--- a/core/rostermanager.lua	Tue Dec 17 00:34:39 2019 +0100
+++ b/core/rostermanager.lua	Thu Dec 19 10:03:16 2019 +0000
@@ -301,6 +301,11 @@
 	local item = roster[jid];
 	return item and item.ask;
 end
+local function is_contact_preapproved(username, host, jid)
+	local roster = load_roster(username, host);
+	local item = roster[jid];
+	return item and (item.approved == "true");
+end
 local function set_contact_pending_out(username, host, jid) -- subscribe
 	local roster = load_roster(username, host);
 	local item = roster[jid];
@@ -331,9 +336,10 @@
 	return save_roster(username, host, roster, jid);
 end
 local function subscribed(username, host, jid)
+	local roster = load_roster(username, host);
+	local item = roster[jid];
+
 	if is_contact_pending_in(username, host, jid) then
-		local roster = load_roster(username, host);
-		local item = roster[jid];
 		if not item then -- FIXME should roster item be auto-created?
 			item = {subscription = "none", groups = {}};
 			roster[jid] = item;
@@ -345,7 +351,17 @@
 		end
 		roster[false].pending[jid] = nil;
 		return save_roster(username, host, roster, jid);
-	end -- TODO else implement optional feature pre-approval (ask = subscribed)
+	elseif not item or item.subscription == "none" or item.subscription == "to" then
+		-- Contact is not subscribed and has not sent a subscription request.
+		-- We store a pre-approval as per RFC6121 3.4
+		if not item then
+			item = {subscription = "none", groups = {}};
+			roster[jid] = item;
+		end
+		item.approved = "true";
+		log("debug", "Storing preapproval for %s", jid);
+		return save_roster(username, host, roster, jid);
+	end
 end
 local function unsubscribed(username, host, jid)
 	local roster = load_roster(username, host);
@@ -403,6 +419,7 @@
 	set_contact_pending_in = set_contact_pending_in;
 	is_contact_pending_out = is_contact_pending_out;
 	set_contact_pending_out = set_contact_pending_out;
+	is_contact_preapproved = is_contact_preapproved;
 	unsubscribe = unsubscribe;
 	subscribed = subscribed;
 	unsubscribed = unsubscribed;

--- a/plugins/mod_presence.lua	Tue Dec 17 00:34:39 2019 +0100
+++ b/plugins/mod_presence.lua	Thu Dec 19 10:03:16 2019 +0000
@@ -181,8 +181,10 @@
 		if rostermanager.subscribed(node, host, to_bare) then
 			rostermanager.roster_push(node, host, to_bare);
 		end
-		core_post_stanza(origin, stanza);
-		send_presence_of_available_resources(node, host, to_bare, origin);
+		if rostermanager.is_contact_subscribed(node, host, to_bare) then
+			core_post_stanza(origin, stanza);
+			send_presence_of_available_resources(node, host, to_bare, origin);
+		end
 		if rostermanager.is_user_subscribed(node, host, to_bare) then
 			core_post_stanza(origin, st.presence({ type = "probe", from = from_bare, to = to_bare }));
 		end
@@ -229,6 +231,12 @@
 			if 0 == send_presence_of_available_resources(node, host, from_bare, origin) then
 				core_post_stanza(hosts[host], st.presence({from=to_bare, to=from_bare, type="unavailable"}), true); -- TODO send last activity
 			end
+		elseif rostermanager.is_contact_preapproved(node, host, from_bare) then
+			if not rostermanager.is_contact_pending_in(node, host, from_bare) then
+				if rostermanager.set_contact_pending_in(node, host, from_bare, stanza) then
+					core_post_stanza(hosts[host], st.presence({from=to_bare, to=from_bare, type="subscribed"}), true);
+				end -- TODO else return error, unable to save
+			end
 		else
 			core_post_stanza(hosts[host], st.presence({from=to_bare, to=from_bare, type="unavailable"}), true); -- acknowledging receipt
 			if not rostermanager.is_contact_pending_in(node, host, from_bare) then

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spec/scansion/presence_preapproval.scs	Thu Dec 19 10:03:16 2019 +0000
@@ -0,0 +1,74 @@
+# server supports contact subscription pre-approval (RFC 6121 3.4)
+
+[Client] Alice
+	jid: preappove-a@localhost
+	password: password
+
+[Client] Bob
+	jid: preapprove-b@localhost
+	password: password
+
+---------
+
+Alice connects
+
+Alice sends:
+	<presence/>
+
+Alice receives:
+	<presence/>
+
+Alice sends:
+	<presence to="${Bob's JID}" type="subscribed"/>
+
+Bob connects
+
+Bob sends:
+	<iq type="get" id="roster1">
+		<query xmlns="jabber:iq:roster"/>
+	</iq>
+
+Bob receives:
+	<iq type="result" id="roster1">
+		<query xmlns="jabber:iq:roster" ver="{scansion:any}">
+		</query>
+	</iq>
+
+Bob sends:
+	<presence/>
+
+Bob receives:
+	<presence from="${Bob's full JID}"/>
+	
+Bob sends:
+	<presence to="${Alice's JID}" type="subscribe" />
+
+Bob receives:
+	<iq type='set' id='{scansion:any}'>
+		<query ver='1' xmlns='jabber:iq:roster'>
+			<item jid="${Alice's JID}" subscription='none' ask='subscribe' />
+		</query>
+	</iq>
+
+	                                                    
+
+Bob receives:
+	<presence from="${Alice's JID}" type="subscribed" />
+
+Bob disconnects
+
+Alice sends:
+	<iq type="get" id="roster1">
+		<query xmlns="jabber:iq:roster"/>
+	</iq>
+
+Alice receives:
+	<iq type="result" id="roster1">
+		<query xmlns="jabber:iq:roster" ver="{scansion:any}">
+			<item jid="${Bob's JID}" subscription="from" />
+		</query>
+	</iq>
+
+Alice disconnects
+
+Bob disconnects