client/lualibs/dkjson.lua

   1 -- Module options:
   2 local always_use_lpeg = false
   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 - 5.4
   9
  10 Version 2.8
  11
  12
  13 For the documentation see the corresponding readme.txt or visit
  14 <http://dkolf.de/dkjson-lua/>.
  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) 2010-2024 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 =
  46       pairs, type, tostring, tonumber, getmetatable, setmetatable
  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 2.8" }
  56
  57 local jsonlpeg = {}
  58
  59 if register_global_module_table then
  60   if always_use_lpeg then
  61     _G[global_module_name] = jsonlpeg
  62   else
  63     _G[global_module_name] = json
  64   end
  65 end
  66
  67 local _ENV = nil -- blocking globals in Lua 5.2 and later
  68
  69 pcall (function()
  70   -- Enable access to blocked metatables.
  71   -- Don't worry, this module doesn't change anything in them.
  72   local debmeta = require "debug".getmetatable
  73   if debmeta then getmetatable = debmeta end
  74 end)
  75
  76 json.null = setmetatable ({}, {
  77   __tojson = function () return "null" end
  78 })
  79
  80 local function isarray (tbl)
  81   local max, n, arraylen = 0, 0, 0
  82   for k,v in pairs (tbl) do
  83     if k == 'n' and type(v) == 'number' then
  84       arraylen = v
  85       if v > max then
  86         max = v
  87       end
  88     else
  89       if type(k) ~= 'number' or k < 1 or floor(k) ~= k then
  90         return false
  91       end
  92       if k > max then
  93         max = k
  94       end
  95       n = n + 1
  96     end
  97   end
  98   if max > 10 and max > arraylen and max > n * 2 then
  99     return false -- don't create an array with too many holes
 100   end
 101   return true, max
 102 end
 103
 104 local escapecodes = {
 105   ["\""] = "\\\"", ["\\"] = "\\\\", ["\b"] = "\\b", ["\f"] = "\\f",
 106   ["\n"] = "\\n",  ["\r"] = "\\r",  ["\t"] = "\\t"
 107 }
 108
 109 local function escapeutf8 (uchar)
 110   local value = escapecodes[uchar]
 111   if value then
 112     return value
 113   end
 114   local a, b, c, d = strbyte (uchar, 1, 4)
 115   a, b, c, d = a or 0, b or 0, c or 0, d or 0
 116   if a <= 0x7f then
 117     value = a
 118   elseif 0xc0 <= a and a <= 0xdf and b >= 0x80 then
 119     value = (a - 0xc0) * 0x40 + b - 0x80
 120   elseif 0xe0 <= a and a <= 0xef and b >= 0x80 and c >= 0x80 then
 121     value = ((a - 0xe0) * 0x40 + b - 0x80) * 0x40 + c - 0x80
 122   elseif 0xf0 <= a and a <= 0xf7 and b >= 0x80 and c >= 0x80 and d >= 0x80 then
 123     value = (((a - 0xf0) * 0x40 + b - 0x80) * 0x40 + c - 0x80) * 0x40 + d - 0x80
 124   else
 125     return ""
 126   end
 127   if value <= 0xffff then
 128     return strformat ("\\u%.4x", value)
 129   elseif value <= 0x10ffff then
 130     -- encode as UTF-16 surrogate pair
 131     value = value - 0x10000
 132     local highsur, lowsur = 0xD800 + floor (value/0x400), 0xDC00 + (value % 0x400)
 133     return strformat ("\\u%.4x\\u%.4x", highsur, lowsur)
 134   else
 135     return ""
 136   end
 137 end
 138
 139 local function fsub (str, pattern, repl)
 140   -- gsub always builds a new string in a buffer, even when no match
 141   -- exists. First using find should be more efficient when most strings
 142   -- don't contain the pattern.
 143   if strfind (str, pattern) then
 144     return gsub (str, pattern, repl)
 145   else
 146     return str
 147   end
 148 end
 149
 150 local function quotestring (value)
 151   -- based on the regexp "escapable" in https://github.com/douglascrockford/JSON-js
 152   value = fsub (value, "[%z\1-\31\"\\\127]", escapeutf8)
 153   if strfind (value, "[\194\216\220\225\226\239]") then
 154     value = fsub (value, "\194[\128-\159\173]", escapeutf8)
 155     value = fsub (value, "\216[\128-\132]", escapeutf8)
 156     value = fsub (value, "\220\143", escapeutf8)
 157     value = fsub (value, "\225\158[\180\181]", escapeutf8)
 158     value = fsub (value, "\226\128[\140-\143\168-\175]", escapeutf8)
 159     value = fsub (value, "\226\129[\160-\175]", escapeutf8)
 160     value = fsub (value, "\239\187\191", escapeutf8)
 161     value = fsub (value, "\239\191[\176-\191]", escapeutf8)
 162   end
 163   return "\"" .. value .. "\""
 164 end
 165 json.quotestring = quotestring
 166
 167 local function replace(str, o, n)
 168   local i, j = strfind (str, o, 1, true)
 169   if i then
 170     return strsub(str, 1, i-1) .. n .. strsub(str, j+1, -1)
 171   else
 172     return str
 173   end
 174 end
 175
 176 -- locale independent num2str and str2num functions
 177 local decpoint, numfilter
 178
 179 local function updatedecpoint ()
 180   decpoint = strmatch(tostring(0.5), "([^05+])")
 181   -- build a filter that can be used to remove group separators
 182   numfilter = "[^0-9%-%+eE" .. gsub(decpoint, "[%^%$%(%)%%%.%[%]%*%+%-%?]", "%%%0") .. "]+"
 183 end
 184
 185 updatedecpoint()
 186
 187 local function num2str (num)
 188   return replace(fsub(tostring(num), numfilter, ""), decpoint, ".")
 189 end
 190
 191 local function str2num (str)
 192   local num = tonumber(replace(str, ".", decpoint))
 193   if not num then
 194     updatedecpoint()
 195     num = tonumber(replace(str, ".", decpoint))
 196   end
 197   return num
 198 end
 199
 200 local function addnewline2 (level, buffer, buflen)
 201   buffer[buflen+1] = "\n"
 202   buffer[buflen+2] = strrep ("  ", level)
 203   buflen = buflen + 2
 204   return buflen
 205 end
 206
 207 function json.addnewline (state)
 208   if state.indent then
 209     state.bufferlen = addnewline2 (state.level or 0,
 210                            state.buffer, state.bufferlen or #(state.buffer))
 211   end
 212 end
 213
 214 local encode2 -- forward declaration
 215
 216 local function addpair (key, value, prev, indent, level, buffer, buflen, tables, globalorder, state)
 217   local kt = type (key)
 218   if kt ~= 'string' and kt ~= 'number' then
 219     return nil, "type '" .. kt .. "' is not supported as a key by JSON."
 220   end
 221   if prev then
 222     buflen = buflen + 1
 223     buffer[buflen] = ","
 224   end
 225   if indent then
 226     buflen = addnewline2 (level, buffer, buflen)
 227   end
 228   -- When Lua is compiled with LUA_NOCVTN2S this will fail when
 229   -- numbers are mixed into the keys of the table. JSON keys are always
 230   -- strings, so this would be an implicit conversion too and the failure
 231   -- is intentional.
 232   buffer[buflen+1] = quotestring (key)
 233   buffer[buflen+2] = ":"
 234   return encode2 (value, indent, level, buffer, buflen + 2, tables, globalorder, state)
 235 end
 236
 237 local function appendcustom(res, buffer, state)
 238   local buflen = state.bufferlen
 239   if type (res) == 'string' then
 240     buflen = buflen + 1
 241     buffer[buflen] = res
 242   end
 243   return buflen
 244 end
 245
 246 local function exception(reason, value, state, buffer, buflen, defaultmessage)
 247   defaultmessage = defaultmessage or reason
 248   local handler = state.exception
 249   if not handler then
 250     return nil, defaultmessage
 251   else
 252     state.bufferlen = buflen
 253     local ret, msg = handler (reason, value, state, defaultmessage)
 254     if not ret then return nil, msg or defaultmessage end
 255     return appendcustom(ret, buffer, state)
 256   end
 257 end
 258
 259 function json.encodeexception(reason, value, state, defaultmessage)
 260   return quotestring("<" .. defaultmessage .. ">")
 261 end
 262
 263 encode2 = function (value, indent, level, buffer, buflen, tables, globalorder, state)
 264   local valtype = type (value)
 265   local valmeta = getmetatable (value)
 266   valmeta = type (valmeta) == 'table' and valmeta -- only tables
 267   local valtojson = valmeta and valmeta.__tojson
 268   if valtojson then
 269     if tables[value] then
 270       return exception('reference cycle', value, state, buffer, buflen)
 271     end
 272     tables[value] = true
 273     state.bufferlen = buflen
 274     local ret, msg = valtojson (value, state)
 275     if not ret then return exception('custom encoder failed', value, state, buffer, buflen, msg) end
 276     tables[value] = nil
 277     buflen = appendcustom(ret, buffer, state)
 278   elseif value == nil then
 279     buflen = buflen + 1
 280     buffer[buflen] = "null"
 281   elseif valtype == 'number' then
 282     local s
 283     if value ~= value or value >= huge or -value >= huge then
 284       -- This is the behaviour of the original JSON implementation.
 285       s = "null"
 286     else
 287       s = num2str (value)
 288     end
 289     buflen = buflen + 1
 290     buffer[buflen] = s
 291   elseif valtype == 'boolean' then
 292     buflen = buflen + 1
 293     buffer[buflen] = value and "true" or "false"
 294   elseif valtype == 'string' then
 295     buflen = buflen + 1
 296     buffer[buflen] = quotestring (value)
 297   elseif valtype == 'table' then
 298     if tables[value] then
 299       return exception('reference cycle', value, state, buffer, buflen)
 300     end
 301     tables[value] = true
 302     level = level + 1
 303     local isa, n = isarray (value)
 304     if n == 0 and valmeta and valmeta.__jsontype == 'object' then
 305       isa = false
 306     end
 307     local msg
 308     if isa then -- JSON array
 309       buflen = buflen + 1
 310       buffer[buflen] = "["
 311       for i = 1, n do
 312         buflen, msg = encode2 (value[i], indent, level, buffer, buflen, tables, globalorder, state)
 313         if not buflen then return nil, msg end
 314         if i < n then
 315           buflen = buflen + 1
 316           buffer[buflen] = ","
 317         end
 318       end
 319       buflen = buflen + 1
 320       buffer[buflen] = "]"
 321     else -- JSON object
 322       local prev = false
 323       buflen = buflen + 1
 324       buffer[buflen] = "{"
 325       local order = valmeta and valmeta.__jsonorder or globalorder
 326       if order then
 327         local used = {}
 328         n = #order
 329         for i = 1, n do
 330           local k = order[i]
 331           local v = value[k]
 332           if v ~= nil then
 333             used[k] = true
 334             buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder, state)
 335             if not buflen then return nil, msg end
 336             prev = true -- add a seperator before the next element
 337           end
 338         end
 339         for k,v in pairs (value) do
 340           if not used[k] then
 341             buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder, state)
 342             if not buflen then return nil, msg end
 343             prev = true -- add a seperator before the next element
 344           end
 345         end
 346       else -- unordered
 347         for k,v in pairs (value) do
 348           buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder, state)
 349           if not buflen then return nil, msg end
 350           prev = true -- add a seperator before the next element
 351         end
 352       end
 353       if indent then
 354         buflen = addnewline2 (level - 1, buffer, buflen)
 355       end
 356       buflen = buflen + 1
 357       buffer[buflen] = "}"
 358     end
 359     tables[value] = nil
 360   else
 361     return exception ('unsupported type', value, state, buffer, buflen,
 362       "type '" .. valtype .. "' is not supported by JSON.")
 363   end
 364   return buflen
 365 end
 366
 367 function json.encode (value, state)
 368   state = state or {}
 369   local oldbuffer = state.buffer
 370   local buffer = oldbuffer or {}
 371   state.buffer = buffer
 372   updatedecpoint()
 373   local ret, msg = encode2 (value, state.indent, state.level or 0,
 374                    buffer, state.bufferlen or 0, state.tables or {}, state.keyorder, state)
 375   if not ret then
 376     error (msg, 2)
 377   elseif oldbuffer == buffer then
 378     state.bufferlen = ret
 379     return true
 380   else
 381     state.bufferlen = nil
 382     state.buffer = nil
 383     return concat (buffer)
 384   end
 385 end
 386
 387 local function loc (str, where)
 388   local line, pos, linepos = 1, 1, 0
 389   while true do
 390     pos = strfind (str, "\n", pos, true)
 391     if pos and pos < where then
 392       line = line + 1
 393       linepos = pos
 394       pos = pos + 1
 395     else
 396       break
 397     end
 398   end
 399   return strformat ("line %d, column %d", line, where - linepos)
 400 end
 401
 402 local function unterminated (str, what, where)
 403   return nil, strlen (str) + 1, "unterminated " .. what .. " at " .. loc (str, where)
 404 end
 405
 406 local function scanwhite (str, pos)
 407   while true do
 408     pos = strfind (str, "%S", pos)
 409     if not pos then return nil end
 410     local sub2 = strsub (str, pos, pos + 1)
 411     if sub2 == "\239\187" and strsub (str, pos + 2, pos + 2) == "\191" then
 412       -- UTF-8 Byte Order Mark
 413       pos = pos + 3
 414     elseif sub2 == "//" then
 415       pos = strfind (str, "[\n\r]", pos + 2)
 416       if not pos then return nil end
 417     elseif sub2 == "/*" then
 418       pos = strfind (str, "*/", pos + 2)
 419       if not pos then return nil end
 420       pos = pos + 2
 421     else
 422       return pos
 423     end
 424   end
 425 end
 426
 427 local escapechars = {
 428   ["\""] = "\"", ["\\"] = "\\", ["/"] = "/", ["b"] = "\b", ["f"] = "\f",
 429   ["n"] = "\n", ["r"] = "\r", ["t"] = "\t"
 430 }
 431
 432 local function unichar (value)
 433   if value < 0 then
 434     return nil
 435   elseif value <= 0x007f then
 436     return strchar (value)
 437   elseif value <= 0x07ff then
 438     return strchar (0xc0 + floor(value/0x40),
 439                     0x80 + (floor(value) % 0x40))
 440   elseif value <= 0xffff then
 441     return strchar (0xe0 + floor(value/0x1000),
 442                     0x80 + (floor(value/0x40) % 0x40),
 443                     0x80 + (floor(value) % 0x40))
 444   elseif value <= 0x10ffff then
 445     return strchar (0xf0 + floor(value/0x40000),
 446                     0x80 + (floor(value/0x1000) % 0x40),
 447                     0x80 + (floor(value/0x40) % 0x40),
 448                     0x80 + (floor(value) % 0x40))
 449   else
 450     return nil
 451   end
 452 end
 453
 454 local function scanstring (str, pos)
 455   local lastpos = pos + 1
 456   local buffer, n = {}, 0
 457   while true do
 458     local nextpos = strfind (str, "[\"\\]", lastpos)
 459     if not nextpos then
 460       return unterminated (str, "string", pos)
 461     end
 462     if nextpos > lastpos then
 463       n = n + 1
 464       buffer[n] = strsub (str, lastpos, nextpos - 1)
 465     end
 466     if strsub (str, nextpos, nextpos) == "\"" then
 467       lastpos = nextpos + 1
 468       break
 469     else
 470       local escchar = strsub (str, nextpos + 1, nextpos + 1)
 471       local value
 472       if escchar == "u" then
 473         value = tonumber (strsub (str, nextpos + 2, nextpos + 5), 16)
 474         if value then
 475           local value2
 476           if 0xD800 <= value and value <= 0xDBff then
 477             -- we have the high surrogate of UTF-16. Check if there is a
 478             -- low surrogate escaped nearby to combine them.
 479             if strsub (str, nextpos + 6, nextpos + 7) == "\\u" then
 480               value2 = tonumber (strsub (str, nextpos + 8, nextpos + 11), 16)
 481               if value2 and 0xDC00 <= value2 and value2 <= 0xDFFF then
 482                 value = (value - 0xD800)  * 0x400 + (value2 - 0xDC00) + 0x10000
 483               else
 484                 value2 = nil -- in case it was out of range for a low surrogate
 485               end
 486             end
 487           end
 488           value = value and unichar (value)
 489           if value then
 490             if value2 then
 491               lastpos = nextpos + 12
 492             else
 493               lastpos = nextpos + 6
 494             end
 495           end
 496         end
 497       end
 498       if not value then
 499         value = escapechars[escchar] or escchar
 500         lastpos = nextpos + 2
 501       end
 502       n = n + 1
 503       buffer[n] = value
 504     end
 505   end
 506   if n == 1 then
 507     return buffer[1], lastpos
 508   elseif n > 1 then
 509     return concat (buffer), lastpos
 510   else
 511     return "", lastpos
 512   end
 513 end
 514
 515 local scanvalue -- forward declaration
 516
 517 local function scantable (what, closechar, str, startpos, nullval, objectmeta, arraymeta)
 518   local tbl, n = {}, 0
 519   local pos = startpos + 1
 520   if what == 'object' then
 521     setmetatable (tbl, objectmeta)
 522   else
 523     setmetatable (tbl, arraymeta)
 524   end
 525   while true do
 526     pos = scanwhite (str, pos)
 527     if not pos then return unterminated (str, what, startpos) end
 528     local char = strsub (str, pos, pos)
 529     if char == closechar then
 530       return tbl, pos + 1
 531     end
 532     local val1, err
 533     val1, pos, err = scanvalue (str, pos, nullval, objectmeta, arraymeta)
 534     if err then return nil, pos, err end
 535     pos = scanwhite (str, pos)
 536     if not pos then return unterminated (str, what, startpos) end
 537     char = strsub (str, pos, pos)
 538     if char == ":" then
 539       if val1 == nil then
 540         return nil, pos, "cannot use nil as table index (at " .. loc (str, pos) .. ")"
 541       end
 542       pos = scanwhite (str, pos + 1)
 543       if not pos then return unterminated (str, what, startpos) end
 544       local val2
 545       val2, pos, err = scanvalue (str, pos, nullval, objectmeta, arraymeta)
 546       if err then return nil, pos, err end
 547       tbl[val1] = val2
 548       pos = scanwhite (str, pos)
 549       if not pos then return unterminated (str, what, startpos) end
 550       char = strsub (str, pos, pos)
 551     else
 552       n = n + 1
 553       tbl[n] = val1
 554     end
 555     if char == "," then
 556       pos = pos + 1
 557     end
 558   end
 559 end
 560
 561 scanvalue = function (str, pos, nullval, objectmeta, arraymeta)
 562   pos = pos or 1
 563   pos = scanwhite (str, pos)
 564   if not pos then
 565     return nil, strlen (str) + 1, "no valid JSON value (reached the end)"
 566   end
 567   local char = strsub (str, pos, pos)
 568   if char == "{" then
 569     return scantable ('object', "}", str, pos, nullval, objectmeta, arraymeta)
 570   elseif char == "[" then
 571     return scantable ('array', "]", str, pos, nullval, objectmeta, arraymeta)
 572   elseif char == "\"" then
 573     return scanstring (str, pos)
 574   else
 575     local pstart, pend = strfind (str, "^%-?[%d%.]+[eE]?[%+%-]?%d*", pos)
 576     if pstart then
 577       local number = str2num (strsub (str, pstart, pend))
 578       if number then
 579         return number, pend + 1
 580       end
 581     end
 582     pstart, pend = strfind (str, "^%a%w*", pos)
 583     if pstart then
 584       local name = strsub (str, pstart, pend)
 585       if name == "true" then
 586         return true, pend + 1
 587       elseif name == "false" then
 588         return false, pend + 1
 589       elseif name == "null" then
 590         return nullval, pend + 1
 591       end
 592     end
 593     return nil, pos, "no valid JSON value at " .. loc (str, pos)
 594   end
 595 end
 596
 597 local function optionalmetatables(...)
 598   if select("#", ...) > 0 then
 599     return ...
 600   else
 601     return {__jsontype = 'object'}, {__jsontype = 'array'}
 602   end
 603 end
 604
 605 function json.decode (str, pos, nullval, ...)
 606   local objectmeta, arraymeta = optionalmetatables(...)
 607   return scanvalue (str, pos, nullval, objectmeta, arraymeta)
 608 end
 609
 610 function json.use_lpeg ()
 611   local g = require ("lpeg")
 612
 613   if type(g.version) == 'function' and g.version() == "0.11" then
 614     error "due to a bug in LPeg 0.11, it cannot be used for JSON matching"
 615   end
 616
 617   local pegmatch = g.match
 618   local P, S, R = g.P, g.S, g.R
 619
 620   local function ErrorCall (str, pos, msg, state)
 621     if not state.msg then
 622       state.msg = msg .. " at " .. loc (str, pos)
 623       state.pos = pos
 624     end
 625     return false
 626   end
 627
 628   local function Err (msg)
 629     return g.Cmt (g.Cc (msg) * g.Carg (2), ErrorCall)
 630   end
 631
 632   local function ErrorUnterminatedCall (str, pos, what, state)
 633     return ErrorCall (str, pos - 1, "unterminated " .. what, state)
 634   end
 635
 636   local SingleLineComment = P"//" * (1 - S"\n\r")^0
 637   local MultiLineComment = P"/*" * (1 - P"*/")^0 * P"*/"
 638   local Space = (S" \n\r\t" + P"\239\187\191" + SingleLineComment + MultiLineComment)^0
 639
 640   local function ErrUnterminated (what)
 641     return g.Cmt (g.Cc (what) * g.Carg (2), ErrorUnterminatedCall)
 642   end
 643
 644   local PlainChar = 1 - S"\"\\\n\r"
 645   local EscapeSequence = (P"\\" * g.C (S"\"\\/bfnrt" + Err "unsupported escape sequence")) / escapechars
 646   local HexDigit = R("09", "af", "AF")
 647   local function UTF16Surrogate (match, pos, high, low)
 648     high, low = tonumber (high, 16), tonumber (low, 16)
 649     if 0xD800 <= high and high <= 0xDBff and 0xDC00 <= low and low <= 0xDFFF then
 650       return true, unichar ((high - 0xD800)  * 0x400 + (low - 0xDC00) + 0x10000)
 651     else
 652       return false
 653     end
 654   end
 655   local function UTF16BMP (hex)
 656     return unichar (tonumber (hex, 16))
 657   end
 658   local U16Sequence = (P"\\u" * g.C (HexDigit * HexDigit * HexDigit * HexDigit))
 659   local UnicodeEscape = g.Cmt (U16Sequence * U16Sequence, UTF16Surrogate) + U16Sequence/UTF16BMP
 660   local Char = UnicodeEscape + EscapeSequence + PlainChar
 661   local String = P"\"" * (g.Cs (Char ^ 0) * P"\"" + ErrUnterminated "string")
 662   local Integer = P"-"^(-1) * (P"0" + (R"19" * R"09"^0))
 663   local Fractal = P"." * R"09"^0
 664   local Exponent = (S"eE") * (S"+-")^(-1) * R"09"^1
 665   local Number = (Integer * Fractal^(-1) * Exponent^(-1))/str2num
 666   local Constant = P"true" * g.Cc (true) + P"false" * g.Cc (false) + P"null" * g.Carg (1)
 667   local SimpleValue = Number + String + Constant
 668   local ArrayContent, ObjectContent
 669
 670   -- The functions parsearray and parseobject parse only a single value/pair
 671   -- at a time and store them directly to avoid hitting the LPeg limits.
 672   local function parsearray (str, pos, nullval, state)
 673     local obj, cont
 674     local start = pos
 675     local npos
 676     local t, nt = {}, 0
 677     repeat
 678       obj, cont, npos = pegmatch (ArrayContent, str, pos, nullval, state)
 679       if cont == 'end' then
 680         return ErrorUnterminatedCall (str, start, "array", state)
 681       end
 682       pos = npos
 683       if cont == 'cont' or cont == 'last' then
 684         nt = nt + 1
 685         t[nt] = obj
 686       end
 687     until cont ~= 'cont'
 688     return pos, setmetatable (t, state.arraymeta)
 689   end
 690
 691   local function parseobject (str, pos, nullval, state)
 692     local obj, key, cont
 693     local start = pos
 694     local npos
 695     local t = {}
 696     repeat
 697       key, obj, cont, npos = pegmatch (ObjectContent, str, pos, nullval, state)
 698       if cont == 'end' then
 699         return ErrorUnterminatedCall (str, start, "object", state)
 700       end
 701       pos = npos
 702       if cont == 'cont' or cont == 'last' then
 703         t[key] = obj
 704       end
 705     until cont ~= 'cont'
 706     return pos, setmetatable (t, state.objectmeta)
 707   end
 708
 709   local Array = P"[" * g.Cmt (g.Carg(1) * g.Carg(2), parsearray)
 710   local Object = P"{" * g.Cmt (g.Carg(1) * g.Carg(2), parseobject)
 711   local Value = Space * (Array + Object + SimpleValue)
 712   local ExpectedValue = Value + Space * Err "value expected"
 713   local ExpectedKey = String + Err "key expected"
 714   local End = P(-1) * g.Cc'end'
 715   local ErrInvalid = Err "invalid JSON"
 716   ArrayContent = (Value * Space * (P"," * g.Cc'cont' + P"]" * g.Cc'last'+ End + ErrInvalid)  + g.Cc(nil) * (P"]" * g.Cc'empty' + End  + ErrInvalid)) * g.Cp()
 717   local Pair = g.Cg (Space * ExpectedKey * Space * (P":" + Err "colon expected") * ExpectedValue)
 718   ObjectContent = (g.Cc(nil) * g.Cc(nil) * P"}" * g.Cc'empty' + End + (Pair * Space * (P"," * g.Cc'cont' + P"}" * g.Cc'last' + End + ErrInvalid) + ErrInvalid)) * g.Cp()
 719   local DecodeValue = ExpectedValue * g.Cp ()
 720
 721   jsonlpeg.version = json.version
 722   jsonlpeg.encode = json.encode
 723   jsonlpeg.null = json.null
 724   jsonlpeg.quotestring = json.quotestring
 725   jsonlpeg.addnewline = json.addnewline
 726   jsonlpeg.encodeexception = json.encodeexception
 727   jsonlpeg.using_lpeg = true
 728
 729   function jsonlpeg.decode (str, pos, nullval, ...)
 730     local state = {}
 731     state.objectmeta, state.arraymeta = optionalmetatables(...)
 732     local obj, retpos = pegmatch (DecodeValue, str, pos, nullval, state)
 733     if state.msg then
 734       return nil, state.pos, state.msg
 735     else
 736       return obj, retpos
 737     end
 738   end
 739
 740   -- cache result of this function:
 741   json.use_lpeg = function () return jsonlpeg end
 742   jsonlpeg.use_lpeg = json.use_lpeg
 743
 744   return jsonlpeg
 745 end
 746
 747 if always_use_lpeg then
 748   return json.use_lpeg()
 749 end
 750
 751 return json
 752