From c57908ce9e2b04a2f048e97015c93020867fa50b Mon Sep 17 00:00:00 2001
From: Ciaran Woodward <ciaranwoodward@gmail.com>
Date: Wed, 30 Aug 2017 16:37:52 +0100
Subject: [PATCH] [meshcop] give priority to better matches during join, not
 channel (#2137)

Previous behaviour of the joiner would result in the joiner joining
the network with the highest channel number, rather than the most
suitable. This commit utilizes the priority specified in thread spec
1.1.1 section 8.4.4.1.2 to choose the most suited network for joining.
This removes the bug where it would be impossible to join the desired
network due to another network on a higher channel allowing all joiners
in the steering data.
---
 src/core/meshcop/joiner.cpp | 31 ++++++++++++++++++++++++-------
 src/core/meshcop/joiner.hpp |  2 ++
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/src/core/meshcop/joiner.cpp b/src/core/meshcop/joiner.cpp
index 58efebd32..d3eb6ad26 100644
--- a/src/core/meshcop/joiner.cpp
+++ b/src/core/meshcop/joiner.cpp
@@ -67,7 +67,9 @@ Joiner::Joiner(ThreadNetif &aNetif):
     mContext(NULL),
     mCcitt(0),
     mAnsi(0),
+    mJoinerRouterIsSpecific(false),
     mJoinerRouterChannel(0),
+    mJoinerRouterRssi(0),
     mJoinerRouterPanId(0),
     mJoinerUdpPort(0),
     mVendorName(NULL),
@@ -119,6 +121,8 @@ otError Joiner::Start(const char *aPSKd, const char *aProvisioningUrl,
     SuccessOrExit(error);
 
     mJoinerRouterPanId = Mac::kPanIdBroadcast;
+    mJoinerRouterRssi = 0;
+    mJoinerRouterIsSpecific = false;
     SuccessOrExit(error = netif.GetMle().Discover(0, netif.GetMac().GetPanId(), true, false, HandleDiscoverResult,
                                                   this));
 
@@ -197,19 +201,32 @@ void Joiner::HandleDiscoverResult(otActiveScanResult *aResult)
         steeringData.SetLength(aResult->mSteeringData.mLength);
         memcpy(steeringData.GetValue(), aResult->mSteeringData.m8, steeringData.GetLength());
 
-        if (steeringData.DoesAllowAny() ||
-            (steeringData.GetBit(mCcitt % steeringData.GetNumBits()) &&
-             steeringData.GetBit(mAnsi % steeringData.GetNumBits())))
+        if (steeringData.DoesAllowAny())
         {
-            mJoinerUdpPort = aResult->mJoinerUdpPort;
-            mJoinerRouterPanId = aResult->mPanId;
-            mJoinerRouterChannel = aResult->mChannel;
-            memcpy(&mJoinerRouter, &aResult->mExtAddress, sizeof(mJoinerRouter));
+            VerifyOrExit(!mJoinerRouterIsSpecific);
+            VerifyOrExit(aResult->mRssi > mJoinerRouterRssi);
+        }
+        else if (steeringData.GetBit(mCcitt % steeringData.GetNumBits()) &&
+                 steeringData.GetBit(mAnsi % steeringData.GetNumBits()))
+        {
+            if (mJoinerRouterIsSpecific)
+            {
+                VerifyOrExit(aResult->mRssi > mJoinerRouterRssi);
+            }
+
+            mJoinerRouterIsSpecific = true;
         }
         else
         {
             otLogDebgMeshCoP(GetInstance(), "Steering data does not include this device");
+            ExitNow();
         }
+
+        mJoinerUdpPort = aResult->mJoinerUdpPort;
+        mJoinerRouterPanId = aResult->mPanId;
+        mJoinerRouterChannel = aResult->mChannel;
+        mJoinerRouterRssi = aResult->mRssi;
+        memcpy(&mJoinerRouter, &aResult->mExtAddress, sizeof(mJoinerRouter));
     }
     else if (mJoinerRouterPanId != Mac::kPanIdBroadcast)
     {
diff --git a/src/core/meshcop/joiner.hpp b/src/core/meshcop/joiner.hpp
index e67b67a6e..6a3478504 100644
--- a/src/core/meshcop/joiner.hpp
+++ b/src/core/meshcop/joiner.hpp
@@ -140,7 +140,9 @@ private:
     uint16_t mCcitt;
     uint16_t mAnsi;
 
+    bool mJoinerRouterIsSpecific;
     uint8_t mJoinerRouterChannel;
+    int8_t mJoinerRouterRssi;
     uint16_t mJoinerRouterPanId;
     uint16_t mJoinerUdpPort;
     Mac::ExtAddress mJoinerRouter;