modules: avoid ffi.new in hotpath

this fixes a bug when a text-declared type wasn’t reused and LJ eventually segfaulted in ffi.new after a lot of redeclarations

daemon/lua/kres.lua

@@ -274,6 +274,7 @@ int kr_dnssec_key_match(const uint8_t *key_a_rdata, size_t key_a_rdlen,
 ]]
 
 -- Metatype for sockaddr
+local addr_buf = ffi.new('char[16]')
 local sockaddr_t = ffi.typeof('struct sockaddr')
 ffi.metatype( sockaddr_t, {
 	__index = {
@@ -429,11 +430,10 @@ local kres = {
 	dname2str = dname2str,
 	rr2str = rr2str,
 	str2ip = function (ip)
-		local buf = ffi.new('char [16]')
 		local family = C.kr_straddr_family(ip)
-		local ret = C.inet_pton(family, ip, buf)
+		local ret = C.inet_pton(family, ip, addr_buf)
 		if ret ~= 1 then return nil end
-		return ffi.string(buf, C.kr_family_len(family))
+		return ffi.string(addr_buf, C.kr_family_len(family))
 	end,
 	context = function () return ffi.cast('struct kr_context *', __engine) end,
 }

modules/dns64/dns64.lua

@@ -3,6 +3,7 @@ local ffi = require('ffi')
 local bit = require('bit')
 local mod = {}
 local MARK_DNS64 = bit.lshift(1, 31)
+local addr_buf = ffi.new('char[16]')
 -- Config
 function mod.config (confstr)
 	if confstr == nil then return end
@@ -27,19 +28,17 @@ mod.layer = {
 				local rr = answer[i]
 				-- Synthesise AAAA from A
 				if rr.type == kres.type.A then
-					local rdata = ffi.new('char [16]')
-					ffi.copy(rdata, mod.proxy)
-					ffi.copy(rdata + 12, rr.rdata, 4)
-					req.answer:put(rr.owner, rr.ttl, rr.class, kres.type.AAAA, ffi.string(rdata, 16))
+					ffi.copy(addr_buf, mod.proxy)
+					ffi.copy(addr_buf + 12, rr.rdata, 4)
+					req.answer:put(rr.owner, rr.ttl, rr.class, kres.type.AAAA, ffi.string(addr_buf, 16))
 				end
 			end
-			return state
-		end
-		-- Observe AAAA NODATA responses
-		local is_nodata = (pkt:rcode() == kres.rcode.NOERROR) and (#answer == 0)
-		if pkt:qtype() == kres.type.AAAA and is_nodata and pkt:qname() == qry:name() and qry:final() then
-			local next = req:push(pkt:qname(), kres.type.A, kres.class.IN, 0, qry)
-			next.flags = bit.band(qry.flags, kres.query.DNSSEC_WANT) + kres.query.AWAIT_CUT + MARK_DNS64
+		else -- Observe AAAA NODATA responses
+			local is_nodata = (pkt:rcode() == kres.rcode.NOERROR) and (#answer == 0)
+			if pkt:qtype() == kres.type.AAAA and is_nodata and pkt:qname() == qry:name() and qry:final() then
+				local next = req:push(pkt:qname(), kres.type.A, kres.class.IN, 0, qry)
+				next.flags = bit.band(qry.flags, kres.query.DNSSEC_WANT) + kres.query.AWAIT_CUT + MARK_DNS64
+			end
 		end
 		return state
 	end

modules/renumber/renumber.lua

@@ -18,6 +18,7 @@ local function match_subnet(family, subnet, bitlen, addr)
 	return (#addr >= bitlen / 8) and (ffi.C.kr_bitcmp(subnet, addr, bitlen) == 0)
 end
 -- Renumber address record
+local addr_buf = ffi.new('char[16]')
 local function renumber(tbl, rr)
 	for i = 1, #tbl do
 		local prefix = tbl[i]
@@ -26,11 +27,11 @@ local function renumber(tbl, rr)
 			local chunks = to_copy / 8
 			local rdlen = #rr.rdata
 			if rdlen < chunks then return rr end -- Address length mismatch
-			local rd = ffi.new('char [?]', rdlen, rr.rdata)
-			ffi.copy(rd, prefix[4], chunks)
+			ffi.copy(addr_buf, rr.rdata, rdlen)
+			ffi.copy(addr_buf, prefix[4], chunks)
 			-- @todo: CIDR not supported
 			to_copy = to_copy - chunks * 8
-			rr.rdata = ffi.string(rd, rdlen)
+			rr.rdata = ffi.string(addr_buf, rdlen)
 			return rr
 		end
 	end