-- mod_s2s_auth_dane
-- Copyright (C) 2013-2014 Kim Alvefur
--
-- This file is MIT/X11 licensed.
--
-- Could be done much cleaner if mod_s2s was using util.async


module:set_global();

local dns_lookup = require"net.adns".lookup;
local hashes = require"util.hashes";
local base64 = require"util.encodings".base64;

local s2sout = module:depends"s2s".route_to_new_session.s2sout;

local bogus = {};

local pat = "%-%-%-%-%-BEGIN ([A-Z ]+)%-%-%-%-%-\r?\n"..
"([0-9A-Za-z=+/\r\n]*)\r?\n%-%-%-%-%-END %1%-%-%-%-%-";
local function pem2der(pem)
	local typ, data = pem:match(pat);
	if typ and data then
		return base64.decode(data), typ;
	end
end

-- TODO Things to test/handle:
-- Negative or bogus answers
-- No SRV records
-- No encryption offered
-- Different hostname before and after STARTTLS - mod_s2s should complain

-- This function is called when a new SRV target has been picked
-- the original function does A/AAAA resolution before continuing
local _try_connect = s2sout.try_connect;
function s2sout.try_connect(host_session, connect_host, connect_port, err)
	local srv_hosts = host_session.srv_hosts;
	local srv_choice = host_session.srv_choice;
	if srv_hosts and srv_hosts.answer.secure and srv_hosts[srv_choice].dane == nil then
		srv_hosts[srv_choice].dane = dns_lookup(function(answer)
			if answer and #answer > 0 and answer.secure then
				srv_hosts[srv_choice].dane = answer;
			elseif answer.bogus then
				srv_hosts[srv_choice].dane = bogus;
			else
				srv_hosts[srv_choice].dane = false;
			end
			-- "blocking" until TLSA reply, but no race condition
			return _try_connect(host_session, connect_host, connect_port, err);
		end, ("_%d._tcp.%s"):format(connect_port, connect_host), "TLSA");
		return true
	end
	return _try_connect(host_session, connect_host, connect_port, err);
end

module:hook("s2s-check-certificate", function(event)
	local session, cert = event.session, event.cert;
	local srv_hosts = session.srv_hosts;
	local srv_choice = session.srv_choice;
	local choosen = srv_hosts and srv_hosts[srv_choice] or session;
	if choosen.dane then
		local use, select, match, tlsa, certdata, match_found, supported_found;
		for i, rr in ipairs(choosen.dane) do
			tlsa = rr.tlsa;
			module:log("debug", "TLSA %s %s %s %d bytes of data", tlsa:getUsage(), tlsa:getSelector(), tlsa:getMatchType(), #tlsa.data);
			use, select, match, certdata = tlsa.use, tlsa.select, tlsa.match;

			-- PKIX-EE or DANE-EE
			if use == 1 or use == 3 then
				supported_found = true

				if select == 0 then
					certdata = pem2der(cert:pem());
				elseif select == 1 and cert.pubkey then
					certdata = pem2der(cert:pubkey()); -- Not supported in stock LuaSec
				else
					module:log("warn", "DANE selector %s is unsupported", tlsa:getSelector() or select);
				end

				if match == 1 then
					certdata = hashes.sha256(certdata);
				elseif match == 2 then
					certdata = hashes.sha512(certdata);
				elseif match ~= 0 then
					module:log("warn", "DANE match rule %s is unsupported", tlsa:getMatchType() or match);
					certdata = nil;
				end

				-- Should we check if the cert subject matches?
				if certdata and certdata == tlsa.data then
					(session.log or module._log)("info", "DANE validation successful");
					session.cert_identity_status = "valid";
					if use == 3 then -- DANE-EE, chain status equals DNSSEC chain status
						session.cert_chain_status = "valid";
						-- for usage 1, PKIX-EE, the chain has to be valid already
					end
					match_found = true;
					break;
				end
			else
				module:log("warn", "DANE usage %s is unsupported", tlsa:getUsage() or use);
				-- PKIX-TA checks needs to loop over the chain and stuff
				-- LuaSec does not expose anything for validating a random chain, so DANE-TA is not possible atm
			end
		end
		if supported_found and not match_found then
			-- No TLSA matched or response was bogus
			(session.log or module._log)("warn", "DANE validation failed");
			session.cert_identity_status = "invalid";
			session.cert_chain_status = "invalid";
		end
	end
end);

function module.add_host(module)
	module:hook("s2s-authenticated", function(event)
		local session = event.session;
		local srv_hosts = session.srv_hosts;
		local srv_choice = session.srv_choice;
		if (session.dane or srv_hosts and srv_hosts[srv_choice].dane) and not session.secure then
			-- TLSA record but no TLS, not ok.
			-- TODO Optional?
			-- Bogus replies will trigger this path
			session:close({
				condition = "policy-violation",
				text = "Encrypted server-to-server communication is required but was not "
					..((session.direction == "outgoing" and "offered") or "used")
			});
			return false;
		end
	end);

	-- DANE for s2sin
	-- Looks for TLSA at the same QNAME as the SRV record
	-- FIXME This has a race condition
	module:hook("s2s-stream-features", function(event)
		local origin = event.origin;
		if not origin.from_host or origin.dane ~= nil then return end

		origin.dane = dns_lookup(function(answer)
			if answer and #answer > 0 and answer.secure then
				srv_hosts[srv_choice].dane = answer;
			elseif answer.bogus then
				srv_hosts[srv_choice].dane = bogus;
			else
				origin.dane = false;
			end
		end, ("_xmpp-server._tcp.%s."):format(origin.from_host), "TLSA");
	end, 1);
end

function module.unload()
	-- Restore the original try_connect function
	s2sout.try_connect = _try_connect;
end