[dataset] enforce maximum delay timer value and improve handling (#10023)

This commit makes the following improvements to Delay Timer TLV
handling in Pending Operational Datasets:

- Enforces maximum delay adhering to the Thread spec's maximum Delay
  Timer value (72 hours), clamping larger values.
- Defines min, max, and default delay timer constants in
  `DelayTimerTlv`.
- Adds `CalculateRemainingDelay()` helper method to calculate
  remaining delay.
- Removes code handling delay values exceeding the OpenThread `Timer`
  limitation (now redundant due to the stricter 72-hour maximum).

src/core/meshcop/dataset.cpp

@@ -473,19 +473,9 @@ Error Dataset::AppendMleDatasetTlv(Type aType, Message &aMessage) const
         }
         else if (cur->GetType() == Tlv::kDelayTimer)
         {
-            uint32_t elapsed    = TimerMilli::GetNow() - mUpdateTime;
-            uint32_t delayTimer = cur->ReadValueAs<DelayTimerTlv>();
+            uint32_t remainingDelay = DelayTimerTlv::CalculateRemainingDelay(*cur, mUpdateTime);
 
-            if (delayTimer > elapsed)
-            {
-                delayTimer -= elapsed;
-            }
-            else
-            {
-                delayTimer = 0;
-            }
-
-            SuccessOrExit(error = Tlv::Append<DelayTimerTlv>(aMessage, delayTimer));
+            SuccessOrExit(error = Tlv::Append<DelayTimerTlv>(aMessage, remainingDelay));
         }
         else
         {

src/core/meshcop/dataset_local.cpp

@@ -106,25 +106,10 @@ Error DatasetLocal::Read(Dataset &aDataset) const
     }
     else
     {
-        uint32_t elapsed;
-        uint32_t delayTimer;
-        Tlv     *tlv = aDataset.FindTlv(Tlv::kDelayTimer);
+        Tlv *tlv = aDataset.FindTlv(Tlv::kDelayTimer);
 
         VerifyOrExit(tlv != nullptr);
-
-        elapsed    = TimerMilli::GetNow() - mUpdateTime;
-        delayTimer = tlv->ReadValueAs<DelayTimerTlv>();
-
-        if (delayTimer > elapsed)
-        {
-            delayTimer -= elapsed;
-        }
-        else
-        {
-            delayTimer = 0;
-        }
-
-        tlv->WriteValueAs<DelayTimerTlv>(delayTimer);
+        tlv->WriteValueAs<DelayTimerTlv>(DelayTimerTlv::CalculateRemainingDelay(*tlv, mUpdateTime));
     }
 
     aDataset.mUpdateTime = TimerMilli::GetNow();

src/core/meshcop/dataset_manager.cpp

@@ -725,10 +725,7 @@ void PendingDatasetManager::StartDelayTimer(void)
     tlv = dataset.FindTlv(Tlv::kDelayTimer);
     VerifyOrExit(tlv != nullptr);
 
-    delay = tlv->ReadValueAs<DelayTimerTlv>();
-
-    // the Timer implementation does not support the full 32 bit range
-    delay = Min(delay, Timer::kMaxDelay);
+    delay = Min(tlv->ReadValueAs<DelayTimerTlv>(), DelayTimerTlv::kMaxDelay);
 
     mDelayTimer.StartAt(dataset.GetUpdateTime(), delay);
     LogInfo("delay timer started %lu", ToUlong(delay));
@@ -739,25 +736,9 @@ exit:
 
 void PendingDatasetManager::HandleDelayTimer(void)
 {
-    Tlv    *tlv;
     Dataset dataset;
 
     IgnoreError(Read(dataset));
-
-    // if the Delay Timer value is larger than what our Timer implementation can handle, we have to compute
-    // the remainder and wait some more.
-    if ((tlv = dataset.FindTlv(Tlv::kDelayTimer)) != nullptr)
-    {
-        uint32_t elapsed = mDelayTimer.GetFireTime() - dataset.GetUpdateTime();
-        uint32_t delay   = tlv->ReadValueAs<DelayTimerTlv>();
-
-        if (elapsed < delay)
-        {
-            mDelayTimer.StartAt(mDelayTimer.GetFireTime(), delay - elapsed);
-            ExitNow();
-        }
-    }
-
     LogInfo("pending delay timer expired");
 
     dataset.ConvertToActive();
@@ -765,9 +746,6 @@ void PendingDatasetManager::HandleDelayTimer(void)
     Get<ActiveDatasetManager>().Save(dataset);
 
     Clear();
-
-exit:
-    return;
 }
 
 template <>

src/core/meshcop/dataset_manager.hpp

@@ -182,12 +182,6 @@ public:
 #endif
 
 protected:
-    /**
-     * Default Delay Timer value for a Pending Operational Dataset (ms)
-     *
-     */
-    static constexpr uint32_t kDefaultDelayTimer = OPENTHREAD_CONFIG_TMF_PENDING_DATASET_DEFAULT_DELAY;
-
     /**
      * Defines a generic Dataset TLV to read from a message.
      *

src/core/meshcop/dataset_manager_ftd.cpp

@@ -202,11 +202,11 @@ Error DatasetManager::HandleSet(Coap::Message &aMessage, const Ip6::MessageInfo
 
             case Tlv::kDelayTimer:
             {
-                uint32_t delayTimer = datasetTlv.ReadValueAs<DelayTimerTlv>();
+                uint32_t delayTimer = Min(datasetTlv.ReadValueAs<DelayTimerTlv>(), DelayTimerTlv::kMaxDelay);
 
-                if (doesAffectNetworkKey && delayTimer < kDefaultDelayTimer)
+                if (doesAffectNetworkKey && delayTimer < DelayTimerTlv::kDefaultDelay)
                 {
-                    delayTimer = kDefaultDelayTimer;
+                    delayTimer = DelayTimerTlv::kDefaultDelay;
                 }
                 else
                 {

src/core/meshcop/meshcop_leader.cpp

@@ -58,7 +58,7 @@ RegisterLogModule("MeshCoPLeader");
 Leader::Leader(Instance &aInstance)
     : InstanceLocator(aInstance)
     , mTimer(aInstance)
-    , mDelayTimerMinimal(kMinDelayTimer)
+    , mDelayTimerMinimal(DelayTimerTlv::kMinDelay)
     , mSessionId(Random::NonCrypto::GetUint16())
 {
 }
@@ -218,7 +218,7 @@ Error Leader::SetDelayTimerMinimal(uint32_t aDelayTimerMinimal)
 {
     Error error = kErrorNone;
 
-    VerifyOrExit((aDelayTimerMinimal != 0 && aDelayTimerMinimal < kMinDelayTimer), error = kErrorInvalidArgs);
+    VerifyOrExit((aDelayTimerMinimal != 0 && aDelayTimerMinimal < DelayTimerTlv::kMinDelay), error = kErrorInvalidArgs);
     mDelayTimerMinimal = aDelayTimerMinimal;
 
 exit:

src/core/meshcop/meshcop_leader.hpp

@@ -104,7 +104,6 @@ public:
     void SetEmptyCommissionerData(void);
 
 private:
-    static constexpr uint32_t kMinDelayTimer         = OPENTHREAD_CONFIG_TMF_PENDING_DATASET_MINIMUM_DELAY; // (msec)
     static constexpr uint32_t kTimeoutLeaderPetition = 50; // TIMEOUT_LEAD_PET (seconds)
 
     OT_TOOL_PACKED_BEGIN

src/core/meshcop/meshcop_tlvs.cpp

@@ -158,6 +158,23 @@ const char *StateTlv::StateToString(State aState)
     return aState == kReject ? kStateStrings[2] : kStateStrings[aState];
 }
 
+uint32_t DelayTimerTlv::CalculateRemainingDelay(const Tlv &aDelayTimerTlv, TimeMilli aUpdateTime)
+{
+    uint32_t delay   = Min(aDelayTimerTlv.ReadValueAs<DelayTimerTlv>(), kMaxDelay);
+    uint32_t elapsed = TimerMilli::GetNow() - aUpdateTime;
+
+    if (delay > elapsed)
+    {
+        delay -= elapsed;
+    }
+    else
+    {
+        delay = 0;
+    }
+
+    return delay;
+}
+
 bool ChannelMaskTlv::IsValid(void) const
 {
     uint32_t channelMask;

src/core/meshcop/meshcop_tlvs.hpp

@@ -611,7 +611,48 @@ typedef SimpleTlvInfo<Tlv::kPendingTimestamp, Timestamp> PendingTimestampTlv;
  * Defines Delay Timer TLV constants and types.
  *
  */
-typedef UintTlvInfo<Tlv::kDelayTimer, uint32_t> DelayTimerTlv;
+class DelayTimerTlv : public UintTlvInfo<Tlv::kDelayTimer, uint32_t>
+{
+public:
+    /**
+     * Minimum Delay Timer value (in msec).
+     *
+     */
+    static constexpr uint32_t kMinDelay = OPENTHREAD_CONFIG_TMF_PENDING_DATASET_MINIMUM_DELAY;
+
+    /**
+     * Maximum Delay Timer value (in msec).
+     *
+     */
+    static constexpr uint32_t kMaxDelay = (72 * Time::kOneHourInMsec);
+
+    /**
+     * Default Delay Timer value (in msec).
+     *
+     */
+    static constexpr uint32_t kDefaultDelay = OPENTHREAD_CONFIG_TMF_PENDING_DATASET_DEFAULT_DELAY;
+
+    /**
+     * Calculates the remaining delay in milliseconds, based on the value read from a Delay Timer TLV and the specified
+     * update time.
+     *
+     * Ensures that the calculated delay does not exceed `kMaxDelay`. Also accounts for time already elapsed since
+     * @p aUpdateTime.
+     *
+     * Caller MUST ensure that @p aDelayTimerTlv is a Delay Timer TLV, otherwise behavior is undefined.
+     *
+     * @param[in] aDelayTimerTlv   The delay timer TLV to read delay from.
+     * @param[in] aUpdateTimer     The update time of the Dataset.
+     *
+     * @return The remaining delay (in msec).
+     *
+     */
+    static uint32_t CalculateRemainingDelay(const Tlv &aDelayTimerTlv, TimeMilli aUpdateTime);
+
+    static_assert(kMinDelay <= kMaxDelay, "TMF_PENDING_DATASET_MINIMUM_DELAY is larger than max allowed");
+    static_assert(kDefaultDelay <= kMaxDelay, "TMF_PENDING_DATASET_DEFAULT_DELAY is larger than max allowed");
+    static_assert(kDefaultDelay >= kMinDelay, "TMF_PENDING_DATASET_DEFAULT_DELAY is smaller than min allowed");
+};
 
 /**
  * Implements Channel Mask TLV generation and parsing.