[border-agent] signal TXT data change when Id is updated (openthread#11457)

This commit updates the `BorderAgent` to ensure that if its `Id` is
changed using the `SetId()` method, any consequent changes to the
generated TXT data for the MeshCoP service are correctly signaled.
This signaling is performed using the "Service TXT Data changed
callback". This commit also updates `test_border_agent` to validate
this.

Author: abtink

src/core/meshcop/border_agent.cpp

@@ -73,7 +73,7 @@ Error BorderAgent::GetId(Id &aId)
 
     if (Get<Settings>().Read<Settings::BorderAgentId>(mId) != kErrorNone)
     {
-        Random::NonCrypto::Fill(mId);
+        mId.GenerateRandom();
         SuccessOrExit(error = Get<Settings>().Save<Settings::BorderAgentId>(mId));
     }
 
@@ -88,9 +88,15 @@ Error BorderAgent::SetId(const Id &aId)
 {
     Error error = kErrorNone;
 
+    if (mIdInitialized)
+    {
+        VerifyOrExit(aId != mId);
+    }
+
     SuccessOrExit(error = Get<Settings>().Save<Settings::BorderAgentId>(aId));
     mId            = aId;
     mIdInitialized = true;
+    PostServiceTask();
 
 exit:
     return error;

src/core/meshcop/border_agent.hpp

@@ -49,6 +49,7 @@
 #include "common/non_copyable.hpp"
 #include "common/notifier.hpp"
 #include "common/owned_ptr.hpp"
+#include "common/random.hpp"
 #include "common/tasklet.hpp"
 #include "meshcop/dataset.hpp"
 #include "meshcop/secure_transport.hpp"
@@ -77,7 +78,6 @@ class BorderAgent : public InstanceLocator, private NonCopyable
     class CoapDtlsSession;
 
 public:
-    typedef otBorderAgentId                            Id;                     ///< Border Agent ID.
     typedef otBorderAgentCounters                      Counters;               ///< Border Agent Counters.
     typedef otBorderAgentSessionInfo                   SessionInfo;            ///< A session info.
     typedef otBorderAgentMeshCoPServiceChangedCallback ServiceChangedCallback; ///< Service changed callback.
@@ -121,6 +121,21 @@ class BorderAgent : public InstanceLocator, private NonCopyable
     explicit BorderAgent(Instance &aInstance);
 
 #if OPENTHREAD_CONFIG_BORDER_AGENT_ID_ENABLE
+    /**
+     *  Represents a Border Agent Identifier.
+     */
+    struct Id : public otBorderAgentId, public Clearable<Id>, public Equatable<Id>
+    {
+        static constexpr uint16_t kLength = OT_BORDER_AGENT_ID_LENGTH; ///< The ID length (number of bytes).
+
+        /**
+         * Generates a random ID.
+         */
+        void GenerateRandom(void) { Random::NonCrypto::Fill(mId); }
+    };
+
+    static_assert(sizeof(Id) == Id::kLength, "sizeof(Id) is not valid");
+
     /**
      * Gets the randomly generated Border Agent ID.
      *
@@ -142,7 +157,7 @@ class BorderAgent : public InstanceLocator, private NonCopyable
      * to set the ID only once after factory reset. If the ID has never been set by calling this
      * method, a random ID will be generated and returned when `GetId()` is called.
      *
-     * @param[out] aId  specifies the Border Agent ID.
+     * @param[in] aId   The Border Agent ID.
      *
      * @retval kErrorNone  If successfully set the Border Agent ID.
      * @retval ...         If failed to set the Border Agent ID.

tests/nexus/test_border_agent.cpp

@@ -751,6 +751,7 @@ class TxtDataTester
         : mBorderAgent(aBorderAgent)
         , mIsRunning(false)
         , mUdpPort(0)
+        , mCallbackInvoked(false)
     {
     }
 
@@ -761,6 +762,7 @@ class TxtDataTester
         mIsRunning = mBorderAgent.IsRunning();
         mUdpPort   = mBorderAgent.GetUdpPort();
         SuccessOrQuit(mBorderAgent.PrepareServiceTxtData(mTxtData));
+        mCallbackInvoked = true;
     }
 
     bool FindTxtEntry(const char *aKey, TxtEntry &aTxtEntry)
@@ -785,6 +787,7 @@ class TxtDataTester
     BorderAgent::ServiceTxtData mTxtData;
     bool                        mIsRunning;
     uint16_t                    mUdpPort;
+    bool                        mCallbackInvoked;
 };
 
 template <typename ObjectType> bool CheckObjectSameAsTxtEntryData(const TxtEntry &aTxtEntry, const ObjectType &aObject)
@@ -802,15 +805,19 @@ template <> bool CheckObjectSameAsTxtEntryData<NameData>(const TxtEntry &aTxtEnt
 
 void TestBorderAgentTxtDataCallback(void)
 {
-    Core  nexus;
-    Node &node0 = nexus.CreateNode();
+    Core          nexus;
+    Node         &node0 = nexus.CreateNode();
+    TxtDataTester txtDataTester(node0.Get<BorderAgent>());
+    TxtEntry      txtEntry;
+#if OPENTHREAD_CONFIG_BORDER_AGENT_ID_ENABLE
+    BorderAgent::Id id;
+    BorderAgent::Id newId;
+#endif
 
     Log("------------------------------------------------------------------------------------------------------");
     Log("TestBorderAgentTxtDataCallback");
 
     nexus.AdvanceTime(0);
-    TxtDataTester txtDataTester(node0.Get<BorderAgent>());
-    TxtEntry      txtEntry;
 
     // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     // 1. Set MeshCoP service change callback. Will get initial values.
@@ -819,9 +826,9 @@ void TestBorderAgentTxtDataCallback(void)
     nexus.AdvanceTime(1);
 
     // 1.1 Check the initial TXT entries
+    VerifyOrQuit(txtDataTester.mCallbackInvoked);
 #if OPENTHREAD_CONFIG_BORDER_AGENT_ID_ENABLE
     VerifyOrQuit(txtDataTester.FindTxtEntry("id", txtEntry));
-    BorderAgent::Id id;
     VerifyOrQuit(node0.Get<BorderAgent>().GetId(id) == kErrorNone);
     VerifyOrQuit(CheckObjectSameAsTxtEntryData(txtEntry, id));
 #endif
@@ -844,11 +851,13 @@ void TestBorderAgentTxtDataCallback(void)
 
     // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     // 2. Join Thread network and check updated values and states.
+    txtDataTester.mCallbackInvoked = false;
     Log("Join Thread network and check updated Txt data and states");
     node0.Form();
     nexus.AdvanceTime(50 * Time::kOneSecondInMsec);
 
     // 2.1 Check the initial TXT entries
+    VerifyOrQuit(txtDataTester.mCallbackInvoked);
 #if OPENTHREAD_CONFIG_BORDER_AGENT_ID_ENABLE
     VerifyOrQuit(txtDataTester.FindTxtEntry("id", txtEntry));
     VerifyOrQuit(node0.Get<BorderAgent>().GetId(id) == kErrorNone);
@@ -872,6 +881,33 @@ void TestBorderAgentTxtDataCallback(void)
     // 2.2 Check the Border Agent state
     VerifyOrQuit(txtDataTester.mIsRunning == true);
     VerifyOrQuit(txtDataTester.mUdpPort != 0);
+
+    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+#if OPENTHREAD_CONFIG_BORDER_AGENT_ID_ENABLE
+    Log("Change the Border Agent ID and validate that TXT data changed and callback is invoked");
+
+    newId.GenerateRandom();
+    VerifyOrQuit(newId != id);
+
+    txtDataTester.mCallbackInvoked = false;
+    SuccessOrQuit(node0.Get<BorderAgent>().SetId(newId));
+
+    nexus.AdvanceTime(1);
+
+    VerifyOrQuit(txtDataTester.mCallbackInvoked);
+    VerifyOrQuit(txtDataTester.FindTxtEntry("id", txtEntry));
+    VerifyOrQuit(CheckObjectSameAsTxtEntryData(txtEntry, newId));
+
+    // Validate that setting the ID to the same value as before is
+    // correctly detected and does not trigger the callback.
+
+    txtDataTester.mCallbackInvoked = false;
+    SuccessOrQuit(node0.Get<BorderAgent>().SetId(newId));
+    nexus.AdvanceTime(1);
+    VerifyOrQuit(!txtDataTester.mCallbackInvoked);
+
+#endif // OPENTHREAD_CONFIG_BORDER_AGENT_ID_ENABLE
 }
 
 } // namespace Nexus