-- Prosody IM

-- Copyright (C) 2012 Florian Zeitz

-- Copyright (C) 2014 Daurnimator

--

-- This project is MIT/X11 licensed. Please see the

-- COPYING file in the source package for more information.

--

local softreq = require "util.dependencies".softreq;

local log = require "util.logger".init "websocket.frames";

local random_bytes = require "util.random".bytes;

local bit = assert(softreq"bit" or softreq"bit32",

	"No bit module found. See https://prosody.im/doc/depends#bitop");

local band = bit.band;

local bor = bit.bor;

local bxor = bit.bxor;

local lshift = bit.lshift;

local rshift = bit.rshift;

local t_concat = table.concat;

local s_byte = string.byte;

local s_char= string.char;

local s_sub = string.sub;

local function read_uint16be(str, pos)

	local l1, l2 = s_byte(str, pos, pos+1);

	return l1*256 + l2;

end

-- FIXME: this may lose precision

local function read_uint64be(str, pos)

	local l1, l2, l3, l4, l5, l6, l7, l8 = s_byte(str, pos, pos+7);

	local h = lshift(l1, 24) + lshift(l2, 16) + lshift(l3, 8) + l4;

	local l = lshift(l5, 24) + lshift(l6, 16) + lshift(l7, 8) + l8;

	return h * 2^32 + l;

end

local function pack_uint16be(x)

	return s_char(rshift(x, 8), band(x, 0xFF));

end

local function get_byte(x, n)

	return band(rshift(x, n), 0xFF);

end

local function pack_uint64be(x)

	local h = band(x / 2^32, 2^32-1);

	return s_char(get_byte(h, 24), get_byte(h, 16), get_byte(h, 8), band(h, 0xFF));

		get_byte(x, 24), get_byte(x, 16), get_byte(x, 8), band(x, 0xFF);

end

local function parse_frame_header(frame)

	if #frame < 2 then return; end

	local byte1, byte2 = s_byte(frame, 1, 2);

	local result = {

		FIN = band(byte1, 0x80) > 0;

		RSV1 = band(byte1, 0x40) > 0;

		RSV2 = band(byte1, 0x20) > 0;

		RSV3 = band(byte1, 0x10) > 0;

		opcode = band(byte1, 0x0F);

		MASK = band(byte2, 0x80) > 0;

		length = band(byte2, 0x7F);

	};

	local length_bytes = 0;

	if result.length == 126 then

		length_bytes = 2;

	elseif result.length == 127 then

		length_bytes = 8;

	end

	local header_length = 2 + length_bytes + (result.MASK and 4 or 0);

	if #frame < header_length then return; end

	if length_bytes == 2 then

		result.length = read_uint16be(frame, 3);

	elseif length_bytes == 8 then

		result.length = read_uint64be(frame, 3);

	end

	if result.MASK then

		result.key = { s_byte(frame, length_bytes+3, length_bytes+6) };

	end

	return result, header_length;

end

-- XORs the string `str` with the array of bytes `key`

-- TODO: optimize

local function apply_mask(str, key, from, to)

	from = from or 1

	if from < 0 then from = #str + from + 1 end -- negative indicies

	to = to or #str

	if to < 0 then to = #str + to + 1 end -- negative indicies

	local key_len = #key

	local counter = 0;

	local data = {};

	for i = from, to do

		local key_index = counter%key_len + 1;

		counter = counter + 1;

		data[counter] = s_char(bxor(key[key_index], s_byte(str, i)));

	end

	return t_concat(data);

end

local function parse_frame_body(frame, header, pos)

	if header.MASK then

		return apply_mask(frame, header.key, pos, pos + header.length - 1);

	else

		return frame:sub(pos, pos + header.length - 1);

	end

end

local function parse_frame(frame)

	local result, pos = parse_frame_header(frame);

	if result == nil or #frame < (pos + result.length) then return; end

	result.data = parse_frame_body(frame, result, pos+1);

	return result, pos + result.length;

end

local function build_frame(desc)

	local data = desc.data or "";

	assert(desc.opcode and desc.opcode >= 0 and desc.opcode <= 0xF, "Invalid WebSocket opcode");

	if desc.opcode >= 0x8 then

		-- RFC 6455 5.5

		assert(#data <= 125, "WebSocket control frames MUST have a payload length of 125 bytes or less.");

	end

	local b1 = bor(desc.opcode,

		desc.FIN and 0x80 or 0,

		desc.RSV1 and 0x40 or 0,

		desc.RSV2 and 0x20 or 0,

		desc.RSV3 and 0x10 or 0);

	local b2 = #data;

	local length_extra;

	if b2 <= 125 then -- 7-bit length

		length_extra = "";

	elseif b2 <= 0xFFFF then -- 2-byte length

		b2 = 126;

		length_extra = pack_uint16be(#data);

	else -- 8-byte length

		b2 = 127;

		length_extra = pack_uint64be(#data);

	end

	local key = ""

	if desc.MASK then

		local key_a = desc.key

		if key_a then

			key = s_char(unpack(key_a, 1, 4));

		else

			key = random_bytes(4);

			key_a = {key:byte(1,4)};

		end

		b2 = bor(b2, 0x80);

		data = apply_mask(data, key_a);

	end

	return s_char(b1, b2) .. length_extra .. key .. data

end

local function parse_close(data)

	local code, message

	if #data >= 2 then

		code = read_uint16be(data, 1);

		if #data > 2 then

			message = s_sub(data, 3);

		end

	end

	return code, message

end

local function build_close(code, message, mask)

	local data = pack_uint16be(code);

	if message then

		assert(#message<=123, "Close reason must be <=123 bytes");

		data = data .. message;

	end

	return build_frame({

		opcode = 0x8;

		FIN = true;

		MASK = mask;

		data = data;

	});

end

return {

	parse_header = parse_frame_header;

	parse_body = parse_frame_body;

	parse = parse_frame;

	build = build_frame;

	parse_close = parse_close;

	build_close = build_close;

};