[dataset] add WriteTimestamp() and RemoveTimestamp() (#10333)

This commit introduces new helper methods in the `Dataset` class to
write or remove a Timestamp TLV (Active or Pending) to/from the
Dataset. These are added alongside the existing `ReadTimestamp()`
method.

src/core/meshcop/dataset.cpp

@@ -352,11 +352,6 @@ exit:
     return error;
 }
 
-Error Dataset::ReadTimestamp(Type aType, Timestamp &aTimestamp) const
-{
-    return (aType == kActive) ? Read<ActiveTimestampTlv>(aTimestamp) : Read<PendingTimestampTlv>(aTimestamp);
-}
-
 Error Dataset::WriteTlv(Tlv::Type aType, const void *aValue, uint8_t aLength)
 {
     Error    error          = kErrorNone;
@@ -530,6 +525,30 @@ void Dataset::RemoveTlv(Tlv *aTlv)
     }
 }
 
+Error Dataset::ReadTimestamp(Type aType, Timestamp &aTimestamp) const
+{
+    Error      error = kErrorNone;
+    const Tlv *tlv   = FindTlv(TimestampTlvFor(aType));
+
+    VerifyOrExit(tlv != nullptr, error = kErrorNotFound);
+
+    // Since both `ActiveTimestampTlv` and `PendingTimestampTlv` use
+    // `Timestamp` as their TLV value format, we can safely use
+    // `ReadValueAs<ActiveTimestampTlv>()` for both.
+
+    aTimestamp = tlv->ReadValueAs<ActiveTimestampTlv>();
+
+exit:
+    return error;
+}
+
+Error Dataset::WriteTimestamp(Type aType, const Timestamp &aTimestamp)
+{
+    return WriteTlv(TimestampTlvFor(aType), &aTimestamp, sizeof(Timestamp));
+}
+
+void Dataset::RemoveTimestamp(Type aType) { RemoveTlv(TimestampTlvFor(aType)); }
+
 bool Dataset::IsSubsetOf(const Dataset &aOther) const
 {
     bool isSubset = false;

src/core/meshcop/dataset.hpp

@@ -365,18 +365,6 @@ public:
         return (tlv == nullptr) ? kErrorNotFound : (aValue = tlv->ReadValueAs<UintTlvType>(), kErrorNone);
     }
 
-    /**
-     * Reads the Timestamp (Active or Pending).
-     *
-     * @param[in]  aType       The type: active or pending.
-     * @param[out] aTimestamp  A reference to a `Timestamp` to output the value.
-     *
-     * @retval kErrorNone      Timestamp was read successfully. @p aTimestamp is updated.
-     * @retval kErrorNotFound  Could not find the requested Timestamp TLV.
-     *
-     */
-    Error ReadTimestamp(Type aType, Timestamp &aTimestamp) const;
-
     /**
      * Writes a TLV to the Dataset.
      *
@@ -513,6 +501,40 @@ public:
      */
     void RemoveTlv(Tlv::Type aType);
 
+    /**
+     * Reads the Timestamp TLV (Active or Pending).
+     *
+     * @param[in]  aType       The timestamp type, active or pending.
+     * @param[out] aTimestamp  A reference to a `Timestamp` to output the value.
+     *
+     * @retval kErrorNone      Timestamp was read successfully. @p aTimestamp is updated.
+     * @retval kErrorNotFound  Could not find the requested Timestamp TLV.
+     *
+     */
+    Error ReadTimestamp(Type aType, Timestamp &aTimestamp) const;
+
+    /**
+     * Writes the Timestamp TLV (Active or Pending).
+     *
+     * If the TLV already exists, it will be replaced. Otherwise, the TLV will be appended.
+     *
+     * @param[in] aType       The timestamp type, active or pending.
+     * @param[in] aTimestamp  The timestamp value.
+     *
+     * @retval kErrorNone    Successfully updated the Timestamp TLV.
+     * @retval kErrorNoBufs  Could not append the Timestamp TLV due to insufficient buffer space.
+     *
+     */
+    Error WriteTimestamp(Type aType, const Timestamp &aTimestamp);
+
+    /**
+     * Removes the Timestamp TLV (Active or Pending) from the Dataset.
+     *
+     * @param[in] aType       The timestamp type, active or pending.
+     *
+     */
+    void RemoveTimestamp(Type aType);
+
     /**
      * Returns a pointer to the byte representation of the Dataset.
      *
@@ -712,6 +734,11 @@ public:
 private:
     void RemoveTlv(Tlv *aTlv);
 
+    static Tlv::Type TimestampTlvFor(Type aType)
+    {
+        return (aType == kActive) ? Tlv::kActiveTimestamp : Tlv::kPendingTimestamp;
+    }
+
     uint8_t   mTlvs[kMaxLength];
     uint8_t   mLength;
     TimeMilli mUpdateTime; // Local time last updated

src/core/meshcop/dataset_manager.cpp

@@ -286,14 +286,7 @@ Error DatasetManager::Save(const Timestamp &aTimestamp, const Message &aMessage,
     SuccessOrExit(error = dataset.SetFrom(aMessage, aOffset, aLength));
     SuccessOrExit(error = dataset.ValidateTlvs());
 
-    if (IsActiveDataset())
-    {
-        SuccessOrExit(error = dataset.Write<ActiveTimestampTlv>(aTimestamp));
-    }
-    else
-    {
-        SuccessOrExit(error = dataset.Write<PendingTimestampTlv>(aTimestamp));
-    }
+    SuccessOrExit(error = dataset.WriteTimestamp(mType, aTimestamp));
 
     error = Save(dataset);
 

src/core/meshcop/dataset_manager_ftd.cpp

@@ -76,7 +76,7 @@ Error DatasetManager::AppendMleDatasetTlv(Message &aMessage) const
     // appending to the message. The timestamp is appended as its own
     // MLE TLV to the message.
 
-    dataset.RemoveTlv(IsActiveDataset() ? Tlv::kActiveTimestamp : Tlv::kPendingTimestamp);
+    dataset.RemoveTimestamp(mType);
 
     return Tlv::AppendTlv(aMessage, mleTlvType, dataset.GetBytes(), dataset.GetLength());
 }