s2smanager, mod_s2s, mod_s2s/s2sout: Split connection handling out of s2smanager into mod_s2s, and further split connection logic for s2sout to a module lib, s2sout.lib.lua

2 files changed, 761 insertions, 0 deletions

diff --git a/plugins/s2s/mod_s2s.lua b/plugins/s2s/mod_s2s.lua
new file mode 100644
index 00000000..5be4d84b
--- /dev/null
+++ b/plugins/s2s/mod_s2s.lua
@@ -0,0 +1,447 @@
+-- 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.
+--
+
+module:set_global();
+
+local tostring, type = tostring, type;
+local xpcall, traceback = xpcall, debug.traceback;
+
+local add_task = require "util.timer".add_task;
+local st = require "util.stanza";
+local initialize_filters = require "util.filters".initialize;
+local new_xmpp_stream = require "util.xmppstream".new;
+local s2s_new_incoming = require "core.s2smanager".new_incoming;
+local s2s_new_outgoing = require "core.s2smanager".new_outgoing;
+local s2s_destroy_session = require "core.s2smanager".destroy_session;
+
+local s2sout = module:require("s2sout");
+
+local connect_timeout = module:get_option_number("s2s_timeout", 60);
+
+local sessions = module:shared("sessions");
+
+--- Handle stanzas to remote domains
+
+local bouncy_stanzas = { message = true, presence = true, iq = true };
+local function bounce_sendq(session, reason)
+	local sendq = session.sendq;
+	if not sendq then return; end
+	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
+
+function send_to_host(from_host, to_host, stanza)
+	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 (stanza.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(stanza), stanza.attr.type ~= "error" and stanza.attr.type ~= "result" and st.reply(stanza)});
+			else host.sendq = { {tostring(stanza), stanza.attr.type ~= "error" and stanza.attr.type ~= "result" and st.reply(stanza)} }; end
+			host.log("debug", "stanza [%s] queued ", stanza.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(stanza));
+			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(stanza);
+			host.log("debug", "stanza sent over "..host.type);
+		end
+	else
+		log("debug", "opening a new outgoing connection for this stanza");
+		local host_session = s2s_new_outgoing(from_host, to_host);
+
+		-- Store in buffer
+		host_session.bounce_sendq = bounce_sendq;
+		host_session.sendq = { {tostring(stanza), stanza.attr.type ~= "error" and stanza.attr.type ~= "result" and st.reply(stanza)} };
+		log("debug", "stanza [%s] queued until connection complete", tostring(stanza.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 s2s_destroy_session(host_session, "Connection failed") then
+				-- Already destroyed, we need to bounce our stanza
+				host_session:bounce_sendq(host_session.destruction_reason);
+			end
+			return false;
+		end
+		s2sout.initiate_connection(host_session);
+	end
+	return true;
+end
+
+module:hook("route/remote", function (event)
+	return send_to_host(event.from_host, event.to_host, event.stanza);
+end);
+
+--- Helper to check that a session peer's certificate is valid
+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
+
+--- XMPP stream event handlers
+
+local stream_callbacks = { default_ns = "jabber:server", handlestanza =  core_process_stanza };
+
+local xmlns_xmpp_streams = "urn:ietf:params:xml:ns:xmpp-streams";
+
+function stream_callbacks.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
+				s2s_mark_connected(session);
+			end
+		end
+	end
+	session.notopen = nil;
+end
+
+function stream_callbacks.streamclosed(session)
+	(session.log or log)("debug", "Received </stream:stream>");
+	session:close();
+end
+
+function stream_callbacks.streamdisconnected(session, err)
+	if err and err ~= "closed" then
+		(session.log or log)("debug", "s2s connection attempt failed: %s", err);
+		if s2sout.attempt_connection(session, err) then
+			(session.log or log)("debug", "...so we're going to try another target");
+			return true; -- Session lives for now
+		end
+	end
+	(session.log or log)("info", "s2s disconnected: %s->%s (%s)", tostring(session.from_host), tostring(session.to_host), tostring(err or "closed"));
+	sessions[session.conn]  = nil;
+	s2s_destroy_session(session, err);
+end
+
+function stream_callbacks.error(session, error, data)
+	if error == "no-stream" then
+		session:close("invalid-namespace");
+	elseif error == "parse-error" then
+		session.log("debug", "Server-to-server XML parse error: %s", tostring(error));
+		session:close("not-well-formed");
+	elseif error == "stream-error" then
+		local condition, text = "undefined-condition";
+		for child in data:children() do
+			if child.attr.xmlns == xmlns_xmpp_streams then
+				if child.name ~= "text" then
+					condition = child.name;
+				else
+					text = child:get_text();
+				end
+				if condition ~= "undefined-condition" and text then
+					break;
+				end
+			end
+		end
+		text = condition .. (text and (" ("..text..")") or "");
+		session.log("info", "Session closed by remote with error: %s", text);
+		session:close(nil, text);
+	end
+end
+
+local function handleerr(err) log("error", "Traceback[s2s]: %s: %s", tostring(err), traceback()); end
+function stream_callbacks.handlestanza(session, stanza)
+	if stanza.attr.xmlns == "jabber:client" then --COMPAT: Prosody pre-0.6.2 may send jabber:client
+		stanza.attr.xmlns = nil;
+	end
+	stanza = session.filter("stanzas/in", stanza);
+	if stanza then
+		return xpcall(function () return core_process_stanza(session, stanza) end, handleerr);
+	end
+end
+
+local listener = { default_port = 5269, default_mode = "*a", default_interface = "*" };
+
+--- Session methods
+local stream_xmlns_attr = {xmlns='urn:ietf:params:xml:ns:xmpp-streams'};
+local default_stream_attr = { ["xmlns:stream"] = "http://etherx.jabber.org/streams", xmlns = stream_callbacks.default_ns, version = "1.0", id = "" };
+local function session_close(session, reason, remote_reason)
+	local log = session.log or log;
+	if session.conn then
+		if session.notopen then
+			session.sends2s("<?xml version='1.0'?>");
+			session.sends2s(st.stanza("stream:stream", default_stream_attr):top_tag());
+		end
+		if reason then
+			if type(reason) == "string" then -- assume stream error
+				log("info", "Disconnecting %s[%s], <stream:error> is: %s", session.host or "(unknown host)", session.type, reason);
+				session.sends2s(st.stanza("stream:error"):tag(reason, {xmlns = 'urn:ietf:params:xml:ns:xmpp-streams' }));
+			elseif type(reason) == "table" then
+				if reason.condition then
+					local stanza = st.stanza("stream:error"):tag(reason.condition, stream_xmlns_attr):up();
+					if reason.text then
+						stanza:tag("text", stream_xmlns_attr):text(reason.text):up();
+					end
+					if reason.extra then
+						stanza:add_child(reason.extra);
+					end
+					log("info", "Disconnecting %s[%s], <stream:error> is: %s", session.host or "(unknown host)", session.type, tostring(stanza));
+					session.sends2s(stanza);
+				elseif reason.name then -- a stanza
+					log("info", "Disconnecting %s->%s[%s], <stream:error> is: %s", session.from_host or "(unknown host)", session.to_host or "(unknown host)", session.type, tostring(reason));
+					session.sends2s(reason);
+				end
+			end
+		end
+		session.sends2s("</stream:stream>");
+		if session.notopen or not session.conn:close() then
+			session.conn:close(true); -- Force FIXME: timer?
+		end
+		session.conn:close();
+		listener.ondisconnect(session.conn, remote_reason or (reason and (reason.text or reason.condition)) or reason or "stream closed");
+	end
+end
+
+-- Session initialization logic shared by incoming and outgoing
+local function initialize_session(session)
+	local stream = new_xmpp_stream(session, stream_callbacks);
+	session.stream = stream;
+	
+	session.notopen = true;
+		
+	function session.reset_stream()
+		session.notopen = true;
+		session.stream:reset();
+	end
+	
+	local filter = session.filter;
+	function session.data(data)
+		data = filter("bytes/in", data);
+		if data then
+			local ok, err = stream:feed(data);
+			if ok then return; end
+			(session.log or log)("warn", "Received invalid XML: %s", data);
+			(session.log or log)("warn", "Problem was: %s", err);
+			session:close("not-well-formed");
+		end
+	end
+
+	session.close = session_close;
+
+	local handlestanza = stream_callbacks.handlestanza;
+	function session.dispatch_stanza(session, stanza)
+		return handlestanza(session, stanza);
+	end
+
+	local conn = session.conn;
+	add_task(connect_timeout, function ()
+		if session.conn ~= conn or session.connecting
+		or session.type == "s2sin" or session.type == "s2sout" 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);
+end
+
+function listener.onconnect(conn)
+	if not sessions[conn] then -- May be an existing outgoing session
+		local session = s2s_new_incoming(conn);
+		sessions[conn] = session;
+		session.log("debug", "Incoming s2s connection");
+
+		local filter = initialize_filters(session);
+		local w = conn.write;
+		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
+	
+		initialize_session(session);
+	end
+end
+
+function listener.onincoming(conn, data)
+	local session = sessions[conn];
+	if session then
+		session.data(data);
+	end
+end
+	
+function listener.onstatus(conn, status)
+	if status == "ssl-handshake-complete" then
+		local session = sessions[conn];
+		if session and session.direction == "outgoing" then
+			local to_host, from_host = session.to_host, session.from_host;
+			session.log("debug", "Sending stream header...");
+			session:open_stream(session.from_host, session.to_host);
+		end
+	end
+end
+
+function listener.ondisconnect(conn, err)
+	local session = sessions[conn];
+	if session then
+		if stream_callbacks.streamdisconnected(session, err) then
+			return; -- Connection lives, for now
+		end
+	end
+	sessions[conn]  = nil;
+end
+
+function listener.register_outgoing(conn, session)
+	session.direction = "outgoing";
+	sessions[conn] = session;
+	initialize_session(session);
+end
+
+s2sout.set_listener(listener);
+
+require "core.portmanager".register_service("s2s", {
+	listener = listener;
+	default_port = 5269;
+	encryption = "starttls";
+});
+
diff --git a/plugins/s2s/s2sout.lib.lua b/plugins/s2s/s2sout.lib.lua
new file mode 100644
index 00000000..094126e7
--- /dev/null
+++ b/plugins/s2s/s2sout.lib.lua
@@ -0,0 +1,314 @@
+-- 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.
+--
+
+--- Module containing all the logic for connecting to a remote server
+
+local initialize_filters = require "util.filters".initialize;
+local idna_to_ascii = require "util.encodings".idna.to_ascii;
+local add_task = require "util.timer".add_task;
+local socket = require "socket";
+
+local s2s_destroy_session = require "core.s2smanager".destroy_session;
+
+local s2sout = {};
+
+local s2s_listener;
+
+function s2sout.set_listener(listener)
+	s2s_listener = listener;
+end
+
+local function compare_srv_priorities(a,b)
+	return a.priority < b.priority or (a.priority == b.priority and a.weight > b.weight);
+end
+
+local 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
+
+function s2sout.initiate_connection(host_session)
+	initialize_filters(host_session);
+	session.open_stream = session_open_stream;
+	
+	-- Kick the connection attempting machine into life
+	if not s2sout.attempt_connection(host_session) then
+		-- Intentionally not returning here, the
+		-- session is needed, connected or not
+		s2s_destroy_session(host_session);
+	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
+end
+
+function s2sout.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");
+					s2s_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 = s2sout.try_connect(host_session, connect_host, connect_port);
+			if not ok then
+				if not s2sout.attempt_connection(host_session, err) then
+					-- No more attempts will be made
+					s2s_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 s2sout.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 s2sout.try_connect(host_session, connect_host, connect_port);
+end
+
+function s2sout.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= s2sout.make_connect(host_session, ip.ip, ip.port);
+	if not ok then
+		if not s2sout.attempt_connection(host_session, err or "closed") then
+			err = err and (": "..err) or "";
+			s2s_destroy_session(host_session, "Connection failed"..err);
+		end
+	end
+end
+
+function s2sout.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 =  {};
+			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;
+					s2sout.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 s2sout.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 "";
+						s2s_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;
+					s2sout.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 s2sout.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 "";
+						s2s_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
+		s2sout.try_next_ip(host_session);
+	else
+		host_session.ip_hosts = nil;
+		if not s2sout.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 "";
+			s2s_destroy_session(host_session, "Connecting failed"..err); -- End of the line, we can't
+			return false;
+		end
+	end
+
+	return true;
+end
+
+function s2sout.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();
+	else
+		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
+	
+	conn = wrapclient(conn, connect_host.addr, connect_port, s2s_listener, "*a");
+	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
+	s2s_listener.register_outgoing(conn, host_session);
+	
+	host_session:open_stream(from_host, to_host);
+	
+	log("debug", "Connection attempt in progress...");
+	return true;
+end
+
+return s2sout;