-- XEP-0198: Stream Management for Prosody IM

--

-- Copyright (C) 2010-2015 Matthew Wild

-- Copyright (C) 2010 Waqas Hussain

-- Copyright (C) 2012-2021 Kim Alvefur

-- Copyright (C) 2012 Thijs Alkemade

-- Copyright (C) 2014 Florian Zeitz

-- Copyright (C) 2016-2020 Thilo Molitor

--

-- This project is MIT/X11 licensed. Please see the

-- COPYING file in the source package for more information.

--

local st = require "util.stanza";

local dep = require "util.dependencies";

local cache = dep.softreq("util.cache");	-- only available in prosody 0.10+

local uuid_generate = require "util.uuid".generate;

local jid = require "util.jid";

local t_remove = table.remove;

local math_min = math.min;

local math_max = math.max;

local os_time = os.time;

local tonumber, tostring = tonumber, tostring;

local add_filter = require "util.filters".add_filter;

local timer = require "util.timer";

local datetime = require "util.datetime";

local xmlns_mam2 = "urn:xmpp:mam:2";

local xmlns_sm2 = "urn:xmpp:sm:2";

local xmlns_sm3 = "urn:xmpp:sm:3";

local xmlns_errors = "urn:ietf:params:xml:ns:xmpp-stanzas";

local xmlns_delay = "urn:xmpp:delay";

local sm2_attr = { xmlns = xmlns_sm2 };

local sm3_attr = { xmlns = xmlns_sm3 };

local resume_timeout = module:get_option_number("smacks_hibernation_time", 600);

local s2s_smacks = module:get_option_boolean("smacks_enabled_s2s", true);

local s2s_resend = module:get_option_boolean("smacks_s2s_resend", false);

local max_unacked_stanzas = module:get_option_number("smacks_max_unacked_stanzas", 0);

local max_inactive_unacked_stanzas = module:get_option_number("smacks_max_inactive_unacked_stanzas", 256);

local delayed_ack_timeout = module:get_option_number("smacks_max_ack_delay", 30);

local max_hibernated_sessions = module:get_option_number("smacks_max_hibernated_sessions", 10);

local max_old_sessions = module:get_option_number("smacks_max_old_sessions", 10);

local core_process_stanza = prosody.core_process_stanza;

local sessionmanager = require"core.sessionmanager";

assert(max_hibernated_sessions > 0, "smacks_max_hibernated_sessions must be greater than 0");

assert(max_old_sessions > 0, "smacks_max_old_sessions must be greater than 0");

local c2s_sessions = module:shared("/*/c2s/sessions");

local function init_session_cache(max_entries, evict_callback)

	-- old prosody version < 0.10 (no limiting at all!)

	if not cache then

		local store = {};

		return {

			get = function(user, key)

				if not user then return nil; end

				if not key then return nil; end

				return store[key];

			end;

			set = function(user, key, value)

				if not user then return nil; end

				if not key then return nil; end

				store[key] = value;

			end;

		};

	end

	-- use per user limited cache for prosody >= 0.10

	local stores = {};

	return {

			get = function(user, key)

				if not user then return nil; end

				if not key then return nil; end

				if not stores[user] then

					stores[user] = cache.new(max_entries, evict_callback);

				end

				return stores[user]:get(key);

			end;

			set = function(user, key, value)

				if not user then return nil; end

				if not key then return nil; end

				if not stores[user] then stores[user] = cache.new(max_entries, evict_callback); end

				stores[user]:set(key, value);

				-- remove empty caches completely

				if not stores[user]:count() then stores[user] = nil; end

			end;

		};

end

local old_session_registry = init_session_cache(max_old_sessions, nil);

local session_registry = init_session_cache(max_hibernated_sessions, function(resumption_token, session)

	if session.destroyed then return true; end		-- destroyed session can always be removed from cache

	session.log("warn", "User has too much hibernated sessions, removing oldest session (token: %s)", resumption_token);

	-- store old session's h values on force delete

	-- save only actual h value and username/host (for security)

	old_session_registry.set(session.username, resumption_token, {

		h = session.handled_stanza_count,

		username = session.username,

		host = session.host

	});

	return true;	-- allow session to be removed from full cache to make room for new one

end);

local function stoppable_timer(delay, callback)

	local stopped = false;

	local timer = module:add_timer(delay, function (t)

		if stopped then return; end

		return callback(t);

	end);

	if timer and timer.stop then return timer; end		-- new prosody api includes stop() function

	return {

		stop = function(self) stopped = true end;

		timer;

	};

end

local function delayed_ack_function(session, stanza)

	-- fire event only if configured to do so and our session is not already hibernated or destroyed

	if delayed_ack_timeout > 0 and session.awaiting_ack

	and not session.hibernating and not session.destroyed then

		session.log("debug", "Firing event 'smacks-ack-delayed', queue = %d",

			session.outgoing_stanza_queue and #session.outgoing_stanza_queue or 0);

		module:fire_event("smacks-ack-delayed", {origin = session, queue = session.outgoing_stanza_queue, stanza = stanza});

	end

	session.delayed_ack_timer = nil;

end

local function can_do_smacks(session, advertise_only)

	if session.smacks then return false, "unexpected-request", "Stream management is already enabled"; end

	local session_type = session.type;

	if session.username then

		if not(advertise_only) and not(session.resource) then -- Fail unless we're only advertising sm

			return false, "unexpected-request", "Client must bind a resource before enabling stream management";

		end

		return true;

	elseif s2s_smacks and (session_type == "s2sin" or session_type == "s2sout") then

		return true;

	end

	return false, "service-unavailable", "Stream management is not available for this stream";

end

module:hook("stream-features",

		function (event)

			if can_do_smacks(event.origin, true) then

				event.features:tag("sm", sm2_attr):tag("optional"):up():up();

				event.features:tag("sm", sm3_attr):tag("optional"):up():up();

			end

		end);

module:hook("s2s-stream-features",

		function (event)

			if can_do_smacks(event.origin, true) then

				event.features:tag("sm", sm2_attr):tag("optional"):up():up();

				event.features:tag("sm", sm3_attr):tag("optional"):up():up();

			end

		end);

local function request_ack_if_needed(session, force, reason, stanza)

	local queue = session.outgoing_stanza_queue;

	local expected_h = session.last_acknowledged_stanza + #queue;

	-- session.log("debug", "*** SMACKS(1) ***: awaiting_ack=%s, hibernating=%s", tostring(session.awaiting_ack), tostring(session.hibernating));

	if session.awaiting_ack == nil and not session.hibernating then

		local max_unacked = max_unacked_stanzas;

		if session.state == "inactive"  then

			max_unacked = max_inactive_unacked_stanzas;

		end

		-- this check of last_requested_h prevents ack-loops if missbehaving clients report wrong

		-- stanza counts. it is set when an <r> is really sent (e.g. inside timer), preventing any

		-- further requests until a higher h-value would be expected.

		-- session.log("debug", "*** SMACKS(2) ***: #queue=%s, max_unacked_stanzas=%s, expected_h=%s, last_requested_h=%s", tostring(#queue), tostring(max_unacked_stanzas), tostring(expected_h), tostring(session.last_requested_h));

		if (#queue > max_unacked and expected_h ~= session.last_requested_h) or force then

			session.log("debug", "Queuing <r> (in a moment) from %s - #queue=%d", reason, #queue);

			session.awaiting_ack = false;

			session.awaiting_ack_timer = stoppable_timer(1e-06, function ()

				-- session.log("debug", "*** SMACKS(3) ***: awaiting_ack=%s, hibernating=%s", tostring(session.awaiting_ack), tostring(session.hibernating));

				-- only request ack if needed and our session is not already hibernated or destroyed

				if not session.awaiting_ack and not session.hibernating and not session.destroyed then

					session.log("debug", "Sending <r> (inside timer, before send) from %s - #queue=%d", reason, #queue);

					(session.sends2s or session.send)(st.stanza("r", { xmlns = session.smacks }))

					session.awaiting_ack = true;

					-- expected_h could be lower than this expression e.g. more stanzas added to the queue meanwhile)

					session.last_requested_h = session.last_acknowledged_stanza + #queue;

					session.log("debug", "Sending <r> (inside timer, after send) from %s - #queue=%d", reason, #queue);

					if not session.delayed_ack_timer then

						session.delayed_ack_timer = stoppable_timer(delayed_ack_timeout, function()

							delayed_ack_function(session, nil);		-- we don't know if this is the only new stanza in the queue

						end);

					end

				end

			end);

		end

	end

	-- Trigger "smacks-ack-delayed"-event if we added new (ackable) stanzas to the outgoing queue

	-- and there isn't already a timer for this event running.

	-- If we wouldn't do this, stanzas added to the queue after the first "smacks-ack-delayed"-event

	-- would not trigger this event (again).

	if #queue > max_unacked_stanzas and session.awaiting_ack and session.delayed_ack_timer == nil then

		session.log("debug", "Calling delayed_ack_function directly (still waiting for ack)");

		delayed_ack_function(session, stanza);		-- this is the only new stanza in the queue --> provide it to other modules

	end

end

local function outgoing_stanza_filter(stanza, session)

	-- XXX: Normally you wouldn't have to check the xmlns for a stanza as it's

	-- supposed to be nil.

	-- However, when using mod_smacks with mod_websocket, then mod_websocket's

	-- stanzas/out filter can get called before this one and adds the xmlns.

	local is_stanza = stanza.attr and

		(not stanza.attr.xmlns or stanza.attr.xmlns == 'jabber:client')

		and not stanza.name:find":";

	if is_stanza and not stanza._cached then

		local queue = session.outgoing_stanza_queue;

		local cached_stanza = st.clone(stanza);

		cached_stanza._cached = true;

		if cached_stanza and cached_stanza.name ~= "iq" and cached_stanza:get_child("delay", xmlns_delay) == nil then

			cached_stanza = cached_stanza:tag("delay", {

				xmlns = xmlns_delay,

				from = jid.bare(session.full_jid or session.host),

				stamp = datetime.datetime()

			});

		end

		queue[#queue+1] = cached_stanza;

		if session.hibernating then

			session.log("debug", "hibernating, stanza queued");

			module:fire_event("smacks-hibernation-stanza-queued", {origin = session, queue = queue, stanza = cached_stanza});

			return nil;

		end

		request_ack_if_needed(session, false, "outgoing_stanza_filter", stanza);

	end

	return stanza;

end

local function count_incoming_stanzas(stanza, session)

	if not stanza.attr.xmlns then

		session.handled_stanza_count = session.handled_stanza_count + 1;

		session.log("debug", "Handled %d incoming stanzas", session.handled_stanza_count);

	end

	return stanza;

end

local function wrap_session_out(session, resume)

	if not resume then

		session.outgoing_stanza_queue = {};

		session.last_acknowledged_stanza = 0;

	end

	add_filter(session, "stanzas/out", outgoing_stanza_filter, -999);

	local session_close = session.close;

	function session.close(...)

		if session.resumption_token then

			session_registry.set(session.username, session.resumption_token, nil);

			old_session_registry.set(session.username, session.resumption_token, nil);

			session.resumption_token = nil;

		end

		-- send out last ack as per revision 1.5.2 of XEP-0198

		if session.smacks and session.conn then

			(session.sends2s or session.send)(st.stanza("a", { xmlns = session.smacks, h = string.format("%d", session.handled_stanza_count) }));

		end

		return session_close(...);

	end

	return session;

end

local function wrap_session_in(session, resume)

	if not resume then

		session.handled_stanza_count = 0;

	end

	add_filter(session, "stanzas/in", count_incoming_stanzas, 999);

	return session;

end

local function wrap_session(session, resume)

	wrap_session_out(session, resume);

	wrap_session_in(session, resume);

	return session;

end

function handle_enable(session, stanza, xmlns_sm)

	local ok, err, err_text = can_do_smacks(session);

	if not ok then

		session.log("warn", "Failed to enable smacks: %s", err_text); -- TODO: XEP doesn't say we can send error text, should it?

		(session.sends2s or session.send)(st.stanza("failed", { xmlns = xmlns_sm }):tag(err, { xmlns = xmlns_errors}));

		return true;

	end

	module:log("debug", "Enabling stream management");

	session.smacks = xmlns_sm;

	wrap_session(session, false);

	local resume_token;

	local resume = stanza.attr.resume;

	if resume == "true" or resume == "1" then

		resume_token = uuid_generate();

		session_registry.set(session.username, resume_token, session);

		session.resumption_token = resume_token;

	end

	(session.sends2s or session.send)(st.stanza("enabled", { xmlns = xmlns_sm, id = resume_token, resume = resume, max = tostring(resume_timeout) }));

	return true;

end

module:hook_stanza(xmlns_sm2, "enable", function (session, stanza) return handle_enable(session, stanza, xmlns_sm2); end, 100);

module:hook_stanza(xmlns_sm3, "enable", function (session, stanza) return handle_enable(session, stanza, xmlns_sm3); end, 100);

module:hook_stanza("http://etherx.jabber.org/streams", "features",

		function (session, stanza)

			stoppable_timer(1e-6, function ()

				if can_do_smacks(session) then

					if stanza:get_child("sm", xmlns_sm3) then

						session.sends2s(st.stanza("enable", sm3_attr));

						session.smacks = xmlns_sm3;

					elseif stanza:get_child("sm", xmlns_sm2) then

						session.sends2s(st.stanza("enable", sm2_attr));

						session.smacks = xmlns_sm2;

					else

						return;

					end

					wrap_session_out(session, false);

				end

			end);

		end);

function handle_enabled(session, stanza, xmlns_sm)

	module:log("debug", "Enabling stream management");

	session.smacks = xmlns_sm;

	wrap_session_in(session, false);

	-- FIXME Resume?

	return true;

end

module:hook_stanza(xmlns_sm2, "enabled", function (session, stanza) return handle_enabled(session, stanza, xmlns_sm2); end, 100);

module:hook_stanza(xmlns_sm3, "enabled", function (session, stanza) return handle_enabled(session, stanza, xmlns_sm3); end, 100);

function handle_r(origin, stanza, xmlns_sm)

	if not origin.smacks then

		module:log("debug", "Received ack request from non-smack-enabled session");

		return;

	end

	module:log("debug", "Received ack request, acking for %d", origin.handled_stanza_count);

	-- Reply with <a>

	(origin.sends2s or origin.send)(st.stanza("a", { xmlns = xmlns_sm, h = string.format("%d", origin.handled_stanza_count) }));

	-- piggyback our own ack request if needed (see request_ack_if_needed() for explanation of last_requested_h)