From 21da048a004506bc3df8bae566314abdc9e924f8 Mon Sep 17 00:00:00 2001
From: Abtin Keshavarzian <abtink@google.com>
Date: Tue, 29 Oct 2019 11:39:57 -0700
Subject: [PATCH] [mac] add Mac::GenerateRandomPanId() (#4283)

This commit adds a helper function `Mac::GenerateRandomPanId()` which
generates a random PAN Identifier (excluding the broadcast PAN Id
`kPanIdBroadcast`).
---
 src/core/mac/mac_types.cpp               | 12 ++++++++++++
 src/core/mac/mac_types.hpp               |  8 ++++++++
 src/core/meshcop/dataset_manager_ftd.cpp |  5 +----
 src/core/thread/mesh_forwarder.cpp       |  9 +--------
 4 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/src/core/mac/mac_types.cpp b/src/core/mac/mac_types.cpp
index 355cf8b66..a0b33a385 100644
--- a/src/core/mac/mac_types.cpp
+++ b/src/core/mac/mac_types.cpp
@@ -42,6 +42,18 @@
 namespace ot {
 namespace Mac {
 
+PanId GenerateRandomPanId(void)
+{
+    PanId panId;
+
+    do
+    {
+        panId = Random::NonCrypto::GetUint16();
+    } while (panId == kPanIdBroadcast);
+
+    return panId;
+}
+
 void ExtAddress::GenerateRandom(void)
 {
     Random::NonCrypto::FillBuffer(m8, sizeof(ExtAddress));
diff --git a/src/core/mac/mac_types.hpp b/src/core/mac/mac_types.hpp
index 6f093bf12..3f7fa60cb 100644
--- a/src/core/mac/mac_types.hpp
+++ b/src/core/mac/mac_types.hpp
@@ -73,6 +73,14 @@ typedef otPanId PanId;
  */
 typedef otShortAddress ShortAddress;
 
+/**
+ * This function generates a random IEEE 802.15.4 PAN ID.
+ *
+ * @returns A randomly generated IEEE 802.15.4 PAN ID (excluding `kPanIdBroadcast`).
+ *
+ */
+PanId GenerateRandomPanId(void);
+
 /**
  * This structure represents an IEEE 802.15.4 Extended Address.
  *
diff --git a/src/core/meshcop/dataset_manager_ftd.cpp b/src/core/meshcop/dataset_manager_ftd.cpp
index 786bd1f7d..8dc2bb6c4 100644
--- a/src/core/meshcop/dataset_manager_ftd.cpp
+++ b/src/core/meshcop/dataset_manager_ftd.cpp
@@ -345,10 +345,7 @@ otError ActiveDataset::CreateNewNetwork(otOperationalDataset &aDataset)
     aDataset.mChannel     = preferredChannels.ChooseRandomChannel();
     aDataset.mChannelMask = supportedChannels.GetMask();
 
-    do
-    {
-        aDataset.mPanId = Random::NonCrypto::GetUint16();
-    } while (aDataset.mPanId == Mac::kPanIdBroadcast);
+    aDataset.mPanId = Mac::GenerateRandomPanId();
 
     snprintf(aDataset.mNetworkName.m8, sizeof(aDataset.mNetworkName), "OpenThread-%04x", aDataset.mPanId);
 
diff --git a/src/core/thread/mesh_forwarder.cpp b/src/core/thread/mesh_forwarder.cpp
index 95528fa11..1a17eda7e 100644
--- a/src/core/thread/mesh_forwarder.cpp
+++ b/src/core/thread/mesh_forwarder.cpp
@@ -496,14 +496,7 @@ otError MeshForwarder::HandleFrameRequest(Mac::TxFrame &aFrame)
             // value.
             if (mSendMessage->GetPanId() == Mac::kPanIdBroadcast && Get<Mac::Mac>().GetPanId() == Mac::kPanIdBroadcast)
             {
-                uint16_t panid;
-
-                do
-                {
-                    panid = Random::NonCrypto::GetUint16();
-                } while (panid == Mac::kPanIdBroadcast);
-
-                Get<Mac::Mac>().SetPanId(panid);
+                Get<Mac::Mac>().SetPanId(Mac::GenerateRandomPanId());
             }
         }