
+    };
+    match res {
+        NO_ERROR => {
+            // Trigger an initial update.
+            // This is allowed to race with true updates because it
+            // will always calculate a diff and discard no-ops.
+            handle_notif(&mut *state.lock().unwrap());
+            // Then return the handle
+            Ok(WatchHandle { hnd, _state: state })
+        }
+        ERROR_INVALID_HANDLE => Err(Error::Internal),
+        ERROR_INVALID_PARAMETER => Err(Error::Internal),
+        ERROR_NOT_ENOUGH_MEMORY => Err(Error::Internal),
+        _ => Err(Error::Internal), // TODO: Use FormatMessage and get real error
+    }
+}
+
+unsafe extern "system" fn notif(
+    ctx: *const c_void,
+    _row: *const MIB_UNICASTIPADDRESS_ROW,
+    _notification_type: MIB_NOTIFICATION_TYPE,
+) {
+    let state_ptr = ctx as *const Mutex<WatchState>;
+    unsafe {
+        let state_guard = &mut *state_ptr.as_ref().unwrap().lock().unwrap();
+        handle_notif(state_guard);
+    }
+}
+
+fn handle_notif(state: &mut WatchState) {
+    let Ok(new_list) = crate::list::list_interfaces() else {
+        return;
+    };
+    if new_list == state.prev_list {
+        return;
+    }
+    let update = Update {
+        interfaces: new_list.0.clone(),
+        diff: new_list.diff_from(&state.prev_list),
+    };
+    (state.cb)(update);
+    state.prev_list = new_list;
+}