Block on dropping handle on Linux

[netwatcher] / src / watch_linux.rs

diff --git a/src/watch_linux.rs b/src/watch_linux.rs
index e5842117994da2f0951bb66a5b1cc31e43ab86e2..dc9957211a698fc4269911e4adf674bfd4f8cfc4 100644 (file)
--- a/src/watch_linux.rs
+++ b/src/watch_linux.rs
@@ -1,74 +1,94 @@
 use std::os::fd::AsRawFd;
 use std::os::fd::OwnedFd;
+use std::sync::mpsc;
 
 use nix::libc::poll;
 use nix::libc::pollfd;
 use nix::libc::POLLIN;
-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 nix::sys::socket::SOCK_NONBLOCK;
 use nix::unistd::pipe;
 
 use crate::Error;
 use crate::List;
 use crate::Update;
 
+const RTMGRP_IPV4_IFADDR: u32 = 0x10;
+const RTMGRP_IPV6_IFADDR: u32 = 0x20;
+const RTMGRP_LINK: u32 = 0x01;
+
 pub(crate) struct WatchHandle {
-    // Dropping will close the fd which will be detected by poll
-    _pipefd: OwnedFd,
+    // Close on drop, which will be detected by poll in background thread
+    pipefd: Option<OwnedFd>,
+
+    // Detect when thread has completed
+    complete: Option<mpsc::Receiver<()>>,
+}
+
+impl Drop for WatchHandle {
+    fn drop(&mut self) {
+        drop(self.pipefd.take());
+        let _ = self.complete.take().recv();
+    }
 }
 
 pub(crate) fn watch_interfaces<F: FnMut(Update) + Send + 'static>(
     callback: F,
 ) -> Result<WatchHandle, Error> {
-    let pipefd = start_watcher_thread(callback)?;
-    Ok(WatchHandle { _pipefd: pipefd })
+    let (pipefd, complete) = start_watcher_thread(callback)?;
+    Ok(WatchHandle {
+        pipefd: Some(pipefd),
+        complete: Some(complete),
+    })
 }
 
 fn start_watcher_thread<F: FnMut(Update) + Send + 'static>(
     mut callback: F,
-) -> Result<OwnedFd, Error> {
+) -> Result<(OwnedFd, mpsc::Receiver<()>), Error> {
     let sockfd = socket(
         AddressFamily::Netlink,
         SockType::Raw,
-        SockFlag::empty(),
+        SOCK_NONBLOCK,
         Some(SockProtocol::NetlinkRoute),
     )
-    .map_err(|_| Error::Internal)?; // TODO: proper errors
+    .map_err(|e| Error::CreateSocket(e.to_string()))?;
+    sockfd.set_nonblocking(true);
     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 (pipe_rd, pipe_wr) = pipe().map_err(|_| Error::Internal)?;
+    bind(sockfd.as_raw_fd(), &sa_nl).map_err(|e| Error::Bind(e.to_string()))?;
+    let (pipe_rd, pipe_wr) = pipe().map_err(|e| Error::CreatePipe(e.to_string()))?;
 
-    std::thread::spawn(move || {
-        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;
+    let mut prev_list = List::default();
+    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);
-        };
+    // Now that netlink socket is open, provide an initial update.
+    // By having this outside the thread we can return an error synchronously if it
+    // looks like we're going to have trouble listing interfaces.
+    handle_update(crate::list::list_interfaces()?);
+
+    let (complete_tx, complete_rx) = mpsc::channel();
+
+    std::thread::spawn(move || {
+        let mut buf = [0u8; 4096];
 
         loop {
             let mut fds = [
@@ -100,6 +120,8 @@ fn start_watcher_thread<F: FnMut(Update) + Send + 'static>(
                 break;
             }
         }
+
+        drop(complete_tx);
     });
 
     Ok(pipe_wr)