examples/lua/sock-parse-dns.lua

#!/usr/bin/env bcc-lua
--[[
Copyright 2016 Marek Vavrusa <mvavrusa@cloudflare.com>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
]]
-- Simple parsing example of UDP/DNS that counts frequency of QTYPEs.
-- It shows how to parse packet variable-length packet structures.
local ffi = require("ffi")
local bpf = require("bpf")
local S = require("syscall")

-- Shared part of the program
local map = assert(bpf.map('array', 256))
-- Kernel-space part of the program
local prog = bpf.socket('lo', function (skb)
	local ip = pkt.ip   -- Accept only UDP messages
	if ip.proto ~= c.ip.proto_udp then return false end
	local udp = ip.udp  -- Only messages >12 octets (DNS header)
	if udp.length < 12 then return false end
	-- Unroll QNAME (up to 2 labels)
	udp = udp.data + 12
	local label = udp[0]
	if label > 0 then
		udp = udp + label + 1
		label = udp[0]
		if label > 0 then
			udp = udp + label + 1
		end
	end
	-- Track QTYPE (low types)
	if udp[0] == 0 then
		local qtype = udp[2] -- Low octet from QTYPE
		xadd(map[qtype], 1)
	end
end)
-- User-space part of the program
for _ = 1, 10 do
	for k,v in map.pairs,map,0 do
		v = tonumber(v)
		if v > 0 then
			print(string.format('TYPE%d: %d', k, v))
		end
	end
	S.sleep(1)
end