--- a/plugins/mod_csi_simple.lua	Sat Nov 16 16:45:33 2019 +0100
+++ b/plugins/mod_csi_simple.lua	Sat Nov 16 16:52:31 2019 +0100
@@ -9,40 +9,7 @@
 local jid = require "util.jid";
 local st = require "util.stanza";
 local dt = require "util.datetime";
-local new_queue = require "util.queue".new;
-
-local function new_pump(output, ...)
-	-- luacheck: ignore 212/self
-	local q = new_queue(...);
-	local flush = true;
-	function q:pause()
-		flush = false;
-	end
-	function q:resume()
-		flush = true;
-		return q:flush();
-	end
-	local push = q.push;
-	function q:push(item)
-		local ok = push(self, item);
-		if not ok then
-			q:flush();
-			output(item, self);
-		elseif flush then
-			return q:flush();
-		end
-		return true;
-	end
-	function q:flush()
-		local item = self:pop();
-		while item do
-			output(item, self);
-			item = self:pop();
-		end
-		return true;
-	end
-	return q;
-end
+local filters = require "util.filters";
 
 local queue_size = module:get_option_number("csi_queue_size", 256);
 
@@ -84,37 +51,98 @@
 	return true;
 end, -1);
 
+local function with_timestamp(stanza, from)
+	if st.is_stanza(stanza) and stanza.attr.xmlns == nil and stanza.name ~= "iq" then
+		stanza = st.clone(stanza);
+		stanza:add_direct_child(st.stanza("delay", {xmlns = "urn:xmpp:delay", from = from, stamp = dt.datetime()}));
+	end
+	return stanza;
+end
+
+local function manage_buffer(stanza, session)
+	local ctr = session.csi_counter or 0;
+	if ctr >= queue_size then
+		session.log("debug", "Queue size limit hit, flushing buffer (queue size is %d)", session.csi_counter);
+		session.conn:resume_writes();
+	elseif module:fire_event("csi-is-stanza-important", { stanza = stanza, session = session }) then
+		session.log("debug", "Important stanza, flushing buffer (queue size is %d)", session.csi_counter);
+		session.conn:resume_writes();
+	else
+		stanza = with_timestamp(stanza, jid.join(session.username, session.host))
+	end
+	session.csi_counter = ctr + 1;
+	return stanza;
+end
+
+local function flush_buffer(data, session)
+	if session.csi_flushing then
+		return data;
+	end
+	session.csi_flushing = true;
+	session.log("debug", "Client sent something, flushing buffer once (queue size is %d)", session.csi_counter);
+	session.conn:resume_writes();
+	return data;
+end
+
+function enable_optimizations(session)
+	if session.conn and session.conn.pause_writes then
+		session.conn:pause_writes();
+		filters.add_filter(session, "stanzas/out", manage_buffer);
+		filters.add_filter(session, "bytes/in", flush_buffer);
+	else
+		session.log("warn", "Session connection does not support write pausing");
+	end
+end
+
+function disable_optimizations(session)
+	session.csi_flushing = nil;
+	filters.remove_filter(session, "stanzas/out", manage_buffer);
+	filters.remove_filter(session, "bytes/in", flush_buffer);
+	if session.conn and session.conn.resume_writes then
+		session.conn:resume_writes();
+	end
+end
+
 module:hook("csi-client-inactive", function (event)
 	local session = event.origin;
-	if session.pump then
-		session.pump:pause();
-	else
-		local bare_jid = jid.join(session.username, session.host);
-		local send = session.send;
-		session._orig_send = send;
-		local pump = new_pump(session.send, queue_size);
-		pump:pause();
-		session.pump = pump;
-		function session.send(stanza)
-			if session.state == "active" or module:fire_event("csi-is-stanza-important", { stanza = stanza, session = session }) then
-				pump:flush();
-				send(stanza);
-			else
-				if st.is_stanza(stanza) and stanza.attr.xmlns == nil and stanza.name ~= "iq" then
-					stanza = st.clone(stanza);
-					stanza:add_direct_child(st.stanza("delay", {xmlns = "urn:xmpp:delay", from = bare_jid, stamp = dt.datetime()}));
-				end
-				pump:push(stanza);
-			end
-			return true;
-		end
-	end
+	enable_optimizations(session);
 end);
 
 module:hook("csi-client-active", function (event)
 	local session = event.origin;
-	if session.pump then
-		session.pump:resume();
+	disable_optimizations(session);
+end);
+
+module:hook("pre-resource-unbind", function (event)
+	local session = event.session;
+	disable_optimizations(session);
+end);
+
+module:hook("c2s-ondrain", function (event)
+	local session = event.session;
+	if session.state == "inactive" and session.conn and session.conn.pause_writes then
+		session.conn:pause_writes();
+		session.log("debug", "Buffer flushed, resuming inactive mode (queue size was %d)", session.csi_counter);
+		session.csi_counter = 0;
 	end
 end);
 
+function module.load()
+	for _, user_session in pairs(prosody.hosts[module.host].sessions) do
+		for _, session in pairs(user_session.sessions) do
+			if session.state == "inactive" then
+				enable_optimizations(session);
+			end
+		end
+	end
+end
+
+function module.unload()
+	for _, user_session in pairs(prosody.hosts[module.host].sessions) do
+		for _, session in pairs(user_session.sessions) do
+			if session.state == "inactive" then
+				disable_optimizations(session);
+			end
+		end
+	end
+end