mod_s2s: Enable outgoing Direct TLS connections Makes it faster by cutting out the roundtrips involved in <starttls/>, at the cost of making an additional SRV lookup. Since we already ignore a missing <starttls/> offer and try anyway there is not much difference in security. The fact that XMPP is used and the hostnames involved might still be visible until the future Encrypted ClientHello extension allows hiding those too.

author: Kim Alvefur <zash@zash.se>
date: Fri, 21 Jan 2022 17:59:19 +0100
parent: 11867:bb20cfd4884f
child: 12207:65e252940337
--- a/plugins/mod_s2s.lua	Fri Jan 21 17:57:47 2022 +0100
+++ b/plugins/mod_s2s.lua	Fri Jan 21 17:59:19 2022 +0100
@@ -29,6 +29,7 @@
 local runner = require "util.async".runner;
 local connect = require "net.connect".connect;
 local service = require "net.resolvers.service";
+local resolver_chain = require "net.resolvers.chain";
 local errors = require "util.error";
 local set = require "util.set";
 
@@ -217,8 +218,14 @@
 	log("debug", "stanza [%s] queued until connection complete", stanza.name);
 	-- FIXME Cleaner solution to passing extra data from resolvers to net.server
 	-- This mt-clone allows resolvers to add extra data, currently used for DANE TLSA records
-	local extra = setmetatable({}, s2s_service_options_mt);
-	connect(service.new(to_host, "xmpp-server", "tcp", extra), listener, nil, { session = host_session });
+	local xmpp_extra = setmetatable({}, s2s_service_options_mt);
+	local sslctx = require"core.certmanager".create_context(from_host, "client"); -- TODO this should live in mod_tls ?
+	local xmpps_extra = setmetatable({ default_port = false; servername = to_host; sslctx = sslctx }, s2s_service_options_mt);
+	local direct_and_normal = resolver_chain.new({
+		service.new(to_host, "xmpps-server", "tcp", xmpps_extra);
+		service.new(to_host, "xmpp-server", "tcp", xmpp_extra);
+	});
+	connect(direct_and_normal, listener, nil, { session = host_session });
 	m_initiated_connections:with_labels(from_host):add(1)
 	return true;
 end