From 0c0cedc48136927a49e0ace11faf0b14bdd3ebff Mon Sep 17 00:00:00 2001
From: Abtin Keshavarzian <abtink@google.com>
Date: Mon, 5 Feb 2024 10:23:57 -0800
Subject: [PATCH] [ip6] `SelectSourceAddress()` rule 1 on preferring same
 address (#9830)

This commit moves the check for rule 1 on preferring same address as
the destination before the `(bestAddr == nullptr)` check. This
ensures that rule 1 will be correctly applied even when the address
happens to be first one in the `GetUnicastAddresses()` list.
---
 src/core/net/ip6.cpp | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/core/net/ip6.cpp b/src/core/net/ip6.cpp
index 2334aa712..3637b9008 100644
--- a/src/core/net/ip6.cpp
+++ b/src/core/net/ip6.cpp
@@ -1330,18 +1330,18 @@ const Address *Ip6::SelectSourceAddress(const Address &aDestination) const
             overrideScope = destScope;
         }
 
-        if (bestAddr == nullptr)
-        {
-            // Rule 0: Prefer any address
-            bestAddr     = &addr;
-            bestMatchLen = matchLen;
-        }
-        else if (addr.GetAddress() == aDestination)
+        if (addr.GetAddress() == aDestination)
         {
             // Rule 1: Prefer same address
             bestAddr = &addr;
             ExitNow();
         }
+
+        if (bestAddr == nullptr)
+        {
+            bestAddr     = &addr;
+            bestMatchLen = matchLen;
+        }
         else if (addr.GetScope() < bestAddr->GetScope())
         {
             // Rule 2: Prefer appropriate scope