[meshcop-leader] simplify adding CommissioningData (#9540)

This commit contains smaller changes in` MeshCoP::Leader` class:
- Changes `CommissioningData` to be a `private` type in this class
- Adds `Init()` to `CommisioningData()` to init all sub-tlvs.

src/core/meshcop/meshcop_leader.cpp

@@ -87,18 +87,8 @@ template <> void Leader::HandleTmf<kUriLeaderPetition>(Coap::Message &aMessage,
         ResignCommissioner();
     }
 
-    data.mBorderAgentLocator.Init();
-    data.mBorderAgentLocator.SetBorderAgentLocator(aMessageInfo.GetPeerAddr().GetIid().GetLocator());
-
-    data.mCommissionerSessionId.Init();
-    data.mCommissionerSessionId.SetCommissionerSessionId(++mSessionId);
-
-    data.mSteeringData.Init();
-    data.mSteeringData.SetLength(1);
-    data.mSteeringData.Clear();
-
-    SuccessOrExit(
-        Get<NetworkData::Leader>().SetCommissioningData(reinterpret_cast<uint8_t *>(&data), data.GetLength()));
+    data.Init(aMessageInfo.GetPeerAddr().GetIid().GetLocator(), ++mSessionId);
+    SuccessOrExit(Get<NetworkData::Leader>().SetCommissioningData(&data, data.GetLength()));
 
     mCommissionerId = commissionerId;
 
@@ -263,8 +253,7 @@ void Leader::SetEmptyCommissionerData(void)
     sessionIdTlv.Init();
     sessionIdTlv.SetCommissionerSessionId(++mSessionId);
 
-    IgnoreError(Get<NetworkData::Leader>().SetCommissioningData(reinterpret_cast<uint8_t *>(&sessionIdTlv),
-                                                                sizeof(Tlv) + sessionIdTlv.GetLength()));
+    IgnoreError(Get<NetworkData::Leader>().SetCommissioningData(&sessionIdTlv, sizeof(CommissionerSessionIdTlv)));
 }
 
 void Leader::ResignCommissioner(void)
@@ -275,6 +264,25 @@ void Leader::ResignCommissioner(void)
     LogInfo("commissioner inactive");
 }
 
+void Leader::CommissioningData::Init(uint16_t aBorderAgentRloc16, uint16_t aSessionId)
+{
+    mBorderAgentLocatorTlv.Init();
+    mBorderAgentLocatorTlv.SetBorderAgentLocator(aBorderAgentRloc16);
+
+    mSessionIdTlv.Init();
+    mSessionIdTlv.SetCommissionerSessionId(aSessionId);
+
+    mSteeringDataTlv.Init();
+    mSteeringDataTlv.SetLength(1);
+    mSteeringDataTlv.Clear();
+}
+
+uint8_t Leader::CommissioningData::GetLength(void) const
+{
+    return static_cast<uint8_t>(sizeof(BorderAgentLocatorTlv) + sizeof(CommissionerSessionIdTlv) +
+                                mSteeringDataTlv.GetSize());
+}
+
 } // namespace MeshCoP
 } // namespace ot
 

src/core/meshcop/meshcop_leader.hpp

@@ -49,21 +49,6 @@
 namespace ot {
 namespace MeshCoP {
 
-OT_TOOL_PACKED_BEGIN
-class CommissioningData
-{
-public:
-    uint8_t GetLength(void) const
-    {
-        return sizeof(Tlv) + mBorderAgentLocator.GetLength() + sizeof(Tlv) + mCommissionerSessionId.GetLength() +
-               sizeof(Tlv) + mSteeringData.GetLength();
-    }
-
-    BorderAgentLocatorTlv    mBorderAgentLocator;
-    CommissionerSessionIdTlv mCommissionerSessionId;
-    SteeringDataTlv          mSteeringData;
-} OT_TOOL_PACKED_END;
-
 class Leader : public InstanceLocator, private NonCopyable
 {
     friend class Tmf::Agent;
@@ -113,6 +98,19 @@ public:
 private:
     static constexpr uint32_t kTimeoutLeaderPetition = 50; // TIMEOUT_LEAD_PET (seconds)
 
+    OT_TOOL_PACKED_BEGIN
+    class CommissioningData
+    {
+    public:
+        void    Init(uint16_t aBorderAgentRloc16, uint16_t aSessionId);
+        uint8_t GetLength(void) const;
+
+    private:
+        BorderAgentLocatorTlv    mBorderAgentLocatorTlv;
+        CommissionerSessionIdTlv mSessionIdTlv;
+        SteeringDataTlv          mSteeringDataTlv;
+    } OT_TOOL_PACKED_END;
+
     void HandleTimer(void);
 
     template <Uri kUri> void HandleTmf(Coap::Message &aMessage, const Ip6::MessageInfo &aMessageInfo);

src/core/thread/network_data_leader.cpp

@@ -428,7 +428,7 @@ exit:
     return error;
 }
 
-Error LeaderBase::SetCommissioningData(const uint8_t *aValue, uint8_t aValueLength)
+Error LeaderBase::SetCommissioningData(const void *aValue, uint8_t aValueLength)
 {
     Error                 error = kErrorNone;
     CommissioningDataTlv *commissioningDataTlv;

src/core/thread/network_data_leader.hpp

@@ -240,7 +240,7 @@ public:
      * @retval kErrorNoBufs   Insufficient space to add the Commissioning Data.
      *
      */
-    Error SetCommissioningData(const uint8_t *aValue, uint8_t aValueLength);
+    Error SetCommissioningData(const void *aValue, uint8_t aValueLength);
 
     /**
      * Checks if the steering data includes a Joiner.