Properly implement TEventLoop::poll for AvahiEventLoop

As of Avahi 0.7, the sleep_time arg passed to
`avahi_simple_poll_iterate()` is utilized. Properly implementing this
reduces CPU spent polling while improving responsiveness.

zeroconf/src/linux/event_loop.rs

@@ -3,6 +3,7 @@
 use super::poll::ManagedAvahiSimplePoll;
 use crate::event_loop::TEventLoop;
 use crate::Result;
+use std::convert::TryInto;
 use std::marker::PhantomData;
 use std::sync::Arc;
 use std::time::Duration;
@@ -16,10 +17,9 @@ pub struct AvahiEventLoop<'a> {
 impl<'a> TEventLoop for AvahiEventLoop<'a> {
     /// Polls for new events.
     ///
-    /// Internally calls `ManagedAvahiSimplePoll::iterate(0)`, the `timeout` parameter does not
-    /// currently do anything in the Avahi implementation.
-    fn poll(&self, _timeout: Duration) -> Result<()> {
-        self.poll.iterate(0);
-        Ok(())
+    /// The `timeout` parameter defines the maximum time to sleep, but it will return earlier if
+    /// an event occurs.
+    fn poll(&self, timeout: Duration) -> Result<()> {
+        self.poll.iterate(timeout.as_millis().try_into().unwrap_or(-1))
     }
 }

zeroconf/src/linux/poll.rs

@@ -38,8 +38,15 @@ impl ManagedAvahiSimplePoll {
     /// Delegate function for [`avahi_simple_poll_iterate()`].
     ///
     /// [`avahi_simple_poll_iterate()`]: https://avahi.org/doxygen/html/simple-watch_8h.html#ad5b7c9d3b7a6584d609241ee6f472a2e
-    pub fn iterate(&self, sleep_time: i32) {
-        unsafe { avahi_simple_poll_iterate(self.0, sleep_time) };
+    pub fn iterate(&self, sleep_time: i32) -> Result<()> {
+        let err = unsafe { avahi_simple_poll_iterate(self.0, sleep_time) };
+        if err < 0 {
+            avahi!(err, "AvahiSimplePoll poll failed")
+        } else if err > 0 {
+            Err("AvahiSimplePoll requested quit".into())
+        } else {
+            Ok(())
+        }
     }
 
     pub(super) fn inner(&self) -> *mut AvahiSimplePoll {