From d360c4b601201c1ce7762b5e2d08d2f4a8954b9c Mon Sep 17 00:00:00 2001
From: Simon Lin <simonlin@google.com>
Date: Fri, 25 Jun 2021 01:30:49 +0800
Subject: [PATCH] [backbone-router] fix Leader isn't always selected as PBBR
 (#6751)

---
 src/core/thread/network_data_service.cpp | 24 +++++++++++++++++++-----
 src/core/thread/network_data_service.hpp |  7 +++++++
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/src/core/thread/network_data_service.cpp b/src/core/thread/network_data_service.cpp
index e1493dd19..4f14c2bdf 100644
--- a/src/core/thread/network_data_service.cpp
+++ b/src/core/thread/network_data_service.cpp
@@ -119,11 +119,7 @@ void Manager::GetBackboneRouterPrimary(ot::BackboneRouter::BackboneRouterConfig
         serverData = reinterpret_cast<const BackboneRouter::ServerData *>(iterator.mServerSubTlv->GetServerData());
 
         if (rvalServerTlv == nullptr ||
-            (iterator.mServerSubTlv->GetServer16() ==
-             Mle::Mle::Rloc16FromRouterId(Get<Mle::MleRouter>().GetLeaderId())) ||
-            serverData->GetSequenceNumber() > rvalServerData->GetSequenceNumber() ||
-            (serverData->GetSequenceNumber() == rvalServerData->GetSequenceNumber() &&
-             iterator.mServerSubTlv->GetServer16() > rvalServerTlv->GetServer16()))
+            IsBackboneRouterPreferredTo(*iterator.mServerSubTlv, *serverData, *rvalServerTlv, *rvalServerData))
         {
             rvalServerTlv  = iterator.mServerSubTlv;
             rvalServerData = serverData;
@@ -141,6 +137,24 @@ exit:
     return;
 }
 
+bool Manager::IsBackboneRouterPreferredTo(const ServerTlv &                 aServerTlv,
+                                          const BackboneRouter::ServerData &aServerData,
+                                          const ServerTlv &                 aOtherServerTlv,
+                                          const BackboneRouter::ServerData &aOtherServerData) const
+{
+    bool     isPreferred;
+    uint16_t leaderRloc16 = Mle::Mle::Rloc16FromRouterId(Get<Mle::MleRouter>().GetLeaderId());
+
+    VerifyOrExit(aServerTlv.GetServer16() != leaderRloc16, isPreferred = true);
+    VerifyOrExit(aOtherServerTlv.GetServer16() != leaderRloc16, isPreferred = false);
+
+    isPreferred = aServerData.GetSequenceNumber() > aOtherServerData.GetSequenceNumber() ||
+                  (aServerData.GetSequenceNumber() == aOtherServerData.GetSequenceNumber() &&
+                   aServerTlv.GetServer16() > aOtherServerTlv.GetServer16());
+exit:
+    return isPreferred;
+}
+
 #endif // (OPENTHREAD_CONFIG_THREAD_VERSION >= OT_THREAD_VERSION_1_2)
 
 Error Manager::GetNextDnsSrpAnycastInfo(Iterator &aIterator, DnsSrpAnycast::Info &aInfo) const
diff --git a/src/core/thread/network_data_service.hpp b/src/core/thread/network_data_service.hpp
index 3a7ceef62..a93759a51 100644
--- a/src/core/thread/network_data_service.hpp
+++ b/src/core/thread/network_data_service.hpp
@@ -623,6 +623,13 @@ private:
                        bool        aServerStable,
                        uint8_t &   aServiceId) const;
     Error IterateToNextServer(Iterator &aIterator) const;
+
+#if (OPENTHREAD_CONFIG_THREAD_VERSION >= OT_THREAD_VERSION_1_2)
+    bool IsBackboneRouterPreferredTo(const ServerTlv &                 aServerTlv,
+                                     const BackboneRouter::ServerData &aServerData,
+                                     const ServerTlv &                 aOtherServerTlv,
+                                     const BackboneRouter::ServerData &aOtherServerData) const;
+#endif
 };
 
 } // namespace Service