lua:add dkjson

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

share/Makefile.am

@@ -149,6 +149,7 @@ nobase_vlclib_DATA = \
 	lua/meta/art/01_googleimage.luac \
 	lua/meta/fetcher/tvrage.luac \
 	lua/meta/reader/filename.luac \
+	lua/modules/dkjson.luac \
 	lua/modules/sandbox.luac \
 	lua/modules/simplexml.luac \
 	lua/playlist/anevia_streams.luac \
@@ -215,6 +216,7 @@ EXTRA_DIST += \
 	lua/meta/fetcher/tvrage.lua \
 	lua/meta/reader/README.txt \
 	lua/meta/reader/filename.lua \
+	lua/modules/dkjson.lua \
 	lua/modules/sandbox.lua \
 	lua/modules/simplexml.lua \
 	lua/playlist/README.txt \

share/lua/modules/dkjson.lua

+    --[==[
+
+David Kolf's JSON module for Lua 5.1/5.2
+========================================
+
+*Version 2.1*
+
+This module writes no global values, not even the module table.
+Import it using
+
+    json = require ("dkjson")
+
+Exported functions and values:
+
+`json.encode (object [, state])`
+--------------------------------
+
+Create a string representing the object. `Object` can be a table,
+a string, a number, a boolean, `nil`, `json.null` or any object with
+a function `__tojson` in its metatable. A table can only use strings
+and numbers as keys and its values have to be valid objects as
+well. It raises an error for any invalid data types or reference
+cycles.
+
+`state` is an optional table with the following fields:
+
+  - `indent`  
+    When `indent` (a boolean) is set, the created string will contain
+    newlines and indentations. Otherwise it will be one long line.
+  - `keyorder`  
+    `keyorder` is an array to specify the ordering of keys in the
+    encoded output. If an object has keys which are not in this array
+    they are written after the sorted keys.
+  - `level`  
+    This is the initial level of indentation used when `indent` is
+    set. For each level two spaces are added. When absent it is set
+    to 0.
+  - `buffer`  
+    `buffer` is an array to store the strings for the result so they
+    can be concatenated at once. When it isn't given, the encode
+    function will create it temporary and will return the
+    concatenated result.
+  - `bufferlen`  
+    When `bufferlen` is set, it has to be the index of the last
+    element of `buffer`.
+  - `tables`  
+    `tables` is a set to detect reference cycles. It is created
+    temporary when absent. Every table that is currently processed
+    is used as key, the value is `true`.
+
+When `state.buffer` was set, the return value will be `true` on
+success. Without `state.buffer` the return value will be a string.
+
+`json.decode (string [, position [, null]])`
+--------------------------------------------
+
+Decode `string` starting at `position` or at 1 if `position` was
+omitted.
+
+`null` is an optional value to be returned for null values. The
+default is `nil`, but you could set it to `json.null` or any other
+value.
+
+The return values are the object or `nil`, the position of the next
+character that doesn't belong to the object, and in case of errors
+an error message.
+
+Two metatables are created. Every array or object that is decoded gets
+a metatable with the `__jsontype` field set to either `array` or
+`object`. If you want to provide your own metatables use the syntax
+
+    json.decode (string, position, null, objectmeta, arraymeta)
+
+`<metatable>.__jsonorder`
+-------------------------
+
+`__jsonorder` can overwrite the `keyorder` for a specific table.
+
+`<metatable>.__jsontype`
+------------------------
+
+`__jsontype` can be either `"array"` or `"object"`. This is mainly useful
+for tables that can be empty. (The default for empty tables is
+`"array"`).
+
+`<metatable>.__tojson (self, state)`
+------------------------------------
+
+You can provide your own `__tojson` function in a metatable. In this
+function you can either add directly to the buffer and return true,
+or you can return a string. On errors nil and a message should be
+returned.
+
+`json.null`
+-----------
+
+You can use this value for setting explicit `null` values.
+
+`json.version`
+--------------
+
+Set to `"dkjson 2.1"`.
+
+`json.quotestring (string)`
+---------------------------
+
+Quote a UTF-8 string and escape critical characters using JSON
+escape sequences. This function is only necessary when you build
+your own `__tojson` functions.
+
+`json.addnewline (state)`
+-------------------------
+
+When `state.indent` is set, add a newline to `state.buffer` and spaces
+according to `state.level`.
+
+LPeg support
+------------
+
+When the local configuration variable
+`always_try_using_lpeg` is set, this module tries to load LPeg to
+replace the functions `quotestring` and `decode`. The speed increase
+is significant. You can get the LPeg module at
+  <http://www.inf.puc-rio.br/~roberto/lpeg/>.
+When LPeg couldn't be loaded, the pure Lua functions stay active.
+
+In case you don't want this module to require LPeg on its own,
+disable this option:
+
+    --]==]
+    local always_try_using_lpeg = true
+    --[==[
+
+In this case you can later load LPeg support using
+
+### `json.use_lpeg ()`
+
+Require the LPeg module and replace the functions `quotestring` and
+and `decode` with functions that use LPeg patterns.
+This function returns the module table, so you can load the module
+using:
+
+    json = require "dkjson".use_lpeg()
+
+Alternatively you can use `pcall` so the JSON module still works when
+LPeg isn't found.
+
+    json = require "dkjson"
+    pcall (json.use_lpeg)
+
+### `json.using_lpeg`
+
+This variable is set to `true` when LPeg was loaded successfully.
+
+You can contact the author by sending an e-mail to 'kolf' at the
+e-mail provider 'gmx.de'.
+
+---------------------------------------------------------------------
+
+*Copyright (C) 2010, 2011 David Heiko Kolf*
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+
+<!-- This documentation can be parsed using Markdown to generate HTML.
+     The source code is enclosed in a HTML comment so it won't be displayed
+     by browsers, but it should be removed from the final HTML file as
+     it isn't a valid HTML comment (and wastes space).
+  -->
+
+  <!--]==]
+
+-- global dependencies:
+local pairs, type, tostring, tonumber, getmetatable, setmetatable, rawset =
+      pairs, type, tostring, tonumber, getmetatable, setmetatable, rawset
+local error, require, pcall = error, require, pcall 
+local floor, huge = math.floor, math.huge
+local strrep, gsub, strsub, strbyte, strchar, strfind, strlen, strformat =
+      string.rep, string.gsub, string.sub, string.byte, string.char,
+      string.find, string.len, string.format
+local concat = table.concat
+
+if _VERSION == 'Lua 5.1' then
+  local function noglobals (s,k,v) error ("global access: " .. k, 2) end
+  setfenv (1, setmetatable ({}, { __index = noglobals, __newindex = noglobals }))
+end
+local _ENV = nil -- blocking globals in Lua 5.2
+
+local json = { version = "dkjson 2.1" }
+
+pcall (function()
+  -- Enable access to blocked metatables.
+  -- Don't worry, this module doesn't change anything in them.
+  local debmeta = require "debug".getmetatable
+  if debmeta then getmetatable = debmeta end
+end)
+
+json.null = setmetatable ({}, {
+  __tojson = function () return "null" end
+})
+
+local function isarray (tbl)
+  local max, n, arraylen = 0, 0, 0
+  for k,v in pairs (tbl) do
+    if k == 'n' and type(v) == 'number' then
+      arraylen = v
+      if v > max then
+        max = v
+      end
+    else
+      if type(k) ~= 'number' or k < 1 or floor(k) ~= k then
+        return false
+      end
+      if k > max then
+        max = k
+      end
+      n = n + 1
+    end
+  end
+  if max > 10 and max > arraylen and max > n * 2 then
+    return false -- don't create an array with too many holes
+  end
+  return true, max
+end
+
+local escapecodes = {
+  ["\""] = "\\\"", ["\\"] = "\\\\", ["\b"] = "\\b", ["\f"] = "\\f",
+  ["\n"] = "\\n",  ["\r"] = "\\r",  ["\t"] = "\\t"
+}
+
+local function escapeutf8 (uchar)
+  local value = escapecodes[uchar]
+  if value then
+    return value
+  end
+  local a, b, c, d = strbyte (uchar, 1, 4)
+  a, b, c, d = a or 0, b or 0, c or 0, d or 0
+  if a <= 0x7f then
+    value = a
+  elseif 0xc0 <= a and a <= 0xdf and b >= 0x80 then
+    value = (a - 0xc0) * 0x40 + b - 0x80
+  elseif 0xe0 <= a and a <= 0xef and b >= 0x80 and c >= 0x80 then
+    value = ((a - 0xe0) * 0x40 + b - 0x80) * 0x40 + c - 0x80
+  elseif 0xf0 <= a and a <= 0xf7 and b >= 0x80 and c >= 0x80 and d >= 0x80 then
+    value = (((a - 0xf0) * 0x40 + b - 0x80) * 0x40 + c - 0x80) * 0x40 + d - 0x80
+  else
+    return ""
+  end
+  if value <= 0xffff then
+    return strformat ("\\u%.4x", value)
+  elseif value <= 0x10ffff then
+    -- encode as UTF-16 surrogate pair
+    value = value - 0x10000
+    local highsur, lowsur = 0xD800 + floor (value/0x400), 0xDC00 + (value % 0x400)
+    return strformat ("\\u%.4x\\u%.4x", highsur, lowsur)
+  else
+    return ""
+  end
+end
+
+local function fsub (str, pattern, repl)
+  -- gsub always builds a new string in a buffer, even when no match
+  -- exists. First using find should be more efficient when most strings
+  -- don't contain the pattern.
+  if strfind (str, pattern) then
+    return gsub (str, pattern, repl)
+  else
+    return str
+  end
+end
+
+local function quotestring (value)
+  -- based on the regexp "escapable" in https://github.com/douglascrockford/JSON-js
+  value = fsub (value, "[%z\1-\31\"\\\127]", escapeutf8)
+  if strfind (value, "[\194\216\220\225\226\239]") then
+    value = fsub (value, "\194[\128-\159\173]", escapeutf8)
+    value = fsub (value, "\216[\128-\132]", escapeutf8)
+    value = fsub (value, "\220\143", escapeutf8)
+    value = fsub (value, "\225\158[\180\181]", escapeutf8)
+    value = fsub (value, "\226\128[\140-\143\168\175]", escapeutf8)
+    value = fsub (value, "\226\129[\160-\175]", escapeutf8)
+    value = fsub (value, "\239\187\191", escapeutf8)
+    value = fsub (value, "\239\191[\176\191]", escapeutf8)
+  end
+  return "\"" .. value .. "\""
+end
+json.quotestring = quotestring
+
+local function addnewline2 (level, buffer, buflen)
+  buffer[buflen+1] = "\n"
+  buffer[buflen+2] = strrep ("  ", level)
+  buflen = buflen + 2
+  return buflen
+end
+
+function json.addnewline (state)
+  if state.indent then
+    state.bufferlen = addnewline2 (state.level or 0,
+                           state.buffer, state.bufferlen or #(state.buffer))
+  end
+end
+
+local encode2 -- forward declaration
+
+local function addpair (key, value, prev, indent, level, buffer, buflen, tables, globalorder)
+  local kt = type (key)
+  if kt ~= 'string' and kt ~= 'number' then
+    return nil, "type '" .. kt .. "' is not supported as a key by JSON."
+  end
+  if prev then
+    buflen = buflen + 1
+    buffer[buflen] = ","
+  end
+  if indent then
+    buflen = addnewline2 (level, buffer, buflen)
+  end
+  buffer[buflen+1] = quotestring (key)
+  buffer[buflen+2] = ":"
+  return encode2 (value, indent, level, buffer, buflen + 2, tables, globalorder)
+end
+
+encode2 = function (value, indent, level, buffer, buflen, tables, globalorder)
+  local valtype = type (value)
+  local valmeta = getmetatable (value)
+  valmeta = type (valmeta) == 'table' and valmeta -- only tables
+  local valtojson = valmeta and valmeta.__tojson
+  if valtojson then
+    if tables[value] then
+      return nil, "reference cycle"
+    end
+    tables[value] = true
+    local state = {
+        indent = indent, level = level, buffer = buffer,
+        bufferlen = buflen, tables = tables, keyorder = globalorder
+    }
+    local ret, msg = valtojson (value, state)
+    if not ret then return nil, msg end
+    tables[value] = nil
+    buflen = state.bufferlen
+    if type (ret) == 'string' then
+      buflen = buflen + 1
+      buffer[buflen] = ret
+    end
+  elseif value == nil then
+    buflen = buflen + 1
+    buffer[buflen] = "null"
+  elseif valtype == 'number' then
+    local s
+    if value ~= value or value >= huge or -value >= huge then
+      -- This is the behaviour of the original JSON implementation.
+      s = "null"
+    else
+      s = tostring (value)
+    end
+    buflen = buflen + 1
+    buffer[buflen] = s
+  elseif valtype == 'boolean' then
+    buflen = buflen + 1
+    buffer[buflen] = value and "true" or "false"
+  elseif valtype == 'string' then
+    buflen = buflen + 1
+    buffer[buflen] = quotestring (value)
+  elseif valtype == 'table' then
+    if tables[value] then
+      return nil, "reference cycle"
+    end
+    tables[value] = true
+    level = level + 1
+    local metatype = valmeta and valmeta.__jsontype
+    local isa, n
+    if metatype == 'array' then
+      isa = true
+      n = value.n or #value
+    elseif metatype == 'object' then
+      isa = false
+    else
+      isa, n = isarray (value)
+    end
+    local msg
+    if isa then -- JSON array
+      buflen = buflen + 1
+      buffer[buflen] = "["
+      for i = 1, n do
+        buflen, msg = encode2 (value[i], indent, level, buffer, buflen, tables, globalorder)
+        if not buflen then return nil, msg end
+        if i < n then
+          buflen = buflen + 1
+          buffer[buflen] = ","
+        end
+      end
+      buflen = buflen + 1
+      buffer[buflen] = "]"
+    else -- JSON object
+      local prev = false
+      buflen = buflen + 1
+      buffer[buflen] = "{"
+      local order = valmeta and valmeta.__jsonorder or globalorder
+      if order then
+        local used = {}
+        n = #order
+        for i = 1, n do
+          local k = order[i]
+          local v = value[k]
+          if v then
+            used[k] = true
+            buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder)
+            prev = true -- add a seperator before the next element
+          end
+        end
+        for k,v in pairs (value) do
+          if not used[k] then
+            buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder)
+            if not buflen then return nil, msg end
+            prev = true -- add a seperator before the next element
+          end
+        end
+      else -- unordered
+        for k,v in pairs (value) do
+          buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder)
+          if not buflen then return nil, msg end
+          prev = true -- add a seperator before the next element
+        end
+      end
+      if indent then
+        buflen = addnewline2 (level - 1, buffer, buflen)
+      end
+      buflen = buflen + 1
+      buffer[buflen] = "}"
+    end
+    tables[value] = nil
+  else
+    return nil, "type '" .. valtype .. "' is not supported by JSON."
+  end
+  return buflen
+end
+
+function json.encode (value, state)
+  state = state or {}
+  local oldbuffer = state.buffer
+  local buffer = oldbuffer or {}
+  local ret, msg = encode2 (value, state.indent, state.level or 0,
+                   buffer, state.bufferlen or 0, state.tables or {}, state.keyorder)
+  if not ret then
+    error (msg, 2)
+  elseif oldbuffer then
+    state.bufferlen = ret
+    return true
+  else
+    return concat (buffer)
+  end
+end
+
+local function loc (str, where)
+  local line, pos, linepos = 1, 1, 1
+  while true do
+    pos = strfind (str, "\n", pos, true)
+    if pos and pos < where then
+      line = line + 1
+      linepos = pos
+      pos = pos + 1
+    else
+      break
+    end
+  end
+  return "line " .. line .. ", column " .. (where - linepos)
+end
+
+local function unterminated (str, what, where)
+  return nil, strlen (str) + 1, "unterminated " .. what .. " at " .. loc (str, where)
+end
+
+local function scanwhite (str, pos)
+  while true do
+    pos = strfind (str, "%S", pos)
+    if not pos then return nil end
+    if strsub (str, pos, pos + 2) == "\239\187\191" then
+      -- UTF-8 Byte Order Mark
+      pos = pos + 3
+    else
+      return pos
+    end
+  end
+end
+
+local escapechars = {
+  ["\""] = "\"", ["\\"] = "\\", ["/"] = "/", ["b"] = "\b", ["f"] = "\f",
+  ["n"] = "\n", ["r"] = "\r", ["t"] = "\t"
+}
+
+local function unichar (value)
+  if value < 0 then
+    return nil
+  elseif value <= 0x007f then
+    return strchar (value)
+  elseif value <= 0x07ff then
+    return strchar (0xc0 + floor(value/0x40),
+                    0x80 + (floor(value) % 0x40))
+  elseif value <= 0xffff then
+    return strchar (0xe0 + floor(value/0x1000),
+                    0x80 + (floor(value/0x40) % 0x40),
+                    0x80 + (floor(value) % 0x40))
+  elseif value <= 0x10ffff then
+    return strchar (0xf0 + floor(value/0x40000),
+                    0x80 + (floor(value/0x1000) % 0x40),
+                    0x80 + (floor(value/0x40) % 0x40),
+                    0x80 + (floor(value) % 0x40))
+  else
+    return nil
+  end
+end
+
+local function scanstring (str, pos)
+  local lastpos = pos + 1
+  local buffer, n = {}, 0
+  while true do
+    local nextpos = strfind (str, "[\"\\]", lastpos)
+    if not nextpos then
+      return unterminated (str, "string", pos)
+    end
+    if nextpos > lastpos then
+      n = n + 1
+      buffer[n] = strsub (str, lastpos, nextpos - 1)
+    end
+    if strsub (str, nextpos, nextpos) == "\"" then
+      lastpos = nextpos + 1
+      break
+    else
+      local escchar = strsub (str, nextpos + 1, nextpos + 1)
+      local value
+      if escchar == "u" then
+        value = tonumber (strsub (str, nextpos + 2, nextpos + 5), 16)
+        if value then
+          local value2
+          if 0xD800 <= value and value <= 0xDBff then
+            -- we have the high surrogate of UTF-16. Check if there is a
+            -- low surrogate escaped nearby to combine them.
+            if strsub (str, nextpos + 6, nextpos + 7) == "\\u" then
+              value2 = tonumber (strsub (str, nextpos + 8, nextpos + 11), 16)
+              if value2 and 0xDC00 <= value2 and value2 <= 0xDFFF then
+                value = (value - 0xD800)  * 0x400 + (value2 - 0xDC00) + 0x10000
+              else
+                value2 = nil -- in case it was out of range for a low surrogate
+              end
+            end
+          end
+          value = value and unichar (value)
+          if value then
+            if value2 then
+              lastpos = nextpos + 12
+            else
+              lastpos = nextpos + 6
+            end
+          end
+        end
+      end
+      if not value then
+        value = escapechars[escchar] or escchar
+        lastpos = nextpos + 2
+      end
+      n = n + 1
+      buffer[n] = value
+    end
+  end
+  if n == 1 then
+    return buffer[1], lastpos
+  elseif n > 1 then
+    return concat (buffer), lastpos
+  else
+    return "", lastpos
+  end
+end
+
+local scanvalue -- forward declaration
+
+local function scantable (what, closechar, str, startpos, nullval, objectmeta, arraymeta)
+  local len = strlen (str)
+  local tbl, n = {}, 0
+  local pos = startpos + 1
+  if what == 'object' then
+    setmetatable (tbl, objectmeta)
+  else
+    setmetatable (tbl, arraymeta)
+  end
+  while true do
+    pos = scanwhite (str, pos)
+    if not pos then return unterminated (str, what, startpos) end
+    local char = strsub (str, pos, pos)
+    if char == closechar then
+      return tbl, pos + 1
+    end
+    local val1, err
+    val1, pos, err = scanvalue (str, pos, nullval, objectmeta, arraymeta)
+    if err then return nil, pos, err end
+    pos = scanwhite (str, pos)
+    if not pos then return unterminated (str, what, startpos) end
+    char = strsub (str, pos, pos)
+    if char == ":" then
+      if val1 == nil then
+        return nil, pos, "cannot use nil as table index (at " .. loc (str, pos) .. ")"
+      end
+      pos = scanwhite (str, pos + 1)
+      if not pos then return unterminated (str, what, startpos) end
+      local val2
+      val2, pos, err = scanvalue (str, pos, nullval, objectmeta, arraymeta)
+      if err then return nil, pos, err end
+      tbl[val1] = val2
+      pos = scanwhite (str, pos)
+      if not pos then return unterminated (str, what, startpos) end
+      char = strsub (str, pos, pos)
+    else
+      n = n + 1
+      tbl[n] = val1
+    end
+    if char == "," then
+      pos = pos + 1
+    end
+  end
+end
+
+scanvalue = function (str, pos, nullval, objectmeta, arraymeta)
+  pos = pos or 1
+  pos = scanwhite (str, pos)
+  if not pos then
+    return nil, strlen (str) + 1, "no valid JSON value (reached the end)"
+  end
+  local char = strsub (str, pos, pos)
+  if char == "{" then
+    return scantable ('object', "}", str, pos, nullval, objectmeta, arraymeta)
+  elseif char == "[" then
+    return scantable ('array', "]", str, pos, nullval, objectmeta, arraymeta)
+  elseif char == "\"" then
+    return scanstring (str, pos)
+  else
+    local pstart, pend = strfind (str, "^%-?[%d%.]+[eE]?[%+%-]?%d*", pos)
+    if pstart then
+      local number = tonumber (strsub (str, pstart, pend))
+      if number then
+        return number, pend + 1
+      end
+    end
+    pstart, pend = strfind (str, "^%a%w*", pos)
+    if pstart then
+      local name = strsub (str, pstart, pend)
+      if name == "true" then
+        return true, pend + 1
+      elseif name == "false" then
+        return false, pend + 1
+      elseif name == "null" then
+        return nullval, pend + 1
+      end
+    end
+    return nil, pos, "no valid JSON value at " .. loc (str, pos)
+  end
+end
+
+function json.decode (str, pos, nullval, objectmeta, arraymeta)
+  objectmeta = objectmeta or {__jsontype = 'object'}
+  arraymeta = arraymeta or {__jsontype = 'array'}
+  return scanvalue (str, pos, nullval, objectmeta, arraymeta)
+end
+
+function json.use_lpeg ()
+  local g = require ("lpeg")
+  local pegmatch = g.match
+  local P, S, R, V = g.P, g.S, g.R, g.V
+
+  local SpecialChars = (R"\0\31" + S"\"\\\127" +
+    P"\194" * (R"\128\159" + P"\173") +
+    P"\216" * R"\128\132" +
+    P"\220\132" +
+    P"\225\158" * S"\180\181" +
+    P"\226\128" * (R"\140\143" + S"\168\175") +
+    P"\226\129" * R"\160\175" +
+    P"\239\187\191" +
+    P"\229\191" + R"\176\191") / escapeutf8
+
+  local QuoteStr = g.Cs (g.Cc "\"" * (SpecialChars + 1)^0 * g.Cc "\"")
+
+  quotestring = function (str)
+    return pegmatch (QuoteStr, str)
+  end
+  json.quotestring = quotestring
+
+  local function ErrorCall (str, pos, msg, state)
+    if not state.msg then
+      state.msg = msg .. " at " .. loc (str, pos)
+      state.pos = pos
+    end
+    return false
+  end
+
+  local function Err (msg)
+    return g.Cmt (g.Cc (msg) * g.Carg (2), ErrorCall)
+  end
+
+  local Space = (S" \n\r\t" + P"\239\187\191")^0
+
+  local PlainChar = 1 - S"\"\\\n\r"
+  local EscapeSequence = (P"\\" * g.C (S"\"\\/bfnrt" + Err "unsupported escape sequence")) / escapechars
+  local HexDigit = R("09", "af", "AF")
+  local function UTF16Surrogate (match, pos, high, low)
+    high, low = tonumber (high, 16), tonumber (low, 16)
+    if 0xD800 <= high and high <= 0xDBff and 0xDC00 <= low and low <= 0xDFFF then
+      return true, unichar ((high - 0xD800)  * 0x400 + (low - 0xDC00) + 0x10000)
+    else
+      return false
+    end
+  end
+  local function UTF16BMP (hex)
+    return unichar (tonumber (hex, 16))
+  end
+  local U16Sequence = (P"\\u" * g.C (HexDigit * HexDigit * HexDigit * HexDigit))
+  local UnicodeEscape = g.Cmt (U16Sequence * U16Sequence, UTF16Surrogate) + U16Sequence/UTF16BMP
+  local Char = UnicodeEscape + EscapeSequence + PlainChar
+  local String = P"\"" * g.Cs (Char ^ 0) * (P"\"" + Err "unterminated string")
+  local Integer = P"-"^(-1) * (P"0" + (R"19" * R"09"^0))
+  local Fractal = P"." * R"09"^0
+  local Exponent = (S"eE") * (S"+-")^(-1) * R"09"^1
+  local Number = (Integer * Fractal^(-1) * Exponent^(-1))/tonumber
+  local Constant = P"true" * g.Cc (true) + P"false" * g.Cc (false) + P"null" * g.Carg (1)
+  local SimpleValue = Number + String + Constant
+  local ArrayContent, ObjectContent
+
+  -- The functions parsearray and parseobject parse only a single value/pair
+  -- at a time and store them directly to avoid hitting the LPeg limits.
+  local function parsearray (str, pos, nullval, state)
+    local obj, cont
+    local npos
+    local t, nt = {}, 0
+    repeat
+      obj, cont, npos = pegmatch (ArrayContent, str, pos, nullval, state)
+      if not npos then break end
+      pos = npos
+      nt = nt + 1
+      t[nt] = obj
+    until cont == 'last'
+    return pos, setmetatable (t, state.arraymeta)
+  end
+
+  local function parseobject (str, pos, nullval, state)
+    local obj, key, cont
+    local npos
+    local t = {}
+    repeat
+      key, obj, cont, npos = pegmatch (ObjectContent, str, pos, nullval, state)
+      if not npos then break end
+      pos = npos
+      t[key] = obj
+    until cont == 'last'
+    return pos, setmetatable (t, state.objectmeta)
+  end
+
+  local Array = P"[" * g.Cmt (g.Carg(1) * g.Carg(2), parsearray) * Space * (P"]" + Err "']' expected")
+  local Object = P"{" * g.Cmt (g.Carg(1) * g.Carg(2), parseobject) * Space * (P"}" + Err "'}' expected")
+  local Value = Space * (Array + Object + SimpleValue)
+  local ExpectedValue = Value + Space * Err "value expected"
+  ArrayContent = Value * Space * (P"," * g.Cc'cont' + g.Cc'last') * g.Cp()
+  local Pair = g.Cg (Space * String * Space * (P":" + Err "colon expected") * ExpectedValue)
+  ObjectContent = Pair * Space * (P"," * g.Cc'cont' + g.Cc'last') * g.Cp()
+  local DecodeValue = ExpectedValue * g.Cp ()
+
+  function json.decode (str, pos, nullval, objectmeta, arraymeta)
+    local state = {
+      objectmeta = objectmeta or {__jsontype = 'object'},
+      arraymeta = arraymeta or {__jsontype = 'array'}
+    }
+    local obj, retpos = pegmatch (DecodeValue, str, pos, nullval, state)
+    if state.msg then
+      return nil, state.pos, state.msg
+    else
+      return obj, retpos
+    end
+  end
+
+  -- use this function only once:
+  json.use_lpeg = function () return json end
+
+  json.using_lpeg = true
+
+  return json -- so you can get the module using json = require "dkjson".use_lpeg()
+end
+
+if always_try_using_lpeg then
+  pcall (json.use_lpeg)
+end
+
+return json
+
+-->