Support for roster versioning (EJAB-964)

Introduces two options for mod_roster and mod_roster_odbc:
- {versioning, true | false}   Enable or disable roster versioning on ejabberd.
- {store_current_id, true | false}   If true, the current roster version is stored on DB (internal or odbc). Otherwise it is calculated on the fly each time.

Performance:
Setting store_current_id to true should help in reducing the load for both ejabberd and the DB.

Details: 
If store_current_id is false,  the roster version is a hash of the entire roster. If store_current_id is true, the roster version is a hash, but of the current time
(this has to do with transactional semantics; we need to perform both the roster update and the version update on the same transaction, but we don't   
have the entire roster when we are changing a single item on DB. Loading it there requires significant changes to be introduced, so I opted for this simpler approach).

In either case, there is no difference for the clients, the roster version ID is opaque.

IMPORTANT:
mod_shared_roster is not compatible with the option 'store_current_id'.  Shared roster and roster versioning can be both enabled, but store_current_id MUST be set to false.

SVN Revision: 2428

src/ejabberd_c2s.erl

@@ -310,12 +310,17 @@ wait_for_stream({xmlstreamstart, #xmlel{ns = NS} = Opening}, StateData) ->
 				_ ->
 				    case StateData#state.resource of
 					undefined ->
+					    RosterVersioningFeature =
+					    	case roster_versioning:is_enabled(ServerB) of
+							true -> [roster_versioning:stream_feature()];
+							false -> []
+						end,
 					    send_element(
 					      StateData,
 					      exmpp_stream:features([
 						  exmpp_server_binding:feature(),
 						  exmpp_server_session:feature()
-						])),
+						| RosterVersioningFeature])),
 					    fsm_next_state(wait_for_bind,
 						       StateData#state{
 							 server = ServerB,

src/mod_roster.erl

@@ -42,7 +42,8 @@
 	 get_jid_info/4,
 	 item_to_xml/1,
 	 webadmin_page/3,
-	 webadmin_user/4]).
+	 webadmin_user/4,
+	 roster_versioning_enabled/1]).
 
 -include_lib("exmpp/include/exmpp.hrl").
 
@@ -74,8 +75,11 @@ start(Host, Opts) when is_list(Host) ->
     IQDisc = gen_mod:get_opt(iqdisc, Opts, one_queue),
     mnesia:create_table(roster,[{disc_copies, [node()]},
 				{attributes, record_info(fields, roster)}]),
+    mnesia:create_table(roster_version, [{disc_copies, [node()]},
+				{attributes, record_info(fields, roster_version)}]),
     update_table(),
     mnesia:add_table_index(roster, us),
+    mnesia:add_table_index(roster_version, us),
     ejabberd_hooks:add(roster_get, HostB,
 		       ?MODULE, get_user_roster, 50),
     ejabberd_hooks:add(roster_in_subscription, HostB,
@@ -127,6 +131,16 @@ stop(Host) when is_list(Host) ->
     gen_iq_handler:remove_iq_handler(ejabberd_sm, HostB,
 				     ?NS_ROSTER).
 
+%% @spec (Host) -> true | false
+%% @type Host = binary()
+roster_versioning_enabled(Host)  ->
+	gen_mod:get_module_opt(binary_to_list(Host), ?MODULE, versioning, false).
+
+%% @spec (Host) -> true | false
+%% @type Host = binary()
+roster_version_on_db(Host) ->
+	gen_mod:get_module_opt(binary_to_list(Host), ?MODULE, store_current_id, false).
+
 %% @spec (From, To, IQ_Rec) -> IQ_Result
 %%     From = exmpp_jid:jid()
 %%     To = exmpp_jid:jid()
@@ -156,23 +170,90 @@ process_local_iq(From, To, #iq{type = set} = IQ_Rec)
   when ?IS_JID(From), ?IS_JID(To), ?IS_IQ_RECORD(IQ_Rec) ->
     process_iq_set(From, To, IQ_Rec).
 
+roster_hash(Items) ->
+	sha:sha(term_to_binary(
+		lists:sort(
+			[R#roster{groups = lists:sort(Grs)} || 
+				R = #roster{groups = Grs} <- Items]))).
+		
+roster_version(LServer ,LUser) ->
+	US = {LUser, LServer},
+	case roster_version_on_db(LServer) of
+		true ->
+			case mnesia:dirty_read(roster_version, US) of
+				[#roster_version{version =V}] -> V;
+				[] -> not_found
+			end;
+		false ->
+			roster_hash(ejabberd_hooks:run_fold(roster_get, LServer, [], [US]))
+	end.
+
 %% @spec (From, To, IQ_Rec) -> IQ_Result
 %%     From = exmpp_jid:jid()
 %%     To = exmpp_jid:jid()
 %%     IQ_Rec = exmpp_iq:iq()
 %%     IQ_Result = exmpp_iq:iq()
-
+%% Load roster from DB only if neccesary
+%% It is neccesary if
+%%  	- roster versioning is disabled in server OR
+%%	- roster versioning is not used by the client OR
+%%	- roster versioning is used by server and client BUT the server isn't storing version IDs on db OR
+%%	- the roster version from client don't match current version
 process_iq_get(From, To, IQ_Rec) ->
-    US = {exmpp_jid:prep_node(From), exmpp_jid:prep_domain(From)},
+    US = {_, LServer} = {exmpp_jid:prep_node(From), exmpp_jid:prep_domain(From)},
-    case catch ejabberd_hooks:run_fold(roster_get, exmpp_jid:prep_domain(To), [], [US]) of
+    try
-	Items when is_list(Items) ->
+	    {ItemsToSend, VersionToSend} = 
-	    XItems = lists:map(fun item_to_xml/1, Items),
+		case {exmpp_xml:get_attribute_as_list(exmpp_iq:get_request(IQ_Rec), ver,  not_found), 
-	    Result = #xmlel{ns = ?NS_ROSTER, name = 'query',
+		      roster_versioning_enabled(LServer),
-	      children = XItems},
+		      roster_version_on_db(LServer)} of
-	    exmpp_iq:result(IQ_Rec, Result);
+		{not_found, _ , _} ->
-	_ ->
+			{lists:map(fun item_to_xml/1, 
-	    exmpp_iq:error(IQ_Rec, 'internal-server-error')
+					ejabberd_hooks:run_fold(roster_get, exmpp_jid:prep_domain(To), [], [US])), false};
-    end.
+		{_, false, _} ->
+			{lists:map(fun item_to_xml/1, 
+					ejabberd_hooks:run_fold(roster_get, exmpp_jid:prep_domain(To), [], [US])), false};
+		
+		{RequestedVersion, true, true} ->
+			%% Retrieve version from DB. Only load entire roster
+			%% when neccesary.
+			case mnesia:dirty_read(roster_version, US) of
+				[#roster_version{version = RequestedVersion}] ->
+					{false, false};
+				[#roster_version{version = NewVersion}] ->
+					{lists:map(fun item_to_xml/1, 
+						ejabberd_hooks:run_fold(roster_get, exmpp_jid:prep_domain(To), [], [US])), NewVersion};
+				[] ->
+					RosterVersion = sha:sha(term_to_binary(now())),
+					mnesia:dirty_write(#roster_version{us = US, version = RosterVersion}),
+					{lists:map(fun item_to_xml/1,
+						ejabberd_hooks:run_fold(roster_get, exmpp_jid:prep_domain(To), [], [US])), RosterVersion}
+			end;
+		{RequestedVersion, true, false} ->
+			RosterItems = ejabberd_hooks:run_fold(roster_get, exmpp_jid:prep_domain(To), [] , [US]),
+			case roster_hash(RosterItems) of
+				RequestedVersion ->
+					{false, false};
+				New ->
+					{lists:map(fun item_to_xml/1, RosterItems), New}
+			end
+			
+		end,
+		case {ItemsToSend, VersionToSend} of
+			{false, false} -> 
+				exmpp_iq:result(IQ_Rec);
+			{Items, false} -> 
+				exmpp_iq:result(IQ_Rec, exmpp_xml:element(?NS_ROSTER, 'query', [] , Items));
+			{Items, Version} -> 
+				exmpp_iq:result(IQ_Rec, exmpp_xml:element(?NS_ROSTER, 'query', [?XMLATTR('ver', Version)], Items))
+		end
+    catch 
+    	_:_ ->  
+ 	    exmpp_iq:error(IQ_Rec, 'internal-server-error')
+     end.
+
+
+
+
 
 %% @spec (Acc, US) -> New_Acc
 %%     Acc = [rosteritem()]
@@ -279,6 +360,10 @@ process_item_set(From, To, #xmlel{} = El) ->
 		    %% subscription information from there:
 		    Item3 = ejabberd_hooks:run_fold(roster_process_item,
 						    exmpp_jid:prep_domain(From), Item2, [exmpp_jid:prep_domain(From)]),
+		    case roster_version_on_db(LServer) of
+		    	true -> mnesia:write(#roster_version{us = {LUser, LServer}, version = sha:sha(term_to_binary(now()))});
+			false -> ok
+		    end,
 		    {Item, Item3}
 	    end,
 	case mnesia:transaction(F) of
@@ -389,9 +474,15 @@ push_item(User, Server, From, Item)
 		       [{item,
 			 Item#roster.jid,
 			 Item#roster.subscription}]}),
-    lists:foreach(fun(Resource) ->
+
-			  push_item(User, Server, Resource, From, Item)
+    case roster_versioning_enabled(Server) of
-		  end, ejabberd_sm:get_user_resources(User, Server)).
+    	true ->
+		roster_versioning:push_item(Server, User, From, Item, roster_version(Server, User));
+	false ->
+	    lists:foreach(fun(Resource) ->
+ 			  push_item(User, Server, Resource, From, Item)
+		  end, ejabberd_sm:get_user_resources(User, Server))
+    end.
 
 %% @spec (User, Server, Resource, From, Item) -> term()
 %%     User = binary()
@@ -548,6 +639,10 @@ process_subscription(Direction, User, Server, JID1, Type, Reason)
 						  ask = Pending,
 						  askmessage = AskBinary},
 			    mnesia:write(NewItem),
+			    case roster_version_on_db(Server) of
+				true -> mnesia:write(#roster_version{us = {User, Server}, version = sha:sha(term_to_binary(now()))});
+				false -> ok
+			    end,
 			    {{push, NewItem}, AutoReply}
 		    end
 	    end,

src/mod_roster.hrl

@@ -29,3 +29,5 @@
 		 askmessage = <<>>,
 		 xs = []}).
 
+-record(roster_version, {us,
+			version}).

src/mod_roster_odbc.erl

@@ -41,7 +41,8 @@
 	 remove_user/2,
 	 get_jid_info/4,
 	 webadmin_page/3,
-	 webadmin_user/4]).
+	 webadmin_user/4,
+	 roster_versioning_enabled/1]).
 
 -include_lib("exmpp/include/exmpp.hrl").
 
@@ -102,6 +103,12 @@ stop(Host) ->
     gen_iq_handler:remove_iq_handler(ejabberd_sm, HostB, ?NS_ROSTER).
 
 
+roster_versioning_enabled(Host)  ->
+	gen_mod:get_module_opt(binary_to_list(Host), ?MODULE, versioning, false).
+
+roster_version_on_db(Host) ->
+	gen_mod:get_module_opt(binary_to_list(Host), ?MODULE, store_current_id, false).
+
 process_iq(From, To, IQ_Rec) ->
     LServer = exmpp_jid:prep_domain_as_list(From),
     case lists:member(LServer, ?MYHOSTS) of
@@ -118,17 +125,84 @@ process_local_iq(From, To, #iq{type = set} = IQ_Rec) ->
 
 
 
+roster_hash(Items) ->
+	sha:sha(term_to_binary(
+		lists:sort(
+			[R#roster{groups = lists:sort(Grs)} || 
+				R = #roster{groups = Grs} <- Items]))).
+		
+roster_version(LServer ,LUser) ->
+	US = {LUser, LServer},
+	case roster_version_on_db(LServer) of
+		true ->
+			case odbc_queries:get_roster_version(ejabberd_odbc:escape(LServer), ejabberd_odbc:escape(LUser)) of
+				{selected, ["version"], [{Version}]} -> Version;
+				{selected, ["version"], []} -> not_found
+			end;
+		false ->
+			roster_hash(ejabberd_hooks:run_fold(roster_get, LServer, [], [US]))
+	end.
+ 
+%% Load roster from DB only if neccesary. 
+%% It is neccesary if
+%%     - roster versioning is disabled in server OR
+%%     - roster versioning is not used by the client OR
+%%     - roster versioning is used by server and client, BUT the server isn't storing versions on db OR
+%%     - the roster version from client don't match current version.
 process_iq_get(From, To, IQ_Rec) ->
-    US = {exmpp_jid:prep_node(From), exmpp_jid:prep_domain(From)},
+    US = {LUser, LServer} = {exmpp_jid:prep_node(From), exmpp_jid:prep_domain(From)},
-    case catch ejabberd_hooks:run_fold(roster_get, exmpp_jid:prep_domain(To), [], [US]) of
+    try
-	Items when is_list(Items) ->
+	    {ItemsToSend, VersionToSend} = 
-	    XItems = lists:map(fun item_to_xml/1, Items),
+		case {exmpp_xml:get_attribute_as_list(exmpp_iq:get_request(IQ_Rec), ver,  not_found), 
-	    Result = #xmlel{ns = ?NS_ROSTER, name = 'query',
+		      roster_versioning_enabled(LServer),
-	      children = XItems},
+		      roster_version_on_db(LServer)} of
-	    exmpp_iq:result(IQ_Rec, Result);
+		{not_found, _ , _} ->
-	_ ->
+			{lists:map(fun item_to_xml/1, 
-	    exmpp_iq:error(IQ_Rec, 'internal-server-error')
+					ejabberd_hooks:run_fold(roster_get, exmpp_jid:prep_domain(To), [], [US])), false};
-    end.
+		{_, false, _} ->
+			{lists:map(fun item_to_xml/1, 
+					ejabberd_hooks:run_fold(roster_get, exmpp_jid:prep_domain(To), [], [US])), false};
+		
+		{RequestedVersion, true, true} ->
+			%% Retrieve version from DB. Only load entire roster
+			%% when neccesary.
+			case odbc_queries:get_roster_version(ejabberd_odbc:escape(LServer), ejabberd_odbc:escape(LUser)) of
+				{selected, ["version"], [{RequestedVersion}]} ->
+					{false, false};
+				{selected, ["version"], [{NewVersion}]} ->
+					{lists:map(fun item_to_xml/1, 
+						ejabberd_hooks:run_fold(roster_get, exmpp_jid:prep_domain(To), [], [US])), NewVersion};
+				{selected, ["version"], []} ->
+					RosterVersion = sha:sha(term_to_binary(now())),
+					{atomic, {updated,1}} = odbc_queries:sql_transaction(binary_to_list(LServer), fun() ->
+									odbc_queries:set_roster_version(ejabberd_odbc:escape(LUser), RosterVersion)
+								  end),
+					{lists:map(fun item_to_xml/1,
+						ejabberd_hooks:run_fold(roster_get, exmpp_jid:prep_domain(To), [], [US])), RosterVersion}
+			end;
+
+		{RequestedVersion, true, false} ->
+			RosterItems = ejabberd_hooks:run_fold(roster_get, exmpp_jid:prep_domain(To), [] , [US]),
+			case roster_hash(RosterItems) of
+				RequestedVersion ->
+					{false, false};
+				New ->
+					{lists:map(fun item_to_xml/1, RosterItems), New}
+			end
+			
+		end,
+		case {ItemsToSend, VersionToSend} of
+			{false, false} -> 
+				exmpp_iq:result(IQ_Rec);
+			{Items, false} -> 
+				exmpp_iq:result(IQ_Rec, exmpp_xml:element(?NS_ROSTER, 'query', [] , Items));
+			{Items, Version} -> 
+				exmpp_iq:result(IQ_Rec, exmpp_xml:element(?NS_ROSTER, 'query', [?XMLATTR('ver', Version)], Items))
+		end
+    catch 
+    	_:_ ->  
+ 	    exmpp_iq:error(IQ_Rec, 'internal-server-error')
+     end.
 
 get_user_roster(Acc, {LUser, LServer}) ->
     Items = get_roster(LUser, LServer),
@@ -263,6 +337,11 @@ process_item_set(From, To, #xmlel{} = El) ->
 		    %% subscription information from there:
 		    Item3 = ejabberd_hooks:run_fold(roster_process_item,
 						    exmpp_jid:prep_domain(From), Item2, [exmpp_jid:prep_domain(From)]),
+		    case roster_version_on_db(Server) of
+		    	true -> odbc_queries:set_roster_version(Username, sha:sha(term_to_binary(now())));
+			false -> ok
+		    end,
+ 
 		    {Item, Item3}
 	    end,
 	case odbc_queries:sql_transaction(LServer, F) of
@@ -352,9 +431,15 @@ push_item(User, Server, From, Item) when is_binary(User), is_binary(Server) ->
 		       [{item,
 			 Item#roster.jid,
 			 Item#roster.subscription}]}),
-    lists:foreach(fun(Resource) ->
+    case roster_versioning_enabled(Server) of
-			  push_item(User, Server, Resource, From, Item)
+    	true ->
-		  end, ejabberd_sm:get_user_resources(User, Server)).
+		roster_versioning:push_item(Server, User, From, Item, roster_version(Server, User));
+	false ->
+	    lists:foreach(fun(Resource) ->
+ 			  push_item(User, Server, Resource, From, Item)
+		  end, ejabberd_sm:get_user_resources(User, Server))
+    end.
+ 
 
 % TODO: don't push to those who not load roster
 push_item(User, Server, Resource, From, Item) ->
@@ -492,6 +577,10 @@ process_subscription(Direction, User, Server, JID1, Type, Reason)
 						  askmessage = AskBinary},
 			    ItemVals = record_to_string(NewItem),
 			    odbc_queries:roster_subscribe(LServer, Username, SJID, ItemVals),
+			    case roster_version_on_db(Server) of
+			    	true -> odbc_queries:set_roster_version(Username, sha:sha(term_to_binary(now())));
+				false -> ok
+			    end,
 			    {{push, NewItem}, AutoReply}
 		    end
 	    end,

src/odbc/mssql2000.sql

@@ -209,6 +209,14 @@ CREATE TABLE [dbo].[privacy_list_data] (
 ) ON [PRIMARY]
 GO
 
+/* Not tested on mssql */
+CREATE TABLE [dbo].[roster_version] (
+	[username] [varchar] (250) NOT NULL ,
+	[version] [varchar] (64) NOT NULL 
+) ON [PRIMARY]
+GO
+
+
 /* Constraints to add:
 - id in privacy_list is a SERIAL autogenerated number
 - id in privacy_list_data must exist in the table privacy_list */
@@ -244,6 +252,13 @@ ALTER TABLE [dbo].[users] WITH NOCHECK ADD
 	) WITH  FILLFACTOR = 90  ON [PRIMARY] 
 GO
 
+ALTER TABLE [dbo].[roster_version] WITH NOCHECK ADD 
+	CONSTRAINT [PK_roster_version] PRIMARY KEY  CLUSTERED 
+	(
+		[username]
+	) WITH  FILLFACTOR = 90  ON [PRIMARY] 
+GO
+
 ALTER TABLE [dbo].[vcard] WITH NOCHECK ADD 
 	CONSTRAINT [PK_vcard] PRIMARY KEY  CLUSTERED 
 	(

src/odbc/mysql.sql

@@ -148,6 +148,12 @@ CREATE TABLE private_storage (
 CREATE INDEX i_private_storage_username USING BTREE ON private_storage(username);
 CREATE UNIQUE INDEX i_private_storage_username_namespace USING BTREE ON private_storage(username(75), namespace(75));
 
+-- Not tested in mysql
+CREATE TABLE roster_version (
+    username varchar(250) PRIMARY KEY,
+    version text NOT NULL
+) CHARACTER SET utf8;
+
 -- To update from 1.x:
 -- ALTER TABLE rosterusers ADD COLUMN askmessage text AFTER ask;
 -- UPDATE rosterusers SET askmessage = '';

src/odbc/odbc_queries.erl

@@ -78,7 +78,9 @@
 	 set_vcard/26,
 	 get_vcard/2,
 	 escape/1,
-	 count_records_where/3]).
+	 count_records_where/3,
+	 get_roster_version/2,
+	 set_roster_version/2]).
 
 %% We have only two compile time options for db queries:
 %-define(generic, true).
@@ -555,6 +557,12 @@ count_records_where(LServer, Table, WhereClause) ->
     ejabberd_odbc:sql_query(
       LServer,
       ["select count(*) from ", Table, " ", WhereClause, ";"]).
+
+get_roster_version(LServer, LUser) ->
+	ejabberd_odbc:sql_query(LServer,
+		["select version from roster_version where username = '", LUser, "'"]).
+set_roster_version(LUser, Version) ->
+	update_t("roster_version", ["username", "version"], [LUser, Version], ["username = '", LUser, "'"]).
 -endif.
 
 %% -----------------
@@ -791,4 +799,10 @@ count_records_where(LServer, Table, WhereClause) ->
     ejabberd_odbc:sql_query(
       LServer,
       ["select count(*) from ", Table, " ", WhereClause, " with (nolock)"]).
+
+get_roster_version(LServer, LUser) ->
+	ejabberd_odbc:sql_query(LServer, 
+		["select version from dbo.roster_version where username = '", LUser, "'"]).
+set_roster_version(LUser, Version) ->
+	update_t("dbo.roster_version", ["username", "version"], [LUser, Version], ["username = '", LUser, "'"]).
 -endif.

src/odbc/pg.sql

@@ -145,7 +145,10 @@ CREATE TABLE private_storage (
 CREATE INDEX i_private_storage_username ON private_storage USING btree (username);
 CREATE UNIQUE INDEX i_private_storage_username_namespace ON private_storage USING btree (username, namespace);
 
-
+CREATE TABLE roster_version (
+    username text PRIMARY KEY,
+    version text NOT NULL
+);
 -- To update from 0.9.8:
 -- CREATE SEQUENCE spool_seq_seq;
 -- ALTER TABLE spool ADD COLUMN seq integer;

src/roster_versioning.erl

@@ -0,0 +1,75 @@
+%%%----------------------------------------------------------------------
+%%% File    : mod_roster.erl
+%%% Author  : Pablo Polvorin <pablo.polvorin@process-one.net>
+%%% Purpose : Common utility functions for XEP-0237 (Roster Versioning)
+%%% Created : 19 Jul 2009 by Pablo Polvorin <pablo.polvorin@process-one.net>
+%%%
+%%%
+%%% ejabberd, Copyright (C) 2009   ProcessOne
+%%%
+%%% This program is free software; you can redistribute it and/or
+%%% modify it under the terms of the GNU General Public License as
+%%% published by the Free Software Foundation; either version 2 of the
+%%% License, or (at your option) any later version.
+%%%
+%%% This program is distributed in the hope that it will be useful,
+%%% but WITHOUT ANY WARRANTY; without even the implied warranty of
+%%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+%%% General Public License for more details.
+%%%
+%%% You should have received a copy of the GNU General Public License
+%%% along with this program; if not, write to the Free Software
+%%% Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+%%% 02111-1307 USA
+%%%
+%%%
+%%% @doc The roster versioning follows an all-or-nothing strategy:
+%%%            - If the version supplied by the client is the lastest, return an empty response
+%%%            - If not, return the entire new roster (with updated version string).
+%%%       Roster version is a hash digest of the entire roster.
+%%%       No additional data is stored in DB.
+%%%----------------------------------------------------------------------
+-module(roster_versioning).
+-author('pablo.polvorin@process-one.net').
+
+%%API
+-export([is_enabled/1, 
+	stream_feature/0,
+	push_item/5]).
+
+
+-include("mod_roster.hrl").
+-include_lib("exmpp/include/exmpp.hrl").
+
+-define(NS_ROSTER_VER, "urn:xmpp:features:rosterver").
+
+%%@doc is roster versioning enabled?
+is_enabled(Host) ->
+	case gen_mod:is_loaded(binary_to_list(Host), mod_roster) of 
+		true ->	mod_roster:roster_versioning_enabled(Host);
+		false -> mod_roster_odbc:roster_versioning_enabled(Host)
+	end.
+
+stream_feature() ->
+	exmpp_xml:element(?NS_ROSTER_VER, 'ver', [], [exmpp_xml:element(?NS_ROSTER_VER, 'optional')]).
+
+
+
+   
+%% @doc Roster push, calculate and include the version attribute.
+%% TODO: don't push to those who didn't load roster
+push_item(Server, User, From, Item, RosterVersion)  ->
+    	lists:foreach(fun(Resource) ->
+			  push_item(User, Server, Resource, From, Item, RosterVersion)
+		end, ejabberd_sm:get_user_resources(User, Server)).
+
+push_item(User, Server, Resource, From, Item, RosterVersion) ->
+    Request = #xmlel{ns = ?NS_ROSTER, name = 'query', attrs = [?XMLATTR('ver', RosterVersion)],
+      children = [mod_roster:item_to_xml(Item)]},
+    ResIQ = exmpp_iq:set(?NS_JABBER_CLIENT, Request,
+      "push" ++ randoms:get_string()),
+    ejabberd_router:route(
+      From,
+      exmpp_jid:make(User, Server, Resource),
+      ResIQ).
+