Groundwork for watching interface changes on Linux

[netwatcher] / src / watch_linux.rs

diff --git a/src/watch_linux.rs b/src/watch_linux.rs
index a987919360fc789c79a3478e19da048d9c47c963..4e4049b8856ba87dece34d25677f1116c49ae7a5 100644 (file)
--- a/src/watch_linux.rs
+++ b/src/watch_linux.rs
@@ -1,13 +1,57 @@
+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;
+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::Update;
 
-pub(crate) struct WatchHandle;
+pub(crate) struct WatchHandle {
+    // PROBLEM: close() doesn't cancel recv() for a netlink socket
+    sockfd: OwnedFd,
+}
 
 pub(crate) fn watch_interfaces<F: FnMut(Update) + '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) + 'static>(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 buf = [0u8; 4096];
+        // recvmsg?
+        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
+        }
+        println!("netlink recv thread terminating");
+    });
+    
+    Ok(sockfd)
 }