[network-diag] introduce RouterNeighborTlv (#12827)

This commit updates `RouterNeighborTlv` to follow the `SimpleTlvInfo`
pattern, separating the TLV value structure from its type/length
header.

Specifically, it defines `RouterNeighborTlvValue` to hold the data
fields for a router neighbor's diagnostic information, while
`RouterNeighborTlv` is redefined as a `SimpleTlvInfo` using the value
structure and the `kRouterNeighbor` type.

This allows the use of generic `Tlv::Append<RouterNeighborTlv>()` and
`tlvInfo.Read<RouterNeighborTlv>()` methods,  which are generally
safer and allow value type reuse.

The `NetworkDiagnostic`  and `MeshDiag` module are updated to
utilize these new methods.

src/core/thread/network_diagnostic.cpp

@@ -162,15 +162,15 @@ exit:
 
 Error Server::AppendRouterNeighborTlvs(Message &aMessage)
 {
-    Error             error = kErrorNone;
-    RouterNeighborTlv neighborTlv;
+    Error                  error = kErrorNone;
+    RouterNeighborTlvValue neighborTlvValue;
 
     for (Router &router : Get<RouterTable>())
     {
         if (router.IsStateValid())
         {
-            neighborTlv.InitFrom(router);
-            SuccessOrExit(error = neighborTlv.AppendTo(aMessage));
+            neighborTlvValue.InitFrom(router);
+            SuccessOrExit(error = Tlv::Append<RouterNeighborTlv>(aMessage, neighborTlvValue));
         }
     }
 
@@ -755,8 +755,8 @@ exit:
 
 Error Server::AppendRouterNeighborTlvs(Coap::Message *&aAnswer, AnswerInfo &aInfo)
 {
-    Error             error = kErrorNone;
-    RouterNeighborTlv neighborTlv;
+    Error                  error = kErrorNone;
+    RouterNeighborTlvValue neighborTlvValue;
 
     for (Router &router : Get<RouterTable>())
     {
@@ -765,9 +765,9 @@ Error Server::AppendRouterNeighborTlvs(Coap::Message *&aAnswer, AnswerInfo &aInf
             continue;
         }
 
-        neighborTlv.InitFrom(router);
+        neighborTlvValue.InitFrom(router);
 
-        SuccessOrExit(error = neighborTlv.AppendTo(*aAnswer));
+        SuccessOrExit(error = Tlv::Append<RouterNeighborTlv>(*aAnswer, neighborTlvValue));
         SuccessOrExit(error = CheckAnswerLength(aAnswer, aInfo));
     }
 

src/core/thread/network_diagnostic_tlvs.cpp

@@ -170,15 +170,12 @@ void ChildTlvValue::InitFrom(const Child &aChild)
 }
 
 //---------------------------------------------------------------------------------------------------------------------
-// RouterNeighborTlv
+// RouterNeighborTlvValue
 
-void RouterNeighborTlv::InitFrom(const Router &aRouter)
+void RouterNeighborTlvValue::InitFrom(const Router &aRouter)
 {
     Clear();
 
-    SetType(kRouterNeighbor);
-    SetLength(sizeof(*this) - sizeof(Tlv));
-
     mFlags |= kFlagsTrackErrRate;
     mRloc16           = BigEndian::HostSwap16(aRouter.GetRloc16());
     mExtAddress       = aRouter.GetExtAddress();

src/core/thread/network_diagnostic_tlvs.hpp

@@ -647,10 +647,10 @@ private:
 } OT_TOOL_PACKED_END;
 
 /**
- * Implements Router Neighbor TLV generation and parsing.
+ * Implements Router Neighbor TLV Value generation and parsing.
  */
 OT_TOOL_PACKED_BEGIN
-class RouterNeighborTlv : public Tlv, public TlvInfo<Tlv::kRouterNeighbor>, public Clearable<RouterNeighborTlv>
+class RouterNeighborTlvValue : public Clearable<RouterNeighborTlvValue>
 {
 public:
     static constexpr uint8_t kFlagsTrackErrRate = 1 << 7; ///< Supports tracking error rates.
@@ -751,6 +751,11 @@ private:
     uint16_t        mMessageErrorRate; // (IPv6) msg error rate (0x0000->0%, 0xffff->100%)
 } OT_TOOL_PACKED_END;
 
+/**
+ * Defines Router Neighbor TLV constants and types.
+ */
+typedef SimpleTlvInfo<Tlv::kRouterNeighbor, RouterNeighborTlvValue> RouterNeighborTlv;
+
 #endif // OPENTHREAD_FTD
 
 /**

src/core/utils/mesh_diag.cpp

@@ -325,21 +325,20 @@ exit:
 
 bool MeshDiag::ProcessRouterNeighborTableAnswer(Coap::Message &aMessage, const Ip6::MessageInfo &aMessageInfo)
 {
-    bool                didProcess = false;
-    RouterNeighborTlv   neighborTlv;
-    RouterNeighborEntry entry;
-    uint16_t            offset;
+    bool                   didProcess = false;
+    Tlv::Info              tlvInfo;
+    RouterNeighborTlvValue neighborTlvValue;
+    RouterNeighborEntry    entry;
 
     SuccessOrExit(ProcessMessage(aMessage, aMessageInfo, mQueryRouterNeighborTable.mRouterRloc16));
 
     while (true)
     {
-        SuccessOrExit(Tlv::FindTlv(aMessage, neighborTlv, offset));
-        VerifyOrExit(!neighborTlv.IsExtended());
+        SuccessOrExit(tlvInfo.FindIn(aMessage, RouterNeighborTlv::kType));
 
         didProcess = true;
 
-        if (neighborTlv.GetLength() == 0)
+        if (tlvInfo.GetLength() == 0)
         {
             // We reached end of the list.
             mState = kStateIdle;
@@ -348,16 +347,16 @@ bool MeshDiag::ProcessRouterNeighborTableAnswer(Coap::Message &aMessage, const I
             ExitNow();
         }
 
-        VerifyOrExit(neighborTlv.GetLength() >= sizeof(RouterNeighborTlv) - sizeof(Tlv));
+        SuccessOrExit(tlvInfo.Read<RouterNeighborTlv>(aMessage, neighborTlvValue));
 
-        entry.SetFrom(neighborTlv);
+        entry.SetFrom(neighborTlvValue);
         mQueryRouterNeighborTable.mCallback.InvokeIfSet(kErrorPending, &entry);
 
         // Make sure query operation is not canceled from the
         // callback.
         VerifyOrExit(mState == kStateQueryRouterNeighborTable);
 
-        aMessage.SetOffset(static_cast<uint16_t>(offset + neighborTlv.GetSize()));
+        aMessage.SetOffset(tlvInfo.GetTlvOffsetRange().GetEndOffset());
     }
 
 exit:
@@ -607,18 +606,18 @@ void MeshDiag::ChildEntry::SetFrom(const ChildTlvValue &aChildTlvValue)
 //---------------------------------------------------------------------------------------------------------------------
 // MeshDiag::RouterNeighborEntry
 
-void MeshDiag::RouterNeighborEntry::SetFrom(const RouterNeighborTlv &aTlv)
+void MeshDiag::RouterNeighborEntry::SetFrom(const RouterNeighborTlvValue &aTlvValue)
 {
-    mSupportsErrRate  = (aTlv.GetFlags() & RouterNeighborTlv::kFlagsTrackErrRate);
-    mRloc16           = aTlv.GetRloc16();
-    mExtAddress       = aTlv.GetExtAddress();
-    mVersion          = aTlv.GetVersion();
-    mConnectionTime   = aTlv.GetConnectionTime();
-    mLinkMargin       = aTlv.GetLinkMargin();
-    mAverageRssi      = aTlv.GetAverageRssi();
-    mLastRssi         = aTlv.GetLastRssi();
-    mFrameErrorRate   = aTlv.GetFrameErrorRate();
-    mMessageErrorRate = aTlv.GetMessageErrorRate();
+    mSupportsErrRate  = (aTlvValue.GetFlags() & RouterNeighborTlvValue::kFlagsTrackErrRate);
+    mRloc16           = aTlvValue.GetRloc16();
+    mExtAddress       = aTlvValue.GetExtAddress();
+    mVersion          = aTlvValue.GetVersion();
+    mConnectionTime   = aTlvValue.GetConnectionTime();
+    mLinkMargin       = aTlvValue.GetLinkMargin();
+    mAverageRssi      = aTlvValue.GetAverageRssi();
+    mLastRssi         = aTlvValue.GetLastRssi();
+    mFrameErrorRate   = aTlvValue.GetFrameErrorRate();
+    mMessageErrorRate = aTlvValue.GetMessageErrorRate();
 }
 
 } // namespace Utils

src/core/utils/mesh_diag.hpp

@@ -294,7 +294,7 @@ private:
         friend class MeshDiag;
 
     private:
-        void SetFrom(const NetworkDiagnostic::RouterNeighborTlv &aTlv);
+        void SetFrom(const NetworkDiagnostic::RouterNeighborTlvValue &aTlvValue);
     };
 
     Error SendQuery(uint16_t aRloc16, const uint8_t *aTlvs, uint8_t aTlvsLength);