Find IPs that match known VPNs and proxy servers in Garry's Mod.

gmod_find_vpns.lua

local BASE_URL = "https://raw.githubusercontent.com/X4BNet/lists_vpn/main/ipv4.txt"
local IP_PATTERN = "(%d%d?%d?)%.(%d%d?%d?)%.(%d%d?%d?)%.(%d%d?%d?)"
local IP_RANGE_PATTERN = "(%d%d?%d?%.%d%d?%d?%.%d%d?%d?%.%d%d?%d?)/(%d+)"

local function str_to_ip(str)
	local o1, o2, o3, o4 = str:match(IP_PATTERN)
	o1, o2, o3, o4 = tonumber(o1), tonumber(o2), tonumber(o3), tonumber(o4)

	return bit.bor(
		o1 * 2 ^ 24,
		o2 * 2 ^ 16,
		o3 * 2 ^ 8,
		o4
	)
end

local lookup = {}
local lookup_count = 0
http.Fetch(BASE_URL, function(body)
	for str_ip, net_mask_str in body:gmatch(IP_RANGE_PATTERN) do
		local ip = str_to_ip(str_ip)
		if not lookup[ip] then
			lookup[ip] = {}
			lookup_count = lookup_count + 1
		end

		local net_mask = tonumber(net_mask_str)
		if not net_mask then continue end

		table.insert(lookup[ip], net_mask)
	end
end)

local function compare_ips(source_ip, net_ip, net_mask)
	local mask = bit.bnot(2 ^ (32 - net_mask) - 1)
	return bit.band(source_ip, mask) == bit.band(net_ip, mask)
end

local function check_vpn(ip_str, callback)
	return coroutine.create(function()
		if lookup_count == 0 then
			callback(false, -1, -1)
			return
		end

		local i = 0
		local source_ip = str_to_ip(ip_str)
		for target_ip, net_masks in pairs(lookup) do
			for _, net_mask in ipairs(net_masks) do
				local is_in_range = compare_ips(source_ip, target_ip, net_mask)
				if is_in_range then
					callback(true, target_ip, net_mask)
					return
				end

				i = i + 1
				if i % 1000 == 0 then
					coroutine.yield()
				end
			end
		end

		callback(false, -1, -1)
	end)
end

local callback_id = 0
function util.CheckVPN(ip_addr, callback)
	local co = check_vpn(ip_addr, callback)
	local hook_name = ("CheckVPN_[%d]"):format(callback_id)
	hook.Add("Think", hook_name, function()
		local status, result = coroutine.resume(co)
		if not status then
			hook.Remove("Think", hook_name)
			error(result)
		end

		if result or coroutine.status(co) == "dead" then
			hook.Remove("Think", hook_name)
		end
	end)

	callback_id = callback_id + 1
end