[thread-tlvs] add Ip6AddressesTlv::AppendTo() helper method (#13049)

This commit extracts the logic for appending an `Ip6AddressesTlv` into
a new `static` helper method, `Ip6AddressesTlv::AppendTo()`.

Previously, multiple locations in the codebase manually managed the
TLV construction and appending. This change centralizes this logic,
simplifying the call sites in `BackboneRouter::Manager` and
`MlrManager`.

src/core/BUILD.gn

@@ -775,6 +775,7 @@ openthread_core_files = [
   "thread/thread_link_info.hpp",
   "thread/thread_netif.cpp",
   "thread/thread_netif.hpp",
+  "thread/thread_tlvs.cpp",
   "thread/thread_tlvs.hpp",
   "thread/time_sync_service.cpp",
   "thread/time_sync_service.hpp",

src/core/CMakeLists.txt

@@ -278,6 +278,7 @@ set(COMMON_SOURCES
     thread/src_match_controller.cpp
     thread/thread_link_info.cpp
     thread/thread_netif.cpp
+    thread/thread_tlvs.cpp
     thread/time_sync_service.cpp
     thread/tmf.cpp
     thread/uri_paths.cpp

src/core/backbone_router/bbr_manager.cpp

@@ -291,16 +291,7 @@ void Manager::SendMulticastListenerRegistrationResponse(const Coap::Msg &aMsg,
 
     if (aFailedAddressNum > 0)
     {
-        Tlv::Bookmark tlvBookmark;
-
-        SuccessOrExit(error = Tlv::StartTlv(*message, Ip6AddressesTlv::kType, tlvBookmark));
-
-        for (uint8_t i = 0; i < aFailedAddressNum; i++)
-        {
-            SuccessOrExit(error = message->Append(aFailedAddresses[i]));
-        }
-
-        SuccessOrExit(error = Tlv::EndTlv(*message, tlvBookmark));
+        SuccessOrExit(error = Ip6AddressesTlv::AppendTo(*message, aFailedAddresses, aFailedAddressNum));
     }
 
     SuccessOrExit(error = Get<Tmf::Agent>().SendMessage(*message, aMsg.mMessageInfo));
@@ -317,7 +308,6 @@ void Manager::SendBackboneMulticastListenerRegistration(const Ip6::Address *aAdd
     Error             error   = kErrorNone;
     Coap::Message    *message = nullptr;
     Ip6::MessageInfo  messageInfo;
-    Tlv::Bookmark     tlvBookmark;
     BackboneTmfAgent &backboneTmf = Get<BackboneRouter::BackboneTmfAgent>();
 
     OT_ASSERT(aAddressNum >= kMlrMinIp6Addresses && aAddressNum <= kMlrMaxIp6Addresses);
@@ -325,9 +315,7 @@ void Manager::SendBackboneMulticastListenerRegistration(const Ip6::Address *aAdd
     message = backboneTmf.AllocateAndInitNonConfirmablePostMessage(kUriBackboneMlr);
     VerifyOrExit(message != nullptr, error = kErrorNoBufs);
 
-    SuccessOrExit(error = Tlv::StartTlv(*message, Ip6AddressesTlv::kType, tlvBookmark));
-    SuccessOrExit(error = message->AppendBytes(aAddresses, sizeof(Ip6::Address) * aAddressNum));
-    SuccessOrExit(error = Tlv::EndTlv(*message, tlvBookmark));
+    SuccessOrExit(error = Ip6AddressesTlv::AppendTo(*message, aAddresses, aAddressNum));
 
     SuccessOrExit(error = Tlv::Append<ThreadTimeoutTlv>(*message, aTimeout));
 

src/core/thread/mlr_manager.cpp

@@ -358,16 +358,13 @@ Error MlrManager::SendMlrMessage(const Ip6::Address         *aAddresses,
     Error          error   = kErrorNone;
     Coap::Message *message = nullptr;
     Ip6::Address   destAddr;
-    Tlv::Bookmark  tlvBookmark;
 
     VerifyOrExit(Get<BackboneRouter::Leader>().HasPrimary(), error = kErrorInvalidState);
 
     message = Get<Tmf::Agent>().AllocateAndInitConfirmablePostMessage(kUriMlr);
     VerifyOrExit(message != nullptr, error = kErrorNoBufs);
 
-    SuccessOrExit(error = Tlv::StartTlv(*message, Ip6AddressesTlv::kType, tlvBookmark));
-    SuccessOrExit(error = message->AppendBytes(aAddresses, sizeof(Ip6::Address) * aAddressNum));
-    SuccessOrExit(error = Tlv::EndTlv(*message, tlvBookmark));
+    SuccessOrExit(error = Ip6AddressesTlv::AppendTo(*message, aAddresses, aAddressNum));
 
 #if OPENTHREAD_FTD && OPENTHREAD_CONFIG_TMF_PROXY_MLR_ENABLE && OPENTHREAD_CONFIG_COMMISSIONER_ENABLE
     if (Get<MeshCoP::Commissioner>().IsActive())

src/core/thread/thread_tlvs.cpp

@@ -0,0 +1,55 @@
+/*
+ *  Copyright (c) 2026, The OpenThread Authors.
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions are met:
+ *  1. Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *  2. Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *  3. Neither the name of the copyright holder nor the
+ *     names of its contributors may be used to endorse or promote products
+ *     derived from this software without specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ *  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ *  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ *  POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * @file
+ *   This file implements methods for generating and processing Thread Network Layer TLVs.
+ */
+
+#include "thread_tlvs.hpp"
+
+namespace ot {
+
+#if OPENTHREAD_CONFIG_THREAD_VERSION >= OT_THREAD_VERSION_1_2
+
+Error Ip6AddressesTlv::AppendTo(Message &aMessage, const Ip6::Address *aAddresses, uint16_t aNumAddresses)
+{
+    Error         error;
+    Tlv::Bookmark tlvBookmark;
+
+    SuccessOrExit(error = Tlv::StartTlv(aMessage, kType, tlvBookmark));
+    SuccessOrExit(error = aMessage.AppendBytes(aAddresses, aNumAddresses * sizeof(Ip6::Address)));
+    error = Tlv::EndTlv(aMessage, tlvBookmark);
+
+exit:
+    return error;
+}
+
+#endif
+
+} // namespace ot

src/core/thread/thread_tlvs.hpp

@@ -149,9 +149,25 @@ typedef TlvInfo<ThreadTlv::kThreadNetworkData> ThreadNetworkDataTlv;
 #if OPENTHREAD_CONFIG_THREAD_VERSION >= OT_THREAD_VERSION_1_2
 
 /**
- * Defines IPv6 Addresses TLV constants and types.
+ * Defines IPv6 Addresses TLV constants and types and helper methods.
  */
-typedef TlvInfo<ThreadTlv::kIp6Addresses> Ip6AddressesTlv;
+class Ip6AddressesTlv : public TlvInfo<ThreadTlv::kIp6Addresses>
+{
+public:
+    /**
+     * Appends an IPv6 Addresses TLV to a message.
+     *
+     * @param[in,out] aMessage       The message to append to.
+     * @param[in]     aAddresses     A pointer to an array of IPv6 addresses.
+     * @param[in]     aNumAddresses  The number of IPv6 addresses in the @p aAddresses array.
+     *
+     * @retval kErrorNone     Successfully appended the TLV.
+     * @retval kErrorNoBufs   Insufficient available buffers to grow the message.
+     */
+    static Error AppendTo(Message &aMessage, const Ip6::Address *aAddresses, uint16_t aNumAddresses);
+
+    Ip6AddressesTlv(void) = delete;
+};
 
 #endif // OPENTHREAD_CONFIG_THREAD_VERSION >= OT_THREAD_VERSION_1_2
 

tests/nexus/test_1_2_BBR_TC_2.cpp

@@ -295,7 +295,6 @@ void Test_1_2_BBR_TC_2(void)
     {
         Ip6::Address   ma1;
         Coap::Message *message;
-        Tlv::Bookmark  tlvBookmark;
         Ip6::Address   destAddr;
 
         SuccessOrQuit(ma1.FromString(kMa1Address));
@@ -303,9 +302,7 @@ void Test_1_2_BBR_TC_2(void)
         message = router1.Get<Tmf::Agent>().AllocateAndInitConfirmablePostMessage(kUriMlr);
         VerifyOrQuit(message != nullptr);
 
-        SuccessOrQuit(Tlv::StartTlv(*message, Ip6AddressesTlv::kType, tlvBookmark));
-        SuccessOrQuit(message->Append(ma1));
-        SuccessOrQuit(Tlv::EndTlv(*message, tlvBookmark));
+        SuccessOrQuit(Ip6AddressesTlv::AppendTo(*message, &ma1, 1));
 
         destAddr = br1.Get<Mle::Mle>().GetMeshLocalEid();
         SuccessOrQuit(router1.Get<Tmf::Agent>().SendMessageTo(*message, destAddr, nullptr, nullptr));