MUC: Add support for presence probes (fixes #1535)

The following patch allows Prosody to respond to `probe` presences and send out the probed occupant's current presence.

This is based on line 17.3 in XEP-0045:

    A MUC service MAY handle presence probes sent to the room JID <room@service> or an occupant JID <room@service/nick>
    (e.g, these might be sent by an occupant's home server to determine if the room is still online or to synchronize
    presence information if the user or the user's server has gone offline temporarily or has started sharing presence again,
    as for instance when Stanza Interception and Filtering Technology (XEP-0273) is used).

2 files changed, 87 insertions, 24 deletions

diff --git a/plugins/muc/hats.lib.lua b/plugins/muc/hats.lib.lua
index 77051af2..358e5100 100644
--- a/plugins/muc/hats.lib.lua
+++ b/plugins/muc/hats.lib.lua
@@ -6,8 +6,10 @@ local xmlns_hats = "xmpp:prosody.im/protocol/hats:1";
 -- Strip any hats claimed by the client (to prevent spoofing)
 muc_util.add_filtered_namespace(xmlns_hats);
 
+
 module:hook("muc-build-occupant-presence", function (event)
-	local aff_data = event.room:get_affiliation_data(event.occupant.bare_jid);
+	local bare_jid = event.occupant and event.occupant.bare_jid or event.bare_jid;
+	local aff_data = event.room:get_affiliation_data(bare_jid);
 	local hats = aff_data and aff_data.hats;
 	if not hats then return; end
 	local hats_el;
diff --git a/plugins/muc/muc.lib.lua b/plugins/muc/muc.lib.lua
index c338373a..5bbc28f1 100644
--- a/plugins/muc/muc.lib.lua
+++ b/plugins/muc/muc.lib.lua
@@ -216,9 +216,10 @@ local function can_see_real_jids(whois, occupant)
 	end
 end
 
+
 -- Broadcasts an occupant's presence to the whole room
 -- Takes the x element that goes into the stanzas
-function room_mt:publicise_occupant_status(occupant, x, nick, actor, reason, prev_role, force_unavailable)
+function room_mt:publicise_occupant_status(occupant, x, nick, actor, reason, prev_role, force_unavailable, recipient)
 	local base_x = x.base or x;
 	-- Build real jid and (optionally) occupant jid template presences
 	local base_presence do
@@ -238,7 +239,9 @@ function room_mt:publicise_occupant_status(occupant, x, nick, actor, reason, pre
 		reason = reason;
 	}
 	module:fire_event("muc-build-occupant-presence", event);
-	module:fire_event("muc-broadcast-presence", event);
+	if not recipient then
+		module:fire_event("muc-broadcast-presence", event);
+	end
 
 	-- Allow muc-broadcast-presence listeners to change things
 	nick = event.nick;
@@ -281,19 +284,27 @@ function room_mt:publicise_occupant_status(occupant, x, nick, actor, reason, pre
 		self_p = st.clone(base_presence):add_child(self_x);
 	end
 
-	local broadcast_roles = self:get_presence_broadcast();
+	local function get_p(rec_occupant)
+		local pr;
+		if can_see_real_jids(whois, rec_occupant) then
+			pr = get_full_p();
+		elseif occupant.bare_jid == rec_occupant.bare_jid then
+			pr = self_p;
+		else
+			pr = get_anon_p();
+		end
+		return pr
+	end
 
+	if recipient then
+		return self:route_to_occupant(recipient, get_p(recipient));
+	end
+
+	local broadcast_roles = self:get_presence_broadcast();
 	-- General populace
 	for occupant_nick, n_occupant in self:each_occupant() do
 		if occupant_nick ~= occupant.nick then
-			local pr;
-			if can_see_real_jids(whois, n_occupant) then
-				pr = get_full_p();
-			elseif occupant.bare_jid == n_occupant.bare_jid then
-				pr = self_p;
-			else
-				pr = get_anon_p();
-			end
+			local pr = get_p(n_occupant);
 			if broadcast_roles[occupant.role or "none"] or force_unavailable then
 				self:route_to_occupant(n_occupant, pr);
 			elseif prev_role and broadcast_roles[prev_role] then
@@ -323,18 +334,8 @@ end
 
 function room_mt:send_occupant_list(to, filter)
 	local to_bare = jid_bare(to);
-	local is_anonymous = false;
-	local whois = self:get_whois();
 	local broadcast_roles = self:get_presence_broadcast();
-	if whois ~= "anyone" then
-		local affiliation = self:get_affiliation(to);
-		if affiliation ~= "admin" and affiliation ~= "owner" then
-			local occupant = self:get_occupant_by_real_jid(to);
-			if not (occupant and can_see_real_jids(whois, occupant)) then
-				is_anonymous = true;
-			end
-		end
-	end
+	local is_anonymous = self:is_anonymous_for(to);
 	local broadcast_bare_jids = {}; -- Track which bare JIDs we have sent presence for
 	for occupant_jid, occupant in self:each_occupant() do
 		broadcast_bare_jids[occupant.bare_jid] = true;
@@ -549,6 +550,52 @@ function room_mt:handle_first_presence(origin, stanza)
 	return true;
 end
 
+
+function room_mt:is_anonymous_for(jid)
+	local is_anonymous = false;
+	local whois = self:get_whois();
+	if whois ~= "anyone" then
+		local affiliation = self:get_affiliation(jid);
+		if affiliation ~= "admin" and affiliation ~= "owner" then
+			local occupant = self:get_occupant_by_real_jid(jid);
+			if not (occupant and can_see_real_jids(whois, occupant)) then
+				is_anonymous = true;
+			end
+		end
+	end
+	return is_anonymous;
+end
+
+
+function room_mt:build_unavailable_presence(from_muc_jid, to_jid)
+	local nick = jid_resource(from_muc_jid);
+	local from_jid = self:get_registered_jid(nick);
+	if (not from_jid) then
+		module:log("debug", "Received presence probe for unavailable nickname that's not registered");
+		return;
+	end
+	local is_anonymous = self:is_anonymous_for(to_jid);
+	local affiliation = self:get_affiliation(from_jid) or "none";
+	local pr = st.presence({ to = to_jid, from = from_muc_jid, type = "unavailable" })
+		:tag("x", { xmlns = 'http://jabber.org/protocol/muc#user' })
+			:tag("item", {
+				affiliation = affiliation;
+				role = "none";
+				nick = nick;
+				jid = not is_anonymous and from_jid or nil }):up()
+			:up();
+
+	local x = pr:get_child("x", "http://jabber.org/protocol/muc");
+	local event = {
+		room = self; stanza = pr; x = x;
+		bare_jid = from_jid;
+		nick = nick;
+	}
+	module:fire_event("muc-build-occupant-presence", event);
+	return event.stanza;
+end
+
+
 function room_mt:handle_normal_presence(origin, stanza)
 	local type = stanza.attr.type;
 	local real_jid = stanza.attr.from;
@@ -568,6 +615,20 @@ function room_mt:handle_normal_presence(origin, stanza)
 	if type == "unavailable" then
 		if orig_occupant == nil then return true; end -- Unavailable from someone not in the room
 		-- dest_occupant = nil
+	elseif type == "probe" then
+		local occupant = self:get_occupant_by_nick(stanza.attr.to);
+		if occupant == nil then
+			local from_muc_jid = stanza.attr.to;
+			local to_jid = real_jid;
+			local pr = self:build_unavailable_presence(from_muc_jid, to_jid);
+			if pr then
+				self:route_stanza(pr);
+			end
+			return true;
+		end
+		local x = st.stanza("x", {xmlns = "http://jabber.org/protocol/muc#user"});
+		self:publicise_occupant_status(occupant, x, nil, nil, nil, nil, false, orig_occupant);
+		return true;
 	elseif orig_occupant and orig_occupant.nick == stanza.attr.to then -- Just a presence update
 		log("debug", "presence update for %s from session %s", orig_occupant.nick, real_jid);
 		dest_occupant = orig_occupant;
@@ -747,7 +808,7 @@ function room_mt:handle_presence_to_occupant(origin, stanza)
 	local type = stanza.attr.type;
 	if type == "error" then -- error, kick em out!
 		return self:handle_kickable(origin, stanza)
-	elseif type == nil or type == "unavailable" then
+	elseif type == nil or type == "unavailable" or type == "probe" then
 		return self:handle_normal_presence(origin, stanza);
 	elseif type ~= 'result' then -- bad type
 		if type ~= 'visible' and type ~= 'invisible' then -- COMPAT ejabberd can broadcast or forward XEP-0018 presences