1 files changed, 62 insertions, 0 deletions
diff --git a/modules/ta_signal_query/ta_signal_query.lua b/modules/ta_signal_query/ta_signal_query.lua
new file mode 100644
index 0000000..413015d
--- /dev/null
+++ b/modules/ta_signal_query/ta_signal_query.lua
@@ -0,0 +1,62 @@
+-- Module implementing RFC 8145 section 5
+-- Signaling Trust Anchor Knowledge in DNS using Key Tag Query
+local kres = require('kres')
+
+local M = {}
+M.layer = {}
+
+-- transform trust anchor keyset structure for one domain name (in wire format)
+-- to signalling query name like _ta-keytag1-keytag2.example.com.
+-- Returns:
+--   string constructed from valid keytags
+--   nil if no valid keytag is present in keyset
+local function prepare_query_name(keyset, name)
+	if not keyset then return nil end
+	local keytags = {}
+	for _, key in ipairs(keyset) do
+		if key.state == "Valid" then
+			table.insert(keytags, key.key_tag)
+		end
+	end
+	if next(keytags) == nil then return nil end
+
+	table.sort(keytags)
+	local query = "_ta"
+	for _, tag in pairs(keytags) do
+		query = string.format("%s-%04x", query, tag)
+	end
+	if name == "\0" then
+		return query .. "."
+	else
+		return query .. "." .. kres.dname2str(name)
+	end
+end
+
+-- construct keytag query for valid keys and send it as asynchronous query
+-- (does nothing if no valid keys are present at given domain name)
+local function send_ta_query(domain)
+	local keyset = trust_anchors.keysets[domain]
+	local qname = prepare_query_name(keyset, domain)
+	if qname ~= nil then
+		if verbose() then
+			log("[ta_signal_query] signalling query trigered: %s", qname)
+		end
+		-- asynchronous query
+		-- we do not care about result or from where it was obtained
+		event.after(0, function ()
+			resolve(qname, kres.type.NULL, kres.class.IN, "NONAUTH")
+		end)
+	end
+end
+
+-- act on DNSKEY queries which were not answered from cache
+function M.layer.consume(state, req, _)
+	req = kres.request_t(req)
+	local qry = req:current()
+	if qry.stype == kres.type.DNSKEY and not qry.flags.CACHED then
+		send_ta_query(qry:name())
+	end
+	return state  -- do not interfere with normal query processing
+end
+
+return M