#!/usr/bin/env lua

local ubus = require "ubus"
local fs = require "nixio.fs"

local conn = ubus.connect()
if not conn then
	error("Failed to connect to ubus")
	return
end

local args = "-n"
local duration = ""
local workdir = "/var/run/packet_capture"
local filterfile = workdir .. "/tcpdump_filter"
local pcapbase = workdir .. "/capture.pcap"
local outputfile = "/tmp/capture.pcap"

local function validate_args(value)
	if type(value) ~= "string" or value == "" then
		return false
	end
	local tokens = {}
	for token in value:gmatch("%S+") do
		tokens[#tokens + 1] = token
	end
	local i = 1
	while i <= #tokens do
		local token = tokens[i]
		if token == "-n" or token == "-e" then
			i = i + 1
		elseif token == "-i" then
			if not tokens[i + 1] or not tokens[i + 1]:match("^[%w_.:-]+$") then return false end
			i = i + 2
		elseif token == "-c" then
			if not tokens[i + 1] or not tokens[i + 1]:match("^%d+$") then return false end
			i = i + 2
		elseif token == "-W" then
			if tokens[i + 1] ~= "2" then return false end
			i = i + 2
		elseif token == "-C" then
			if not tokens[i + 1] or not tokens[i + 1]:match("^%d+$") then return false end
			i = i + 2
		elseif token == "-w" then
			if tokens[i + 1] ~= pcapbase then return false end
			i = i + 2
		elseif token == "-z" then
			if tokens[i + 1] ~= "/usr/libexec/packet_capture_stop" then return false end
			i = i + 2
		elseif token == "-F" then
			if tokens[i + 1] ~= filterfile then return false end
			i = i + 2
		else
			return false
		end
	end
	return true
end

if arg[1] ~= nil then
	args = arg[1]
	if not validate_args(args) then
		error("Invalid tcpdump arguments")
	end
	if arg[2] ~= nil and arg[2] ~= "" then
		duration = arg[2]
		if not duration:match("^%d+$") then
			error("Invalid duration")
		end
	end
end

local filter = fs.stat(filterfile)
if filter then
	args = args .. " -F " .. filterfile
end

local ubus_objects = {
	tcpdump = {
	}
}

conn:add( ubus_objects )

os.execute("sleep 1")

local command = "tcpdump -l " .. args .. " 2>&1"

if duration ~= "" then
	command = "timeout " .. duration .. " " .. command
end

local pipe = io.popen(command)

for line in pipe:lines() do
		local params = {
				data = line
		}
		conn:notify(ubus_objects.tcpdump.__ubusobj, "tcpdump.data", params)
end

local pcap = fs.stat(pcapbase .. "0")
if pcap then
	fs.move(pcapbase .. "0", outputfile)
	fs.remove(pcapbase .. "1")
end

if filter then
	fs.remove(filterfile)
end

conn:close()
pipe:close()

fs.remove("/var/run/packet_capture.pid")