--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_pubsub_subscription/mod_pubsub_subscription.lua	Mon Mar 15 16:31:23 2021 +0100
@@ -0,0 +1,145 @@
+local st = require "util.stanza";
+local uuid = require "util.uuid";
+local mt = require "util.multitable";
+local cache = require "util.cache";
+
+local xmlns_pubsub = "http://jabber.org/protocol/pubsub";
+local xmlns_pubsub_event = "http://jabber.org/protocol/pubsub#event";
+
+-- TODO persist
+-- TODO query known pubsub nodes to sync current subscriptions
+-- TODO subscription ids per 'item' would be handy
+
+local pending_subscription = cache.new(256); -- uuid → node
+local pending_unsubscription = cache.new(256); -- uuid → node
+local active_subscriptions = mt.new() -- service | node | uuid | { item }
+function module.save()
+	return { active_subscriptions = active_subscriptions.data }
+end
+function module.restore(data)
+	if data and data.active_subscriptions then
+		active_subscriptions.data = data.active_subscriptions
+	end
+end
+
+local valid_events = {"subscribed"; "unsubscribed"; "error"; "item"; "retract"; "purge"; "delete"}
+
+local function subscription_added(item_event)
+	local item = item_event.item;
+	assert(item.service, "pubsub subscription item MUST have a 'service' field.");
+	assert(item.node, "pubsub subscription item MUST have a 'node' field.");
+
+	local already_subscibed = false;
+	for _ in active_subscriptions:iter(item.service, item.node, nil) do -- luacheck: ignore 512
+		already_subscibed = true;
+		break
+	end
+
+	item._id = uuid.generate();
+	local iq_id = uuid.generate();
+	pending_subscription:set(iq_id, item._id);
+	active_subscriptions:set(item.service, item.node, item._id, item);
+
+	if not already_subscibed then
+		module:send(st.iq({ type = "set", id = iq_id, from = module.host, to = item.service })
+			:tag("pubsub", { xmlns = xmlns_pubsub })
+				:tag("subscribe", { jid = module.host, node = item.node }));
+	end
+end
+
+for _, event_name in ipairs(valid_events) do
+	module:hook("pubsub-event/host/"..event_name, function (event)
+		for _, _, _, _, cb in active_subscriptions:iter(event.service, event.node, nil, "on_"..event_name) do
+			pcall(cb, event);
+		end
+	end);
+end
+
+module:hook("iq/host", function (event)
+	local stanza = event.stanza;
+	local service = stanza.attr.from;
+
+	if not stanza.attr.id then return end -- shouldn't be possible
+
+	local subscribed_node = pending_subscription:get(stanza.attr.id);
+	pending_subscription:set(stanza.attr.id, nil);
+	local unsubscribed_node = pending_unsubscription:get(stanza.attr.id);
+	pending_unsubscription:set(stanza.attr.id, nil);
+
+	if stanza.attr.type == "result" then
+		local pubsub_wrapper = stanza:get_child("pubsub", xmlns_pubsub);
+		local subscription = pubsub_wrapper and pubsub_wrapper:get_child("subscription");
+		if not subscription then return end
+		local node = subscription.attr.node;
+
+		local what;
+		if subscription.attr.subscription == "subscribed" then
+			what = "on_subscribed";
+		elseif subscription.attr.subscription == "none" then
+			what = "on_unsubscribed";
+		end
+		if not what then return end -- there are other states but we don't handle them
+		for _, _, _, _, cb in active_subscriptions:iter(service, node, nil, what) do
+			cb(event);
+		end
+		return true;
+
+	elseif stanza.attr.type == "error" then
+		local node = subscribed_node or unsubscribed_node;
+		local error_type, error_condition, reason, pubsub_error = stanza:get_error();
+		local err = { type = error_type, condition = error_condition, text = reason, extra = pubsub_error };
+		if active_subscriptions:get(service) then
+			for _, _, _, _, cb in active_subscriptions:iter(service, node, nil, "on_error") do
+				cb(err);
+			end
+			return true;
+		end
+	end
+end, 1);
+
+local function subscription_removed(item_event)
+	local item = item_event.item;
+	active_subscriptions:set(item.service, item.node, item._id, nil);
+	local node_subs = active_subscriptions:get(item.service, item.node);
+	if node_subs and next(node_subs) then return end
+
+	local iq_id = uuid.generate();
+	pending_unsubscription:set(iq_id, item._id);
+
+	module:send(st.iq({ type = "set", id = iq_id, from = module.host, to = item.service })
+		:tag("pubsub", { xmlns = xmlns_pubsub })
+			:tag("unsubscribe", { jid = module.host, node = item.node }))
+end
+
+module:handle_items("pubsub-subscription", subscription_added, subscription_removed, true);
+
+module:hook("message/host", function(event)
+	local origin, stanza = event.origin, event.stanza;
+	local ret = nil;
+	local service = stanza.attr.from;
+	module:log("debug", "Got message/host: %s", stanza:top_tag());
+	for event_container in stanza:childtags("event", xmlns_pubsub_event) do
+		for pubsub_event in event_container:childtags() do
+			module:log("debug", "Got pubsub event %s", pubsub_event:top_tag());
+			local node = pubsub_event.attr.node;
+			module:fire_event("pubsub-event/host/"..pubsub_event.name, {
+					stanza = stanza;
+					origin = origin;
+					event = pubsub_event;
+					service = service;
+					node = node;
+				});
+			ret = true;
+		end
+	end
+	return ret;
+end);
+
+module:hook("pubsub-event/host/items", function (event)
+	for item in event.event:childtags() do
+		module:log("debug", "Got pubsub item event %s", item:top_tag());
+		event.item = item;
+		event.payload = item.tags[1];
+		module:fire_event("pubsub-event/host/"..item.name, event);
+	end
+end);