From a3e804101ea333c3c64ec4b53fe7097f563c15f0 Mon Sep 17 00:00:00 2001
From: Abtin Keshavarzian <abtink@google.com>
Date: Wed, 3 Apr 2024 13:56:25 -0700
Subject: [PATCH] [mle] simplify `CheckReachablity()` (#9989)

This commit simplifies `MleRouter::CheckReachablity()`:

- Remove and inline `Mle::CheckReachability()` which is used
  when `IsChild()`.
- Uses local `isReachable` boolean variable.
---
 src/core/thread/mle.cpp        | 16 ------------
 src/core/thread/mle.hpp        |  1 -
 src/core/thread/mle_router.cpp | 47 +++++++++++++++-------------------
 3 files changed, 21 insertions(+), 43 deletions(-)

diff --git a/src/core/thread/mle.cpp b/src/core/thread/mle.cpp
index 234f405d9..9f3e58810 100644
--- a/src/core/thread/mle.cpp
+++ b/src/core/thread/mle.cpp
@@ -3889,22 +3889,6 @@ bool Mle::IsAnycastLocator(const Ip6::Address &aAddress) const
 
 bool Mle::IsMeshLocalAddress(const Ip6::Address &aAddress) const { return (aAddress.GetPrefix() == mMeshLocalPrefix); }
 
-Error Mle::CheckReachability(uint16_t aMeshDest, const Ip6::Header &aIp6Header)
-{
-    Error error;
-
-    if ((aMeshDest != GetRloc16()) || Get<ThreadNetif>().HasUnicastAddress(aIp6Header.GetDestination()))
-    {
-        error = kErrorNone;
-    }
-    else
-    {
-        error = kErrorNoRoute;
-    }
-
-    return error;
-}
-
 #if OPENTHREAD_CONFIG_MLE_INFORM_PREVIOUS_PARENT_ON_REATTACH
 void Mle::InformPreviousParent(void)
 {
diff --git a/src/core/thread/mle.hpp b/src/core/thread/mle.hpp
index 33d0920cf..208922bcd 100644
--- a/src/core/thread/mle.hpp
+++ b/src/core/thread/mle.hpp
@@ -1240,7 +1240,6 @@ private:
     void       SetAttachState(AttachState aState);
     void       InitNeighbor(Neighbor &aNeighbor, const RxInfo &aRxInfo);
     void       ClearParentCandidate(void) { mParentCandidate.Clear(); }
-    Error      CheckReachability(uint16_t aMeshDest, const Ip6::Header &aIp6Header);
     Error      SendDataRequest(const Ip6::Address &aDestination);
     void       HandleNotifierEvents(Events aEvents);
     void       SendDelayedResponse(TxMessage &aMessage, const DelayedResponseMetadata &aMetadata);
diff --git a/src/core/thread/mle_router.cpp b/src/core/thread/mle_router.cpp
index 40894798a..b7489e651 100644
--- a/src/core/thread/mle_router.cpp
+++ b/src/core/thread/mle_router.cpp
@@ -3238,44 +3238,39 @@ exit:
 
 Error MleRouter::CheckReachability(uint16_t aMeshDest, const Ip6::Header &aIp6Header)
 {
-    Error error = kErrorNone;
+    bool isReachable = false;
 
     if (IsChild())
     {
-        error = Mle::CheckReachability(aMeshDest, aIp6Header);
+        if (aMeshDest == GetRloc16())
+        {
+            isReachable = Get<ThreadNetif>().HasUnicastAddress(aIp6Header.GetDestination());
+        }
+        else
+        {
+            isReachable = true;
+        }
+
         ExitNow();
     }
 
-    if (aMeshDest == Get<Mac::Mac>().GetShortAddress())
-    {
-        if (Get<ThreadNetif>().HasUnicastAddress(aIp6Header.GetDestination()))
-        {
-            // IPv6 destination is this device
-            ExitNow();
-        }
-        else if (mNeighborTable.FindNeighbor(aIp6Header.GetDestination()) != nullptr)
-        {
-            // IPv6 destination is an RFD child
-            ExitNow();
-        }
-    }
-    else if (RouterIdFromRloc16(aMeshDest) == mRouterId)
-    {
-        if (mChildTable.FindChild(aMeshDest, Child::kInStateValidOrRestoring))
-        {
-            // Mesh destination is a child of this device
-            ExitNow();
-        }
-    }
-    else if (GetNextHop(aMeshDest) != Mac::kShortAddrInvalid)
+    if (aMeshDest == GetRloc16())
     {
+        isReachable = Get<ThreadNetif>().HasUnicastAddress(aIp6Header.GetDestination()) ||
+                      (mNeighborTable.FindNeighbor(aIp6Header.GetDestination()) != nullptr);
         ExitNow();
     }
 
-    error = kErrorNoRoute;
+    if (RouterIdFromRloc16(aMeshDest) == mRouterId)
+    {
+        isReachable = (mChildTable.FindChild(aMeshDest, Child::kInStateValidOrRestoring) != nullptr);
+        ExitNow();
+    }
+
+    isReachable = (GetNextHop(aMeshDest) != Mac::kShortAddrInvalid);
 
 exit:
-    return error;
+    return isReachable ? kErrorNone : kErrorNoRoute;
 }
 
 Error MleRouter::SendAddressSolicit(ThreadStatusTlv::Status aStatus)