[nexus] mark pending action when enqueuing packets on infra interface (#13699)

Unlike otTaskletsSignalPending() and otPlatRadioTransmit(), InfraIf
previously enqueued outgoing packets into mPendingTxQueue without
calling Core::Get().MarkPendingAction().

When a higher-index node (e.g., an unattached candidate node1) sends a
packet over InfraIf to a lower-index node (e.g., node0 Border Agent),
ProcessInfraIf(node1) delivers the packet into node0.mInfraIf.Receive()
after Process(node0) has already run in the current Core::AdvanceTime()
pass. Any synchronous response packet enqueued into
node0.mInfraIf.mPendingTxQueue remained undelivered when mPendingAction
stayed false, causing Core::AdvanceTime() to jump mNow forward to the
next unrelated scheduled timer. For a 6-flight DTLS handshake between
node1 and node0, all three server flights stalled until separate
background timers expired, intermittently pushing handshake completion
past 1 second.

Add InfraIf::EnqueueTxPacket() to enqueue outgoing messages and call
Core::Get().MarkPendingAction(), make mPendingTxQueue private with
Core as a friend class, and add InfraIf::Reset() for Node::Reset().

tests/nexus/platform/nexus_infra_if.cpp

@@ -30,6 +30,7 @@
 
 #include <openthread/platform/infra_if.h>
 
+#include "nexus_core.hpp"
 #include "nexus_node.hpp"
 
 namespace ot {
@@ -62,6 +63,8 @@ void InfraIf::AfterInit(void)
     AddAddress(address);
 }
 
+void InfraIf::Reset(void) { mPendingTxQueue.DequeueAndFreeAll(); }
+
 bool InfraIf::HasAddress(const Ip6::Address &aAddress) const { return mAddresses.Contains(aAddress); }
 
 void InfraIf::AddAddress(const Ip6::Address &aAddress)
@@ -177,7 +180,13 @@ void InfraIf::SendIcmp6Nd(const Ip6::Address &aDestAddress, const uint8_t *aBuff
     message->SetOffset(sizeof(Ip6::Header));
     Checksum::UpdateMessageChecksum(*message, ip6Header.GetSource(), ip6Header.GetDestination(), Ip6::kProtoIcmp6);
 
-    mPendingTxQueue.Enqueue(*message);
+    EnqueueTxPacket(*message);
+}
+
+void InfraIf::EnqueueTxPacket(Message &aMessage)
+{
+    mPendingTxQueue.Enqueue(aMessage);
+    Core::Get().MarkPendingAction();
 }
 
 void InfraIf::SendRouterAdvertisement(const Ip6::Address &aDestination,
@@ -341,7 +350,7 @@ void InfraIf::SendIp6(const Ip6::Header &aHeader, OwnedPtr<Message> aMessagePtr)
     Log("InfraIf::SendIp6 from %s to %s (len:%u)", aHeader.GetSource().ToString().AsCString(),
         aHeader.GetDestination().ToString().AsCString(), aMessagePtr->GetLength());
 
-    mPendingTxQueue.Enqueue(*aMessagePtr.Release());
+    EnqueueTxPacket(*aMessagePtr.Release());
 }
 
 void InfraIf::SendEchoRequest(const Ip6::Address &aSrcAddress,
@@ -378,7 +387,7 @@ void InfraIf::SendEchoRequest(const Ip6::Address &aSrcAddress,
 
     SuccessOrQuit(message->Prepend(ip6Header));
 
-    mPendingTxQueue.Enqueue(*message);
+    EnqueueTxPacket(*message);
 }
 
 void InfraIf::SendUdp(const Ip6::Address &aSrcAddress,
@@ -418,7 +427,7 @@ void InfraIf::SendUdp(const Ip6::Address &aSrcAddress,
         loopbackMessage->Free();
     }
 
-    mPendingTxQueue.Enqueue(aPayload);
+    EnqueueTxPacket(aPayload);
 }
 
 void InfraIf::SetDhcp6ListeningEnabled(bool aEnable) { mDhcp6PdListening = aEnable; }
@@ -619,7 +628,7 @@ void InfraIf::HandleEchoRequest(const Ip6::Header &aHeader, Message &aMessage)
 
     SuccessOrQuit(replyMessage->Prepend(replyHeader));
 
-    mPendingTxQueue.Enqueue(*replyMessage);
+    EnqueueTxPacket(*replyMessage);
 }
 
 void InfraIf::HandleEchoReply(const Ip6::Header &aHeader, Message &aMessage)

tests/nexus/platform/nexus_infra_if.hpp

@@ -38,12 +38,15 @@ class Node;
 
 class InfraIf : public InstanceLocator
 {
+    friend class Core;
+
 public:
     using LinkLayerAddress = BorderRouter::InfraIf::LinkLayerAddress;
 
     explicit InfraIf(Instance &aInstance);
 
     void AfterInit(void);
+    void Reset(void);
 
     bool IsInitialized(void) const { return mIfIndex != 0; }
 
@@ -93,9 +96,8 @@ public:
     typedef bool (*UdpHook)(Instance &aInstance, Message &aMessage, const Ip6::MessageInfo &aMessageInfo);
     void SetUdpHook(UdpHook aHook) { mUdpHook = aHook; }
 
-    MessageQueue mPendingTxQueue;
-
 private:
+    void EnqueueTxPacket(Message &aMessage);
     void ProcessIcmp6Nd(const Ip6::Address &aSrcAddress, const uint8_t *aBuffer, uint16_t aBufferLength);
     void SendPeriodicRouterAdvertisement(void);
     void HandlePrefixInfoOption(const Ip6::Nd::PrefixInfoOption &aPio);
@@ -105,6 +107,8 @@ private:
 
     void HandleRaTimer(void);
 
+    MessageQueue mPendingTxQueue;
+
     uint32_t                   mIfIndex;
     Heap::Array<Ip6::Address>  mAddresses;
     Callback<EchoReplyHandler> mEchoReplyCallback;

tests/nexus/platform/nexus_node.cpp

@@ -55,7 +55,7 @@ void Node::Reset(void)
     mAlarmMicro.Reset();
     mMdns.Reset();
     mUpstreamDns.Reset();
-    mInfraIf.mPendingTxQueue.DequeueAndFreeAll();
+    mInfraIf.Reset();
     mPendingTasklet = false;
 
 #if OPENTHREAD_CONFIG_RADIO_LINK_TREL_ENABLE