Make watching work on Linux

[netwatcher] / src / watch_linux.rs

diff --git a/src/watch_linux.rs b/src/watch_linux.rs
index a987919360fc789c79a3478e19da048d9c47c963..efc3842482207998e40f36e868e259af4bc44c72 100644 (file)
--- a/src/watch_linux.rs
+++ b/src/watch_linux.rs
@@ -1,13 +1,73 @@
+use std::os::fd::AsRawFd;
+use std::os::fd::OwnedFd;
+
+use nix::libc::RTMGRP_IPV4_IFADDR;
+use nix::libc::RTMGRP_IPV6_IFADDR;
+use nix::libc::RTMGRP_LINK;
+use nix::sys::socket::bind;
+use nix::sys::socket::recv;
+use nix::sys::socket::socket;
+use nix::sys::socket::AddressFamily;
+use nix::sys::socket::MsgFlags;
+use nix::sys::socket::NetlinkAddr;
+use nix::sys::socket::SockFlag;
+use nix::sys::socket::SockProtocol;
+use nix::sys::socket::SockType;
+
 use crate::Error;
+use crate::List;
 use crate::Update;
 
-pub(crate) struct WatchHandle;
+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> {
-    // stop current worker thread
-    // post this into a thread that will use it
-    drop(callback);
-    Ok(WatchHandle)
+    let sockfd = start_watcher_thread(callback)?;
+    Ok(WatchHandle { sockfd })
+}
+
+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);
+    bind(sockfd.as_raw_fd(), &sa_nl).map_err(|_| Error::Internal)?; // TODO: proper errors
+    let fd = sockfd.as_raw_fd();
+    println!("netlink socket on fd {}", fd);
+
+    std::thread::spawn(move || {
+        println!("watch thread running");
+        let mut prev_list = List::default();
+        let mut buf = [0u8; 4096];
+        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 Ok(new_list) = crate::list::list_interfaces() else {
+                continue;
+            };
+            handle_update(new_list);
+        }
+        println!("netlink recv thread terminating");
+    });
+    
+    Ok(sockfd)
 }