[routing-manager] advertise local OMR in RA after present in netdata (#9703)

This commit adds `OmrPrefixManager::ShouldAdvertiseLocalAsRio()` which
determines whether the local OMR prefix should be advertised as RIO
in emitted RAs. To advertise, we must have decided to publish it, and
it must already be added and present in the Network Data. This
ensures that we only advertise the local OMR prefix in emitted RAs
when, as a Border Router, we can accept and route messages using an
OMR-based address destination, which requires the prefix to be
present in Network Data. Similarly, we stop advertising (and start
deprecating) the OMR prefix in RAs as soon as we decide to remove it.
After requesting its removal from Network Data, it may still be
present in Network Data for a short interval due to delays in
registering changes with the leader.

src/core/border_router/routing_manager.cpp

@@ -2085,6 +2085,45 @@ exit:
     return;
 }
 
+bool RoutingManager::OmrPrefixManager::ShouldAdvertiseLocalAsRio(void) const
+{
+    // Determines whether the local OMR prefix should be advertised as
+    // RIO in emitted RAs. To advertise, we must have decided to
+    // publish it, and it must already be added and present in the
+    // Network Data. This ensures that we only advertise the local
+    // OMR prefix in emitted RAs when, as a Border Router, we can
+    // accept and route messages using an OMR-based address
+    // destination, which requires the prefix to be present in
+    // Network Data. Similarly, we stop advertising (and start
+    // deprecating) the OMR prefix in RAs as soon as we decide to
+    // remove it. After requesting its removal from Network Data, it
+    // may still be present in Network Data for a short interval due
+    // to delays in registering changes with the leader.
+
+    bool                            shouldAdvertise = false;
+    NetworkData::Iterator           iterator        = NetworkData::kIteratorInit;
+    NetworkData::OnMeshPrefixConfig prefixConfig;
+
+    VerifyOrExit(mIsLocalAddedInNetData);
+
+    while (Get<NetworkData::Leader>().GetNextOnMeshPrefix(iterator, prefixConfig) == kErrorNone)
+    {
+        if (!IsValidOmrPrefix(prefixConfig))
+        {
+            continue;
+        }
+
+        if (prefixConfig.GetPrefix() == mLocalPrefix.GetPrefix())
+        {
+            shouldAdvertise = true;
+            break;
+        }
+    }
+
+exit:
+    return shouldAdvertise;
+}
+
 Error RoutingManager::OmrPrefixManager::AddLocalToNetData(void)
 {
     Error error = kErrorNone;
@@ -2822,7 +2861,7 @@ void RoutingManager::RioAdvertiser::AppendRios(Ip6::Nd::RouterAdvertMessage &aRa
 
     // (1) Local OMR prefix.
 
-    if (omrPrefixManager.IsLocalAddedInNetData())
+    if (omrPrefixManager.ShouldAdvertiseLocalAsRio())
     {
         mPrefixes.Add(omrPrefixManager.GetLocalPrefix().GetPrefix());
     }
@@ -2840,16 +2879,14 @@ void RoutingManager::RioAdvertiser::AppendRios(Ip6::Nd::RouterAdvertMessage &aRa
 
     while (Get<NetworkData::Leader>().GetNextOnMeshPrefix(iterator, prefixConfig) == kErrorNone)
     {
-        // Local OMR prefix is added to the array depending on
-        // `omrPrefixManager.IsLocalAddedInNetData()` at step (1).
-        // As we iterate through the Network Data prefixes, we skip
-        // over entries matching the local OMR prefix. This
-        // ensures that we start deprecating it in emitted RA
-        // message as soon as we decide to remove it from Network
-        // Data. Note that upon requesting it to be removed from
-        // Network Data the change needs to be registered with
-        // leader and can take some time to be updated in Network
-        // Data.
+        // Decision on whether or not to include the local OMR prefix is
+        // delegated to `OmrPrefixManager.ShouldAdvertiseLocalAsRio()`
+        // at step (1). Here as we iterate over the Network Data
+        // prefixes, we skip entries matching the local OMR prefix.
+        // In particular, `OmrPrefixManager` may have decided to remove the
+        // local prefix and not advertise it anymore, but it may still be
+        // present in the Network Data (due to delay of registering changes
+        // with leader).
 
         if (prefixConfig.mDp)
         {

src/core/border_router/routing_manager.hpp

@@ -909,7 +909,7 @@ private:
         void                    Stop(void);
         void                    Evaluate(void);
         void                    UpdateDefaultRouteFlag(bool aDefaultRoute);
-        bool                    IsLocalAddedInNetData(void) const { return mIsLocalAddedInNetData; }
+        bool                    ShouldAdvertiseLocalAsRio(void) const;
         const Ip6::Prefix      &GetGeneratedPrefix(void) const { return mGeneratedPrefix; }
         const OmrPrefix        &GetLocalPrefix(void) const { return mLocalPrefix; }
         const FavoredOmrPrefix &GetFavoredPrefix(void) const { return mFavoredPrefix; }