From e4339c5939c758136fc009075239990ff8dc1d77 Mon Sep 17 00:00:00 2001
From: Abtin Keshavarzian <abtink@google.com>
Date: Thu, 3 Apr 2025 08:32:10 -0700
Subject: [PATCH] [mesh-forwarder] simplify destination MAC address
 determination (#11391)

This commit simplifies the process of determining the destination MAC
address. Specifically, when the destination is a link-local unicast
address, the MAC address is derived directly from its Interface
Identifier (IID). This commit replaces and removes the
`GetMacDestinationAddress()` method, with the calling code now
directly determining the destination MAC address.
---
 src/core/thread/indirect_sender.cpp |  2 +-
 src/core/thread/mesh_forwarder.cpp  | 26 +++++++-------------------
 src/core/thread/mesh_forwarder.hpp  |  1 -
 3 files changed, 8 insertions(+), 21 deletions(-)

diff --git a/src/core/thread/indirect_sender.cpp b/src/core/thread/indirect_sender.cpp
index b465c8de8..500d3179b 100644
--- a/src/core/thread/indirect_sender.cpp
+++ b/src/core/thread/indirect_sender.cpp
@@ -371,7 +371,7 @@ uint16_t IndirectSender::PrepareDataFrame(Mac::TxFrame &aFrame, Child &aChild, M
 
     if (ip6Header.GetDestination().IsLinkLocalUnicast())
     {
-        Get<MeshForwarder>().GetMacDestinationAddress(ip6Header.GetDestination(), macAddrs.mDestination);
+        macAddrs.mDestination.SetExtendedFromIid(ip6Header.GetDestination().GetIid());
     }
     else
     {
diff --git a/src/core/thread/mesh_forwarder.cpp b/src/core/thread/mesh_forwarder.cpp
index ae126fedd..60e7ce684 100644
--- a/src/core/thread/mesh_forwarder.cpp
+++ b/src/core/thread/mesh_forwarder.cpp
@@ -632,9 +632,13 @@ Error MeshForwarder::UpdateIp6Route(Message &aMessage)
 
     if (mle.IsDisabled() || mle.IsDetached())
     {
-        if (ip6Header.GetDestination().IsLinkLocalUnicastOrMulticast())
+        if (ip6Header.GetDestination().IsLinkLocalMulticast())
         {
-            GetMacDestinationAddress(ip6Header.GetDestination(), mMacAddrs.mDestination);
+            mMacAddrs.mDestination.SetShort(Mac::kShortAddrBroadcast);
+        }
+        else if (ip6Header.GetDestination().IsLinkLocalUnicast())
+        {
+            mMacAddrs.mDestination.SetExtendedFromIid(ip6Header.GetDestination().GetIid());
         }
         else
         {
@@ -661,7 +665,7 @@ Error MeshForwarder::UpdateIp6Route(Message &aMessage)
     }
     else if (ip6Header.GetDestination().IsLinkLocalUnicast())
     {
-        GetMacDestinationAddress(ip6Header.GetDestination(), mMacAddrs.mDestination);
+        mMacAddrs.mDestination.SetExtendedFromIid(ip6Header.GetDestination().GetIid());
     }
     else if (mle.IsMinimalEndDevice())
     {
@@ -708,22 +712,6 @@ void MeshForwarder::GetMacSourceAddress(const Ip6::Address &aIp6Addr, Mac::Addre
     }
 }
 
-void MeshForwarder::GetMacDestinationAddress(const Ip6::Address &aIp6Addr, Mac::Address &aMacAddr)
-{
-    if (aIp6Addr.IsMulticast())
-    {
-        aMacAddr.SetShort(Mac::kShortAddrBroadcast);
-    }
-    else if (Get<Mle::MleRouter>().IsRoutingLocator(aIp6Addr))
-    {
-        aMacAddr.SetShort(aIp6Addr.GetIid().GetLocator());
-    }
-    else
-    {
-        aMacAddr.SetExtendedFromIid(aIp6Addr.GetIid());
-    }
-}
-
 Mac::TxFrame *MeshForwarder::HandleFrameRequest(Mac::TxFrames &aTxFrames)
 {
     Mac::TxFrame *frame         = nullptr;
diff --git a/src/core/thread/mesh_forwarder.hpp b/src/core/thread/mesh_forwarder.hpp
index 4a27db389..22dd6be10 100644
--- a/src/core/thread/mesh_forwarder.hpp
+++ b/src/core/thread/mesh_forwarder.hpp
@@ -491,7 +491,6 @@ private:
     Error    CheckReachability(uint16_t aMeshDest, const Ip6::Header &aIp6Header);
     void     UpdateRoutes(RxInfo &aRxInfo);
     Error    FrameToMessage(RxInfo &aRxInfo, uint16_t aDatagramSize, Message *&aMessage);
-    void     GetMacDestinationAddress(const Ip6::Address &aIp6Addr, Mac::Address &aMacAddr);
     void     GetMacSourceAddress(const Ip6::Address &aIp6Addr, Mac::Address &aMacAddr);
     Message *PrepareNextDirectTransmission(void);
     void     HandleMesh(RxInfo &aRxInfo);