From 4abfa61b20e567fdd69ac3ca47a9c218971a30ff Mon Sep 17 00:00:00 2001
From: Thomas Karpiniec <tom.karpiniec@outlook.com>
Date: Fri, 14 Jun 2024 22:08:38 +0100
Subject: [PATCH 1/1] Make watching work on Linux

---
 src/lib.rs         |  2 +-
 src/watch_linux.rs | 34 +++++++++++++++++++++++++---------
 src/watch_win.rs   |  4 ++--
 3 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 7a8298e..69de586 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -145,6 +145,6 @@ pub fn list_interfaces() -> Result<HashMap<IfIndex, Interface>, Error> {
 /// 
 /// The callback will fire once immediately with an initial interface list, and a diff as if
 /// there were originally no interfaces present.
-pub fn watch_interfaces<F: FnMut(Update) + 'static>(callback: F) -> Result<WatchHandle, Error> {
+pub fn watch_interfaces<F: FnMut(Update) + Send + 'static>(callback: F) -> Result<WatchHandle, Error> {
     watch::watch_interfaces(callback).map(|handle| WatchHandle { _inner: handle })
 }
diff --git a/src/watch_linux.rs b/src/watch_linux.rs
index 4e4049b..efc3842 100644
--- a/src/watch_linux.rs
+++ b/src/watch_linux.rs
@@ -1,7 +1,6 @@
 use std::os::fd::AsRawFd;
 use std::os::fd::OwnedFd;
 
-use nix::libc::nlmsghdr;
 use nix::libc::RTMGRP_IPV4_IFADDR;
 use nix::libc::RTMGRP_IPV6_IFADDR;
 use nix::libc::RTMGRP_LINK;
@@ -16,21 +15,23 @@ use nix::sys::socket::SockProtocol;
 use nix::sys::socket::SockType;
 
 use crate::Error;
+use crate::List;
 use crate::Update;
 
 pub(crate) struct WatchHandle {
     // PROBLEM: close() doesn't cancel recv() for a netlink socket
+    // SOLUTION: open a pipe() and use poll() inside the thread to watch for cancellation too
     sockfd: OwnedFd,
 }
 
-pub(crate) fn watch_interfaces<F: FnMut(Update) + 'static>(
+pub(crate) fn watch_interfaces<F: FnMut(Update) + Send + 'static>(
     callback: F,
 ) -> Result<WatchHandle, Error> {
     let sockfd = start_watcher_thread(callback)?;
     Ok(WatchHandle { sockfd })
 }
 
-fn start_watcher_thread<F: FnMut(Update) + 'static>(callback: F) -> Result<OwnedFd, Error> {
+fn start_watcher_thread<F: FnMut(Update) + Send + 'static>(mut callback: F) -> Result<OwnedFd, Error> {
     let sockfd = socket(AddressFamily::Netlink, SockType::Raw, SockFlag::empty(), Some(SockProtocol::NetlinkRoute))
         .map_err(|_| Error::Internal)?; // TODO: proper errors
     let sa_nl = NetlinkAddr::new(0, (RTMGRP_LINK | RTMGRP_IPV4_IFADDR | RTMGRP_IPV6_IFADDR) as u32);
@@ -40,15 +41,30 @@ fn start_watcher_thread<F: FnMut(Update) + 'static>(callback: F) -> Result<Owned
 
     std::thread::spawn(move || {
         println!("watch thread running");
+        let mut prev_list = List::default();
         let mut buf = [0u8; 4096];
-        // recvmsg?
+        let mut handle_update = move |new_list: List| {
+            if new_list == prev_list {
+                return;
+            }
+            let update = Update {
+                interfaces: new_list.0.clone(),
+                diff: new_list.diff_from(&prev_list),
+            };
+            (callback)(update);
+            prev_list = new_list;
+        };
+
+        if let Ok(initial) = crate::list::list_interfaces() {
+            handle_update(initial);
+        };
+
         while let Ok(n) = recv(fd, &mut buf, MsgFlags::empty()) {
             println!("something on the netlink socket: {} bytes", n);
-            let nlmsg_ptr = &buf as *const _ as *const nlmsghdr;
-            let nlmsg = unsafe { &*nlmsg_ptr };
-            // Right conventionally there's some trick here involving macros NLMSG_OK
-            // I can presumably do this using NetlinkGeneric too
-            // It's unclear whether this is worse or not - need to know what those macros do
+            let Ok(new_list) = crate::list::list_interfaces() else {
+                continue;
+            };
+            handle_update(new_list);
         }
         println!("netlink recv thread terminating");
     });
diff --git a/src/watch_win.rs b/src/watch_win.rs
index a225f4a..edd2fe3 100644
--- a/src/watch_win.rs
+++ b/src/watch_win.rs
@@ -23,7 +23,7 @@ struct WatchState {
     /// The last result that we captured, for diffing
     prev_list: List,
     /// User's callback
-    cb: Box<dyn FnMut(Update) + 'static>,
+    cb: Box<dyn FnMut(Update) + Send + 'static>,
 }
 
 pub(crate) struct WatchHandle {
@@ -39,7 +39,7 @@ impl Drop for WatchHandle {
     }
 }
 
-pub(crate) fn watch_interfaces<F: FnMut(Update) + 'static>(
+pub(crate) fn watch_interfaces<F: FnMut(Update) + Send + 'static>(
     callback: F,
 ) -> Result<WatchHandle, Error> {
     let state = Box::pin(Mutex::new(WatchState {
-- 
2.39.5