1 files changed, 42 insertions, 0 deletions
diff --git a/modules/serve_stale/serve_stale.lua b/modules/serve_stale/serve_stale.lua
new file mode 100644
index 0000000..faf07fb
--- /dev/null
+++ b/modules/serve_stale/serve_stale.lua
@@ -0,0 +1,42 @@
+-- SPDX-License-Identifier: GPL-3.0-or-later
+local M = {} -- the module
+
+local ffi = require('ffi')
+
+-- Beware that the timeout is only considered at certain points in time;
+-- approximately at multiples of KR_CONN_RTT_MAX.
+M.timeout = 3*sec
+
+M.callback = ffi.cast("kr_stale_cb",
+	function (ttl) --, name, type, qry)
+		--log_debug(ffi.C.SRVSTALE, '   => called back with TTL: ' .. tostring(ttl))
+		if ttl + 3600 * 24 > 0 then -- at most one day stale
+			return 1
+		else
+			return -1
+		end
+	end)
+
+M.layer = {
+	produce = function (state, req)
+		local qry = req:current()
+		-- Don't do anything for priming, prefetching, etc.
+		-- TODO: not all cases detected ATM.
+		if qry.flags.NO_CACHE then return state end
+
+		local now = ffi.C.kr_now()
+		local deadline = qry.creation_time_mono + M.timeout
+		if now > deadline or qry.flags.NO_NS_FOUND then
+			log_debug(ffi.C.LOG_GRP_SRVSTALE, '   => no reachable NS, using stale data')
+			qry.stale_cb = M.callback
+			-- TODO: probably start the same request that doesn't stale-serve,
+			-- but first we need some detection of non-interactive / internal requests.
+			-- resolve(kres.dname2str(qry.sname), qry.stype, qry.sclass)
+		end
+
+		return state
+	end,
+}
+
+return M
+