ejabberd online status when user loses connection

Question

I have ejabberd setup to be the xmpp server between mobile apps, ie. custom iPhone and Android app.

But I've seemingly run into a limitation of the way ejabberd handles online status's.

Scenario:

• User A is messaging User B via their mobiles.
• User B loses all connectivity, so client can't disconnect from server.
• ejabberd still lists User B as online.
• Since ejabberd assumes User B is still online, any message from User A gets passed on to the dead connection.
• So user B won't get the message, nor does it get saved as an offline message, as ejabberd assumes the user is online.
• Message lost.
• Until ejabberd realises that the connection is stale, it treats it as an online user.

And throw in data connection changes (wifi to 3G to 4G to...) and you'll find this happening quite a lot.

mod_ping:

I tried to implement mod_ping on a 10 second interval.
https://www.process-one.net/docs/ejabberd/guide_en.html#modping
But as the documentation states, the ping will wait 32 seconds for a response before disconnecting the user.
This means there will be a 42 second window where the user can lose their messages.

Ideal Solution:

Even if the ping wait time could be reduce, it's still not a perfect solution.
Is there a way that ejabberd can wait for a 200 response from the client before discarding the message? If no response then save it offline.
Is it possible to write a hook to solve this problem?
Or is there a simple setting I've missed somewhere?

FYI: I am not using BOSH.

Answer 1

Here is the mod I wrote that fixes my problem.

To make it work you'll need receipts to be activated client side and the client should be able to handle duplicate messages.

Firstly I created a table called confirm_delivery. I save every 'chat' message to that table. I set a 10 second timer, if I receive a confirmation back, I delete the table entry.

If I don't get a confirmation back, I save the message manually to the offline_msg table and try and resend it again (this might be over the top, but for you to decide) and then delete it from our confirm_delivery table

I've chopped out all the code I perceive as unnecessary, so I hope this will still compile.

Hope this is of help to other ejabberd devs out there!

https://github.com/johanvorster/ejabberd_confirm_delivery.git

---

%% name of module must match file name
-module(mod_confirm_delivery).

-author("Johan Vorster").

%% Every ejabberd module implements the gen_mod behavior
%% The gen_mod behavior requires two functions: start/2 and stop/1
-behaviour(gen_mod).

%% public methods for this module
-export([start/2, stop/1, send_packet/3, receive_packet/4, get_session/5, set_offline_message/5]).

%% included for writing to ejabberd log file
-include("ejabberd.hrl").

-record(session, {sid, usr, us, priority, info}).
-record(offline_msg, {us, timestamp, expire, from, to, packet}).

-record(confirm_delivery, {messageid, timerref}).

start(_Host, _Opt) -> 

        ?INFO_MSG("mod_confirm_delivery loading", []),
        mnesia:create_table(confirm_delivery, 
            [{attributes, record_info(fields, confirm_delivery)}]),
        mnesia:clear_table(confirm_delivery),
        ?INFO_MSG("created timer ref table", []),

        ?INFO_MSG("start user_send_packet hook", []),
        ejabberd_hooks:add(user_send_packet, _Host, ?MODULE, send_packet, 50),   
        ?INFO_MSG("start user_receive_packet hook", []),
        ejabberd_hooks:add(user_receive_packet, _Host, ?MODULE, receive_packet, 50).   

stop(_Host) -> 
        ?INFO_MSG("stopping mod_confirm_delivery", []),
        ejabberd_hooks:delete(user_send_packet, _Host, ?MODULE, send_packet, 50),
        ejabberd_hooks:delete(user_receive_packet, _Host, ?MODULE, receive_packet, 50). 

send_packet(From, To, Packet) ->    
    ?INFO_MSG("send_packet FromJID ~p ToJID ~p Packet ~p~n",[From, To, Packet]),

    Type = xml:get_tag_attr_s("type", Packet),
    ?INFO_MSG("Message Type ~p~n",[Type]),

    Body = xml:get_path_s(Packet, [{elem, "body"}, cdata]), 
    ?INFO_MSG("Message Body ~p~n",[Body]),

    MessageId = xml:get_tag_attr_s("id", Packet),
    ?INFO_MSG("send_packet MessageId ~p~n",[MessageId]), 

    LUser = element(2, To),
    ?INFO_MSG("send_packet LUser ~p~n",[LUser]), 

    LServer = element(3, To), 
    ?INFO_MSG("send_packet LServer ~p~n",[LServer]), 

    Sessions = mnesia:dirty_index_read(session, {LUser, LServer}, #session.us),
    ?INFO_MSG("Session: ~p~n",[Sessions]),

    case Type =:= "chat" andalso Body =/= [] andalso Sessions =/= [] of
        true ->                

        {ok, Ref} = timer:apply_after(10000, mod_confirm_delivery, get_session, [LUser, LServer, From, To, Packet]),

        ?INFO_MSG("Saving To ~p Ref ~p~n",[MessageId, Ref]),

        F = fun() ->
            mnesia:write(#confirm_delivery{messageid=MessageId, timerref=Ref})
        end,

        mnesia:transaction(F);

    _ ->
        ok
    end.   

receive_packet(_JID, From, To, Packet) ->
    ?INFO_MSG("receive_packet JID: ~p From: ~p To: ~p Packet: ~p~n",[_JID, From, To, Packet]), 

    Received = xml:get_subtag(Packet, "received"), 
    ?INFO_MSG("receive_packet Received Tag ~p~n",[Received]),    

    if Received =/= false andalso Received =/= [] ->
        MessageId = xml:get_tag_attr_s("id", Received),
        ?INFO_MSG("receive_packet MessageId ~p~n",[MessageId]);       
    true ->
        MessageId = []
    end, 

    if MessageId =/= [] ->
        Record = mnesia:dirty_read(confirm_delivery, MessageId),
        ?INFO_MSG("receive_packet Record: ~p~n",[Record]);       
    true ->
        Record = []
    end, 

    if Record =/= [] ->
        [R] = Record,
        ?INFO_MSG("receive_packet Record Elements ~p~n",[R]), 

        Ref = element(3, R),

        ?INFO_MSG("receive_packet Cancel Timer ~p~n",[Ref]), 
        timer:cancel(Ref),

        mnesia:dirty_delete(confirm_delivery, MessageId),
        ?INFO_MSG("confirm_delivery clean up",[]);     
    true ->
        ok
    end.


get_session(User, Server, From, To, Packet) ->   
    ?INFO_MSG("get_session User: ~p Server: ~p From: ~p To ~p Packet ~p~n",[User, Server, From, To, Packet]),   

    ejabberd_router:route(From, To, Packet),
    ?INFO_MSG("Resend message",[]),

    set_offline_message(User, Server, From, To, Packet),
    ?INFO_MSG("Set offline message",[]),

    MessageId = xml:get_tag_attr_s("id", Packet), 
    ?INFO_MSG("get_session MessageId ~p~n",[MessageId]),    

    case MessageId =/= [] of
        true ->        

        mnesia:dirty_delete(confirm_delivery, MessageId),
        ?INFO_MSG("confirm_delivery clean up",[]);

     _ ->
        ok
    end.

set_offline_message(User, Server, From, To, Packet) ->
    ?INFO_MSG("set_offline_message User: ~p Server: ~p From: ~p To ~p Packet ~p~n",[User, Server, From, To, Packet]),    

    F = fun() ->
        mnesia:write(#offline_msg{us = {User, Server}, timestamp = now(), expire = "never", from = From, to = To, packet = Packet})
    end,

    mnesia:transaction(F).    

Answer 2

This is well known limitation of TCP connections. You need to introduce some acknowledgment functionality.

One of options in xep-0184. A message may carry receipt request and when it is delivered the receipt goes back to sender.

Another option is xep-0198. This is stream management which acknowledges stanzas.

You can also implement it entirely in application layer and send messages from recipient to sender. Act accordingly when acknowledgment is not delivered. Mind that Sender -> Server connection also may be severed in that way.

I am not aware of implementation of those xeps and features in ejabberd. I implemented them on my own depending on project requirements.

Answer 3

ejabberd supports stream management as default in latest version. It is implemented in most mobile libraries like Smack for Android and XMPPFramework for iOS.

This is the state of the art in XMPP specification at the moment.

Answer 4

Implementing XEP-198 on ejabberd is quite involved.

Erlang Solutions (I work for them) has an XEP-184 module for ejabberd, with enhanced functionality, that solves this problem. It does the buffering and validation on the server side. As long as client sends messages carrying receipt request and when it is delivered the receipt goes back to sender.

The module validates receipts to see if message has been received. If it hasn't within timeout, it gets saved as an offline message.

Answer 5

I think the better way is that if a message has not be received make user offline and then store message in offline message table and use a push service and configure it for offline message.

Then a push will be send and if there are more message they will be stored on offline message, and for understanding on server that message has not received you can use this https://github.com/Mingism/ejabberd-stanza-ack.

I think Facebook has the same way when a message doesn't deliver it makes user offline until he become online again