I am using ejabberd18.09 for IM application. the application has few features that needed to add extensions to the ejabberd(xmpp) messages.
I created a custom module on the offline_message_hook to capture the offline messages and send them to my own url for further processing .
the messages that are being sent to ejabberd have different cases depending on the type of message as following
if I am sending a photo the message will be as following
<message xmlns="jabber:client" xml:lang="en" to="someuserjid2" from="{someuserjid}" type="chat" id="mP8tO-8">
<mtype xmlns="urn:xmpp:mtype" value="media" />
<url xmlns="urn:xmpp:url" id="myId" mediaType="photo" link="myphotourl.com" />
<body>thumbnail string</body>
</message>
when sending a text
<message xmlns="jabber:client" xml:lang="en" to="someuserjid2" from="{someuserjid}" type="chat" id="mP8tO-8">
<mtype xmlns="urn:xmpp:mtype" value="text" />
<body>Hi John</body>
</message>
when sending a location
<message xmlns="jabber:client" xml:lang="en" to="someuserjid2" from="{someuserjid}" type="chat" id="mP8tO-8">
<mtype xmlns="urn:xmpp:mtype" value="location" />
<location xmlns="urn:xmpp:geo" lat="1.2" lng="2.2 " />
<body>location thumbnailstring</body>
</message>
I used a .erl code to read the body and the message ID as following
create_message(_From, _To, Packet) when (Packet#message.type == chat) and (Packet#message.body /= []) ->
Body = fxml:get_path_s(Packet, [{elem, list_to_binary("body")}, cdata]),
MessageId = fxml:get_tag_attr_s(list_to_binary("id"), Packet),
post_offline_message(_From, _To, Body, MessageId),
ok.
what I want is how (in erlang) can I read the value attribute of the mtype tag the create a switch statement on ( media, location , test ) values so that I can process each message separately ?
You can pass attr in the list of arguments to fxml:get_path_s to pick out the value of an attribute of a certain element:
case fxml:get_path_s(Packet, [{elem, <<"mtype">>}, {attr, <<"value">>}]) of
<<"media">> ->
%% handle media...
<<"location">> ->
%% handle location...
<<"">> ->
%% no mtype element, or missing value attribute!
%% let's handle that case as well
end
Another thought: do you actually need the <mtype> element? It looks like you could just check for the presence of a <location> or <url> element. You could do it like this:
case fxml:get_subtag(Packet, <<"location">>) of
false ->
%% No location. Try url
case fxml:get_subtag(Packet, <<"url">>) of
false ->
%% Neither location nor url
%% Handle this case somehow...
Url ->
%% Do something with Url...
end
Location ->
%% Do something with Location...
end
The code gets a bit messy, since we need to nest the case expressions, unlike the previous version where we just checked the value of a single expression. One thing you could do is writing a helper function that tries each element in turn:
find_one_of(Packet, []) ->
not_found;
find_one_of(Packet, [ElementName | Rest]) ->
case fxml:get_subtag(Packet, ElementName) of
false ->
find_one_of(Packet, Rest);
Element ->
{ElementName, Element}
end.
And then call it like:
case find_one_of(Packet, [<<"location">>, <<"url">>]) of
{<<"location">>, Location} ->
%% Do something with Location...
{<<"url">>, Url} ->
%% Do something with Url...
not_found ->
%% Neither location nor url
end