ncp: Various changes in order to better support address change events (#165)

There are two logical sets of changes presented here:

* core/thread/mle: Follow remove/change/add pattern for unicast addresses

  The goal here is to avoid modifying an address after it has been added to
  the netif. That way we get reliable removal/insertion eventing. This
  pattern has other advantages which will likely become apparent later.

* openthread-types: Add `OT_IP6_ML_ADDR_CHANGED` flag

  This allows us to know precisely when the mesh local address has changed
  its value.

include/openthread-types.h

@@ -221,7 +221,9 @@ enum
     OT_NET_KEY_SEQUENCE     = 1 << 5,  ///< Thread Key Sequence changed
 
     OT_THREAD_CHILD_ADDED   = 1 << 6,  ///< Child was added
-    OT_THREAD_CHILD_REMOVED = 1 << 7   ///< Child was removed
+    OT_THREAD_CHILD_REMOVED = 1 << 7,  ///< Child was removed
+
+    OT_IP6_ML_ADDR_CHANGED  = 1 << 8,  ///< The mesh-local address has changed
 };
 
 /**

src/core/thread/mle.cpp

@@ -102,18 +102,15 @@ Mle::Mle(ThreadNetif &aThreadNetif) :
     memcpy(mMeshLocal64.GetAddress().m8 + 1, mMac.GetExtendedPanId(), 5);
     mMeshLocal64.GetAddress().m8[6] = 0x00;
     mMeshLocal64.GetAddress().m8[7] = 0x00;
-    SetMeshLocalPrefix(mMeshLocal64.GetAddress().m8);
-
     // mesh-local 64
     for (int i = 8; i < 16; i++)
     {
         mMeshLocal64.GetAddress().m8[i] = otPlatRandomGet();
     }
-
     mMeshLocal64.mPrefixLength = 64;
     mMeshLocal64.mPreferredLifetime = 0xffffffff;
     mMeshLocal64.mValidLifetime = 0xffffffff;
-    mNetif.AddUnicastAddress(mMeshLocal64);
+    SetMeshLocalPrefix(mMeshLocal64.GetAddress().m8); // Also calls AddUnicastAddress
 
     // mesh-local 16
     mMeshLocal16.GetAddress().m16[4] = HostSwap16(0x0000);
@@ -350,6 +347,10 @@ const uint8_t *Mle::GetMeshLocalPrefix(void) const
 
 ThreadError Mle::SetMeshLocalPrefix(const uint8_t *aMeshLocalPrefix)
 {
+    // We must remove the old address before adding the new one.
+    mNetif.RemoveUnicastAddress(mMeshLocal64);
+    mNetif.RemoveUnicastAddress(mMeshLocal16);
+
     memcpy(mMeshLocal64.GetAddress().m8, aMeshLocalPrefix, 8);
     memcpy(mMeshLocal16.GetAddress().m8, mMeshLocal64.GetAddress().m8, 8);
 
@@ -359,6 +360,12 @@ ThreadError Mle::SetMeshLocalPrefix(const uint8_t *aMeshLocalPrefix)
     mRealmLocalAllThreadNodes.GetAddress().m8[3] = 64;
     memcpy(mRealmLocalAllThreadNodes.GetAddress().m8 + 4, mMeshLocal64.GetAddress().m8, 8);
 
+    // Add the address back into the table.
+    mNetif.AddUnicastAddress(mMeshLocal64);
+
+    // Changing the prefix also causes the mesh local address to be different.
+    mNetif.SetStateChangedFlags(OT_IP6_ML_ADDR_CHANGED);
+
     return kThreadError_None;
 }
 
@@ -394,6 +401,9 @@ uint16_t Mle::GetRloc16(void) const
 
 ThreadError Mle::SetRloc16(uint16_t aRloc16)
 {
+    mNetif.RemoveUnicastAddress(mLinkLocal16);
+    mNetif.RemoveUnicastAddress(mMeshLocal16);
+
     if (aRloc16 != Mac::kShortAddrInvalid)
     {
         // link-local 16
@@ -404,11 +414,6 @@ ThreadError Mle::SetRloc16(uint16_t aRloc16)
         mMeshLocal16.GetAddress().m16[7] = HostSwap16(aRloc16);
         mNetif.AddUnicastAddress(mMeshLocal16);
     }
-    else
-    {
-        mNetif.RemoveUnicastAddress(mLinkLocal16);
-        mNetif.RemoveUnicastAddress(mMeshLocal16);
-    }
 
     mMac.SetShortAddress(aRloc16);
 
@@ -743,6 +748,7 @@ void Mle::HandleNetifStateChanged(uint32_t aFlags)
         }
 
         mNetif.AddUnicastAddress(mMeshLocal64);
+        mNetif.SetStateChangedFlags(OT_IP6_ML_ADDR_CHANGED);
     }
 
     switch (mDeviceState)

src/ncp/ncp_base.cpp

@@ -386,7 +386,15 @@ void NcpBase::UpdateChangedProps(void *context)
 void NcpBase::UpdateChangedProps()
 {
     if (!mSending) {
-        if ((mChangedFlags & OT_NET_STATE) != 0)
+        if ((mChangedFlags & OT_IP6_ML_ADDR_CHANGED) != 0)
+        {
+            mChangedFlags &= ~OT_IP6_ML_ADDR_CHANGED;
+            HandleCommandPropertyGet(
+                SPINEL_HEADER_FLAG | SPINEL_HEADER_IID_0,
+                SPINEL_PROP_IPV6_ML_ADDR
+            );
+        }
+        else if ((mChangedFlags & OT_NET_STATE) != 0)
         {
             mChangedFlags &= ~OT_NET_STATE;
             HandleCommandPropertyGet(