From d67cf553f8c9811057ad13b43474743af938b228 Mon Sep 17 00:00:00 2001
From: Nir Soffer <nirsof@gmail.com>
Date: Sun, 1 Mar 2026 15:54:15 +0200
Subject: [PATCH] utils/macos/epoll: Fix EV_EOF hangup type mapping
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The code used EV_CLEAR (edge-trigger flag) as a proxy for the event
direction when mapping EV_EOF to a hangup type. This produced the
wrong type: backend WRITE+EOF got READ_HANG_UP, and eventfd READ+EOF
got HANG_UP.

No impact in practice since the worker treats both HANG_UP and
READ_HANG_UP the same way (fatal error, disable networking).

Use the filter type instead:
- EVFILT_READ + EV_EOF  → READ_HANG_UP (half-close)
- EVFILT_WRITE + EV_EOF → HANG_UP (connection broken)

Unlike epoll where EPOLLRDHUP must be explicitly registered, kqueue
always reports EV_EOF. The shim does not track registration, so
READ_HANG_UP is always reported on read EOF. Document this as a
known difference from epoll in ctl().

Signed-off-by: Nir Soffer <nirsof@gmail.com>
---
 src/utils/src/macos/epoll.rs | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/src/utils/src/macos/epoll.rs b/src/utils/src/macos/epoll.rs
index 2f1ad5a8a..af3f86a57 100644
--- a/src/utils/src/macos/epoll.rs
+++ b/src/utils/src/macos/epoll.rs
@@ -144,6 +144,11 @@ impl Epoll {
         }
     }
 
+    /// Register, modify, or remove interest in events for a file descriptor.
+    ///
+    /// Note: `READ_HANG_UP` (`EPOLLRDHUP`) is ignored. kqueue always
+    /// reports `EV_EOF` without opt-in, so `wait()` reports
+    /// `READ_HANG_UP` on read EOF regardless of registration.
     pub fn ctl(
         &self,
         operation: ControlOperation,
@@ -282,15 +287,14 @@ impl Epoll {
         for i in 0..nevents {
             if kevs[i].0.filter == libc::EVFILT_READ {
                 events[i].events = EventSet::IN.bits();
+                if kevs[i].0.flags & libc::EV_EOF != 0 {
+                    events[i].events |= EventSet::READ_HANG_UP.bits();
+                }
             } else if kevs[i].0.filter == libc::EVFILT_WRITE {
                 events[i].events = EventSet::OUT.bits();
-            }
-            if kevs[i].0.flags & libc::EV_EOF != 0 {
-                events[i].events |= if kevs[i].0.flags & libc::EV_CLEAR != 0 {
-                    EventSet::READ_HANG_UP.bits()
-                } else {
-                    EventSet::HANG_UP.bits()
-                };
+                if kevs[i].0.flags & libc::EV_EOF != 0 {
+                    events[i].events |= EventSet::HANG_UP.bits();
+                }
             }
             events[i].u64 = kevs[i].udata();