[topology] adding Child:Clear() and Router::Clear() (#4195)

src/core/thread/child_table.cpp

@@ -102,7 +102,15 @@ ChildTable::ChildTable(Instance &aInstance)
     : InstanceLocator(aInstance)
     , mMaxChildrenAllowed(kMaxChildren)
 {
-    memset(mChildren, 0, sizeof(mChildren));
+    Clear();
+}
+
+void ChildTable::Clear(void)
+{
+    for (Child *child = &mChildren[0]; child < OT_ARRAY_END(mChildren); child++)
+    {
+        child->Clear();
+    }
 }
 
 Child *ChildTable::GetChildAtIndex(uint16_t aChildIndex)
@@ -124,7 +132,7 @@ Child *ChildTable::GetNewChild(void)
     {
         if (child->GetState() == Child::kStateInvalid)
         {
-            memset(child, 0, sizeof(Child));
+            child->Clear();
             ExitNow();
         }
     }

src/core/thread/child_table.hpp

@@ -170,7 +170,7 @@ public:
      * This method clears the child table.
      *
      */
-    void Clear(void) { memset(mChildren, 0, sizeof(mChildren)); }
+    void Clear(void);
 
     /**
      * This method returns the child table index for a given `Child` instance.

src/core/thread/mle.cpp

@@ -117,7 +117,7 @@ Mle::Mle(Instance &aInstance)
 
     memset(&mLeaderData, 0, sizeof(mLeaderData));
     memset(&mParentLeaderData, 0, sizeof(mParentLeaderData));
-    memset(&mParent, 0, sizeof(mParent));
+    mParent.Clear();
     memset(&mChildIdRequest, 0, sizeof(mChildIdRequest));
     memset(&mLinkLocal64, 0, sizeof(mLinkLocal64));
     memset(&mMeshLocal64, 0, sizeof(mMeshLocal64));
@@ -125,7 +125,7 @@ Mle::Mle(Instance &aInstance)
     memset(&mLinkLocalAllThreadNodes, 0, sizeof(mLinkLocalAllThreadNodes));
     memset(&mRealmLocalAllThreadNodes, 0, sizeof(mRealmLocalAllThreadNodes));
     memset(&mLeaderAloc, 0, sizeof(mLeaderAloc));
-    memset(&mParentCandidate, 0, sizeof(mParentCandidate));
+    mParentCandidate.Clear();
     ResetCounters();
 
     // link-local 64
@@ -423,7 +423,7 @@ otError Mle::Restore(void)
             ExitNow();
         }
 
-        memset(&mParent, 0, sizeof(mParent));
+        mParent.Clear();
         mParent.SetExtAddress(*static_cast<Mac::ExtAddress *>(&parentInfo.mExtAddress));
         mParent.SetDeviceMode(DeviceMode(DeviceMode::kModeFullThreadDevice | DeviceMode::kModeRxOnWhenIdle |
                                          DeviceMode::kModeFullNetworkData | DeviceMode::kModeSecureDataRequest));
@@ -3175,8 +3175,7 @@ exit:
 
 void Mle::ResetParentCandidate(void)
 {
-    memset(&mParentCandidate, 0, sizeof(mParentCandidate));
-    mParentCandidate.SetState(Neighbor::kStateInvalid);
+    mParentCandidate.Clear();
 }
 
 otError Mle::HandleParentResponse(const Message &aMessage, const Ip6::MessageInfo &aMessageInfo, uint32_t aKeySequence)

src/core/thread/mle_router.cpp

@@ -1650,8 +1650,6 @@ otError MleRouter::HandleParentRequest(const Message &aMessage, const Ip6::Messa
     {
         VerifyOrExit((child = mChildTable.GetNewChild()) != NULL);
 
-        memset(child, 0, sizeof(*child));
-
         // MAC Address
         child->SetExtAddress(macAddr);
         child->GetLinkInfo().Clear();
@@ -3531,7 +3529,7 @@ void MleRouter::RestoreChildren(void)
             foundDuplicate = true;
         }
 
-        memset(child, 0, sizeof(*child));
+        child->Clear();
 
         child->SetExtAddress(*static_cast<const Mac::ExtAddress *>(&childInfo.mExtAddress));
         child->GetLinkInfo().Clear();

src/core/thread/router_table.cpp

@@ -183,7 +183,7 @@ void RouterTable::UpdateAllocation(void)
 
             if (router.GetRouterId() != routerId)
             {
-                memset(&router, 0, sizeof(router));
+                router.Clear();
                 router.SetRloc16(Mle::Mle::GetRloc16(routerId));
                 router.SetNextHop(Mle::kInvalidRouterId);
             }
@@ -194,7 +194,7 @@ void RouterTable::UpdateAllocation(void)
     for (uint8_t index = mActiveRouterCount; index < Mle::kMaxRouters; index++)
     {
         Router &router = mRouters[index];
-        memset(&router, 0, sizeof(router));
+        router.Clear();
         router.SetRloc16(0xffff);
     }
 }

src/core/thread/topology.cpp

@@ -46,6 +46,12 @@ void Neighbor::GenerateChallenge(void)
     Random::NonCrypto::FillBuffer(mValidPending.mPending.mChallenge, sizeof(mValidPending.mPending.mChallenge));
 }
 
+void Child::Clear(void)
+{
+    memset(reinterpret_cast<void *>(this), 0, sizeof(Child));
+    SetState(kStateInvalid);
+}
+
 bool Child::IsStateValidOrAttaching(void) const
 {
     bool rval = false;
@@ -240,4 +246,10 @@ void Child::GenerateChallenge(void)
     Random::NonCrypto::FillBuffer(mAttachChallenge, sizeof(mAttachChallenge));
 }
 
+void Router::Clear(void)
+{
+    memset(reinterpret_cast<void *>(this), 0, sizeof(Router));
+    SetState(kStateInvalid);
+}
+
 } // namespace ot

src/core/thread/topology.hpp

@@ -434,6 +434,12 @@ public:
         otChildIp6AddressIterator mIndex;
     };
 
+    /**
+     * This method clears the child entry.
+     *
+     */
+    void Clear(void);
+
     /**
      * This method indicates if the child state is valid or being attached or being restored.
      *
@@ -654,6 +660,12 @@ private:
 class Router : public Neighbor
 {
 public:
+    /**
+     * This method clears the router entry.
+     *
+     */
+    void Clear(void);
+
     /**
      * This method gets the router ID of the next hop to this router.
      *