=== Wiring up notifications

==== Introduction

We need to translate OpenFlow messages coming up from the
<<_openflow_protocol_library_developer_guide,OpenFlow Protocol Library>>
into MD-SAL Notification objects and then publish them to the
MD-SAL.

[[mechanics]]
==== Mechanics

.  Create a Translator class
.  Register the Translator
.  Register the notificationPopListener to handle your Notification
Objects

[[create-a-translator-class]]
===== Create a Translator class

You can see an example in
https://git.opendaylight.org/gerrit/gitweb?p=openflowplugin.git;a=blob;f=openflowplugin/src/main/java/org/opendaylight/openflowplugin/openflow/md/core/translator/PacketInTranslator.java;hb=refs/heads/stable/boron[PacketInTranslator.java].

First, simply create the class

---------------------------------------------------------------------------------------------
public class PacketInTranslator implements IMDMessageTranslator<OfHeader, List<DataObject>> {
---------------------------------------------------------------------------------------------

Then implement the translate function:

---------------------------------------------------------------------------------------------
public class PacketInTranslator implements IMDMessageTranslator<OfHeader, List<DataObject>> {

    protected static final Logger LOG = LoggerFactory
            .getLogger(PacketInTranslator.class);
    @Override
    public PacketReceived translate(SwitchConnectionDistinguisher cookie,
            SessionContext sc, OfHeader msg) { 
            ...
    }
---------------------------------------------------------------------------------------------

Make sure to check that you are dealing with the expected type and cast
it:

---------------------------------------------------------------------------
if(msg instanceof PacketInMessage) {
    PacketInMessage message = (PacketInMessage)msg;
    List<DataObject> list = new CopyOnWriteArrayList<DataObject>();
---------------------------------------------------------------------------

Do your transation work and return

-------------------------------------------------------------
PacketReceived pktInEvent = pktInBuilder.build();
list.add(pktInEvent);
return list;
-------------------------------------------------------------

[[register-your-translator-class]]
===== Register your Translator Class

Next you need to go to
https://git.opendaylight.org/gerrit/gitweb?p=openflowplugin.git;a=blob;f=openflowplugin/src/main/java/org/opendaylight/openflowplugin/openflow/md/core/MDController.java;hb=refs/heads/stable/boron[MDController.java]
and in init() add register your Translator:

-----------------------------------------------------------------------------------
public void init() {
        LOG.debug("Initializing!");
        messageTranslators = new ConcurrentHashMap<>();
        popListeners = new ConcurrentHashMap<>();
        //TODO: move registration to factory
        addMessageTranslator(ErrorMessage.class, OF10, new ErrorTranslator());
        addMessageTranslator(ErrorMessage.class, OF13, new ErrorTranslator());
        addMessageTranslator(PacketInMessage.class,OF10, new PacketInTranslator());
        addMessageTranslator(PacketInMessage.class,OF13, new PacketInTranslator());
-----------------------------------------------------------------------------------

Notice that there is a separate registration for each of OpenFlow 1.0 and OpenFlow 1.3.
Basically, you indicate the type of OpenFlow Protocol Library message you wish to
translate for, the OpenFlow version, and an instance of your Translator.

[[register-your-md-sal-message-for-notification-to-the-md-sal]]
===== Register your MD-SAL Message for Notification to the MD-SAL

Now, also in MDController.init() register to have the
notificationPopListener handle your MD-SAL Message:

---------------------------------------------------------------------------------------
addMessagePopListener(PacketReceived.class, new NotificationPopListener<DataObject>());
---------------------------------------------------------------------------------------

[[you-are-done]]
===== You are done

That's all there is to it. Now when a message comes up from the
OpenFlow Protocol Library, it will be translated and published to the MD-SAL.