Diff

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/plugins/mod_s2s.lua	Wed Sep 30 09:50:33 2020 +0100
@@ -0,0 +1,810 @@
+-- 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 prosody = prosody;
+local hosts = prosody.hosts;
+local core_process_stanza = prosody.core_process_stanza;
+
+local tostring, type = tostring, type;
+local t_insert = table.insert;
+local traceback = debug.traceback;
+
+local add_task = require "util.timer".add_task;
+local st = require "util.stanza";
+local initialize_filters = require "util.filters".initialize;
+local nameprep = require "util.encodings".stringprep.nameprep;
+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 uuid_gen = require "util.uuid".generate;
+local fire_global_event = prosody.events.fire_event;
+local runner = require "util.async".runner;
+local connect = require "net.connect".connect;
+local service = require "net.resolvers.service";
+local errors = require "util.error";
+local set = require "util.set";
+
+local connect_timeout = module:get_option_number("s2s_timeout", 90);
+local stream_close_timeout = module:get_option_number("s2s_close_timeout", 5);
+local opt_keepalives = module:get_option_boolean("s2s_tcp_keepalives", module:get_option_boolean("tcp_keepalives", true));
+local secure_auth = module:get_option_boolean("s2s_secure_auth", false); -- One day...
+local secure_domains, insecure_domains =
+	module:get_option_set("s2s_secure_domains", {})._items, module:get_option_set("s2s_insecure_domains", {})._items;
+local require_encryption = module:get_option_boolean("s2s_require_encryption", false);
+local stanza_size_limit = module:get_option_number("s2s_stanza_size_limit"); -- TODO come up with a sensible default (util.xmppstream defaults to 10M)
+
+local measure_connections = module:measure("connections", "amount");
+local measure_ipv6 = module:measure("ipv6", "amount");
+
+local sessions = module:shared("sessions");
+
+local runner_callbacks = {};
+
+local listener = {};
+
+local log = module._log;
+
+local s2s_service_options = {
+	default_port = 5269;
+	use_ipv4 = module:get_option_boolean("use_ipv4", true);
+	use_ipv6 = module:get_option_boolean("use_ipv6", true);
+};
+
+module:hook("stats-update", function ()
+	local count = 0;
+	local ipv6 = 0;
+	for _, session in pairs(sessions) do
+		count = count + 1;
+		if session.ip and session.ip:match(":") then
+			ipv6 = ipv6 + 1;
+		end
+	end
+	measure_connections(count);
+	measure_ipv6(ipv6);
+end);
+
+--- 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 %d queued stanzas because of failed outgoing connection to %s", #sendq, session.to_host);
+	local dummy = {
+		type = "s2sin";
+		send = function ()
+			(session.log or log)("error", "Replying to to an s2s error reply, please report this! Traceback: %s", traceback());
+		end;
+		dummy = true;
+		close = function ()
+			(session.log or log)("error", "Attempting to close the dummy origin of s2s error replies, please report this! Traceback: %s", traceback());
+		end;
+	};
+	-- FIXME Allow for more specific error conditions
+	-- TODO use util.error ?
+	local error_type = "cancel";
+	local condition = "remote-server-not-found";
+	local reason_text;
+	if session.had_stream then -- set when a stream is opened by the remote
+		error_type, condition = "wait", "remote-server-timeout";
+	end
+	if errors.is_err(reason) then
+		error_type, condition, reason_text = reason.type, reason.condition, reason.text;
+	elseif type(reason) == "string" then
+		reason_text = reason;
+	end
+	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 = error_type, by = session.from_host})
+				:tag(condition, {xmlns = "urn:ietf:params:xml:ns:xmpp-stanzas"}):up();
+			if reason_text then
+				reply:tag("text", {xmlns = "urn:ietf:params:xml:ns:xmpp-stanzas"})
+					:text("Server-to-server connection failed: "..reason_text):up();
+			end
+			core_process_stanza(dummy, reply);
+		end
+		sendq[i] = nil;
+	end
+	session.sendq = nil;
+end
+
+-- Handles stanzas to existing s2s sessions
+function route_to_existing_session(event)
+	local from_host, to_host, stanza = event.from_host, event.to_host, event.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
+	if hosts[to_host] then
+		log("warn", "Attempt to route stanza to a remote %s - a host we do serve?!", from_host);
+		return false;
+	end
+	local host = hosts[from_host].s2sout[to_host];
+	if not host then return end
+
+	-- 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
+		local queued_item = {
+			tostring(stanza),
+			stanza.attr.type ~= "error" and stanza.attr.type ~= "result" and st.reply(stanza);
+		};
+		if host.sendq then
+			t_insert(host.sendq, queued_item);
+		else
+			-- luacheck: ignore 122
+			host.sendq = { queued_item };
+		end
+		host.log("debug", "stanza [%s] queued ", stanza.name);
+		return true;
+	elseif host.type == "local" or host.type == "component" then
+		log("error", "Trying to send a stanza to ourselves??")
+		log("error", "Traceback: %s", traceback());
+		log("error", "Stanza: %s", stanza);
+		return false;
+	else
+		if host.sends2s(stanza) then
+			return true;
+		end
+	end
+end
+
+-- Create a new outgoing session for a stanza
+function route_to_new_session(event)
+	local from_host, to_host, stanza = event.from_host, event.to_host, event.stanza;
+	log("debug", "opening a new outgoing connection for this stanza");
+	local host_session = s2s_new_outgoing(from_host, to_host);
+	host_session.version = 1;
+
+	-- 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", stanza.name);
+	connect(service.new(to_host, "xmpp-server", "tcp", s2s_service_options), listener, nil, { session = host_session });
+	return true;
+end
+
+local function keepalive(event)
+	return event.session.sends2s(' ');
+end
+
+module:hook("s2s-read-timeout", keepalive, -1);
+
+function module.add_host(module)
+	if module:get_option_boolean("disallow_s2s", false) then
+		module:log("warn", "The 'disallow_s2s' config option is deprecated, please see https://prosody.im/doc/s2s#disabling");
+		return nil, "This host has disallow_s2s set";
+	end
+	module:hook("route/remote", route_to_existing_session, -1);
+	module:hook("route/remote", route_to_new_session, -10);
+	module:hook("s2s-authenticated", make_authenticated, -1);
+	module:hook("s2s-read-timeout", keepalive, -1);
+	module:hook_stanza("http://etherx.jabber.org/streams", "features", function (session, stanza) -- luacheck: ignore 212/stanza
+		if session.type == "s2sout" then
+			-- Stream is authenticated and we are seem to be done with feature negotiation,
+			-- so the stream is ready for stanzas.  RFC 6120 Section 4.3
+			mark_connected(session);
+			return true;
+		elseif require_encryption and not session.secure then
+			session.log("warn", "Encrypted server-to-server communication is required but was not offered by %s", session.to_host);
+			session:close({
+					condition = "policy-violation",
+					text = "Encrypted server-to-server communication is required but was not offered",
+				}, nil, "Could not establish encrypted connection to remote server");
+			return true;
+		elseif not session.dialback_verifying then
+			session.log("warn", "No SASL EXTERNAL offer and Dialback doesn't seem to be enabled, giving up");
+			session:close({
+					condition = "unsupported-feature",
+					text = "No viable authentication method offered",
+				}, nil, "No viable authentication method offered by remote server");
+			return true;
+		end
+	end, -1);
+end
+
+-- Stream is authorised, and ready for normal stanzas
+function mark_connected(session)
+
+	local sendq = session.sendq;
+
+	local from, to = session.from_host, session.to_host;
+
+	session.log("info", "%s s2s connection %s->%s complete", session.direction:gsub("^.", string.upper), from, to);
+
+	local event_data = { session = session };
+	if session.type == "s2sout" then
+		fire_global_event("s2sout-established", event_data);
+		hosts[from].events.fire_event("s2sout-established", event_data);
+
+		if session.incoming then
+			session.send = function(stanza)
+				return hosts[from].events.fire_event("route/remote", { from_host = from, to_host = to, stanza = stanza });
+			end;
+		end
+
+	else
+		if session.outgoing and not hosts[to].s2sout[from] then
+			session.log("debug", "Setting up to handle route from %s to %s", to, from);
+			hosts[to].s2sout[from] = session; -- luacheck: ignore 122
+		end
+		local host_session = hosts[to];
+		session.send = function(stanza)
+			return host_session.events.fire_event("route/remote", { from_host = to, to_host = from, stanza = stanza });
+		end;
+
+		fire_global_event("s2sin-established", event_data);
+		hosts[to].events.fire_event("s2sin-established", event_data);
+	end
+
+	if session.direction == "outgoing" then
+		if sendq then
+			session.log("debug", "sending %d queued stanzas across new outgoing connection to %s", #sendq, session.to_host);
+			local send = session.sends2s;
+			for i, data in ipairs(sendq) do
+				send(data[1]);
+				sendq[i] = nil;
+			end
+			session.sendq = nil;
+		end
+	end
+end
+
+function make_authenticated(event)
+	local session, host = event.session, event.host;
+	if not session.secure then
+		if require_encryption or (secure_auth and not(insecure_domains[host])) or secure_domains[host] then
+			session:close({
+				condition = "policy-violation",
+				text = "Encrypted server-to-server communication is required but was not "
+				       ..((session.direction == "outgoing" and "offered") or "used")
+			}, nil, "Could not establish encrypted connection to remote server");
+		end
+	end
+	if hosts[host] then
+		session:close({ condition = "undefined-condition", text = "Attempt to authenticate as a host we serve" });
+	end
+	if session.type == "s2sout_unauthed" then
+		session.type = "s2sout";
+	elseif session.type == "s2sin_unauthed" then
+		session.type = "s2sin";
+	elseif session.type ~= "s2sin" and session.type ~= "s2sout" then
+		return false;
+	end
+
+	if session.incoming and host then
+		if not session.hosts[host] then session.hosts[host] = {}; end
+		session.hosts[host].authed = true;
+	end
+	session.log("debug", "connection %s->%s is now authenticated for %s", session.from_host, session.to_host, host);
+
+	if (session.type == "s2sout" and session.external_auth ~= "succeeded") or session.type == "s2sin" then
+		-- Stream either used dialback for authentication or is an incoming stream.
+		mark_connected(session);
+	end
+
+	return true;
+end
+
+--- Helper to check that a session peer's certificate is valid
+function check_cert_status(session)
+	local host = session.direction == "outgoing" and session.to_host or session.from_host
+	local conn = session.conn:socket()
+	local cert
+	if conn.getpeercertificate then
+		cert = conn:getpeercertificate()
+	end
+
+	return module:fire_event("s2s-check-certificate", { host = host, session = session, cert = cert });
+end
+
+--- XMPP stream event handlers
+
+local stream_callbacks = { default_ns = "jabber:server" };
+
+function stream_callbacks.handlestanza(session, stanza)
+	stanza = session.filter("stanzas/in", stanza);
+	session.thread:run(stanza);
+end
+
+local xmlns_xmpp_streams = "urn:ietf:params:xml:ns:xmpp-streams";
+
+function stream_callbacks.streamopened(session, attr)
+	-- run _streamopened in async context
+	session.thread:run({ stream = "opened", attr = attr });
+end
+
+function stream_callbacks._streamopened(session, attr)
+	session.version = tonumber(attr.version) or 0;
+	session.had_stream = true; -- Had a stream opened at least once
+
+	-- TODO: Rename session.secure to session.encrypted
+	if session.secure == false then
+		session.secure = true;
+		session.encrypted = true;
+
+		local sock = session.conn:socket();
+		if sock.info then
+			local info = sock:info();
+			(session.log or log)("info", "Stream encrypted (%s with %s)", info.protocol, info.cipher);
+			session.compressed = info.compression;
+		else
+			(session.log or log)("info", "Stream encrypted");
+		end
+	end
+
+	if session.direction == "incoming" then
+		-- Send a reply stream header
+
+		-- Validate to/from
+		local to, from = attr.to, attr.from;
+		if to then to = nameprep(attr.to); end
+		if from then from = nameprep(attr.from); end
+		if not to and attr.to then -- COMPAT: Some servers do not reliably set 'to' (especially on stream restarts)
+			session:close({ condition = "improper-addressing", text = "Invalid 'to' address" });
+			return;
+		end
+		if not from and attr.from then -- COMPAT: Some servers do not reliably set 'from' (especially on stream restarts)
+			session:close({ condition = "improper-addressing", text = "Invalid 'from' address" });
+			return;
+		end
+
+		-- Set session.[from/to]_host if they have not been set already and if
+		-- this session isn't already authenticated
+		if session.type == "s2sin_unauthed" and from and not session.from_host then
+			session.from_host = from;
+		elseif from ~= session.from_host then
+			session:close({ condition = "improper-addressing", text = "New stream 'from' attribute does not match original" });
+			return;
+		end
+		if session.type == "s2sin_unauthed" and to and not session.to_host then
+			session.to_host = to;
+		elseif to ~= session.to_host then
+			session:close({ condition = "improper-addressing", text = "New stream 'to' attribute does not match original" });
+			return;
+		end
+
+		-- For convenience we'll put the sanitised values into these variables
+		to, from = session.to_host, session.from_host;
+
+		session.streamid = uuid_gen();
+		(session.log or log)("debug", "Incoming s2s received %s", st.stanza("stream:stream", attr):top_tag());
+		if to then
+			if not hosts[to] then
+				-- Attempting to connect to a host we don't serve
+				session:close({
+					condition = "host-unknown";
+					text = "This host does not serve "..to
+				});
+				return;
+			elseif not hosts[to].modules.s2s then
+				-- Attempting to connect to a host that disallows s2s
+				session:close({
+					condition = "policy-violation";
+					text = "Server-to-server communication is disabled for this host";
+				});
+				return;
+			end
+		end
+
+		if hosts[from] then
+			session:close({ condition = "undefined-condition", text = "Attempt to connect from a host we serve" });
+			return;
+		end
+
+		if session.secure and not session.cert_chain_status then
+			if check_cert_status(session) == false then
+				return;
+			end
+		end
+
+		session:open_stream(session.to_host, session.from_host)
+		session.notopen = nil;
+		if session.version >= 1.0 then
+			local features = st.stanza("stream:features");
+
+			if to then
+				hosts[to].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", from or session.ip or "unknown host");
+				fire_global_event("s2s-stream-features-legacy", { origin = session, features = features });
+			end
+
+			if ( session.type == "s2sin" or session.type == "s2sout" ) or features.tags[1] then
+				log("debug", "Sending stream features: %s", features);
+				session.sends2s(features);
+			else
+				(session.log or log)("warn", "No stream features to offer, giving up");
+				session:close({ condition = "undefined-condition", text = "No stream features to offer" });
+			end
+		end
+	elseif session.direction == "outgoing" then
+		session.notopen = nil;
+		if not attr.id then
+			log("warn", "Stream response did not give us a stream id!");
+			session:close({ condition = "undefined-condition", text = "Missing stream ID" });
+			return;
+		end
+		session.streamid = attr.id;
+
+		if session.secure and not session.cert_chain_status then
+			if check_cert_status(session) == false then
+				return;
+			end
+		end
+
+		-- 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
+				hosts[session.from_host].events.fire_event("s2sout-authenticate-legacy", { origin = session });
+			else
+				mark_connected(session);
+			end
+		end
+	end
+end
+
+function stream_callbacks._streamclosed(session)
+	(session.log or log)("debug", "Received </stream:stream>");
+	session:close(false);
+end
+
+function stream_callbacks.streamclosed(session, attr)
+	-- run _streamclosed in async context
+	session.thread:run({ stream = "closed", attr = attr });
+end
+
+function stream_callbacks.error(session, error, data)
+	if error == "no-stream" then
+		session.log("debug", "Invalid opening stream header (%s)", (data:gsub("^([^\1]+)\1", "{%1}")));
+		session:close("invalid-namespace");
+	elseif error == "parse-error" then
+		session.log("debug", "Server-to-server XML parse error: %s", error);
+		session:close("not-well-formed");
+	elseif error == "stream-error" then
+		local condition, text = "undefined-condition";
+		for child in data:childtags(nil, xmlns_xmpp_streams) do
+			if child.name ~= "text" then
+				condition = child.name;
+			else
+				text = child:get_text();
+			end
+			if condition ~= "undefined-condition" and text then
+				break;
+			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
+
+--- Session methods
+local stream_xmlns_attr = {xmlns='urn:ietf:params:xml:ns:xmpp-streams'};
+-- reason: stream error to send to the remote server
+-- remote_reason: stream error received from the remote server
+-- bounce_reason: stanza error to pass to bounce_sendq because stream- and stanza errors are different
+local function session_close(session, reason, remote_reason, bounce_reason)
+	local log = session.log or log;
+	if session.conn then
+		if session.notopen then
+			if session.direction == "incoming" then
+				session:open_stream(session.to_host, session.from_host);
+			else
+				session:open_stream(session.from_host, session.to_host);
+			end
+		end
+		if reason then -- nil == no err, initiated by us, false == initiated by remote
+			local stream_error;
+			if type(reason) == "string" then -- assume stream error
+				stream_error = st.stanza("stream:error"):tag(reason, {xmlns = 'urn:ietf:params:xml:ns:xmpp-streams' });
+			elseif type(reason) == "table" and not st.is_stanza(reason) then
+				stream_error = st.stanza("stream:error"):tag(reason.condition or "undefined-condition", stream_xmlns_attr):up();
+				if reason.text then
+					stream_error:tag("text", stream_xmlns_attr):text(reason.text):up();
+				end
+				if reason.extra then
+					stream_error:add_child(reason.extra);
+				end
+			end
+			if st.is_stanza(stream_error) then
+				-- to and from are never unknown on outgoing connections
+				log("debug", "Disconnecting %s->%s[%s], <stream:error> is: %s",
+					session.from_host or "(unknown host)" or session.ip, session.to_host or "(unknown host)", session.type, reason);
+				session.sends2s(stream_error);
+			end
+		end
+
+		session.sends2s("</stream:stream>");
+		function session.sends2s() return false; end
+
+		-- luacheck: ignore 422/reason
+		-- FIXME reason should be managed in a place common to c2s, s2s, bosh, component etc
+		local reason = remote_reason or (reason and (reason.text or reason.condition)) or reason;
+		session.log("info", "%s s2s stream %s->%s closed: %s", session.direction:gsub("^.", string.upper),
+			session.from_host or "(unknown host)", session.to_host or "(unknown host)", reason or "stream closed");
+
+		-- Authenticated incoming stream may still be sending us stanzas, so wait for </stream:stream> from remote
+		local conn = session.conn;
+		if reason == nil and not session.notopen and session.incoming then
+			add_task(stream_close_timeout, function ()
+				if not session.destroyed then
+					session.log("warn", "Failed to receive a stream close response, closing connection anyway...");
+					s2s_destroy_session(session, reason, bounce_reason);
+					conn:close();
+				end
+			end);
+		else
+			s2s_destroy_session(session, reason, bounce_reason);
+			conn:close(); -- Close immediately, as this is an outgoing connection or is not authed
+		end
+	end
+end
+
+function session_stream_attrs(session, from, to, attr) -- luacheck: ignore 212/session
+	if not from or (hosts[from] and hosts[from].modules.dialback) then
+		attr["xmlns:db"] = 'jabber:server:dialback';
+	end
+	if not from then
+		attr.from = '';
+	end
+	if not to then
+		attr.to = '';
+	end
+end
+
+-- Session initialization logic shared by incoming and outgoing
+local function initialize_session(session)
+	local stream = new_xmpp_stream(session, stream_callbacks, stanza_size_limit);
+
+	session.thread = runner(function (stanza)
+		if st.is_stanza(stanza) then
+			core_process_stanza(session, stanza);
+		elseif stanza.stream == "opened" then
+			stream_callbacks._streamopened(session, stanza.attr);
+		elseif stanza.stream == "closed" then
+			stream_callbacks._streamclosed(session, stanza.attr);
+		end
+	end, runner_callbacks, session);
+
+	local log = session.log or log;
+	session.stream = stream;
+
+	session.notopen = true;
+
+	function session.reset_stream()
+		session.notopen = true;
+		session.streamid = nil;
+		session.stream:reset();
+	end
+
+	session.stream_attrs = session_stream_attrs;
+
+	local filter = initialize_filters(session);
+	local conn = session.conn;
+	local w = conn.write;
+
+	function session.sends2s(t)
+		log("debug", "Sending[%s]: %s", session.type, 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
+
+	function session.data(data)
+		data = filter("bytes/in", data);
+		if data then
+			local ok, err = stream:feed(data);
+			if ok then return; end
+			log("debug", "Received invalid XML (%s) %d bytes: %q", err, #data, data:sub(1, 300));
+			if err == "stanza-too-large" then
+				session:close({ condition = "policy-violation", text = "XML stanza is too big" }, nil, "Received invalid XML from remote server");
+			else
+				session:close("not-well-formed", nil, "Received invalid XML from remote server");
+			end
+		end
+	end
+
+	session.close = session_close;
+
+	local handlestanza = stream_callbacks.handlestanza;
+	function session.dispatch_stanza(session, stanza) -- luacheck: ignore 432/session
+		return handlestanza(session, stanza);
+	end
+
+	module:fire_event("s2s-created", { session = session });
+
+	add_task(connect_timeout, function ()
+		if session.type == "s2sin" or session.type == "s2sout" then
+			return; -- Ok, we're connected
+		elseif session.type == "s2s_destroyed" then
+			return; -- Session already destroyed
+		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 runner_callbacks:ready()
+	self.data.log("debug", "Runner %s ready (%s)", self.thread, coroutine.status(self.thread));
+	self.data.conn:resume();
+end
+
+function runner_callbacks:waiting()
+	self.data.log("debug", "Runner %s waiting (%s)", self.thread, coroutine.status(self.thread));
+	self.data.conn:pause();
+end
+
+function runner_callbacks:error(err)
+	(self.data.log or log)("error", "Traceback[s2s]: %s", err);
+end
+
+function listener.onconnect(conn)
+	conn:setoption("keepalive", opt_keepalives);
+	local session = sessions[conn];
+	if not session then -- New incoming connection
+		session = s2s_new_incoming(conn);
+		sessions[conn] = session;
+		session.log("debug", "Incoming s2s connection");
+		initialize_session(session);
+	else -- Outgoing session connected
+		session:open_stream(session.from_host, session.to_host);
+	end
+	session.ip = conn:ip();
+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
+			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
+		sessions[conn] = nil;
+		(session.log or log)("debug", "s2s disconnected: %s->%s (%s)", session.from_host, session.to_host, err or "connection closed");
+		if session.secure == false and err then
+			-- TODO util.error-ify this
+			err = "Error during negotiation of encrypted connection: "..err;
+		end
+		s2s_destroy_session(session, err);
+	end
+end
+
+function listener.onfail(data, err)
+	local session = data and data.session;
+	if session then
+		if err and session.direction == "outgoing" and session.notopen then
+			(session.log or log)("debug", "s2s connection attempt failed: %s", err);
+		end
+		(session.log or log)("debug", "s2s disconnected: %s->%s (%s)", session.from_host, session.to_host, err or "connection closed");
+		s2s_destroy_session(session, err);
+	end
+end
+
+function listener.onreadtimeout(conn)
+	local session = sessions[conn];
+	if session then
+		local host = session.host or session.to_host;
+		return (hosts[host] or prosody).events.fire_event("s2s-read-timeout", { session = session });
+	end
+end
+
+function listener.register_outgoing(conn, session)
+	sessions[conn] = session;
+	initialize_session(session);
+end
+
+function listener.ondetach(conn)
+	sessions[conn] = nil;
+end
+
+function listener.onattach(conn, data)
+	local session = data and data.session;
+	if session then
+		session.conn = conn;
+		sessions[conn] = session;
+		initialize_session(session);
+	end
+end
+
+-- Complete the sentence "Your certificate " with what's wrong
+local function friendly_cert_error(session) --> string
+	if session.cert_chain_status == "invalid" then
+		if session.cert_chain_errors then
+			local cert_errors = set.new(session.cert_chain_errors[1]);
+			if cert_errors:contains("certificate has expired") then
+				return "has expired";
+			elseif cert_errors:contains("self signed certificate") then
+				return "is self-signed";
+			end
+		end
+		return "is not trusted"; -- for some other reason
+	elseif session.cert_identity_status == "invalid" then
+		return "is not valid for this name";
+	end
+	-- this should normally be unreachable except if no s2s auth module was loaded
+	return "could not be validated";
+end
+
+function check_auth_policy(event)
+	local host, session = event.host, event.session;
+	local must_secure = secure_auth;
+
+	if not must_secure and secure_domains[host] then
+		must_secure = true;
+	elseif must_secure and insecure_domains[host] then
+		must_secure = false;
+	end
+
+	if must_secure and (session.cert_chain_status ~= "valid" or session.cert_identity_status ~= "valid") then
+		local reason = friendly_cert_error(session);
+		session.log("warn", "Forbidding insecure connection to/from %s because its certificate %s", host or session.ip or "(unknown host)", reason);
+		-- XEP-0178 recommends closing outgoing connections without warning
+		-- but does not give a rationale for this.
+		-- In practice most cases are configuration mistakes or forgotten
+		-- certificate renewals. We think it's better to let the other party
+		-- know about the problem so that they can fix it.
+		session:close({ condition = "not-authorized", text = "Your server's certificate "..reason },
+			nil, "Remote server's certificate "..reason);
+		return false;
+	end
+end
+
+module:hook("s2s-check-certificate", check_auth_policy, -1);
+
+module:hook("server-stopping", function(event)
+	local reason = event.reason;
+	for _, session in pairs(sessions) do
+		session:close{ condition = "system-shutdown", text = reason };
+	end
+end, -200);
+
+
+
+module:provides("net", {
+	name = "s2s";
+	listener = listener;
+	default_port = 5269;
+	encryption = "starttls";
+	ssl_config = { -- FIXME This is not used atm, see mod_tls
+		verify = { "peer", "client_once", };
+	};
+	multiplex = {
+		protocol = "xmpp-server";
+		pattern = "^<.*:stream.*%sxmlns%s*=%s*(['\"])jabber:server%1.*>";
+	};
+});
+