TUN inbound: Wait() blocks via kqueue instead of busy-spinning on Darwin (#6580)

Fixes https://github.com/XTLS/Xray-core/issues/6579

proxy/tun/tun_darwin_test.go

@@ -3,7 +3,11 @@
 package tun
 
 import (
+	"sync"
 	"testing"
+	"time"
+
+	"golang.org/x/sys/unix"
 )
 
 func TestSelectDarwinGatewayDefault(t *testing.T) {
@@ -47,3 +51,183 @@ func TestSelectDarwinGatewayRequiresUsableLocalAddress(t *testing.T) {
 		t.Fatal("expected error")
 	}
 }
+
+// newTestSocketpair returns a connected AF_UNIX/SOCK_DGRAM pair -- a real
+// fd DarwinTun.Wait's kqueue can register EVFILT_READ against, without
+// needing an actual utun interface (which requires root/network
+// entitlements this test environment doesn't have). Datagram sockets
+// (unlike pipes) support both "write makes readable" and "close makes
+// readable" the same way a tun fd's read-readiness behaves.
+func newTestSocketpair(t *testing.T) (a, b int) {
+	t.Helper()
+	fds, err := unix.Socketpair(unix.AF_UNIX, unix.SOCK_DGRAM, 0)
+	if err != nil {
+		t.Fatalf("socketpair: %v", err)
+	}
+	t.Cleanup(func() {
+		_ = unix.Close(fds[0])
+		_ = unix.Close(fds[1])
+	})
+	return fds[0], fds[1]
+}
+
+// Reviewer feedback, XTLS/Xray-core#6580: "blocking with no data" case --
+// wait() must not return before the timeout when nothing is written.
+func TestWaitKqueueBlocksWithNoData(t *testing.T) {
+	a, _ := newTestSocketpair(t)
+	kq := newWaitKqueue(a)
+	if kq == nil {
+		t.Fatal("newWaitKqueue returned nil")
+	}
+	defer kq.close()
+
+	start := time.Now()
+	ok := kq.wait(150 * time.Millisecond)
+	elapsed := time.Since(start)
+
+	if !ok {
+		t.Fatal("wait() returned false on a healthy kqueue with a plain timeout")
+	}
+	if elapsed < 100*time.Millisecond {
+		t.Fatalf("wait() returned after only %v, expected it to block close to the 150ms timeout", elapsed)
+	}
+}
+
+// Reviewer feedback: "wake up with a readable fd" case.
+func TestWaitKqueueWakesOnReadable(t *testing.T) {
+	a, b := newTestSocketpair(t)
+	kq := newWaitKqueue(a)
+	if kq == nil {
+		t.Fatal("newWaitKqueue returned nil")
+	}
+	defer kq.close()
+
+	done := make(chan bool, 1)
+	go func() {
+		done <- kq.wait(5 * time.Second)
+	}()
+
+	time.Sleep(20 * time.Millisecond) // let wait() actually enter the syscall first
+	if _, err := unix.Write(b, []byte{0x1}); err != nil {
+		t.Fatalf("write: %v", err)
+	}
+
+	select {
+	case ok := <-done:
+		if !ok {
+			t.Fatal("wait() returned false after the fd became readable")
+		}
+	case <-time.After(2 * time.Second):
+		t.Fatal("wait() did not wake up within 2s of the fd becoming readable")
+	}
+}
+
+// Reviewer feedback: "timeout" case, explicitly (distinct from the
+// no-data test above, which also checks blocking duration -- this one
+// only checks the return value).
+func TestWaitKqueueTimesOut(t *testing.T) {
+	a, _ := newTestSocketpair(t)
+	kq := newWaitKqueue(a)
+	if kq == nil {
+		t.Fatal("newWaitKqueue returned nil")
+	}
+	defer kq.close()
+
+	if !kq.wait(50 * time.Millisecond) {
+		t.Fatal("wait() returned false on a plain timeout with no error condition")
+	}
+}
+
+// Reviewer feedback: "Close() wakes a blocked wait" case, and the
+// no-double-close/no-fd-reuse concern (P1) -- close() while wait() is
+// parked in its syscall must not panic, must not leave wait() hung, and a
+// second close() call (from a caller that, say, calls Close() twice on
+// the same DarwinTun) must be safe.
+func TestWaitKqueueCloseDuringWaitIsSafe(t *testing.T) {
+	a, _ := newTestSocketpair(t)
+	kq := newWaitKqueue(a)
+	if kq == nil {
+		t.Fatal("newWaitKqueue returned nil")
+	}
+
+	started := make(chan struct{})
+	done := make(chan bool, 1)
+	go func() {
+		close(started)
+		done <- kq.wait(5 * time.Second)
+	}()
+
+	<-started
+	time.Sleep(20 * time.Millisecond) // let wait() actually enter the syscall first
+	kq.close()
+	kq.close() // double-close must be idempotent, not panic or double-free the fd
+
+	select {
+	case <-done:
+		// Either true (the close-of-the-underlying-fd unblocked kevent, a
+		// real kqueue behavior) or false (wait() observed the closed flag
+		// first) is acceptable -- what matters is that it returned at all,
+		// promptly, without hanging or crashing.
+	case <-time.After(2 * time.Second):
+		t.Fatal("wait() did not return within 2s of close() being called")
+	}
+
+	// A wait() call *after* close() must return false immediately (the
+	// closed-flag fast path), not attempt a syscall against the
+	// already-closed (and potentially since-reused, on a real system) fd
+	// number.
+	if kq.wait(time.Second) {
+		t.Fatal("wait() returned true after close() -- should short-circuit via the closed flag")
+	}
+}
+
+// Reviewer feedback: "multiple/concurrent close guard" case -- many
+// goroutines calling close() concurrently must close the underlying fd
+// exactly once.
+func TestWaitKqueueConcurrentCloseIsSafe(t *testing.T) {
+	a, _ := newTestSocketpair(t)
+	kq := newWaitKqueue(a)
+	if kq == nil {
+		t.Fatal("newWaitKqueue returned nil")
+	}
+
+	var wg sync.WaitGroup
+	for range 20 {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			kq.close()
+		}()
+	}
+	wg.Wait()
+
+	if !kq.closed.Load() {
+		t.Fatal("closed flag not set after concurrent close() calls")
+	}
+}
+
+// Reviewer feedback: "kevent runtime failure without spinning" case (P2).
+// Simulates a kqueue that has gone bad (closed out from under it, as if a
+// concurrent/erroneous close happened) and confirms wait() reports it as
+// unusable (false) rather than silently returning true forever, which is
+// what DarwinTun.Wait relies on to permanently fall back to the sleep
+// path instead of re-entering a failing syscall on every dispatchLoop
+// iteration.
+func TestWaitKqueueReportsPersistentFailure(t *testing.T) {
+	a, _ := newTestSocketpair(t)
+	kq := newWaitKqueue(a)
+	if kq == nil {
+		t.Fatal("newWaitKqueue returned nil")
+	}
+	// Close the underlying kqueue fd directly (bypassing kq.close(), which
+	// would also set the closed flag) to simulate the fd going bad for a
+	// reason other than this type's own close() -- e.g. some other code
+	// path in the process closing it, or the kernel invalidating it.
+	_ = unix.Close(kq.fd)
+
+	for i := 0; i < 5; i++ {
+		if kq.wait(50 * time.Millisecond) {
+			t.Fatalf("wait() call %d returned true against a closed underlying fd -- should report failure, not spin", i)
+		}
+	}
+}