--- a/net/websocket/frames.lua	Mon Aug 24 17:28:48 2020 +0200
+++ b/net/websocket/frames.lua	Thu Sep 17 13:00:19 2020 +0100
@@ -16,13 +16,12 @@
 local bxor = bit.bxor;
 local lshift = bit.lshift;
 local rshift = bit.rshift;
+local unpack = table.unpack or unpack; -- luacheck: ignore 113
 
 local t_concat = table.concat;
-local s_byte = string.byte;
 local s_char= string.char;
-local s_sub = string.sub;
-local s_pack = string.pack; -- luacheck: ignore 143
-local s_unpack = string.unpack; -- luacheck: ignore 143
+local s_pack = string.pack;
+local s_unpack = string.unpack;
 
 if not s_pack and softreq"struct" then
 	s_pack = softreq"struct".pack;
@@ -30,12 +29,12 @@
 end
 
 local function read_uint16be(str, pos)
-	local l1, l2 = s_byte(str, pos, pos+1);
+	local l1, l2 = str:byte(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 l1, l2, l3, l4, l5, l6, l7, l8 = str:byte(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;
@@ -63,9 +62,15 @@
 
 if s_unpack then
 	function read_uint16be(str, pos)
+		if type(str) ~= "string" then
+			str, pos = str:sub(pos, pos+1), 1;
+		end
 		return s_unpack(">I2", str, pos);
 	end
 	function read_uint64be(str, pos)
+		if type(str) ~= "string" then
+			str, pos = str:sub(pos, pos+7), 1;
+		end
 		return s_unpack(">I8", str, pos);
 	end
 end
@@ -73,7 +78,7 @@
 local function parse_frame_header(frame)
 	if #frame < 2 then return; end
 
-	local byte1, byte2 = s_byte(frame, 1, 2);
+	local byte1, byte2 = frame:byte(1, 2);
 	local result = {
 		FIN = band(byte1, 0x80) > 0;
 		RSV1 = band(byte1, 0x40) > 0;
@@ -102,7 +107,7 @@
 	end
 
 	if result.MASK then
-		result.key = { s_byte(frame, length_bytes+3, length_bytes+6) };
+		result.key = { frame:byte(length_bytes+3, length_bytes+6) };
 	end
 
 	return result, header_length;
@@ -121,7 +126,7 @@
 	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)));
+		data[counter] = s_char(bxor(key[key_index], str:byte(i)));
 	end
 	return t_concat(data);
 end
@@ -189,7 +194,7 @@
 	if #data >= 2 then
 		code = read_uint16be(data, 1);
 		if #data > 2 then
-			message = s_sub(data, 3);
+			message = data:sub(3);
 		end
 	end
 	return code, message