net/websocket/frames.lua

   1 -- Prosody IM
   2 -- Copyright (C) 2012 Florian Zeitz
   3 -- Copyright (C) 2014 Daurnimator
   4 --
   5 -- This project is MIT/X11 licensed. Please see the
   6 -- COPYING file in the source package for more information.
   7 --
   8
   9 local softreq = require "util.dependencies".softreq;
  10 local random_bytes = require "util.random".bytes;
  11
  12 local bit = require "util.bitcompat";
  13 local band = bit.band;
  14 local bor = bit.bor;
  15 local bxor = bit.bxor;
  16 local lshift = bit.lshift;
  17 local rshift = bit.rshift;
  18 local unpack = table.unpack or unpack; -- luacheck: ignore 113
  19
  20 local t_concat = table.concat;
  21 local s_byte = string.byte;
  22 local s_char= string.char;
  23 local s_sub = string.sub;
  24 local s_pack = string.pack;
  25 local s_unpack = string.unpack;
  26
  27 if not s_pack and softreq"struct" then
  28         s_pack = softreq"struct".pack;
  29         s_unpack = softreq"struct".unpack;
  30 end
  31
  32 local function read_uint16be(str, pos)
  33         local l1, l2 = s_byte(str, pos, pos+1);
  34         return l1*256 + l2;
  35 end
  36 -- FIXME: this may lose precision
  37 local function read_uint64be(str, pos)
  38         local l1, l2, l3, l4, l5, l6, l7, l8 = s_byte(str, pos, pos+7);
  39         local h = lshift(l1, 24) + lshift(l2, 16) + lshift(l3, 8) + l4;
  40         local l = lshift(l5, 24) + lshift(l6, 16) + lshift(l7, 8) + l8;
  41         return h * 2^32 + l;
  42 end
  43 local function pack_uint16be(x)
  44         return s_char(rshift(x, 8), band(x, 0xFF));
  45 end
  46 local function get_byte(x, n)
  47         return band(rshift(x, n), 0xFF);
  48 end
  49 local function pack_uint64be(x)
  50         local h = band(x / 2^32, 2^32-1);
  51         return s_char(get_byte(h, 24), get_byte(h, 16), get_byte(h, 8), band(h, 0xFF),
  52                 get_byte(x, 24), get_byte(x, 16), get_byte(x, 8), band(x, 0xFF));
  53 end
  54
  55 if s_pack then
  56         function pack_uint16be(x)
  57                 return s_pack(">I2", x);
  58         end
  59         function pack_uint64be(x)
  60                 return s_pack(">I8", x);
  61         end
  62 end
  63
  64 if s_unpack then
  65         function read_uint16be(str, pos)
  66                 return s_unpack(">I2", str, pos);
  67         end
  68         function read_uint64be(str, pos)
  69                 return s_unpack(">I8", str, pos);
  70         end
  71 end
  72
  73 local function parse_frame_header(frame)
  74         if #frame < 2 then return; end
  75
  76         local byte1, byte2 = s_byte(frame, 1, 2);
  77         local result = {
  78                 FIN = band(byte1, 0x80) > 0;
  79                 RSV1 = band(byte1, 0x40) > 0;
  80                 RSV2 = band(byte1, 0x20) > 0;
  81                 RSV3 = band(byte1, 0x10) > 0;
  82                 opcode = band(byte1, 0x0F);
  83
  84                 MASK = band(byte2, 0x80) > 0;
  85                 length = band(byte2, 0x7F);
  86         };
  87
  88         local length_bytes = 0;
  89         if result.length == 126 then
  90                 length_bytes = 2;
  91         elseif result.length == 127 then
  92                 length_bytes = 8;
  93         end
  94
  95         local header_length = 2 + length_bytes + (result.MASK and 4 or 0);
  96         if #frame < header_length then return; end
  97
  98         if length_bytes == 2 then
  99                 result.length = read_uint16be(frame, 3);
 100         elseif length_bytes == 8 then
 101                 result.length = read_uint64be(frame, 3);
 102         end
 103
 104         if result.MASK then
 105                 result.key = { s_byte(frame, length_bytes+3, length_bytes+6) };
 106         end
 107
 108         return result, header_length;
 109 end
 110
 111 -- XORs the string `str` with the array of bytes `key`
 112 -- TODO: optimize
 113 local function apply_mask(str, key, from, to)
 114         from = from or 1
 115         if from < 0 then from = #str + from + 1 end -- negative indices
 116         to = to or #str
 117         if to < 0 then to = #str + to + 1 end -- negative indices
 118         local key_len = #key
 119         local counter = 0;
 120         local data = {};
 121         for i = from, to do
 122                 local key_index = counter%key_len + 1;
 123                 counter = counter + 1;
 124                 data[counter] = s_char(bxor(key[key_index], s_byte(str, i)));
 125         end
 126         return t_concat(data);
 127 end
 128
 129 local function parse_frame_body(frame, header, pos)
 130         if header.MASK then
 131                 return apply_mask(frame, header.key, pos, pos + header.length - 1);
 132         else
 133                 return frame:sub(pos, pos + header.length - 1);
 134         end
 135 end
 136
 137 local function parse_frame(frame)
 138         local result, pos = parse_frame_header(frame);
 139         if result == nil or #frame < (pos + result.length) then return; end
 140         result.data = parse_frame_body(frame, result, pos+1);
 141         return result, pos + result.length;
 142 end
 143
 144 local function build_frame(desc)
 145         local data = desc.data or "";
 146
 147         assert(desc.opcode and desc.opcode >= 0 and desc.opcode <= 0xF, "Invalid WebSocket opcode");
 148         if desc.opcode >= 0x8 then
 149                 -- RFC 6455 5.5
 150                 assert(#data <= 125, "WebSocket control frames MUST have a payload length of 125 bytes or less.");
 151         end
 152
 153         local b1 = bor(desc.opcode,
 154                 desc.FIN and 0x80 or 0,
 155                 desc.RSV1 and 0x40 or 0,
 156                 desc.RSV2 and 0x20 or 0,
 157                 desc.RSV3 and 0x10 or 0);
 158
 159         local b2 = #data;
 160         local length_extra;
 161         if b2 <= 125 then -- 7-bit length
 162                 length_extra = "";
 163         elseif b2 <= 0xFFFF then -- 2-byte length
 164                 b2 = 126;
 165                 length_extra = pack_uint16be(#data);
 166         else -- 8-byte length
 167                 b2 = 127;
 168                 length_extra = pack_uint64be(#data);
 169         end
 170
 171         local key = ""
 172         if desc.MASK then
 173                 local key_a = desc.key
 174                 if key_a then
 175                         key = s_char(unpack(key_a, 1, 4));
 176                 else
 177                         key = random_bytes(4);
 178                         key_a = {key:byte(1,4)};
 179                 end
 180                 b2 = bor(b2, 0x80);
 181                 data = apply_mask(data, key_a);
 182         end
 183
 184         return s_char(b1, b2) .. length_extra .. key .. data
 185 end
 186
 187 local function parse_close(data)
 188         local code, message
 189         if #data >= 2 then
 190                 code = read_uint16be(data, 1);
 191                 if #data > 2 then
 192                         message = s_sub(data, 3);
 193                 end
 194         end
 195         return code, message
 196 end
 197
 198 local function build_close(code, message, mask)
 199         local data = pack_uint16be(code);
 200         if message then
 201                 assert(#message<=123, "Close reason must be <=123 bytes");
 202                 data = data .. message;
 203         end
 204         return build_frame({
 205                 opcode = 0x8;
 206                 FIN = true;
 207                 MASK = mask;
 208                 data = data;
 209         });
 210 end
 211
 212 return {
 213         parse_header = parse_frame_header;
 214         parse_body = parse_frame_body;
 215         parse = parse_frame;
 216         build = build_frame;
 217         parse_close = parse_close;
 218         build_close = build_close;
 219 };