feat : add the ability to identify if tcp connection has failed

Cargo.toml

@@ -46,6 +46,7 @@ features = [
 [dev-dependencies]
 easy-parallel = "3.1.0"
 fastrand = "2.0.0"
+socket2 = "0.5.5"
 
 [target.'cfg(unix)'.dev-dependencies]
 libc = "0.2"

examples/tcp_client.rs

@@ -0,0 +1,33 @@
+use std::{io, net};
+
+use polling::Event;
+use socket2::Type;
+
+fn main() -> io::Result<()> {
+    let socket = socket2::Socket::new(socket2::Domain::IPV4, Type::STREAM, None)?;
+    let poller = polling::Poller::new()?;
+    unsafe {
+        poller.add(&socket, Event::new(0, true, true))?;
+    }
+    let addr = net::SocketAddr::new(net::Ipv4Addr::LOCALHOST.into(), 8080);
+    socket.set_nonblocking(true)?;
+    let _ = socket.connect(&addr.into());
+
+    let mut events = polling::Events::new();
+
+    events.clear();
+    poller.wait(&mut events, None)?;
+
+    let event = events.iter().next();
+    let Some(event) = event else {
+        println!("no event");
+        return Ok(());
+    };
+
+    println!("event: {:?}", event);
+    if event.is_connect_failed() {
+        println!("connect failed");
+    }
+
+    Ok(())
+}

src/epoll.rs

@@ -365,6 +365,11 @@ impl EventExtra {
     pub fn is_pri(&self) -> bool {
         self.flags.contains(epoll::EventFlags::PRI)
     }
+
+    #[inline]
+    pub fn is_connect_failed(&self) -> bool {
+        self.flags.contains(epoll::EventFlags::ERR) || self.flags.contains(epoll::EventFlags::HUP)
+    }
 }
 
 /// The notifier for Linux.

src/iocp/mod.rs

@@ -681,6 +681,12 @@ impl EventExtra {
     pub fn set_pri(&mut self, active: bool) {
         self.flags.set(AfdPollMask::RECEIVE_EXPEDITED, active);
     }
+
+    /// Check if TCP connect failed.
+    #[inline]
+    pub fn is_connect_failed(&self) -> bool {
+        self.flags.intersects(AfdPollMask::CONNECT_FAIL)
+    }
 }
 
 /// A packet used to wake up the poller with an event.

src/kqueue.rs

@@ -371,6 +371,11 @@ impl EventExtra {
     pub fn is_pri(&self) -> bool {
         false
     }
+
+    #[inline]
+    pub fn is_connect_failed(&self) -> bool {
+        unimplemented!("is connect failed is not supported on kqueue");
+    }
 }
 
 pub(crate) fn mode_to_flags(mode: PollMode) -> kqueue::EventFlags {

src/lib.rs

@@ -332,6 +332,17 @@ impl Event {
         self.extra.is_pri()
     }
 
+    /// Tell if this event is the result of a connect failure.
+    ///
+    /// This indicates a tcp connection has failed, it corresponds to the `EPOLLERR` along with `EPOLLHUP` event in linux
+    /// and `CONNECT_FAILED` event in windows IOCP.
+    ///
+
+    #[inline]
+    pub fn is_connect_failed(&self) -> bool {
+        self.extra.is_connect_failed()
+    }
+
     /// Remove any extra information from this event.
     #[inline]
     pub fn clear_extra(&mut self) {

src/poll.rs

@@ -426,6 +426,13 @@ impl EventExtra {
     pub fn is_pri(&self) -> bool {
         self.flags.contains(PollFlags::PRI)
     }
+
+    #[inline]
+    pub fn is_connect_failed(&self) -> bool {
+        // need reviewer's special attention, as I do not have access to a system that supports this
+        // this is a guess based on the documentation of `poll()`
+        self.flags.contains(PollFlags::ERR) || self.flags.contains(PollFlags::HUP)
+    }
 }
 
 fn cvt_mode_as_remove(mode: PollMode) -> io::Result<bool> {

src/port.rs

@@ -250,4 +250,9 @@ impl EventExtra {
     pub fn is_pri(&self) -> bool {
         self.flags.contains(PollFlags::PRI)
     }
+
+    #[inline]
+    pub fn is_connect_failed(&self) -> bool {
+        self.flags.contains(PollFlags::ERR) || self.flags.contains(PollFlags::HUP)
+    }
 }