[certification] disable auto Thread attaching for Reference Device (#1217)

This commit enhances `OTBR_NO_AUTO_ATTACH` option to disable auto
Thread attaching for Reference Device:
- Use `-DOTBR_NO_AUTO_ATTACH=1` to disable auto Thread attaching

2 files changed, 19 insertions, 2 deletions

diff --git a/src/ncp/ncp_openthread.cpp b/src/ncp/ncp_openthread.cpp
index 42882cc7..8d37e75e 100644
--- a/src/ncp/ncp_openthread.cpp
+++ b/src/ncp/ncp_openthread.cpp
@@ -197,12 +197,25 @@ void ControllerOpenThread::Process(const MainloopContext &aMainloop)
 
     otSysMainloopProcess(mInstance, &aMainloop);
 
-    if (getenv("OTBR_NO_AUTO_ATTACH") == nullptr && mThreadHelper->TryResumeNetwork() == OT_ERROR_NONE)
+    if (IsAutoAttachEnabled() && mThreadHelper->TryResumeNetwork() == OT_ERROR_NONE)
     {
-        setenv("OTBR_NO_AUTO_ATTACH", "1", 0);
+        DisableAutoAttach();
     }
 }
 
+bool ControllerOpenThread::IsAutoAttachEnabled(void)
+{
+    const char *val = getenv("OTBR_NO_AUTO_ATTACH");
+
+    // Auto Thread attaching is enabled if OTBR_NO_AUTO_ATTACH is unset, empty or "0"
+    return (val == nullptr || !strcmp(val, "") || !strcmp(val, "0"));
+}
+
+void ControllerOpenThread::DisableAutoAttach(void)
+{
+    setenv("OTBR_NO_AUTO_ATTACH", "1", 1);
+}
+
 void ControllerOpenThread::PostTimerTask(Milliseconds aDelay, TaskRunner::Task<void> aTask)
 {
     mTaskRunner.Post(std::move(aDelay), std::move(aTask));
diff --git a/src/ncp/ncp_openthread.hpp b/src/ncp/ncp_openthread.hpp
index e8ce0c6e..b79e07ca 100644
--- a/src/ncp/ncp_openthread.hpp
+++ b/src/ncp/ncp_openthread.hpp
@@ -183,6 +183,10 @@ private:
     void        HandleBackboneRouterNdProxyEvent(otBackboneRouterNdProxyEvent aEvent, const otIp6Address *aAddress);
 #endif
 
+    static bool IsAutoAttachEnabled(void);
+
+    static void DisableAutoAttach(void);
+
     otInstance *mInstance;
 
     otPlatformConfig                           mConfig;