[border-agent] use Notifier to update the state (#4788)

src/core/meshcop/border_agent.cpp

@@ -350,6 +350,7 @@ BorderAgent::BorderAgent(Instance &aInstance)
     , mUdpReceiver(BorderAgent::HandleUdpReceive, this)
     , mTimer(aInstance, HandleTimeout, this)
     , mState(OT_BORDER_AGENT_STATE_STOPPED)
+    , mNotifierCallback(aInstance, &BorderAgent::HandleStateChanged, this)
 {
     mCommissionerAloc.Clear();
     mCommissionerAloc.mPrefixLength       = 64;
@@ -359,6 +360,28 @@ BorderAgent::BorderAgent(Instance &aInstance)
     mCommissionerAloc.mScopeOverrideValid = true;
 }
 
+void BorderAgent::HandleStateChanged(Notifier::Callback &aCallback, otChangedFlags aFlags)
+{
+    aCallback.GetOwner<BorderAgent>().HandleStateChanged(aFlags);
+}
+
+void BorderAgent::HandleStateChanged(otChangedFlags aFlags)
+{
+    VerifyOrExit((aFlags & OT_CHANGED_THREAD_ROLE) != 0);
+
+    if (Get<Mle::MleRouter>().IsAttached())
+    {
+        Start();
+    }
+    else
+    {
+        Stop();
+    }
+
+exit:
+    return;
+}
+
 void BorderAgent::HandleProxyTransmit(const Coap::Message &aMessage)
 {
     Message *        message = NULL;

src/core/meshcop/border_agent.hpp

@@ -40,6 +40,7 @@
 
 #include "coap/coap.hpp"
 #include "common/locator.hpp"
+#include "common/notifier.hpp"
 #include "net/udp6.hpp"
 
 namespace ot {
@@ -63,7 +64,7 @@ public:
      * This method starts the Border Agent service.
      *
      * @retval OT_ERROR_NONE    Successfully started the Border Agent service.
-     * @retval OT_ERROR_ALREADY Already started.
+     * @retval OT_ERROR_ALREADY Border Agent is already started.
      *
      */
     otError Start(void);
@@ -71,7 +72,8 @@ public:
     /**
      * This method stops the Border Agent service.
      *
-     * @retval OT_ERROR_NONE  Successfully stopped the Border Agent service.
+     * @retval OT_ERROR_NONE    Successfully stopped the Border Agent service.
+     * @retval OT_ERROR_ALREADY Border Agent is already stopped.
      *
      */
     otError Stop(void);
@@ -85,6 +87,9 @@ public:
     otBorderAgentState GetState(void) const { return mState; }
 
 private:
+    static void HandleStateChanged(Notifier::Callback &aCallback, otChangedFlags aFlags);
+    void        HandleStateChanged(otChangedFlags aFlags);
+
     static void HandleConnected(bool aConnected, void *aContext)
     {
         static_cast<BorderAgent *>(aContext)->HandleConnected(aConnected);
@@ -151,6 +156,8 @@ private:
 
     TimerMilli         mTimer;
     otBorderAgentState mState;
+
+    Notifier::Callback mNotifierCallback;
 };
 
 } // namespace MeshCoP

src/core/thread/mle.cpp

@@ -374,17 +374,6 @@ void Mle::SetRole(DeviceRole aRole)
         mParent.SetState(Neighbor::kStateInvalid);
     }
 
-#if OPENTHREAD_CONFIG_BORDER_AGENT_ENABLE
-    if (IsAttached())
-    {
-        SuccessOrExit(Get<MeshCoP::BorderAgent>().Start());
-    }
-    else
-    {
-        SuccessOrExit(Get<MeshCoP::BorderAgent>().Stop());
-    }
-#endif
-
 exit:
     OT_UNUSED_VARIABLE(oldRole);
 }