Deflake tcp_network_unreachable test

Previously, we make two connect attempts. If the first attempt is still on
going when the second attempt is made, the test will fail. This change deflakes
the situation by not making the second attempt, instead, we poll for the first
attempt's completion and read the errno from SO_ERROR.

PiperOrigin-RevId: 358104769

1 files changed, 17 insertions, 0 deletions

diff --git a/test/packetimpact/testbench/dut.go b/test/packetimpact/testbench/dut.go
index aedcf6013..81634b5f4 100644
--- a/test/packetimpact/testbench/dut.go
+++ b/test/packetimpact/testbench/dut.go
@@ -486,6 +486,23 @@ func (dut *DUT) ListenWithErrno(ctx context.Context, t *testing.T, sockfd, backl
 	return resp.GetRet(), syscall.Errno(resp.GetErrno_())
 }
 
+// PollOne calls poll on the DUT and asserts that the expected event must be
+// signaled on the given fd within the given timeout.
+func (dut *DUT) PollOne(t *testing.T, fd int32, events int16, timeout time.Duration) {
+	t.Helper()
+
+	pfds := dut.Poll(t, []unix.PollFd{{Fd: fd, Events: events}}, timeout)
+	if n := len(pfds); n != 1 {
+		t.Fatalf("Poll returned %d ready file descriptors, expected 1", n)
+	}
+	if readyFd := pfds[0].Fd; readyFd != fd {
+		t.Fatalf("Poll returned an fd %d that was not requested (%d)", readyFd, fd)
+	}
+	if got, want := pfds[0].Revents, int16(events); got&want == 0 {
+		t.Fatalf("Poll returned no events in our interest, got: %#b, want: %#b", got, want)
+	}
+}
+
 // Poll calls poll on the DUT and causes a fatal test failure if it doesn't
 // succeed. If more control over error handling is needed, use PollWithErrno.
 // Only pollfds with non-empty revents are returned, the only way to tie the