How to send custom XML data using the Smack library?

I'm using the Smack API in Java to connect to my XMPP server.

I want to send a customized message packet like this:

<message to="you@MyServer.com" type="chat" MYFIELD="custom stuff">
    <body> hi </body>
    <CUSTOM_STANZA A="..." B="..."> 
        C="..." 
        D="..."
    </CUSTOM_STANZA>
</message>

I'm guessing that I create implement my own Packet with that returns this XML in it's toXML() method. But that doesn't seem to work.

Any help would be appreciated.

Solution

You need to define a custom class that should implements ExtensionElement (as menitioned by @Flow)

A very detailed explanation that produces the following stanza is available in this answer

<message id='923442621149' type='chat'><body>shanraisshan</body>
<reply xmlns='shayan:reply' rText='this is custom attribute'/>
</message>

where reply is a custom extension, which contains

Element (reply)
Namespace (shayan:reply)

the list of default xmpp namespaces are available at Official XMPP website