libnl++: add new func to send raw data with len

Some netlink attrib does not ending with null char.
Currently req.add string will always sending ending null character.
Add a new func called addBuffer that does not send ending null
character.

Bug: 238794143
Test: build, manual test
Change-Id: If51380cab95b2ae725673301b429b9e9889c5b0a
diff --git a/automotive/can/1.0/default/libnetdevice/can.cpp b/automotive/can/1.0/default/libnetdevice/can.cpp
index 083f4f0..2a0545a 100644
--- a/automotive/can/1.0/default/libnetdevice/can.cpp
+++ b/automotive/can/1.0/default/libnetdevice/can.cpp
@@ -80,7 +80,7 @@
 
     {
         auto linkinfo = req.addNested(IFLA_LINKINFO);
-        req.add(IFLA_INFO_KIND, "can");
+        req.addBuffer(IFLA_INFO_KIND, "can");
         {
             auto infodata = req.addNested(IFLA_INFO_DATA);
             /* For CAN FD, it would require to add IFLA_CAN_DATA_BITTIMING
diff --git a/automotive/can/1.0/default/libnetdevice/libnetdevice.cpp b/automotive/can/1.0/default/libnetdevice/libnetdevice.cpp
index 4c5b309..2d3b417 100644
--- a/automotive/can/1.0/default/libnetdevice/libnetdevice.cpp
+++ b/automotive/can/1.0/default/libnetdevice/libnetdevice.cpp
@@ -60,7 +60,7 @@
 
     {
         auto linkinfo = req.addNested(IFLA_LINKINFO);
-        req.add(IFLA_INFO_KIND, type);
+        req.addBuffer(IFLA_INFO_KIND, type);
     }
 
     nl::Socket sock(NETLINK_ROUTE);
diff --git a/automotive/can/1.0/default/libnetdevice/vlan.cpp b/automotive/can/1.0/default/libnetdevice/vlan.cpp
index ee02f7b..35b21b8 100644
--- a/automotive/can/1.0/default/libnetdevice/vlan.cpp
+++ b/automotive/can/1.0/default/libnetdevice/vlan.cpp
@@ -40,7 +40,7 @@
 
     {
         auto linkinfo = req.addNested(IFLA_LINKINFO);
-        req.add(IFLA_INFO_KIND, "vlan");
+        req.addBuffer(IFLA_INFO_KIND, "vlan");
 
         {
             auto linkinfo = req.addNested(IFLA_INFO_DATA);
diff --git a/automotive/can/1.0/default/libnl++/include/libnl++/MessageFactory.h b/automotive/can/1.0/default/libnl++/include/libnl++/MessageFactory.h
index c3d72c5..a5a425e 100644
--- a/automotive/can/1.0/default/libnl++/include/libnl++/MessageFactory.h
+++ b/automotive/can/1.0/default/libnl++/include/libnl++/MessageFactory.h
@@ -106,18 +106,25 @@
      */
     template <class A>
     void add(nlattrtype_t type, const A& attr) {
-        add(type, &attr, sizeof(attr));
+        addInternal(type, &attr, sizeof(attr));
     }
 
+    // It will always send the last null character, otherwise use addBuffer
+    // variant instead
     template <>
     void add(nlattrtype_t type, const std::string& s) {
-        add(type, s.c_str(), s.size() + 1);
+        addInternal(type, s.c_str(), s.size() + 1);
+    }
+
+    void addBuffer(nlattrtype_t type, const std::string_view& s) {
+        addInternal(type, s.data(), s.size());
     }
 
     /** Guard class to frame nested attributes. \see addNested(nlattrtype_t). */
     class [[nodiscard]] NestedGuard {
       public:
-        NestedGuard(MessageFactory & req, nlattrtype_t type) : mReq(req), mAttr(req.add(type)) {}
+        NestedGuard(MessageFactory& req, nlattrtype_t type)
+            : mReq(req), mAttr(req.addInternal(type)) {}
         ~NestedGuard() { closeNested(&mReq.mMessage.header, mAttr); }
 
       private:
@@ -138,7 +145,7 @@
      *    MessageFactory<ifinfomsg> req(RTM_NEWLINK, NLM_F_REQUEST);
      *    {
      *        auto linkinfo = req.addNested(IFLA_LINKINFO);
-     *        req.add(IFLA_INFO_KIND, "can");
+     *        req.addBuffer(IFLA_INFO_KIND, "can");
      *        {
      *            auto infodata = req.addNested(IFLA_INFO_DATA);
      *            req.add(IFLA_CAN_BITTIMING, bitTimingStruct);
@@ -154,7 +161,7 @@
     Message mMessage = {};
     bool mIsGood = true;
 
-    nlattr* add(nlattrtype_t type, const void* data = nullptr, size_t len = 0) {
+    nlattr* addInternal(nlattrtype_t type, const void* data = nullptr, size_t len = 0) {
         if (!mIsGood) return nullptr;
         auto attr = MessageFactoryBase::add(&mMessage.header, sizeof(mMessage), type, data, len);
         if (attr == nullptr) mIsGood = false;