path: root/core/s2smanager.lua

-- Prosody IM
-- Copyright (C) 2008-2010 Matthew Wild
-- Copyright (C) 2008-2010 Waqas Hussain
-- 
-- This project is MIT/X11 licensed. Please see the
-- COPYING file in the source package for more information.
--



local hosts = hosts;
local sessions = sessions;
local core_process_stanza = function(a, b) core_process_stanza(a, b); end
local add_task = require "util.timer".add_task;
local socket = require "socket";
local format = string.format;
local t_insert, t_sort = table.insert, table.sort;
local get_traceback = debug.traceback;
local tostring, pairs, ipairs, getmetatable, newproxy, type, error, tonumber, setmetatable
    = tostring, pairs, ipairs, getmetatable, newproxy, type, error, tonumber, setmetatable;

local idna_to_ascii = require "util.encodings".idna.to_ascii;
local connlisteners_get = require "net.connlisteners".get;
local initialize_filters = require "util.filters".initialize;
local wrapclient = require "net.server".wrapclient;
local st = require "stanza";
local stanza = st.stanza;
local nameprep = require "util.encodings".stringprep.nameprep;
local cert_verify_identity = require "util.x509".verify_identity;
local new_ip = require "util.ip".new_ip;
local rfc3484_dest = require "util.rfc3484".destination;

local fire_event = prosody.events.fire_event;
local uuid_gen = require "util.uuid".generate;

local logger_init = require "util.logger".init;

local log = logger_init("s2smanager");

local sha256_hash = require "util.hashes".sha256;

local adns, dns = require "net.adns", require "net.dns";
local config = require "core.configmanager";
local connect_timeout = config.get("*", "core", "s2s_timeout") or 60;
local dns_timeout = config.get("*", "core", "dns_timeout") or 15;
local max_dns_depth = config.get("*", "core", "dns_max_depth") or 3;
local sources;

dns.settimeout(dns_timeout);

local prosody = _G.prosody;
incoming_s2s = {};
prosody.incoming_s2s = incoming_s2s;
local incoming_s2s = incoming_s2s;

module "s2smanager"

function compare_srv_priorities(a,b)
	return a.priority < b.priority or (a.priority == b.priority and a.weight > b.weight);
end

local bouncy_stanzas = { message = true, presence = true, iq = true };
local function bounce_sendq(session, reason)
	local sendq = session.sendq;
	if sendq then
		session.log("info", "sending error replies for "..#sendq.." queued stanzas because of failed outgoing connection to "..tostring(session.to_host));
		local dummy = {
			type = "s2sin";
			send = function(s)
				(session.log or log)("error", "Replying to to an s2s error reply, please report this! Traceback: %s", get_traceback());
			end;
			dummy = true;
		};
		for i, data in ipairs(sendq) do
			local reply = data[2];
			if reply and not(reply.attr.xmlns) and bouncy_stanzas[reply.name] then
				reply.attr.type = "error";
				reply:tag("error", {type = "cancel"})
					:tag("remote-server-not-found", {xmlns = "urn:ietf:params:xml:ns:xmpp-stanzas"}):up();
				if reason then
					reply:tag("text", {xmlns = "urn:ietf:params:xml:ns:xmpp-stanzas"})
						:text("Server-to-server connection failed: "..reason):up();
				end
				core_process_stanza(dummy, reply);
			end
			sendq[i] = nil;
		end
		session.sendq = nil;
	end
end

function send_to_host(from_host, to_host, data)
	if not hosts[from_host] then
		log("warn", "Attempt to send stanza from %s - a host we don't serve", from_host);
		return false;
	end
	local host = hosts[from_host].s2sout[to_host];
	if host then
		-- We have a connection to this host already
		if host.type == "s2sout_unauthed" and (data.name ~= "db:verify" or not host.dialback_key) then
			(host.log or log)("debug", "trying to send over unauthed s2sout to "..to_host);
			
			-- Queue stanza until we are able to send it
			if host.sendq then t_insert(host.sendq, {tostring(data), data.attr.type ~= "error" and data.attr.type ~= "result" and st.reply(data)});
			else host.sendq = { {tostring(data), data.attr.type ~= "error" and data.attr.type ~= "result" and st.reply(data)} }; end
			host.log("debug", "stanza [%s] queued ", data.name);
		elseif host.type == "local" or host.type == "component" then
			log("error", "Trying to send a stanza to ourselves??")
			log("error", "Traceback: %s", get_traceback());
			log("error", "Stanza: %s", tostring(data));
			return false;
		else
			(host.log or log)("debug", "going to send stanza to "..to_host.." from "..from_host);
			-- FIXME
			if host.from_host ~= from_host then
				log("error", "WARNING! This might, possibly, be a bug, but it might not...");
				log("error", "We are going to send from %s instead of %s", tostring(host.from_host), tostring(from_host));
			end
			host.sends2s(data);
			host.log("debug", "stanza sent over "..host.type);
		end
	else
		log("debug", "opening a new outgoing connection for this stanza");
		local host_session = new_outgoing(from_host, to_host);

		-- Store in buffer
		host_session.sendq = { {tostring(data), data.attr.type ~= "error" and data.attr.type ~= "result" and st.reply(data)} };
		log("debug", "stanza [%s] queued until connection complete", tostring(data.name));
		if (not host_session.connecting) and (not host_session.conn) then
			log("warn", "Connection to %s failed already, destroying session...", to_host);
			if not destroy_session(host_session, "Connection failed") then
				-- Already destroyed, we need to bounce our stanza
				bounce_sendq(host_session, host_session.destruction_reason);
			end
			return false;
		end
	end
	return true;
end

local open_sessions = 0;

function new_incoming(conn)
	local session = { conn = conn, type = "s2sin_unauthed", direction = "incoming", hosts = {} };
	if true then
		session.trace = newproxy(true);
		getmetatable(session.trace).__gc = function () open_sessions = open_sessions - 1; end;
	end
	open_sessions = open_sessions + 1;
	local w, log = conn.write, logger_init("s2sin"..tostring(conn):match("[a-f0-9]+$"));
	session.log = log;
	local filter = initialize_filters(session);
	session.sends2s = function (t)
		log("debug", "sending: %s", t.top_tag and t:top_tag() or t:match("^([^>]*>?)"));
		if t.name then
			t = filter("stanzas/out", t);
		end
		if t then
			t = filter("bytes/out", tostring(t));
			if t then
				return w(conn, t);
			end
		end
	end
	incoming_s2s[session] = true;
	add_task(connect_timeout, function ()
		if session.conn ~= conn or
		   session.type == "s2sin" then
			return; -- Ok, we're connect[ed|ing]
		end
		-- Not connected, need to close session and clean up
		(session.log or log)("debug", "Destroying incomplete session %s->%s due to inactivity",
		    session.from_host or "(unknown)", session.to_host or "(unknown)");
		session:close("connection-timeout");
	end);
	return session;
end

function new_outgoing(from_host, to_host, connect)
		local host_session = { to_host = to_host, from_host = from_host, host = from_host,
		                       notopen = true, type = "s2sout_unauthed", direction = "outgoing",
		                       open_stream = session_open_stream };
		
		hosts[from_host].s2sout[to_host] = host_session;
		
		host_session.close = destroy_session; -- This gets replaced by xmppserver_listener later
		
		local log;
		do
			local conn_name = "s2sout"..tostring(host_session):match("[a-f0-9]*$");
			log = logger_init(conn_name);
			host_session.log = log;
		end
		
		initialize_filters(host_session);
		
		if connect ~= false then
			-- Kick the connection attempting machine into life
			if not attempt_connection(host_session) then
				-- Intentionally not returning here, the
				-- session is needed, connected or not
				destroy_session(host_session);
			end
		end
		
		if not host_session.sends2s then
			-- A sends2s which buffers data (until the stream is opened)
			-- note that data in this buffer will be sent before the stream is authed
			-- and will not be ack'd in any way, successful or otherwise
			local buffer;
			function host_session.sends2s(data)
				if not buffer then
					buffer = {};
					host_session.send_buffer = buffer;
				end
				log("debug", "Buffering data on unconnected s2sout to %s", to_host);
				buffer[#buffer+1] = data;
				log("debug", "Buffered item %d: %s", #buffer, tostring(data));
			end
		end

		return host_session;
end


function attempt_connection(host_session, err)
	local from_host, to_host = host_session.from_host, host_session.to_host;
	local connect_host, connect_port = to_host and idna_to_ascii(to_host), 5269;
	
	if not connect_host then
		return false;
	end
	
	if not err then -- This is our first attempt
		log("debug", "First attempt to connect to %s, starting with SRV lookup...", to_host);
		host_session.connecting = true;
		local handle;
		handle = adns.lookup(function (answer)
			handle = nil;
			host_session.connecting = nil;
			if answer then
				log("debug", to_host.." has SRV records, handling...");
				local srv_hosts = {};
				host_session.srv_hosts = srv_hosts;
				for _, record in ipairs(answer) do
					t_insert(srv_hosts, record.srv);
				end
				if #srv_hosts == 1 and srv_hosts[1].target == "." then
					log("debug", to_host.." does not provide a XMPP service");
					destroy_session(host_session, err); -- Nothing to see here
					return;
				end
				t_sort(srv_hosts, compare_srv_priorities);
				
				local srv_choice = srv_hosts[1];
				host_session.srv_choice = 1;
				if srv_choice then
					connect_host, connect_port = srv_choice.target or to_host, srv_choice.port or connect_port;
					log("debug", "Best record found, will connect to %s:%d", connect_host, connect_port);
				end
			else
				log("debug", to_host.." has no SRV records, falling back to A");
			end
			-- Try with SRV, or just the plain hostname if no SRV
			local ok, err = try_connect(host_session, connect_host, connect_port);
			if not ok then
				if not attempt_connection(host_session, err) then
					-- No more attempts will be made
					destroy_session(host_session, err);
				end
			end
		end, "_xmpp-server._tcp."..connect_host..".", "SRV");
		
		return true; -- Attempt in progress
	elseif host_session.ip_hosts then
		return try_connect(host_session, connect_host, connect_port, err);
	elseif host_session.srv_hosts and #host_session.srv_hosts > host_session.srv_choice then -- Not our first attempt, and we also have SRV
		host_session.srv_choice = host_session.srv_choice + 1;
		local srv_choice = host_session.srv_hosts[host_session.srv_choice];
		connect_host, connect_port = srv_choice.target or to_host, srv_choice.port or connect_port;
		host_session.log("info", "Connection failed (%s). Attempt #%d: This time to %s:%d", tostring(err), host_session.srv_choice, connect_host, connect_port);
	else
		host_session.log("info", "Out of connection options, can't connect to %s", tostring(host_session.to_host));
		-- We're out of options
		return false;
	end
	
	if not (connect_host and connect_port) then
		-- Likely we couldn't resolve DNS
		log("warn", "Hmm, we're without a host (%s) and port (%s) to connect to for %s, giving up :(", tostring(connect_host), tostring(connect_port), tostring(to_host));
		return false;
	end
	
	return try_connect(host_session, connect_host, connect_port);
end

function try_next_ip(host_session)
	host_session.connecting = nil;
	host_session.ip_choice = host_session.ip_choice + 1;
	local ip = host_session.ip_hosts[host_session.ip_choice];
	local ok, err= make_connect(host_session, ip.ip, ip.port);
	if not ok then
		if not attempt_connection(host_session, err or "closed") then
			err = err and (": "..err) or "";
			destroy_session(host_session, "Connection failed"..err);
		end
	end
end

function try_connect(host_session, connect_host, connect_port, err)
	host_session.connecting = true;

	if not err then
		local IPs = {};
		host_session.ip_hosts = IPs;
		local handle4, handle6;
		local has_other = false;

		if not sources then
			sources =  {};
			local cfg_sources = config.get("*", "core", "interface") or connlisteners_get("xmppserver").default_interface;
			if type(cfg_sources) == "string" then
				cfg_sources = { cfg_sources };
			end
			for i, source in ipairs(cfg_sources) do
				if source == "*" then
					sources[i] = new_ip("0.0.0.0", "IPv4");
				else
					sources[i] = new_ip(source, (source:find(":") and "IPv6") or "IPv4");
				end
			end
		end

		handle4 = adns.lookup(function (reply, err)
			handle4 = nil;

			-- COMPAT: This is a compromise for all you CNAME-(ab)users :)
			if not (reply and reply[#reply] and reply[#reply].a) then
				local count = max_dns_depth;
				reply = dns.peek(connect_host, "CNAME", "IN");
				while count > 0 and reply and reply[#reply] and not reply[#reply].a and reply[#reply].cname do
					log("debug", "Looking up %s (DNS depth is %d)", tostring(reply[#reply].cname), count);
					reply = dns.peek(reply[#reply].cname, "A", "IN") or dns.peek(reply[#reply].cname, "CNAME", "IN");
					count = count - 1;
				end
			end
			-- end of CNAME resolving

			if reply and reply[#reply] and reply[#reply].a then
				for _, ip in ipairs(reply) do
					log("debug", "DNS reply for %s gives us %s", connect_host, ip.a);
					IPs[#IPs+1] = new_ip(ip.a, "IPv4");
				end
			end

			if has_other then
				if #IPs > 0 then
					rfc3484_dest(host_session.ip_hosts, sources);
					for i = 1, #IPs do
						IPs[i] = {ip = IPs[i], port = connect_port};
					end
					host_session.ip_choice = 0;
					try_next_ip(host_session);
				else
					log("debug", "DNS lookup failed to get a response for %s", connect_host);
					host_session.ip_hosts = nil;
					if not attempt_connection(host_session, "name resolution failed") then -- Retry if we can
						log("debug", "No other records to try for %s - destroying", host_session.to_host);
						err = err and (": "..err) or "";
						destroy_session(host_session, "DNS resolution failed"..err); -- End of the line, we can't
					end
				end
			else
				has_other = true;
			end
		end, connect_host, "A", "IN");

		handle6 = adns.lookup(function (reply, err)
			handle6 = nil;

			if reply and reply[#reply] and reply[#reply].aaaa then
				for _, ip in ipairs(reply) do
					log("debug", "DNS reply for %s gives us %s", connect_host, ip.aaaa);
					IPs[#IPs+1] = new_ip(ip.aaaa, "IPv6");
				end
			end

			if has_other then
				if #IPs > 0 then
					rfc3484_dest(host_session.ip_hosts, sources);
					for i = 1, #IPs do
						IPs[i] = {ip = IPs[i], port = connect_port};
					end
					host_session.ip_choice = 0;
					try_next_ip(host_session);
				else
					log("debug", "DNS lookup failed to get a response for %s", connect_host);
					host_session.ip_hosts = nil;
					if not attempt_connection(host_session, "name resolution failed") then -- Retry if we can
						log("debug", "No other records to try for %s - destroying", host_session.to_host);
						err = err and (": "..err) or "";
						destroy_session(host_session, "DNS resolution failed"..err); -- End of the line, we can't
					end
				end
			else
				has_other = true;
			end
		end, connect_host, "AAAA", "IN");

		return true;
	elseif host_session.ip_hosts and #host_session.ip_hosts > host_session.ip_choice then -- Not our first attempt, and we also have IPs left to try
		try_next_ip(host_session);
	else
		host_session.ip_hosts = nil;
		if not attempt_connection(host_session, "out of IP addresses") then -- Retry if we can
			log("debug", "No other records to try for %s - destroying", host_session.to_host);
			err = err and (": "..err) or "";
			destroy_session(host_session, "Connecting failed"..err); -- End of the line, we can't
			return false;
		end
	end

	return true;
end

function make_connect(host_session, connect_host, connect_port)
	(host_session.log or log)("info", "Beginning new connection attempt to %s ([%s]:%d)", host_session.to_host, connect_host.addr, connect_port);
	-- Ok, we're going to try to connect
	
	local from_host, to_host = host_session.from_host, host_session.to_host;
	
	local conn, handler;
	if connect_host.proto == "IPv4" then
		conn, handler = socket.tcp();
	elseif socket.tcp6 then
		conn, handler = socket.tcp6();
	end
	
	if not conn then
		log("warn", "Failed to create outgoing connection, system error: %s", handler);
		return false, handler;
	end

	conn:settimeout(0);
	local success, err = conn:connect(connect_host.addr, connect_port);
	if not success and err ~= "timeout" then
		log("warn", "s2s connect() to %s (%s:%d) failed: %s", host_session.to_host, connect_host.addr, connect_port, err);
		return false, err;
	end
	
	local cl = connlisteners_get("xmppserver");
	conn = wrapclient(conn, connect_host.addr, connect_port, cl, cl.default_mode or 1 );
	host_session.conn = conn;
	
	local filter = initialize_filters(host_session);
	local w, log = conn.write, host_session.log;
	host_session.sends2s = function (t)
		log("debug", "sending: %s", (t.top_tag and t:top_tag()) or t:match("^[^>]*>?"));
		if t.name then
			t = filter("stanzas/out", t);
		end
		if t then
			t = filter("bytes/out", tostring(t));
			if t then
				return w(conn, tostring(t));
			end
		end
	end
	
	-- Register this outgoing connection so that xmppserver_listener knows about it
	-- otherwise it will assume it is a new incoming connection
	cl.register_outgoing(conn, host_session);
	
	host_session:open_stream(from_host, to_host);
	
	log("debug", "Connection attempt in progress...");
	add_task(connect_timeout, function ()
		if host_session.conn ~= conn or
		   host_session.type == "s2sout" or
		   host_session.connecting then
			return; -- Ok, we're connect[ed|ing]
		end
		-- Not connected, need to close session and clean up
		(host_session.log or log)("warn", "Destroying incomplete session %s->%s due to inactivity",
		    host_session.from_host or "(unknown)", host_session.to_host or "(unknown)");
		host_session:close("connection-timeout");
	end);
	return true;
end

function session_open_stream(session, from, to)
	session.sends2s(st.stanza("stream:stream", {
		xmlns='jabber:server', ["xmlns:db"]='jabber:server:dialback',
		["xmlns:stream"]='http://etherx.jabber.org/streams',
		from=from, to=to, version='1.0', ["xml:lang"]='en'}):top_tag());
end

local function check_cert_status(session)
	local conn = session.conn:socket()
	local cert
	if conn.getpeercertificate then
		cert = conn:getpeercertificate()
	end

	if cert then
		local chain_valid, errors = conn:getpeerverification()
		-- Is there any interest in printing out all/the number of errors here?
		if not chain_valid then
			(session.log or log)("debug", "certificate chain validation result: invalid");
			session.cert_chain_status = "invalid";
		else
			(session.log or log)("debug", "certificate chain validation result: valid");
			session.cert_chain_status = "valid";

			local host = session.direction == "incoming" and session.from_host or session.to_host

			-- We'll go ahead and verify the asserted identity if the
			-- connecting server specified one.
			if host then
				if cert_verify_identity(host, "xmpp-server", cert) then
					session.cert_identity_status = "valid"
				else
					session.cert_identity_status = "invalid"
				end
			end
		end
	end
end

function streamopened(session, attr)
	local send = session.sends2s;
	
	-- TODO: #29: SASL/TLS on s2s streams
	session.version = tonumber(attr.version) or 0;
	
	-- TODO: Rename session.secure to session.encrypted
	if session.secure == false then
		session.secure = true;
	end

	if session.direction == "incoming" then
		-- Send a reply stream header
		session.to_host = attr.to and nameprep(attr.to);
		session.from_host = attr.from and nameprep(attr.from);
	
		session.streamid = uuid_gen();
		(session.log or log)("debug", "Incoming s2s received <stream:stream>");
		if session.to_host then
			if not hosts[session.to_host] then
				-- Attempting to connect to a host we don't serve
				session:close({
					condition = "host-unknown";
					text = "This host does not serve "..session.to_host
				});
				return;
			elseif hosts[session.to_host].disallow_s2s then
				-- Attempting to connect to a host that disallows s2s
				session:close({
					condition = "policy-violation";
					text = "Server-to-server communication is not allowed to this host";
				});
				return;
			end
		end

		if session.secure and not session.cert_chain_status then check_cert_status(session); end

		send("<?xml version='1.0'?>");
		send(stanza("stream:stream", { xmlns='jabber:server', ["xmlns:db"]='jabber:server:dialback',
				["xmlns:stream"]='http://etherx.jabber.org/streams', id=session.streamid, from=session.to_host, to=session.from_host, version=(session.version > 0 and "1.0" or nil) }):top_tag());
		if session.version >= 1.0 then
			local features = st.stanza("stream:features");
			
			if session.to_host then
				hosts[session.to_host].events.fire_event("s2s-stream-features", { origin = session, features = features });
			else
				(session.log or log)("warn", "No 'to' on stream header from %s means we can't offer any features", session.from_host or "unknown host");
			end
			
			log("debug", "Sending stream features: %s", tostring(features));
			send(features);
		end
	elseif session.direction == "outgoing" then
		-- If we are just using the connection for verifying dialback keys, we won't try and auth it
		if not attr.id then error("stream response did not give us a streamid!!!"); end
		session.streamid = attr.id;

		if session.secure and not session.cert_chain_status then check_cert_status(session); end

		-- Send unauthed buffer
		-- (stanzas which are fine to send before dialback)
		-- Note that this is *not* the stanza queue (which
		-- we can only send if auth succeeds) :)
		local send_buffer = session.send_buffer;
		if send_buffer and #send_buffer > 0 then
			log("debug", "Sending s2s send_buffer now...");
			for i, data in ipairs(send_buffer) do
				session.sends2s(tostring(data));
				send_buffer[i] = nil;
			end
		end
		session.send_buffer = nil;
	
		-- If server is pre-1.0, don't wait for features, just do dialback
		if session.version < 1.0 then
			if not session.dialback_verifying then
				log("debug", "Initiating dialback...");
				initiate_dialback(session);
			else
				mark_connected(session);
			end
		end
	end
	session.notopen = nil;
end

function streamclosed(session)
	(session.log or log)("debug", "Received </stream:stream>");
	session:close();
end

function initiate_dialback(session)
	-- generate dialback key
	session.dialback_key = generate_dialback(session.streamid, session.to_host, session.from_host);
	session.sends2s(format("<db:result from='%s' to='%s'>%s</db:result>", session.from_host, session.to_host, session.dialback_key));
	session.log("info", "sent dialback key on outgoing s2s stream");
end

function generate_dialback(id, to, from)
	return sha256_hash(id..to..from..hosts[from].dialback_secret, true);
end

function verify_dialback(id, to, from, key)
	return key == generate_dialback(id, to, from);
end

function make_authenticated(session, host)
	if not session.secure then
		local local_host = session.direction == "incoming" and session.to_host or session.from_host;
		if config.get(local_host, "core", "s2s_require_encryption") then
			session:close({
				condition = "policy-violation",
				text = "Encrypted server-to-server communication is required but was not "
				       ..((session.direction == "outgoing" and "offered") or "used")
			});
		end
	end
	if session.type == "s2sout_unauthed" then
		session.type = "s2sout";
	elseif session.type == "s2sin_unauthed" then
		session.type = "s2sin";
		if host then
			if not session.hosts[host] then session.hosts[host] = {}; end
			session.hosts[host].authed = true;
		end
	elseif session.type == "s2sin" and host then
		if not session.hosts[host] then session.hosts[host] = {}; end
		session.hosts[host].authed = true;
	else
		return false;
	end
	session.log("debug", "connection %s->%s is now authenticated for %s", session.from_host or "(unknown)", session.to_host or "(unknown)", host);
	
	mark_connected(session);
	
	return true;
end

-- Stream is authorised, and ready for normal stanzas
function mark_connected(session)
	local sendq, send = session.sendq, session.sends2s;
	
	local from, to = session.from_host, session.to_host;
	
	session.log("info", session.direction.." s2s connection "..from.."->"..to.." complete");
	
	local send_to_host = send_to_host;
	function session.send(data) return send_to_host(to, from, data); end
	
	local event_data = { session = session };
	if session.type == "s2sout" then
		prosody.events.fire_event("s2sout-established", event_data);
		hosts[session.from_host].events.fire_event("s2sout-established", event_data);
	else
		prosody.events.fire_event("s2sin-established", event_data);
		hosts[session.to_host].events.fire_event("s2sin-established", event_data);
	end
	
	if session.direction == "outgoing" then
		if sendq then
			session.log("debug", "sending "..#sendq.." queued stanzas across new outgoing connection to "..session.to_host);
			for i, data in ipairs(sendq) do
				send(data[1]);
				sendq[i] = nil;
			end
			session.sendq = nil;
		end
		
		session.srv_hosts = nil;
	end
end

local resting_session = { -- Resting, not dead
		destroyed = true;
		type = "s2s_destroyed";
		open_stream = function (session)
			session.log("debug", "Attempt to open stream on resting session");
		end;
		close = function (session)
			session.log("debug", "Attempt to close already-closed session");
		end;
		filter = function (type, data) return data; end;
	}; resting_session.__index = resting_session;

function retire_session(session, reason)
	local log = session.log or log;
	for k in pairs(session) do
		if k ~= "trace" and k ~= "log" and k ~= "id" then
			session[k] = nil;
		end
	end

	session.destruction_reason = reason;

	function session.send(data) log("debug", "Discarding data sent to resting session: %s", tostring(data)); end
	function session.data(data) log("debug", "Discarding data received from resting session: %s", tostring(data)); end
	return setmetatable(session, resting_session);
end

function destroy_session(session, reason)
	if session.destroyed then return; end
	(session.log or log)("debug", "Destroying "..tostring(session.direction).." session "..tostring(session.from_host).."->"..tostring(session.to_host)..(reason and (": "..reason) or ""));
	
	if session.direction == "outgoing" then
		hosts[session.from_host].s2sout[session.to_host] = nil;
		bounce_sendq(session, reason);
	elseif session.direction == "incoming" then
		incoming_s2s[session] = nil;
	end
	
	local event_data = { session = session, reason = reason };
	if session.type == "s2sout" then
		prosody.events.fire_event("s2sout-destroyed", event_data);
		if hosts[session.from_host] then
			hosts[session.from_host].events.fire_event("s2sout-destroyed", event_data);
		end
	elseif session.type == "s2sin" then
		prosody.events.fire_event("s2sin-destroyed", event_data);
		if hosts[session.to_host] then
			hosts[session.to_host].events.fire_event("s2sin-destroyed", event_data);
		end
	end
	
	retire_session(session, reason); -- Clean session until it is GC'd
	return true;
end

return _M;