git.zerfleddert.de Git - proxmark3-svn/blob - client/lualibs/dkjson.lua

   1 -- Module options:
   2 local always_try_using_lpeg = true
   3 local register_global_module_table = false
   4 local global_module_name = 'json'
   5
   6 --[==[
   7
   8 David Kolf's JSON module for Lua 5.1/5.2
   9
  10 Version 2.5
  11
  12
  13 For the documentation see the corresponding readme.txt or visit
  14 <http://dkolf.de/src/dkjson-lua.fsl/>.
  15
  16 You can contact the author by sending an e-mail to 'david' at the
  17 domain 'dkolf.de'.
  18
  19
  20 Copyright (C) 2010-2013 David Heiko Kolf
  21
  22 Permission is hereby granted, free of charge, to any person obtaining
  23 a copy of this software and associated documentation files (the
  24 "Software"), to deal in the Software without restriction, including
  25 without limitation the rights to use, copy, modify, merge, publish,
  26 distribute, sublicense, and/or sell copies of the Software, and to
  27 permit persons to whom the Software is furnished to do so, subject to
  28 the following conditions:
  29
  30 The above copyright notice and this permission notice shall be
  31 included in all copies or substantial portions of the Software.
  32
  33 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  34 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  35 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  36 NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  37 BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  38 ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  39 CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  40 SOFTWARE.
  41
  42 --]==]
  43
  44 -- global dependencies:
  45 local pairs, type, tostring, tonumber, getmetatable, setmetatable, rawset =
  46       pairs, type, tostring, tonumber, getmetatable, setmetatable, rawset
  47 local error, require, pcall, select = error, require, pcall, select
  48 local floor, huge = math.floor, math.huge
  49 local strrep, gsub, strsub, strbyte, strchar, strfind, strlen, strformat =
  50       string.rep, string.gsub, string.sub, string.byte, string.char,
  51       string.find, string.len, string.format
  52 local strmatch = string.match
  53 local concat = table.concat
  54
  55 local json = { version = "dkjson 2.5" }
  56
  57 if register_global_module_table then
  58   _G[global_module_name] = json
  59 end
  60
  61 local _ENV = nil -- blocking globals in Lua 5.2
  62
  63 pcall (function()
  64   -- Enable access to blocked metatables.
  65   -- Don't worry, this module doesn't change anything in them.
  66   local debmeta = require "debug".getmetatable
  67   if debmeta then getmetatable = debmeta end
  68 end)
  69
  70 json.null = setmetatable ({}, {
  71   __tojson = function () return "null" end
  72 })
  73
  74 local function isarray (tbl)
  75   local max, n, arraylen = 0, 0, 0
  76   for k,v in pairs (tbl) do
  77     if k == 'n' and type(v) == 'number' then
  78       arraylen = v
  79       if v > max then
  80         max = v
  81       end
  82     else
  83       if type(k) ~= 'number' or k < 1 or floor(k) ~= k then
  84         return false
  85       end
  86       if k > max then
  87         max = k
  88       end
  89       n = n + 1
  90     end
  91   end
  92   if max > 10 and max > arraylen and max > n * 2 then
  93     return false -- don't create an array with too many holes
  94   end
  95   return true, max
  96 end
  97
  98 local escapecodes = {
  99   ["\""] = "\\\"", ["\\"] = "\\\\", ["\b"] = "\\b", ["\f"] = "\\f",
 100   ["\n"] = "\\n",  ["\r"] = "\\r",  ["\t"] = "\\t"
 101 }
 102
 103 local function escapeutf8 (uchar)
 104   local value = escapecodes[uchar]
 105   if value then
 106     return value
 107   end
 108   local a, b, c, d = strbyte (uchar, 1, 4)
 109   a, b, c, d = a or 0, b or 0, c or 0, d or 0
 110   if a <= 0x7f then
 111     value = a
 112   elseif 0xc0 <= a and a <= 0xdf and b >= 0x80 then
 113     value = (a - 0xc0) * 0x40 + b - 0x80
 114   elseif 0xe0 <= a and a <= 0xef and b >= 0x80 and c >= 0x80 then
 115     value = ((a - 0xe0) * 0x40 + b - 0x80) * 0x40 + c - 0x80
 116   elseif 0xf0 <= a and a <= 0xf7 and b >= 0x80 and c >= 0x80 and d >= 0x80 then
 117     value = (((a - 0xf0) * 0x40 + b - 0x80) * 0x40 + c - 0x80) * 0x40 + d - 0x80
 118   else
 119     return ""
 120   end
 121   if value <= 0xffff then
 122     return strformat ("\\u%.4x", value)
 123   elseif value <= 0x10ffff then
 124     -- encode as UTF-16 surrogate pair
 125     value = value - 0x10000
 126     local highsur, lowsur = 0xD800 + floor (value/0x400), 0xDC00 + (value % 0x400)
 127     return strformat ("\\u%.4x\\u%.4x", highsur, lowsur)
 128   else
 129     return ""
 130   end
 131 end
 132
 133 local function fsub (str, pattern, repl)
 134   -- gsub always builds a new string in a buffer, even when no match
 135   -- exists. First using find should be more efficient when most strings
 136   -- don't contain the pattern.
 137   if strfind (str, pattern) then
 138     return gsub (str, pattern, repl)
 139   else
 140     return str
 141   end
 142 end
 143
 144 local function quotestring (value)
 145   -- based on the regexp "escapable" in https://github.com/douglascrockford/JSON-js
 146   value = fsub (value, "[%z\1-\31\"\\\127]", escapeutf8)
 147   if strfind (value, "[\194\216\220\225\226\239]") then
 148     value = fsub (value, "\194[\128-\159\173]", escapeutf8)
 149     value = fsub (value, "\216[\128-\132]", escapeutf8)
 150     value = fsub (value, "\220\143", escapeutf8)
 151     value = fsub (value, "\225\158[\180\181]", escapeutf8)
 152     value = fsub (value, "\226\128[\140-\143\168-\175]", escapeutf8)
 153     value = fsub (value, "\226\129[\160-\175]", escapeutf8)
 154     value = fsub (value, "\239\187\191", escapeutf8)
 155     value = fsub (value, "\239\191[\176-\191]", escapeutf8)
 156   end
 157   return "\"" .. value .. "\""
 158 end
 159 json.quotestring = quotestring
 160
 161 local function replace(str, o, n)
 162   local i, j = strfind (str, o, 1, true)
 163   if i then
 164     return strsub(str, 1, i-1) .. n .. strsub(str, j+1, -1)
 165   else
 166     return str
 167   end
 168 end
 169
 170 -- locale independent num2str and str2num functions
 171 local decpoint, numfilter
 172
 173 local function updatedecpoint ()
 174   decpoint = strmatch(tostring(0.5), "([^05+])")
 175   -- build a filter that can be used to remove group separators
 176   numfilter = "[^0-9%-%+eE" .. gsub(decpoint, "[%^%$%(%)%%%.%[%]%*%+%-%?]", "%%%0") .. "]+"
 177 end
 178
 179 updatedecpoint()
 180
 181 local function num2str (num)
 182   return replace(fsub(tostring(num), numfilter, ""), decpoint, ".")
 183 end
 184
 185 local function str2num (str)
 186   local num = tonumber(replace(str, ".", decpoint))
 187   if not num then
 188     updatedecpoint()
 189     num = tonumber(replace(str, ".", decpoint))
 190   end
 191   return num
 192 end
 193
 194 local function addnewline2 (level, buffer, buflen)
 195   buffer[buflen+1] = "\n"
 196   buffer[buflen+2] = strrep ("  ", level)
 197   buflen = buflen + 2
 198   return buflen
 199 end
 200
 201 function json.addnewline (state)
 202   if state.indent then
 203     state.bufferlen = addnewline2 (state.level or 0,
 204                            state.buffer, state.bufferlen or #(state.buffer))
 205   end
 206 end
 207
 208 local encode2 -- forward declaration
 209
 210 local function addpair (key, value, prev, indent, level, buffer, buflen, tables, globalorder, state)
 211   local kt = type (key)
 212   if kt ~= 'string' and kt ~= 'number' then
 213     return nil, "type '" .. kt .. "' is not supported as a key by JSON."
 214   end
 215   if prev then
 216     buflen = buflen + 1
 217     buffer[buflen] = ","
 218   end
 219   if indent then
 220     buflen = addnewline2 (level, buffer, buflen)
 221   end
 222   buffer[buflen+1] = quotestring (key)
 223   buffer[buflen+2] = ":"
 224   return encode2 (value, indent, level, buffer, buflen + 2, tables, globalorder, state)
 225 end
 226
 227 local function appendcustom(res, buffer, state)
 228   local buflen = state.bufferlen
 229   if type (res) == 'string' then
 230     buflen = buflen + 1
 231     buffer[buflen] = res
 232   end
 233   return buflen
 234 end
 235
 236 local function exception(reason, value, state, buffer, buflen, defaultmessage)
 237   defaultmessage = defaultmessage or reason
 238   local handler = state.exception
 239   if not handler then
 240     return nil, defaultmessage
 241   else
 242     state.bufferlen = buflen
 243     local ret, msg = handler (reason, value, state, defaultmessage)
 244     if not ret then return nil, msg or defaultmessage end
 245     return appendcustom(ret, buffer, state)
 246   end
 247 end
 248
 249 function json.encodeexception(reason, value, state, defaultmessage)
 250   return quotestring("<" .. defaultmessage .. ">")
 251 end
 252
 253 encode2 = function (value, indent, level, buffer, buflen, tables, globalorder, state)
 254   local valtype = type (value)
 255   local valmeta = getmetatable (value)
 256   valmeta = type (valmeta) == 'table' and valmeta -- only tables
 257   local valtojson = valmeta and valmeta.__tojson
 258   if valtojson then
 259     if tables[value] then
 260       return exception('reference cycle', value, state, buffer, buflen)
 261     end
 262     tables[value] = true
 263     state.bufferlen = buflen
 264     local ret, msg = valtojson (value, state)
 265     if not ret then return exception('custom encoder failed', value, state, buffer, buflen, msg) end
 266     tables[value] = nil
 267     buflen = appendcustom(ret, buffer, state)
 268   elseif value == nil then
 269     buflen = buflen + 1
 270     buffer[buflen] = "null"
 271   elseif valtype == 'number' then
 272     local s
 273     if value ~= value or value >= huge or -value >= huge then
 274       -- This is the behaviour of the original JSON implementation.
 275       s = "null"
 276     else
 277       s = num2str (value)
 278     end
 279     buflen = buflen + 1
 280     buffer[buflen] = s
 281   elseif valtype == 'boolean' then
 282     buflen = buflen + 1
 283     buffer[buflen] = value and "true" or "false"
 284   elseif valtype == 'string' then
 285     buflen = buflen + 1
 286     buffer[buflen] = quotestring (value)
 287   elseif valtype == 'table' then
 288     if tables[value] then
 289       return exception('reference cycle', value, state, buffer, buflen)
 290     end
 291     tables[value] = true
 292     level = level + 1
 293     local isa, n = isarray (value)
 294     if n == 0 and valmeta and valmeta.__jsontype == 'object' then
 295       isa = false
 296     end
 297     local msg
 298     if isa then -- JSON array
 299       buflen = buflen + 1
 300       buffer[buflen] = "["
 301       for i = 1, n do
 302         buflen, msg = encode2 (value[i], indent, level, buffer, buflen, tables, globalorder, state)
 303         if not buflen then return nil, msg end
 304         if i < n then
 305           buflen = buflen + 1
 306           buffer[buflen] = ","
 307         end
 308       end
 309       buflen = buflen + 1
 310       buffer[buflen] = "]"
 311     else -- JSON object
 312       local prev = false
 313       buflen = buflen + 1
 314       buffer[buflen] = "{"
 315       local order = valmeta and valmeta.__jsonorder or globalorder
 316       if order then
 317         local used = {}
 318         n = #order
 319         for i = 1, n do
 320           local k = order[i]
 321           local v = value[k]
 322           if v then
 323             used[k] = true
 324             buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder, state)
 325             prev = true -- add a seperator before the next element
 326           end
 327         end
 328         for k,v in pairs (value) do
 329           if not used[k] then
 330             buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder, state)
 331             if not buflen then return nil, msg end
 332             prev = true -- add a seperator before the next element
 333           end
 334         end
 335       else -- unordered
 336         for k,v in pairs (value) do
 337           buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder, state)
 338           if not buflen then return nil, msg end
 339           prev = true -- add a seperator before the next element
 340         end
 341       end
 342       if indent then
 343         buflen = addnewline2 (level - 1, buffer, buflen)
 344       end
 345       buflen = buflen + 1
 346       buffer[buflen] = "}"
 347     end
 348     tables[value] = nil
 349   else
 350     return exception ('unsupported type', value, state, buffer, buflen,
 351       "type '" .. valtype .. "' is not supported by JSON.")
 352   end
 353   return buflen
 354 end
 355
 356 function json.encode (value, state)
 357   state = state or {}
 358   local oldbuffer = state.buffer
 359   local buffer = oldbuffer or {}
 360   state.buffer = buffer
 361   updatedecpoint()
 362   local ret, msg = encode2 (value, state.indent, state.level or 0,
 363                    buffer, state.bufferlen or 0, state.tables or {}, state.keyorder, state)
 364   if not ret then
 365     error (msg, 2)
 366   elseif oldbuffer == buffer then
 367     state.bufferlen = ret
 368     return true
 369   else
 370     state.bufferlen = nil
 371     state.buffer = nil
 372     return concat (buffer)
 373   end
 374 end
 375
 376 local function loc (str, where)
 377   local line, pos, linepos = 1, 1, 0
 378   while true do
 379     pos = strfind (str, "\n", pos, true)
 380     if pos and pos < where then
 381       line = line + 1
 382       linepos = pos
 383       pos = pos + 1
 384     else
 385       break
 386     end
 387   end
 388   return "line " .. line .. ", column " .. (where - linepos)
 389 end
 390
 391 local function unterminated (str, what, where)
 392   return nil, strlen (str) + 1, "unterminated " .. what .. " at " .. loc (str, where)
 393 end
 394
 395 local function scanwhite (str, pos)
 396   while true do
 397     pos = strfind (str, "%S", pos)
 398     if not pos then return nil end
 399     local sub2 = strsub (str, pos, pos + 1)
 400     if sub2 == "\239\187" and strsub (str, pos + 2, pos + 2) == "\191" then
 401       -- UTF-8 Byte Order Mark
 402       pos = pos + 3
 403     elseif sub2 == "//" then
 404       pos = strfind (str, "[\n\r]", pos + 2)
 405       if not pos then return nil end
 406     elseif sub2 == "/*" then
 407       pos = strfind (str, "*/", pos + 2)
 408       if not pos then return nil end
 409       pos = pos + 2
 410     else
 411       return pos
 412     end
 413   end
 414 end
 415
 416 local escapechars = {
 417   ["\""] = "\"", ["\\"] = "\\", ["/"] = "/", ["b"] = "\b", ["f"] = "\f",
 418   ["n"] = "\n", ["r"] = "\r", ["t"] = "\t"
 419 }
 420
 421 local function unichar (value)
 422   if value < 0 then
 423     return nil
 424   elseif value <= 0x007f then
 425     return strchar (value)
 426   elseif value <= 0x07ff then
 427     return strchar (0xc0 + floor(value/0x40),
 428                     0x80 + (floor(value) % 0x40))
 429   elseif value <= 0xffff then
 430     return strchar (0xe0 + floor(value/0x1000),
 431                     0x80 + (floor(value/0x40) % 0x40),
 432                     0x80 + (floor(value) % 0x40))
 433   elseif value <= 0x10ffff then
 434     return strchar (0xf0 + floor(value/0x40000),
 435                     0x80 + (floor(value/0x1000) % 0x40),
 436                     0x80 + (floor(value/0x40) % 0x40),
 437                     0x80 + (floor(value) % 0x40))
 438   else
 439     return nil
 440   end
 441 end
 442
 443 local function scanstring (str, pos)
 444   local lastpos = pos + 1
 445   local buffer, n = {}, 0
 446   while true do
 447     local nextpos = strfind (str, "[\"\\]", lastpos)
 448     if not nextpos then
 449       return unterminated (str, "string", pos)
 450     end
 451     if nextpos > lastpos then
 452       n = n + 1
 453       buffer[n] = strsub (str, lastpos, nextpos - 1)
 454     end
 455     if strsub (str, nextpos, nextpos) == "\"" then
 456       lastpos = nextpos + 1
 457       break
 458     else
 459       local escchar = strsub (str, nextpos + 1, nextpos + 1)
 460       local value
 461       if escchar == "u" then
 462         value = tonumber (strsub (str, nextpos + 2, nextpos + 5), 16)
 463         if value then
 464           local value2
 465           if 0xD800 <= value and value <= 0xDBff then
 466             -- we have the high surrogate of UTF-16. Check if there is a
 467             -- low surrogate escaped nearby to combine them.
 468             if strsub (str, nextpos + 6, nextpos + 7) == "\\u" then
 469               value2 = tonumber (strsub (str, nextpos + 8, nextpos + 11), 16)
 470               if value2 and 0xDC00 <= value2 and value2 <= 0xDFFF then
 471                 value = (value - 0xD800)  * 0x400 + (value2 - 0xDC00) + 0x10000
 472               else
 473                 value2 = nil -- in case it was out of range for a low surrogate
 474               end
 475             end
 476           end
 477           value = value and unichar (value)
 478           if value then
 479             if value2 then
 480               lastpos = nextpos + 12
 481             else
 482               lastpos = nextpos + 6
 483             end
 484           end
 485         end
 486       end
 487       if not value then
 488         value = escapechars[escchar] or escchar
 489         lastpos = nextpos + 2
 490       end
 491       n = n + 1
 492       buffer[n] = value
 493     end
 494   end
 495   if n == 1 then
 496     return buffer[1], lastpos
 497   elseif n > 1 then
 498     return concat (buffer), lastpos
 499   else
 500     return "", lastpos
 501   end
 502 end
 503
 504 local scanvalue -- forward declaration
 505
 506 local function scantable (what, closechar, str, startpos, nullval, objectmeta, arraymeta)
 507   local len = strlen (str)
 508   local tbl, n = {}, 0
 509   local pos = startpos + 1
 510   if what == 'object' then
 511     setmetatable (tbl, objectmeta)
 512   else
 513     setmetatable (tbl, arraymeta)
 514   end
 515   while true do
 516     pos = scanwhite (str, pos)
 517     if not pos then return unterminated (str, what, startpos) end
 518     local char = strsub (str, pos, pos)
 519     if char == closechar then
 520       return tbl, pos + 1
 521     end
 522     local val1, err
 523     val1, pos, err = scanvalue (str, pos, nullval, objectmeta, arraymeta)
 524     if err then return nil, pos, err end
 525     pos = scanwhite (str, pos)
 526     if not pos then return unterminated (str, what, startpos) end
 527     char = strsub (str, pos, pos)
 528     if char == ":" then
 529       if val1 == nil then
 530         return nil, pos, "cannot use nil as table index (at " .. loc (str, pos) .. ")"
 531       end
 532       pos = scanwhite (str, pos + 1)
 533       if not pos then return unterminated (str, what, startpos) end
 534       local val2
 535       val2, pos, err = scanvalue (str, pos, nullval, objectmeta, arraymeta)
 536       if err then return nil, pos, err end
 537       tbl[val1] = val2
 538       pos = scanwhite (str, pos)
 539       if not pos then return unterminated (str, what, startpos) end
 540       char = strsub (str, pos, pos)
 541     else
 542       n = n + 1
 543       tbl[n] = val1
 544     end
 545     if char == "," then
 546       pos = pos + 1
 547     end
 548   end
 549 end
 550
 551 scanvalue = function (str, pos, nullval, objectmeta, arraymeta)
 552   pos = pos or 1
 553   pos = scanwhite (str, pos)
 554   if not pos then
 555     return nil, strlen (str) + 1, "no valid JSON value (reached the end)"
 556   end
 557   local char = strsub (str, pos, pos)
 558   if char == "{" then
 559     return scantable ('object', "}", str, pos, nullval, objectmeta, arraymeta)
 560   elseif char == "[" then
 561     return scantable ('array', "]", str, pos, nullval, objectmeta, arraymeta)
 562   elseif char == "\"" then
 563     return scanstring (str, pos)
 564   else
 565     local pstart, pend = strfind (str, "^%-?[%d%.]+[eE]?[%+%-]?%d*", pos)
 566     if pstart then
 567       local number = str2num (strsub (str, pstart, pend))
 568       if number then
 569         return number, pend + 1
 570       end
 571     end
 572     pstart, pend = strfind (str, "^%a%w*", pos)
 573     if pstart then
 574       local name = strsub (str, pstart, pend)
 575       if name == "true" then
 576         return true, pend + 1
 577       elseif name == "false" then
 578         return false, pend + 1
 579       elseif name == "null" then
 580         return nullval, pend + 1
 581       end
 582     end
 583     return nil, pos, "no valid JSON value at " .. loc (str, pos)
 584   end
 585 end
 586
 587 local function optionalmetatables(...)
 588   if select("#", ...) > 0 then
 589     return ...
 590   else
 591     return {__jsontype = 'object'}, {__jsontype = 'array'}
 592   end
 593 end
 594
 595 function json.decode (str, pos, nullval, ...)
 596   local objectmeta, arraymeta = optionalmetatables(...)
 597   return scanvalue (str, pos, nullval, objectmeta, arraymeta)
 598 end
 599
 600 function json.use_lpeg ()
 601   local g = require ("lpeg")
 602
 603   if g.version() == "0.11" then
 604     error "due to a bug in LPeg 0.11, it cannot be used for JSON matching"
 605   end
 606
 607   local pegmatch = g.match
 608   local P, S, R = g.P, g.S, g.R
 609
 610   local function ErrorCall (str, pos, msg, state)
 611     if not state.msg then
 612       state.msg = msg .. " at " .. loc (str, pos)
 613       state.pos = pos
 614     end
 615     return false
 616   end
 617
 618   local function Err (msg)
 619     return g.Cmt (g.Cc (msg) * g.Carg (2), ErrorCall)
 620   end
 621
 622   local SingleLineComment = P"//" * (1 - S"\n\r")^0
 623   local MultiLineComment = P"/*" * (1 - P"*/")^0 * P"*/"
 624   local Space = (S" \n\r\t" + P"\239\187\191" + SingleLineComment + MultiLineComment)^0
 625
 626   local PlainChar = 1 - S"\"\\\n\r"
 627   local EscapeSequence = (P"\\" * g.C (S"\"\\/bfnrt" + Err "unsupported escape sequence")) / escapechars
 628   local HexDigit = R("09", "af", "AF")
 629   local function UTF16Surrogate (match, pos, high, low)
 630     high, low = tonumber (high, 16), tonumber (low, 16)
 631     if 0xD800 <= high and high <= 0xDBff and 0xDC00 <= low and low <= 0xDFFF then
 632       return true, unichar ((high - 0xD800)  * 0x400 + (low - 0xDC00) + 0x10000)
 633     else
 634       return false
 635     end
 636   end
 637   local function UTF16BMP (hex)
 638     return unichar (tonumber (hex, 16))
 639   end
 640   local U16Sequence = (P"\\u" * g.C (HexDigit * HexDigit * HexDigit * HexDigit))
 641   local UnicodeEscape = g.Cmt (U16Sequence * U16Sequence, UTF16Surrogate) + U16Sequence/UTF16BMP
 642   local Char = UnicodeEscape + EscapeSequence + PlainChar
 643   local String = P"\"" * g.Cs (Char ^ 0) * (P"\"" + Err "unterminated string")
 644   local Integer = P"-"^(-1) * (P"0" + (R"19" * R"09"^0))
 645   local Fractal = P"." * R"09"^0
 646   local Exponent = (S"eE") * (S"+-")^(-1) * R"09"^1
 647   local Number = (Integer * Fractal^(-1) * Exponent^(-1))/str2num
 648   local Constant = P"true" * g.Cc (true) + P"false" * g.Cc (false) + P"null" * g.Carg (1)
 649   local SimpleValue = Number + String + Constant
 650   local ArrayContent, ObjectContent
 651
 652   -- The functions parsearray and parseobject parse only a single value/pair
 653   -- at a time and store them directly to avoid hitting the LPeg limits.
 654   local function parsearray (str, pos, nullval, state)
 655     local obj, cont
 656     local npos
 657     local t, nt = {}, 0
 658     repeat
 659       obj, cont, npos = pegmatch (ArrayContent, str, pos, nullval, state)
 660       if not npos then break end
 661       pos = npos
 662       nt = nt + 1
 663       t[nt] = obj
 664     until cont == 'last'
 665     return pos, setmetatable (t, state.arraymeta)
 666   end
 667
 668   local function parseobject (str, pos, nullval, state)
 669     local obj, key, cont
 670     local npos
 671     local t = {}
 672     repeat
 673       key, obj, cont, npos = pegmatch (ObjectContent, str, pos, nullval, state)
 674       if not npos then break end
 675       pos = npos
 676       t[key] = obj
 677     until cont == 'last'
 678     return pos, setmetatable (t, state.objectmeta)
 679   end
 680
 681   local Array = P"[" * g.Cmt (g.Carg(1) * g.Carg(2), parsearray) * Space * (P"]" + Err "']' expected")
 682   local Object = P"{" * g.Cmt (g.Carg(1) * g.Carg(2), parseobject) * Space * (P"}" + Err "'}' expected")
 683   local Value = Space * (Array + Object + SimpleValue)
 684   local ExpectedValue = Value + Space * Err "value expected"
 685   ArrayContent = Value * Space * (P"," * g.Cc'cont' + g.Cc'last') * g.Cp()
 686   local Pair = g.Cg (Space * String * Space * (P":" + Err "colon expected") * ExpectedValue)
 687   ObjectContent = Pair * Space * (P"," * g.Cc'cont' + g.Cc'last') * g.Cp()
 688   local DecodeValue = ExpectedValue * g.Cp ()
 689
 690   function json.decode (str, pos, nullval, ...)
 691     local state = {}
 692     state.objectmeta, state.arraymeta = optionalmetatables(...)
 693     local obj, retpos = pegmatch (DecodeValue, str, pos, nullval, state)
 694     if state.msg then
 695       return nil, state.pos, state.msg
 696     else
 697       return obj, retpos
 698     end
 699   end
 700
 701   -- use this function only once:
 702   json.use_lpeg = function () return json end
 703
 704   json.using_lpeg = true
 705
 706   return json -- so you can get the module using json = require "dkjson".use_lpeg()
 707 end
 708
 709 if always_try_using_lpeg then
 710   pcall (json.use_lpeg)
 711 end
 712
 713 return json
 714