ioc: fix timestamp masking for monitor subscriptions

test/testqsingle.cpp

@@ -1009,6 +1009,25 @@ void testMonitorDBE(TestClient& ctxt)
     testEq(val["value"].as<int32_t>(), 43);
 }
 
+void testMonitorNsecMask(TestClient& ctxt)
+{
+    testDiag("%s", __func__);
+
+    TestSubscription sub(ctxt.monitor("test:nsec")
+                         .maskConnected(true)
+                         .maskDisconnected(true));
+
+    auto val(sub.waitForUpdate());
+
+    // nsec:lsb:8 clears the low 8 bits: 102030 -> 101888, userTag -> 142
+    testFldEq(val, "timeStamp.nanoseconds", int32_t(101888));
+#if DBR_UTAG
+    testFldEq(val, "timeStamp.userTag", int32_t(142));
+#else
+    testSkip(1, "no UTAG");
+#endif
+}
+
 void testiocsh(TestClient& ctxt)
 {
     testDiag("%s", __func__);
@@ -1061,7 +1080,7 @@ void testiocsh(TestClient& ctxt)
 
 MAIN(testqsingle)
 {
-    testPlan(116);
+    testPlan(118);
     testSetup();
     pvxs::logger_config_env();
     generalTimeRegisterCurrentProvider("test", 1, &testTimeCurrent);
@@ -1106,6 +1125,7 @@ MAIN(testqsingle)
             testMonitorAIFilt(mctxt);
             testMonitorDBEAlarm(mctxt);
             testMonitorDBE(mctxt);
+            testMonitorNsecMask(mctxt);
             testiocsh(mctxt);
         }
         timeSim = false;