[netdata-publisher] remove entry immediately when desired num is zero (#12550)

Update `Publisher::Entry::UpdateState()` to support quickly removing
a published entry when the desired number of entries is explicitly
set to zero. In this case, we bypass the random removal delay and
remove the entry immediately. This situation helps with SRP/DNS
unicast entries, where if any service data unicast or anycast entry
is seen, we set the desired number to zero and want to quickly
remove any previously added server data unicast entry.

src/core/thread/network_data_publisher.cpp

@@ -288,6 +288,8 @@ void Publisher::Entry::UpdateState(uint8_t aNumEntries, uint8_t aNumPreferredEnt
     // entries we aim to have in the Network Data to decide whether or
     // not to take any action (add or remove our entry).
 
+    TimeMilli now = TimerMilli::GetNow();
+
     LogInfo("%s in netdata - total:%d, preferred:%d, desired:%d", ToString().AsCString(), aNumEntries,
             aNumPreferredEntries, aDesiredNumEntries);
 
@@ -303,10 +305,10 @@ void Publisher::Entry::UpdateState(uint8_t aNumEntries, uint8_t aNumPreferredEnt
 
         if (aNumEntries < aDesiredNumEntries)
         {
-            mUpdateTime = TimerMilli::GetNow() + Random::NonCrypto::GetUint32InRange(1, kMaxDelayToAdd);
+            mUpdateTime = now + Random::NonCrypto::GetUint32InRange(1, kMaxDelayToAdd);
             SetState(kAdding);
             Get<Publisher>().GetTimer().FireAtIfEarlier(mUpdateTime);
-            LogUpdateTime();
+            LogUpdateTime(now);
         }
         break;
 
@@ -330,28 +332,47 @@ void Publisher::Entry::UpdateState(uint8_t aNumEntries, uint8_t aNumPreferredEnt
         // aDesiredNumEntries`) we add an extra delay before removing
         // the entry. This gives higher chance for a non-preferred
         // entry from another device to be removed before our entry.
+        // If `aDesiredNumEntries` is explicitly set to zero (which
+        // indicates that all entries should be removed), no delay is
+        // added. This helps with SRP/DNS unicast entries, where if
+        // any service data unicast or anycast entry is seen, we set
+        // the desired number to zero to quickly remove any previously
+        // added server data unicast entry.
 
         if (aNumEntries > aDesiredNumEntries)
         {
-            mUpdateTime = TimerMilli::GetNow() + Random::NonCrypto::GetUint32InRange(1, kMaxDelayToRemove);
+            mUpdateTime = now;
 
-            if (aNumPreferredEntries < aDesiredNumEntries)
+            if (aDesiredNumEntries > 0)
             {
-                mUpdateTime += kExtraDelayToRemovePreferred;
+                mUpdateTime += Random::NonCrypto::GetUint32InRange(1, kMaxDelayToRemove);
+
+                if (aNumPreferredEntries < aDesiredNumEntries)
+                {
+                    mUpdateTime += kExtraDelayToRemovePreferred;
+                }
             }
 
             SetState(kRemoving);
             Get<Publisher>().GetTimer().FireAtIfEarlier(mUpdateTime);
-            LogUpdateTime();
+            LogUpdateTime(now);
         }
         break;
 
     case kRemoving:
-        // Our entry is being removed (wait time before remove). If we
-        // now see that there are enough or too few entries, we stop
+        // Our entry is being removed (wait time before remove). If
+        // `aDesiredNumEntries` is zero, we update `mUpdateTime` to
+        // `now` to quickly remove the entry. Otherwise, if we now
+        // see that there are enough or too few entries, we stop
         // removing our entry.
 
-        if (aNumEntries <= aDesiredNumEntries)
+        if ((aDesiredNumEntries == 0) && (mUpdateTime > now))
+        {
+            mUpdateTime = now;
+            Get<Publisher>().GetTimer().FireAtIfEarlier(mUpdateTime);
+            LogUpdateTime(now);
+        }
+        else if (aNumEntries <= aDesiredNumEntries)
         {
             SetState(kAdded);
         }
@@ -483,10 +504,14 @@ exit:
     return string;
 }
 
-void Publisher::Entry::LogUpdateTime(void) const
+#if OT_SHOULD_LOG_AT(OT_LOG_LEVEL_INFO)
+void Publisher::Entry::LogUpdateTime(TimeMilli aNow) const
 {
-    LogInfo("%s - update in %lu msec", ToString().AsCString(), ToUlong(mUpdateTime - TimerMilli::GetNow()));
+    LogInfo("%s - update in %lu msec", ToString().AsCString(), ToUlong(mUpdateTime - aNow));
 }
+#else
+void Publisher::Entry::LogUpdateTime(TimeMilli) const {}
+#endif
 
 const char *Publisher::Entry::StateToString(State aState)
 {

src/core/thread/network_data_publisher.hpp

@@ -379,7 +379,7 @@ private:
     private:
         void               Add(void);
         void               Remove(State aNextState);
-        void               LogUpdateTime(void) const;
+        void               LogUpdateTime(TimeMilli aNow) const;
         static const char *StateToString(State aState);
 
         TimeMilli mUpdateTime;

tests/scripts/thread-cert/test_netdata_publisher.py

@@ -464,10 +464,11 @@ class NetDataPublisher(thread_cert.TestCase):
 
         # Verify that publishing an anycast entry will update the
         # limit for the server data unicast address entry and all are
-        # removed.
+        # removed quickly. We validate this by waiting for a short
+        # time (15 msec) after publishing anycast.
 
         leader.netdata_publish_dnssrp_anycast(ANYCAST_SEQ_NUM)
-        self.simulator.go(WAIT_TIME)
+        self.simulator.go(15)
         services = leader.get_services()
         self.assertEqual(len(services), 1)
         self.verify_anycast_services(services)