-- Prosody IM

-- This file is included with Prosody IM. It has modifications,

-- which are hereby placed in the public domain.

-- todo: quick (default) header generation

-- todo: nxdomain, error handling

-- todo: cache results of encodeName

-- reference: http://tools.ietf.org/html/rfc1035

-- reference: http://tools.ietf.org/html/rfc1876 (LOC)

local socket = require "socket";

local timer = require "util.timer";

local new_ip = require "util.ip".new_ip;

local _, windows = pcall(require, "util.windows");

local is_windows = (_ and windows) or os.getenv("WINDIR");

local coroutine, io, math, string, table =

      coroutine, io, math, string, table;

local ipairs, next, pairs, print, setmetatable, tostring, assert, error, select, type =

      ipairs, next, pairs, print, setmetatable, tostring, assert, error, select, type;

local ztact = { -- public domain 20080404 lua@ztact.com

	get = function(parent, ...)

		local len = select('#', ...);

		for i=1,len do

			parent = parent[select(i, ...)];

			if parent == nil then break; end

		end

		return parent;

	end;

	set = function(parent, ...)

		local len = select('#', ...);

		local key, value = select(len-1, ...);

		local cutpoint, cutkey;

		for i=1,len-2 do

			local key = select (i, ...)

			local child = parent[key]

			if value == nil then

				if child == nil then

					return;

				elseif next(child, next(child)) then

					cutpoint = nil; cutkey = nil;

				elseif cutpoint == nil then

					cutpoint = parent; cutkey = key;

				end

			elseif child == nil then

				child = {};

				parent[key] = child;

			end

			parent = child

		end

		if value == nil and cutpoint then

			cutpoint[cutkey] = nil;

		else

			parent[key] = value;

			return value;

		end

	end;

};

local get, set = ztact.get, ztact.set;

local default_timeout = 15;

-------------------------------------------------- module dns

local _ENV = nil;

local dns = {};

-- dns type & class codes ------------------------------ dns type & class codes

local append = table.insert

local function highbyte(i)    -- - - - - - - - - - - - - - - - - - -  highbyte

	return (i-(i%0x100))/0x100;

end

	local a = {};

		a[i] = s;

		a[s] = s;

		a[string.lower(s)] = s;

	end

	return a;

end

local function encode (t)    -- - - - - - - - - - - - - - - - - - - - -  encode

	local code = {};

	for i,s in pairs(t) do

		local word = string.char(highbyte(i), i%0x100);

		code[i] = word;

		code[s] = word;

		code[string.lower(s)] = word;

	end

	return code;

end

dns.types = {

	'A', 'NS', 'MD', 'MF', 'CNAME', 'SOA', 'MB', 'MG', 'MR', 'NULL', 'WKS',

	'PTR', 'HINFO', 'MINFO', 'MX', 'TXT',

	[ 28] = 'AAAA', [ 29] = 'LOC',   [ 33] = 'SRV',

	[252] = 'AXFR', [253] = 'MAILB', [254] = 'MAILA', [255] = '*' };

dns.classes = { 'IN', 'CS', 'CH', 'HS', [255] = '*' };

dns.typecode  = encode  (dns.types);

dns.classcode = encode  (dns.classes);

local function standardize(qname, qtype, qclass)    -- - - - - - - standardize

	if string.byte(qname, -1) ~= 0x2E then qname = qname..'.';  end

	qname = string.lower(qname);

	return qname, dns.type[qtype or 'A'], dns.class[qclass or 'IN'];

end

local function prune(rrs, time, soft)    -- - - - - - - - - - - - - - -  prune

	time = time or socket.gettime();

	for i,rr in ipairs(rrs) do

		if rr.tod then

			if rr.tod < time then

				rrs[rr[rr.type:lower()]] = nil;

				table.remove(rrs, i);

				return prune(rrs, time, soft); -- Re-iterate

			end

		elseif soft == 'soft' then    -- What is this?  I forget!

			assert(rr.ttl == 0);

			rrs[rr[rr.type:lower()]] = nil;

			table.remove(rrs, i);

		end

	end

end

-- metatables & co. ------------------------------------------ metatables & co.

local resolver = {};

resolver.__index = resolver;

resolver.timeout = default_timeout;

local function default_rr_tostring(rr)

	local rr_val = rr.type and rr[rr.type:lower()];

	if type(rr_val) ~= "string" then

		return "<UNKNOWN RDATA TYPE>";

	end

	return rr_val;

end

local special_tostrings = {

	LOC = resolver.LOC_tostring;

	MX  = function (rr)

		return string.format('%2i %s', rr.pref, rr.mx);

	end;

	SRV = function (rr)

		local s = rr.srv;

		return string.format('%5d %5d %5d %s', s.priority, s.weight, s.port, s.target);

	end;

};

local rr_metatable = {};   -- - - - - - - - - - - - - - - - - - -  rr_metatable

function rr_metatable.__tostring(rr)

	local rr_string = (special_tostrings[rr.type] or default_rr_tostring)(rr);

	return string.format('%2s %-5s %6i %-28s %s', rr.class, rr.type, rr.ttl, rr.name, rr_string);

end

local rrs_metatable = {};    -- - - - - - - - - - - - - - - - - -  rrs_metatable

function rrs_metatable.__tostring(rrs)

	local t = {};

	for _, rr in ipairs(rrs) do

		append(t, tostring(rr)..'\n');

	end

	return table.concat(t);

end

local cache_metatable = {};    -- - - - - - - - - - - - - - - -  cache_metatable

function cache_metatable.__tostring(cache)

	local time = socket.gettime();

	local t = {};

	for class,types in pairs(cache) do

		for type,names in pairs(types) do

			for name,rrs in pairs(names) do

				prune(rrs, time);

				append(t, tostring(rrs));

			end

		end

	end

	return table.concat(t);

end

-- packet layer -------------------------------------------------- packet layer

function dns.random(...)    -- - - - - - - - - - - - - - - - - - -  dns.random

	math.randomseed(math.floor(10000*socket.gettime()) % 0x80000000);

	dns.random = math.random;

	return dns.random(...);

end

local function encodeHeader(o)    -- - - - - - - - - - - - - - -  encodeHeader

	o = o or {};

	o.id = o.id or dns.random(0, 0xffff); -- 16b	(random) id

	o.rd = o.rd or 1;		--  1b  1 recursion desired

	o.tc = o.tc or 0;		--  1b	1 truncated response

	o.aa = o.aa or 0;		--  1b	1 authoritative response

	o.opcode = o.opcode or 0;	--  4b	0 query

				--  1 inverse query

				--	2 server status request

				--	3-15 reserved

	o.qr = o.qr or 0;		--  1b	0 query, 1 response

	o.rcode = o.rcode or 0;	--  4b  0 no error

				--	1 format error

				--	2 server failure

				--	3 name error

				--	4 not implemented

				--	5 refused

				--	6-15 reserved

	o.z = o.z  or 0;		--  3b  0 resvered

	o.ra = o.ra or 0;		--  1b  1 recursion available

	o.qdcount = o.qdcount or 1;	-- 16b	number of question RRs

	o.ancount = o.ancount or 0;	-- 16b	number of answers RRs

	o.nscount = o.nscount or 0;	-- 16b	number of nameservers RRs

	o.arcount = o.arcount or 0;	-- 16b  number of additional RRs

	-- string.char() rounds, so prevent roundup with -0.4999

	local header = string.char(

		highbyte(o.id), o.id %0x100,

		o.rd + 2*o.tc + 4*o.aa + 8*o.opcode + 128*o.qr,

		o.rcode + 16*o.z + 128*o.ra,

		highbyte(o.qdcount),  o.qdcount %0x100,

		highbyte(o.ancount),  o.ancount %0x100,

		highbyte(o.nscount),  o.nscount %0x100,

		highbyte(o.arcount),  o.arcount %0x100

	);

	return header, o.id;

end

local function encodeName(name)    -- - - - - - - - - - - - - - - - encodeName

	local t = {};

	for part in string.gmatch(name, '[^.]+') do

		append(t, string.char(string.len(part)));

		append(t, part);

	end

	append(t, string.char(0));

	return table.concat(t);

end

local function encodeQuestion(qname, qtype, qclass)    -- - - - encodeQuestion

	qname  = encodeName(qname);

	qtype  = dns.typecode[qtype or 'a'];

	qclass = dns.classcode[qclass or 'in'];

	return qname..qtype..qclass;

end

function resolver:byte(len)    -- - - - - - - - - - - - - - - - - - - - - byte

	len = len or 1;

	local offset = self.offset;

	local last = offset + len - 1;

	if last > #self.packet then

		error(string.format('out of bounds: %i>%i', last, #self.packet));

	end

	self.offset = offset + len;

	return string.byte(self.packet, offset, last);

end

function resolver:word()    -- - - - - - - - - - - - - - - - - - - - - -  word

	local b1, b2 = self:byte(2);

	return 0x100*b1 + b2;

end

function resolver:dword ()    -- - - - - - - - - - - - - - - - - - - - -  dword

	local b1, b2, b3, b4 = self:byte(4);

	--print('dword', b1, b2, b3, b4);

	return 0x1000000*b1 + 0x10000*b2 + 0x100*b3 + b4;

end

function resolver:sub(len)    -- - - - - - - - - - - - - - - - - - - - - - sub

	len = len or 1;

	local s = string.sub(self.packet, self.offset, self.offset + len - 1);

	self.offset = self.offset + len;

	return s;

end

function resolver:header(force)    -- - - - - - - - - - - - - - - - - - header

	local id = self:word();

	--print(string.format(':header  id  %x', id));

	if not self.active[id] and not force then return nil; end

	local h = { id = id };

	local b1, b2 = self:byte(2);

	h.rd      = b1 %2;

	h.tc      = b1 /2%2;

	h.aa      = b1 /4%2;

	h.opcode  = b1 /8%16;

	h.qr      = b1 /128;

	h.rcode   = b2 %16;

	h.z       = b2 /16%8;

	h.ra      = b2 /128;

	h.qdcount = self:word();

	h.ancount = self:word();

	h.nscount = self:word();

	h.arcount = self:word();

	for k,v in pairs(h) do h[k] = v-v%1; end

	return h;

end

function resolver:name()    -- - - - - - - - - - - - - - - - - - - - - -  name

	local remember, pointers = nil, 0;

	local len = self:byte();

	local n = {};

	if len == 0 then return "." end -- Root label

	while len > 0 do

		if len >= 0xc0 then    -- name is "compressed"

			pointers = pointers + 1;

			if pointers >= 20 then error('dns error: 20 pointers'); end;

			local offset = ((len-0xc0)*0x100) + self:byte();

			remember = remember or self.offset;

			self.offset = offset + 1;    -- +1 for lua

		else    -- name is not compressed

			append(n, self:sub(len)..'.');

		end

		len = self:byte();

	end

	self.offset = remember or self.offset;

	return table.concat(n);