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erlangejabberdmongoose-im

Ejabberd error while xml,append_subtags

I am new in erlang and ejabbered/mongooseIM. I am trying to write a very simple mongoose module that will add an extra child element to the packets before sending. Below is my code:

-module(mod_test).

-behavior(gen_mod).


-export([start/2, stop/1]).
-export([add_child/1]).

-include("ejabberd.hrl").

start(Host, Opts) ->
    ejabberd_hooks:add(filter_packet, Host, ?MODULE, add_child, 0),
    ?DEBUG(" MOD_TEST Started",[]),
    ok.

stop(Host) ->
    ejabberd_hooks:delete(filter_packet, Host, ?MODULE, add_child, 0),
    ok.

add_child({From, To, XML} = Packet) ->
    Tag = {"a","b"},
    NewPacket = xml:append_subtags(Packet, [Tag]),
    ?INFO_MSG("  To party: ~p~n",[To]),
    NewPacket.

I can compile and start the module successfully. However, I get the below error while running:

2015-03-04 12:16:30.506 [error] <0.760.0>@ejabberd_hooks:run_fold1:259 
{function_clause,
[{xml,append_subtags,[{{jid,<<"user2">>,<<"localhost">>,<<"Damien">>,<<"user2">>,<<"localhost">>,<<"Damien">>},{jid,<<"user1">>,<<"localhost">>,<<"Gajim">>,<<"user1">>,<<"localhost">>,<<"Gajim">>},{xmlel,<<"message">>,[{<<"xml:lang">>,<<"en">>},{<<"type">>,<<"chat">>},{<<"to">>,<<"user1@localhost/Gajim">>},{<<"id">>,<<"ab68a">>}],[{xmlcdata,<<"\n">>},{xmlel,<<"body">>,[],[{xmlcdata,<<"mmmmm">>}]},{xmlcdata,<<"\n">>},{xmlel,<<"active">>,[{<<"xmlns">>,<<"http://jabber.org/protocol/chatstates">>}],[]},{xmlcdata,<<"\n">>}]}},
[{"a","b"}]],[{file,"src/xml.erl"},{line,276}]},
{safely,apply,3,[{file,"src/safely.erl"},{line,19}]},
{ejabberd_hooks,run_fold1,4,[{file,"src/ejabberd_hooks.erl"},{line,255}]},
{ejabberd_router,do_route,3,[{file,"src/ejabberd_router.erl"},{line,246}]},
{ejabberd_router,route,3,[{file,"src/ejabberd_router.erl"},{line,78}]},
{ejabberd_c2s,session_established2,2,[{file,"src/ejabberd_c2s.erl"},{line,1098}]},
{p1_fsm_old,handle_msg,10,[{file,"src/p1_fsm_old.erl"},{line,542}]},
{proc_lib,wake_up,3,[{file,"proc_lib.erl"},{line,247}]}]}

What is the issue and how to fix it?

Solution

  • You're passing Packet (a tuple: {From, To, XML}) to xml:append_subtags/2 while you should pass just XML. Your add_child/1 should look more like:

    add_child({From, To, XML} = Packet) ->
    Tag = {<<"a">>, <<"b">>},
    NewPacket = {From, To, xml:append_subtags(XML, [Tag])},
    ?INFO_MSG("  To party: ~p~n",[To]),
    NewPacket.

    I also changed {"a", "b"} to {<<"a">>, <<"b">>} since binaries are used for string processing everywhere in MongooseIM code base.

    Moreover, using priority 0 (the last parameter to ejabberd_hooks:add/5) is not advised, since this gives you little flexibility in case you actually wanted to insert some handler before this particular one into the handler chain.