Diff

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/plugins/mod_smacks.lua	Tue Nov 16 21:15:22 2021 +0100
@@ -0,0 +1,690 @@
+-- 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));
+	local max_unacked = max_unacked_stanzas;
+	if session.state == "inactive"  then
+		max_unacked = max_inactive_unacked_stanzas;
+	end
+	if session.awaiting_ack == nil and not session.hibernating then
+		-- 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 }))
+					if session.destroyed then return end -- sending something can trigger destruction
+					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 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 since %s, stanza queued", datetime.datetime(session.hibernating));
+			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 and session.handled_stanza_count 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)
+	local expected_h = origin.last_acknowledged_stanza + #origin.outgoing_stanza_queue;
+	if #origin.outgoing_stanza_queue > 0 and expected_h ~= origin.last_requested_h then
+		request_ack_if_needed(origin, true, "piggybacked by handle_r", nil);
+	end
+	return true;
+end
+module:hook_stanza(xmlns_sm2, "r", function (origin, stanza) return handle_r(origin, stanza, xmlns_sm2); end);
+module:hook_stanza(xmlns_sm3, "r", function (origin, stanza) return handle_r(origin, stanza, xmlns_sm3); end);
+
+function handle_a(origin, stanza)
+	if not origin.smacks then return; end
+	origin.awaiting_ack = nil;
+	if origin.awaiting_ack_timer then
+		origin.awaiting_ack_timer:stop();
+	end
+	if origin.delayed_ack_timer then
+		origin.delayed_ack_timer:stop();
+		origin.delayed_ack_timer = nil;
+	end
+	-- Remove handled stanzas from outgoing_stanza_queue
+	-- origin.log("debug", "ACK: h=%s, last=%s", stanza.attr.h or "", origin.last_acknowledged_stanza or "");
+	local h = tonumber(stanza.attr.h);
+	if not h then
+		origin:close{ condition = "invalid-xml"; text = "Missing or invalid 'h' attribute"; };
+		return;
+	end
+	local handled_stanza_count = h-origin.last_acknowledged_stanza;
+	local queue = origin.outgoing_stanza_queue;
+	if handled_stanza_count > #queue then
+		origin.log("warn", "The client says it handled %d new stanzas, but we only sent %d :)",
+			handled_stanza_count, #queue);
+		origin.log("debug", "Client h: %d, our h: %d", tonumber(stanza.attr.h), origin.last_acknowledged_stanza);
+		for i=1,#queue do
+			origin.log("debug", "Q item %d: %s", i, tostring(queue[i]));
+		end
+        origin:close{ condition = "undefined-condition"; text = "Client acknowledged more stanzas than sent by server"; };
+        return;
+	end
+
+	for i=1,math_min(handled_stanza_count,#queue) do
+		local handled_stanza = t_remove(origin.outgoing_stanza_queue, 1);
+		module:fire_event("delivery/success", { session = origin, stanza = handled_stanza });
+	end
+
+	origin.log("debug", "#queue = %d", #queue);
+	origin.last_acknowledged_stanza = origin.last_acknowledged_stanza + handled_stanza_count;
+	request_ack_if_needed(origin, false, "handle_a", nil)
+	return true;
+end
+module:hook_stanza(xmlns_sm2, "a", handle_a);
+module:hook_stanza(xmlns_sm3, "a", handle_a);
+
+--TODO: Optimise... incoming stanzas should be handled by a per-session
+-- function that has a counter as an upvalue (no table indexing for increments,
+-- and won't slow non-198 sessions). We can also then remove the .handled flag
+-- on stanzas
+
+local function handle_unacked_stanzas(session)
+	local queue = session.outgoing_stanza_queue;
+	local error_attr = { type = "cancel" };
+	if #queue > 0 then
+		session.outgoing_stanza_queue = {};
+		for i=1,#queue do
+			if not module:fire_event("delivery/failure", { session = session, stanza = queue[i] }) then
+				if queue[i].attr.type ~= "error" then
+					local reply = st.reply(queue[i]);
+					if reply.attr.to ~= session.full_jid then
+						reply.attr.type = "error";
+						reply:tag("error", error_attr)
+							:tag("recipient-unavailable", {xmlns = "urn:ietf:params:xml:ns:xmpp-stanzas"});
+						core_process_stanza(session, reply);
+					end
+				end
+			end
+		end
+	end
+end
+
+-- don't send delivery errors for messages which will be delivered by mam later on
+-- check if stanza was archived --> this will allow us to send back errors for stanzas not archived
+-- because the user configured the server to do so ("no-archive"-setting for one special contact for example)
+local function get_stanza_id(stanza, by_jid)
+	for tag in stanza:childtags("stanza-id", "urn:xmpp:sid:0") do
+		if tag.attr.by == by_jid then
+			return tag.attr.id;
+		end
+	end
+	return nil;
+end
+module:hook("delivery/failure", function(event)
+	local session, stanza = event.session, event.stanza;
+	-- Only deal with authenticated (c2s) sessions
+	if session.username then
+		if stanza.name == "message" and stanza.attr.xmlns == nil and
+				( stanza.attr.type == "chat" or ( stanza.attr.type or "normal" ) == "normal" ) then
+			-- don't store messages in offline store if they are mam results
+			local mam_result = stanza:get_child("result", xmlns_mam2);
+			if mam_result ~= nil then
+				return true;		-- stanza already "handled", don't send an error and don't add it to offline storage
+			end
+			-- do nothing here for normal messages and don't send out "message delivery errors",
+			-- because messages are already in MAM at this point (no need to frighten users)
+			local stanza_id = get_stanza_id(stanza, jid.bare(session.full_jid));
+			if session.mam_requested and stanza_id ~= nil then
+				session.log("debug", "mod_smacks delivery/failure returning true for mam-handled stanza: mam-archive-id=%s", tostring(stanza_id));
+				return true;		-- stanza handled, don't send an error
+			end
+			-- store message in offline store, if this client does not use mam *and* was the last client online
+			local sessions = prosody.hosts[module.host].sessions[session.username] and
+					prosody.hosts[module.host].sessions[session.username].sessions or nil;
+			if sessions and next(sessions) == session.resource and next(sessions, session.resource) == nil then
+				local ok = module:fire_event("message/offline/handle", { origin = session, username = session.username, stanza = stanza });
+				session.log("debug", "mod_smacks delivery/failuere returning %s for offline-handled stanza", tostring(ok));
+				return ok;			-- if stanza was handled, don't send an error
+			end
+		end
+	end
+end);
+
+module:hook("pre-resource-unbind", function (event)
+	local session, err = event.session, event.error;
+	if session.smacks then
+		if not session.resumption_token then
+			local queue = session.outgoing_stanza_queue;
+			if #queue > 0 then
+				session.log("debug", "Destroying session with %d unacked stanzas", #queue);
+				handle_unacked_stanzas(session);
+			end
+		else
+			session.log("debug", "mod_smacks hibernating session for up to %d seconds", resume_timeout);
+			local hibernate_time = os_time(); -- Track the time we went into hibernation
+			session.hibernating = hibernate_time;
+			local resumption_token = session.resumption_token;
+			module:fire_event("smacks-hibernation-start", {origin = session, queue = session.outgoing_stanza_queue});
+			timer.add_task(resume_timeout, function ()
+				session.log("debug", "mod_smacks hibernation timeout reached...");
+				-- We need to check the current resumption token for this resource
+				-- matches the smacks session this timer is for in case it changed
+				-- (for example, the client may have bound a new resource and
+				-- started a new smacks session, or not be using smacks)
+				local curr_session = full_sessions[session.full_jid];
+				if session.destroyed then
+					session.log("debug", "The session has already been destroyed");
+				elseif curr_session and curr_session.resumption_token == resumption_token
+				-- Check the hibernate time still matches what we think it is,
+				-- otherwise the session resumed and re-hibernated.
+				and session.hibernating == hibernate_time then
+					-- wait longer if the timeout isn't reached because push was enabled for this session
+					-- session.first_hibernated_push is the starting point for hibernation timeouts of those push enabled clients
+					-- wait for an additional resume_timeout seconds if no push occurred since hibernation at all
+					local current_time = os_time();
+					local timeout_start = math_max(session.hibernating, session.first_hibernated_push or session.hibernating);
+					if session.push_identifier ~= nil and not session.first_hibernated_push then
+						session.log("debug", "No push happened since hibernation started, hibernating session for up to %d extra seconds", resume_timeout);
+						return resume_timeout;
+					end
+					if session.push_identifier ~= nil and current_time-timeout_start < resume_timeout then
+						session.log("debug", "A push happened since hibernation started, hibernating session for up to %d extra seconds", resume_timeout-(current_time-timeout_start));
+						return resume_timeout-(current_time-timeout_start);		-- time left to wait
+					end
+					session.log("debug", "Destroying session for hibernating too long");
+					session_registry.set(session.username, session.resumption_token, nil);
+					-- save only actual h value and username/host (for security)
+					old_session_registry.set(session.username, session.resumption_token, {
+						h = session.handled_stanza_count,
+						username = session.username,
+						host = session.host
+					});
+					session.resumption_token = nil;
+					sessionmanager.destroy_session(session);
+				else
+					session.log("debug", "Session resumed before hibernation timeout, all is well")
+				end
+			end);
+			return true; -- Postpone destruction for now
+		end
+	end
+end);
+
+local function handle_s2s_destroyed(event)
+	local session = event.session;
+	local queue = session.outgoing_stanza_queue;
+	if queue and #queue > 0 then
+		session.log("warn", "Destroying session with %d unacked stanzas", #queue);
+		if s2s_resend then
+			for i = 1, #queue do
+				module:send(queue[i]);
+			end
+			session.outgoing_stanza_queue = nil;
+		else
+			handle_unacked_stanzas(session);
+		end
+	end
+end
+
+module:hook("s2sout-destroyed", handle_s2s_destroyed);
+module:hook("s2sin-destroyed", handle_s2s_destroyed);
+
+local function get_session_id(session)
+	return session.id or (tostring(session):match("[a-f0-9]+$"));
+end
+
+function handle_resume(session, stanza, xmlns_sm)
+	if session.full_jid then
+		session.log("warn", "Tried to resume after resource binding");
+		session.send(st.stanza("failed", { xmlns = xmlns_sm })
+			:tag("unexpected-request", { xmlns = xmlns_errors })
+		);
+		return true;
+	end
+
+	local id = stanza.attr.previd;
+	local original_session = session_registry.get(session.username, id);
+	if not original_session then
+		session.log("debug", "Tried to resume non-existent session with id %s", id);
+		local old_session = old_session_registry.get(session.username, id);
+		if old_session and session.username == old_session.username
+		and session.host == old_session.host
+		and old_session.h then
+			session.send(st.stanza("failed", { xmlns = xmlns_sm, h = string.format("%d", old_session.h) })
+				:tag("item-not-found", { xmlns = xmlns_errors })
+			);
+		else
+			session.send(st.stanza("failed", { xmlns = xmlns_sm })
+				:tag("item-not-found", { xmlns = xmlns_errors })
+			);
+		end;
+	elseif session.username == original_session.username
+	and session.host == original_session.host then
+		session.log("debug", "mod_smacks resuming existing session %s...", get_session_id(original_session));
+		original_session.log("debug", "mod_smacks session resumed from %s...", get_session_id(session));
+		-- TODO: All this should move to sessionmanager (e.g. session:replace(new_session))
+		if original_session.conn then
+			original_session.log("debug", "mod_smacks closing an old connection for this session");
+			local conn = original_session.conn;
+			c2s_sessions[conn] = nil;
+			conn:close();
+		end
+		local migrated_session_log = session.log;
+		original_session.ip = session.ip;
+		original_session.conn = session.conn;
+		original_session.send = session.send;
+		original_session.close = session.close;
+		original_session.filter = session.filter;
+		original_session.filter.session = original_session;
+		original_session.filters = session.filters;
+		original_session.stream = session.stream;
+		original_session.secure = session.secure;
+		original_session.hibernating = nil;
+		session.log = original_session.log;
+		session.type = original_session.type;
+		wrap_session(original_session, true);
+		-- Inform xmppstream of the new session (passed to its callbacks)
+		original_session.stream:set_session(original_session);
+		-- Similar for connlisteners
+		c2s_sessions[session.conn] = original_session;
+
+		original_session.send(st.stanza("resumed", { xmlns = xmlns_sm,
+			h = string.format("%d", original_session.handled_stanza_count), previd = id }));
+
+		-- Fake an <a> with the h of the <resume/> from the client
+		original_session:dispatch_stanza(st.stanza("a", { xmlns = xmlns_sm,
+			h = stanza.attr.h }));
+
+		-- Ok, we need to re-send any stanzas that the client didn't see
+		-- ...they are what is now left in the outgoing stanza queue
+		-- We have to use the send of "session" because we don't want to add our resent stanzas
+		-- to the outgoing queue again
+		local queue = original_session.outgoing_stanza_queue;
+		session.log("debug", "resending all unacked stanzas that are still queued after resume, #queue = %d", #queue);
+		for i=1,#queue do
+			session.send(queue[i]);
+		end
+		session.log("debug", "all stanzas resent, now disabling send() in this migrated session, #queue = %d", #queue);
+		function session.send(stanza)
+			migrated_session_log("error", "Tried to send stanza on old session migrated by smacks resume (maybe there is a bug?): %s", tostring(stanza));
+			return false;
+		end
+		module:fire_event("smacks-hibernation-end", {origin = session, resumed = original_session, queue = queue});
+		request_ack_if_needed(original_session, true, "handle_resume", nil);
+	else
+		module:log("warn", "Client %s@%s[%s] tried to resume stream for %s@%s[%s]",
+			session.username or "?", session.host or "?", session.type,
+			original_session.username or "?", original_session.host or "?", original_session.type);
+		session.send(st.stanza("failed", { xmlns = xmlns_sm })
+			:tag("not-authorized", { xmlns = xmlns_errors }));
+	end
+	return true;
+end
+module:hook_stanza(xmlns_sm2, "resume", function (session, stanza) return handle_resume(session, stanza, xmlns_sm2); end);
+module:hook_stanza(xmlns_sm3, "resume", function (session, stanza) return handle_resume(session, stanza, xmlns_sm3); end);
+
+module:hook("csi-client-active", function (event)
+	if event.origin.smacks then
+		request_ack_if_needed(event.origin, true, "csi-active", nil);
+	end
+end);
+
+module:hook("csi-flushing", function(event)
+	local session = event.session;
+	if session.smacks then
+		if not session.awaiting_ack and not session.hibernating and not session.destroyed then
+			session.log("debug", "Sending <r> (csi-flushing)");
+			session.awaiting_ack = true; -- The send() call may invoke this event again, so set this first
+			(session.sends2s or session.send)(st.stanza("r", { xmlns = session.smacks }))
+		end
+	end
+end);
+
+local function handle_read_timeout(event)
+	local session = event.session;
+	if session.smacks then
+		if session.awaiting_ack then
+			if session.awaiting_ack_timer then
+				session.awaiting_ack_timer:stop();
+			end
+			if session.delayed_ack_timer then
+				session.delayed_ack_timer:stop();
+				session.delayed_ack_timer = nil;
+			end
+			return false; -- Kick the session
+		end
+		session.log("debug", "Sending <r> (read timeout)");
+		(session.sends2s or session.send)(st.stanza("r", { xmlns = session.smacks }));
+		session.awaiting_ack = true;
+		if not session.delayed_ack_timer then
+			session.delayed_ack_timer = stoppable_timer(delayed_ack_timeout, function()
+				delayed_ack_function(session, nil);
+			end);
+		end
+		return true;
+	end
+end
+
+module:hook("s2s-read-timeout", handle_read_timeout);
+module:hook("c2s-read-timeout", handle_read_timeout);