[nexus] migrate anycast locator test to Nexus (openthread#12962)

This commit migrates the anycast locator test from the thread-cert
functional tests to the Nexus simulation framework.

The new Nexus test 'test_anycast_locator.cpp' covers:
- Anycast Locator (ALOC) resolution for the Leader from all nodes.
- Custom service ALOC resolution when only one node provides it.
- Closest-node ALOC resolution when multiple nodes provide the same
  service in a line topology (LEADER-R1-R2-R3-R4).
- Verification that nodes resolve to the nearest service instance.

The original Python test 'test_anycast_locator.py' is removed as its
functionality is now fully covered by the Nexus test.

Author: jwhui

tests/nexus/CMakeLists.txt

@@ -384,6 +384,7 @@ ot_nexus_test(1_4_CS_TC_3 "cert;nexus")
 ot_nexus_test(inform_previous_parent_on_reattach "cert;nexus")
 
 # Misc tests
+ot_nexus_test(anycast_locator "core;nexus")
 ot_nexus_test(br_upgrade_router_role "core;nexus")
 ot_nexus_test(border_admitter "core;nexus")
 ot_nexus_test(border_agent "core;nexus")

tests/nexus/test_anycast_locator.cpp

@@ -0,0 +1,238 @@
+/*
+ *  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.
+ */
+
+#include <initializer_list>
+#include <stdio.h>
+#include <string.h>
+
+#include "platform/nexus_core.hpp"
+#include "platform/nexus_node.hpp"
+
+namespace ot {
+namespace Nexus {
+
+struct LocateResult
+{
+    Error        mError;
+    Ip6::Address mMeshLocalAddress;
+    uint16_t     mRloc16;
+    bool         mCallbackInvoked;
+
+    void Clear(void)
+    {
+        mError = kErrorNone;
+        mMeshLocalAddress.Clear();
+        mRloc16          = 0;
+        mCallbackInvoked = false;
+    }
+};
+
+static void HandleLocateResult(void *aContext, otError aError, const otIp6Address *aAddress, uint16_t aRloc16)
+{
+    LocateResult *result = static_cast<LocateResult *>(aContext);
+
+    result->mError           = aError;
+    result->mCallbackInvoked = true;
+    result->mRloc16          = aRloc16;
+
+    if (aAddress != nullptr)
+    {
+        result->mMeshLocalAddress = AsCoreType(aAddress);
+    }
+}
+
+static void Locate(Core &aNexus, Node &aNode, const Ip6::Address &aAnycastAddress, LocateResult &aResult)
+{
+    aResult.Clear();
+    SuccessOrQuit(aNode.Get<AnycastLocator>().Locate(aAnycastAddress, HandleLocateResult, &aResult));
+
+    for (uint32_t i = 0; i < 10000; i++)
+    {
+        aNexus.AdvanceTime(10);
+        if (aResult.mCallbackInvoked)
+        {
+            break;
+        }
+    }
+
+    VerifyOrQuit(aResult.mCallbackInvoked);
+    SuccessOrQuit(aResult.mError);
+}
+
+void TestAnycastLocator(void)
+{
+    // Topology:
+    //   LEADER -- ROUTER1 -- ROUTER2 -- ROUTER3 -- ROUTER4
+
+    Core nexus;
+
+    Node &leader  = nexus.CreateNode();
+    Node &router1 = nexus.CreateNode();
+    Node &router2 = nexus.CreateNode();
+    Node &router3 = nexus.CreateNode();
+    Node &router4 = nexus.CreateNode();
+
+    leader.SetName("LEADER");
+    router1.SetName("ROUTER1");
+    router2.SetName("ROUTER2");
+    router3.SetName("ROUTER3");
+    router4.SetName("ROUTER4");
+
+    Node *nodes[] = {&leader, &router1, &router2, &router3, &router4};
+
+    nexus.AdvanceTime(0);
+
+    Log("---------------------------------------------------------------------------------------");
+    Log("Form network with line topology");
+
+    AllowLinkBetween(leader, router1);
+    AllowLinkBetween(router1, router2);
+    AllowLinkBetween(router2, router3);
+    AllowLinkBetween(router3, router4);
+
+    leader.Form();
+    nexus.AdvanceTime(20 * 1000);
+
+    for (uint8_t i = 1; i < GetArrayLength(nodes); i++)
+    {
+        nodes[i]->Join(*nodes[i - 1]);
+        nexus.AdvanceTime(20 * 1000);
+    }
+
+    // Wait for all to become routers and network to stabilize
+    nexus.AdvanceTime(300 * 1000);
+
+    for (Node *node : nodes)
+    {
+        VerifyOrQuit(node->Get<Mle::Mle>().IsRouter() || node->Get<Mle::Mle>().IsLeader());
+    }
+
+    Log("---------------------------------------------------------------------------------------");
+    Log("1. Locate leader ALOC from all nodes");
+
+    Ip6::Address leaderAloc;
+    leader.Get<Mle::Mle>().GetLeaderAloc(leaderAloc);
+
+    LocateResult result;
+
+    for (Node *node : nodes)
+    {
+        Log("Node %s locating leader ALOC", node->GetName());
+        Locate(nexus, *node, leaderAloc, result);
+        VerifyOrQuit(result.mMeshLocalAddress == leader.Get<Mle::Mle>().GetMeshLocalEid());
+        VerifyOrQuit(result.mRloc16 == leader.Get<Mle::Mle>().GetRloc16());
+    }
+
+    Log("---------------------------------------------------------------------------------------");
+    Log("2. Add a service on router4 and locate its ALOC");
+
+    uint32_t                 enterpriseNumber = 44970;
+    NetworkData::ServiceData serviceData;
+    NetworkData::ServerData  serverData;
+    uint8_t                  sData[] = {0x57, 0x12, 0x34};
+    uint8_t                  rData[] = {0x00};
+
+    serviceData.Init(sData, sizeof(sData));
+    serverData.Init(rData, sizeof(rData));
+
+    SuccessOrQuit(router4.Get<NetworkData::Local>().AddService(enterpriseNumber, serviceData, true, serverData));
+    router4.Get<NetworkData::Notifier>().HandleServerDataUpdated();
+    nexus.AdvanceTime(20 * 1000);
+
+    // Get the service ALOC from router4
+    Ip6::Address serviceAloc;
+    bool         found = false;
+
+    for (const Ip6::Netif::UnicastAddress &addr : router4.Get<ThreadNetif>().GetUnicastAddresses())
+    {
+        if (router4.Get<Mle::Mle>().IsAnycastLocator(addr.GetAddress()) &&
+            addr.GetAddress().GetIid().IsAnycastLocator())
+        {
+            // The leader ALOC is also an ALOC, so we need to make sure it's not the leader ALOC.
+            if (addr.GetAddress() != leaderAloc)
+            {
+                serviceAloc = addr.GetAddress();
+                found       = true;
+                break;
+            }
+        }
+    }
+    VerifyOrQuit(found);
+
+    for (Node *node : nodes)
+    {
+        Log("Node %s locating service ALOC", node->GetName());
+        Locate(nexus, *node, serviceAloc, result);
+        VerifyOrQuit(result.mMeshLocalAddress == router4.Get<Mle::Mle>().GetMeshLocalEid());
+        VerifyOrQuit(result.mRloc16 == router4.Get<Mle::Mle>().GetRloc16());
+    }
+
+    Log("---------------------------------------------------------------------------------------");
+    Log("3. Add same service on leader and ensure we locate the closest ALOC destination");
+
+    SuccessOrQuit(leader.Get<NetworkData::Local>().AddService(enterpriseNumber, serviceData, true, serverData));
+    leader.Get<NetworkData::Notifier>().HandleServerDataUpdated();
+    nexus.AdvanceTime(20 * 1000);
+
+    // leader and router1 should locate leader as closest service ALOC
+    for (Node *node : {&leader, &router1})
+    {
+        Log("Node %s locating service ALOC (expected leader)", node->GetName());
+        Locate(nexus, *node, serviceAloc, result);
+        VerifyOrQuit(result.mMeshLocalAddress == leader.Get<Mle::Mle>().GetMeshLocalEid());
+        VerifyOrQuit(result.mRloc16 == leader.Get<Mle::Mle>().GetRloc16());
+    }
+
+    // router3 and router4 should locate router4
+    for (Node *node : {&router3, &router4})
+    {
+        Log("Node %s locating service ALOC (expected router4)", node->GetName());
+        Locate(nexus, *node, serviceAloc, result);
+        VerifyOrQuit(result.mMeshLocalAddress == router4.Get<Mle::Mle>().GetMeshLocalEid());
+        VerifyOrQuit(result.mRloc16 == router4.Get<Mle::Mle>().GetRloc16());
+    }
+
+    // router2 is in middle and can locate either one
+    Log("Node %s locating service ALOC (expected either leader or router4)", router2.GetName());
+    Locate(nexus, router2, serviceAloc, result);
+    VerifyOrQuit((result.mMeshLocalAddress == leader.Get<Mle::Mle>().GetMeshLocalEid() &&
+                  result.mRloc16 == leader.Get<Mle::Mle>().GetRloc16()) ||
+                 (result.mMeshLocalAddress == router4.Get<Mle::Mle>().GetMeshLocalEid() &&
+                  result.mRloc16 == router4.Get<Mle::Mle>().GetRloc16()));
+
+    Log("All tests passed");
+}
+
+} // namespace Nexus
+} // namespace ot
+
+int main(void)
+{
+    ot::Nexus::TestAnycastLocator();
+    return 0;
+}