ejabberd : How to extract data from xml element

I have this packet :

{xmlelement,"presence", [{"xml:lang","en"}, {"ver","6.00.00"}, {"to", "[email protected]/user"}],
                        [{xmlelement,"c", [{"xmlns", "http://jabber.org/protocol/caps"}, {"node", "http://www.google.com/xmpp/client/caps/"}, {"ver", "eVvrsq8jya/4AZMjFl5BeDKSmg4="}, {"hash","sha-1"}], []},
                        {xmlelement,"nick", [{"xmlns", "http://jabber.org/protocol/nick"}], [{xmlcdata,<<"user">>}]},
                        {xmlelement,"x", [{"xmlns", "http://jabber.org/protocol/muc"}], [{xmlelement,"history", [{"maxstanzas","20"}, {"maxchars","32768"}], []}]}]}

And I want to extract data from : ("maxchars" && "node")

What I'm doing is using functions located in xml.erl but i don't know how to do it .

Example for what I tried :

xml:get_subtag(Packet, "maxchars")

Solution

With a recent version of ejabberd (= that is less than 3 years old), you can do as follow.

I assume packet is binary xmlel record:

P = {xmlel,<<"presence">>, [{<<"xml:lang">>,<<"en">>}, {<<"ver">>,<<"6.00.00">>}, {<<"to">>, <<"[email protected]/user">>}],
     [{xmlel,<<"c">>, [{<<"xmlns">>, <<"http://jabber.org/protocol/caps">>}, {<<"node">>, <<"http://www.google.com/xmpp/client/caps/">>}, {<<"ver">>, <<"eVvrsq8jya/4AZMjFl5BeDKSmg4=">>}, {<<"hash">>,<<"sha-1">>}], []},
      {xmlel,<<"nick">>, [{<<"xmlns">>, <<"http://jabber.org/protocol/nick">>}], [{xmlcdata,<<"user">>}]},
      {xmlel,<<"x">>, [{<<"xmlns">>, <<"http://jabber.org/protocol/muc">>}], [{xmlel,<<"history">>, [{<<"maxstanzas">>,<<"20">>}, {<<"maxchars">>,<<"32768">>}], []}]}]}.

You can then do:

X = fxml:get_subtag_with_xmlns(P, <<"x">>, <<"http://jabber.org/protocol/muc">>).                                                                                        
H = fxml:get_subtag(X, <<"history">>).
{value, MS} = fxml:get_tag_attr(<<"maxstanzas">>, H).
{value, MC} = fxml:get_tag_attr(<<"maxchars">>, H).

MS and MC contains your values:

MS = <<"20">>
MC = <<"32768">>