From fc307401a6aee332b36a94816033c8884ed283c5 Mon Sep 17 00:00:00 2001
From: Abtin Keshavarzian <abtink@google.com>
Date: Wed, 11 Oct 2023 17:20:16 -0700
Subject: [PATCH] [ip6] add `PrepareMulticastToLargerThanRealmLocal()` (#9513)

This commit adds `Ip6::PrepareMulticastToLargerThanRealmLocal()`,
which prepares to transmit a multicast message with destination
larger than realm-local address. It checks if any sleepy child of
device is subscribed to the multicast address and clones the message
for indirect tx if needed, before adding the IP-in-IP tunnel header.
The new method helps remove repeated code in `SendRaw()` and
`SenDatagram()`.
---
 src/core/net/ip6.cpp | 58 +++++++++++++++-----------------------------
 src/core/net/ip6.hpp |  2 +-
 2 files changed, 21 insertions(+), 39 deletions(-)

diff --git a/src/core/net/ip6.cpp b/src/core/net/ip6.cpp
index 22b383450..61926c5d9 100644
--- a/src/core/net/ip6.cpp
+++ b/src/core/net/ip6.cpp
@@ -200,12 +200,29 @@ exit:
     return error;
 }
 
-Error Ip6::AddTunneledMplOption(Message &aMessage, Header &aHeader)
+Error Ip6::PrepareMulticastToLargerThanRealmLocal(Message &aMessage, const Header &aHeader)
 {
     Error          error = kErrorNone;
     Header         tunnelHeader;
     const Address *source;
 
+#if OPENTHREAD_FTD
+    if (aHeader.GetDestination().IsMulticastLargerThanRealmLocal() &&
+        Get<ChildTable>().HasSleepyChildWithAddress(aHeader.GetDestination()))
+    {
+        Message *messageCopy = aMessage.Clone();
+
+        if (messageCopy != nullptr)
+        {
+            EnqueueDatagram(*messageCopy);
+        }
+        else
+        {
+            LogWarn("Failed to clone mcast message for indirect tx to sleepy children");
+        }
+    }
+#endif
+
     // Use IP-in-IP encapsulation (RFC2473) and ALL_MPL_FORWARDERS address.
     tunnelHeader.InitVersionTrafficClassFlow();
     tunnelHeader.SetHopLimit(static_cast<uint8_t>(kDefaultHopLimit));
@@ -280,25 +297,7 @@ Error Ip6::InsertMplOption(Message &aMessage, Header &aHeader)
     }
     else
     {
-#if OPENTHREAD_FTD
-        if (aHeader.GetDestination().IsMulticastLargerThanRealmLocal() &&
-            Get<ChildTable>().HasSleepyChildWithAddress(aHeader.GetDestination()))
-        {
-            Message *messageCopy = nullptr;
-
-            if ((messageCopy = aMessage.Clone()) != nullptr)
-            {
-                IgnoreError(HandleDatagram(*messageCopy));
-                LogInfo("Message copy for indirect transmission to sleepy children");
-            }
-            else
-            {
-                LogWarn("No enough buffer for message copy for indirect transmission to sleepy children");
-            }
-        }
-#endif
-
-        SuccessOrExit(error = AddTunneledMplOption(aMessage, aHeader));
+        SuccessOrExit(error = PrepareMulticastToLargerThanRealmLocal(aMessage, aHeader));
     }
 
 exit:
@@ -469,24 +468,7 @@ Error Ip6::SendDatagram(Message &aMessage, MessageInfo &aMessageInfo, uint8_t aI
 
     if (aMessageInfo.GetPeerAddr().IsMulticastLargerThanRealmLocal())
     {
-#if OPENTHREAD_FTD
-        if (Get<ChildTable>().HasSleepyChildWithAddress(header.GetDestination()))
-        {
-            Message *messageCopy = aMessage.Clone();
-
-            if (messageCopy != nullptr)
-            {
-                LogInfo("Message copy for indirect transmission to sleepy children");
-                EnqueueDatagram(*messageCopy);
-            }
-            else
-            {
-                LogWarn("No enough buffer for message copy for indirect transmission to sleepy children");
-            }
-        }
-#endif
-
-        SuccessOrExit(error = AddTunneledMplOption(aMessage, header));
+        SuccessOrExit(error = PrepareMulticastToLargerThanRealmLocal(aMessage, header));
     }
 
     aMessage.SetMulticastLoop(aMessageInfo.GetMulticastLoop());
diff --git a/src/core/net/ip6.hpp b/src/core/net/ip6.hpp
index 46e0b05f7..c2a2e530e 100644
--- a/src/core/net/ip6.hpp
+++ b/src/core/net/ip6.hpp
@@ -387,7 +387,7 @@ private:
     void SendIcmpError(Message &aMessage, Icmp::Header::Type aIcmpType, Icmp::Header::Code aIcmpCode);
 #endif
     Error AddMplOption(Message &aMessage, Header &aHeader);
-    Error AddTunneledMplOption(Message &aMessage, Header &aHeader);
+    Error PrepareMulticastToLargerThanRealmLocal(Message &aMessage, const Header &aHeader);
     Error InsertMplOption(Message &aMessage, Header &aHeader);
     Error RemoveMplOption(Message &aMessage);
     Error HandleOptions(Message &aMessage, Header &aHeader, bool &aReceive);