6 files changed, 750 insertions, 47 deletions

diff --git a/spec/config_spec.lua b/spec/config_spec.lua
index 885b022a..05da0007 100644
--- a/spec/config_spec.lua
+++ b/spec/config_spec.lua
@@ -23,17 +23,9 @@ describe("LuaRocks config tests #integration", function()
       end)
 
       it("--json", function()
-         assert.is_true(run.luarocks_nocov("install dkjson"))
-         finally(function()
-            assert.is_true(run.luarocks_nocov("remove dkjson"))
-         end)
          assert.match('"rocks_servers":[', run.luarocks("config --json"), 1, true)
       end)
 
-      it("--json fails without a json library", function()
-         assert.falsy(run.luarocks_bool("config --json"))
-      end)
-
       it("with --tree respects custom config", function()
          write_file("my_config.lua", [[
             rocks_trees = {
@@ -167,18 +159,10 @@ describe("LuaRocks config tests #integration", function()
       end)
 
       it("can read as JSON", function()
-         assert.is_true(run.luarocks_nocov("install dkjson"))
-         finally(function()
-            assert.is_true(run.luarocks_nocov("remove dkjson"))
-         end)
          local output = run.luarocks("config rocks_trees --json")
          assert.match('^%["', output)
       end)
 
-      it("--json does not work without a json library", function()
-         assert.is_false(run.luarocks_bool("config rocks_trees --json"))
-      end)
-
       it("reads an array -> hash config key", function()
          local output = run.luarocks("config rocks_trees[2].name")
          assert.match("[a-z]+", output)
diff --git a/spec/upload_spec.lua b/spec/upload_spec.lua
index 73f26cd7..119d34b6 100644
--- a/spec/upload_spec.lua
+++ b/spec/upload_spec.lua
@@ -27,7 +27,6 @@ describe("luarocks upload #integration", function()
    end)
 
    it("force #unix", function()
-      assert.is_true(test_env.need_rock("dkjson"))
       assert.is_false(run.luarocks_bool("upload --api-key=\"invalid\" --force " .. testing_paths.testing_server .. "/luasocket-${LUASOCKET}.rockspec"))
    end)
 
diff --git a/src/luarocks/cmd/config.lua b/src/luarocks/cmd/config.lua
index 7ad28777..3b100429 100644
--- a/src/luarocks/cmd/config.lua
+++ b/src/luarocks/cmd/config.lua
@@ -8,6 +8,7 @@ local util = require("luarocks.util")
 local deps = require("luarocks.deps")
 local dir = require("luarocks.dir")
 local fs = require("luarocks.fs")
+local json = require("luarocks.vendor.dkjson")
 
 function config_cmd.add_to_parser(parser)
    local cmd = parser:command("config", [[
@@ -135,11 +136,6 @@ local function traverse_varstring(var, tbl, fn, missing_parent)
 end
 
 local function print_json(value)
-   local json_ok, json = util.require_json()
-   if not json_ok then
-      return nil, "A JSON library is required for this command. "..json
-   end
-
    print(json.encode(value))
    return true
 end
diff --git a/src/luarocks/upload/api.lua b/src/luarocks/upload/api.lua
index cbfe6e9f..8e26f66a 100644
--- a/src/luarocks/upload/api.lua
+++ b/src/luarocks/upload/api.lua
@@ -7,6 +7,7 @@ local dir = require("luarocks.dir")
 local util = require("luarocks.util")
 local persist = require("luarocks.persist")
 local multipart = require("luarocks.upload.multipart")
+local json = require("luarocks.vendor.dkjson")
 
 local Api = {}
 
@@ -118,8 +119,6 @@ if not ltn12_ok then -- If not using LuaSocket and/or LuaSec...
 
 function Api:request(url, params, post_params)
    local vars = cfg.variables
-   local json_ok, json = util.require_json()
-   if not json_ok then return nil, "A JSON library is required for this command. "..json end
 
    if fs.which_tool("downloader") == "wget" then
       local curl_ok, err = fs.is_tool_available(vars.CURL, "curl")
@@ -182,8 +181,6 @@ else -- use LuaSocket and LuaSec
 local warned_luasec = false
 
 function Api:request(url, params, post_params)
-   local json_ok, json = util.require_json()
-   if not json_ok then return nil, "A JSON library is required for this command. "..json end
    local server = tostring(self.config.server)
    local http_ok, http
    local via = "luasocket"
diff --git a/src/luarocks/util.lua b/src/luarocks/util.lua
index 0a900ecc..902656fd 100644
--- a/src/luarocks/util.lua
+++ b/src/luarocks/util.lua
@@ -388,27 +388,6 @@ function util.deep_copy(tbl)
    return copy
 end
 
--- An ode to the multitude of JSON libraries out there...
-function util.require_json()
-   local list = { "cjson", "dkjson", "json" }
-   for _, lib in ipairs(list) do
-      local json_ok, json = pcall(require, lib)
-      if json_ok then
-         pcall(json.use_lpeg) -- optional feature in dkjson
-         return json_ok, json
-      end
-   end
-   local errmsg = "Failed loading "
-   for i, name in ipairs(list) do
-      if i == #list then
-         errmsg = errmsg .."and '"..name.."'. Use 'luarocks search <partial-name>' to search for a library and 'luarocks install <name>' to install one."
-      else
-         errmsg = errmsg .."'"..name.."', "
-      end
-   end
-   return nil, errmsg
-end
-
 -- A portable version of fs.exists that can be used at early startup,
 -- before the platform has been determined and luarocks.fs has been
 -- initialized.
diff --git a/src/luarocks/vendor/dkjson.lua b/src/luarocks/vendor/dkjson.lua
new file mode 100644
index 00000000..95e4d884
--- /dev/null
+++ b/src/luarocks/vendor/dkjson.lua
@@ -0,0 +1,748 @@
+-- Module options:
+local always_use_lpeg = false
+local register_global_module_table = false
+local global_module_name = 'json'
+
+--[==[
+
+David Kolf's JSON module for Lua 5.1 - 5.4
+
+Version 2.6
+
+
+For the documentation see the corresponding readme.txt or visit
+<http://dkolf.de/src/dkjson-lua.fsl/>.
+
+You can contact the author by sending an e-mail to 'david' at the
+domain 'dkolf.de'.
+
+
+Copyright (C) 2010-2021 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.
+
+--]==]
+
+-- global dependencies:
+local pairs, type, tostring, tonumber, getmetatable, setmetatable =
+      pairs, type, tostring, tonumber, getmetatable, setmetatable
+local error, require, pcall, select = error, require, pcall, select
+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 strmatch = string.match
+local concat = table.concat
+
+local json = { version = "dkjson 2.6" }
+
+local jsonlpeg = {}
+
+if register_global_module_table then
+  if always_use_lpeg then
+    _G[global_module_name] = jsonlpeg
+  else
+    _G[global_module_name] = json
+  end
+end
+-- blocking globals in Lua 5.2 and later
+local _ENV = nil  -- luacheck: ignore 211
+
+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 replace(str, o, n)
+  local i, j = strfind (str, o, 1, true)
+  if i then
+    return strsub(str, 1, i-1) .. n .. strsub(str, j+1, -1)
+  else
+    return str
+  end
+end
+
+-- locale independent num2str and str2num functions
+local decpoint, numfilter
+
+local function updatedecpoint ()
+  decpoint = strmatch(tostring(0.5), "([^05+])")
+  -- build a filter that can be used to remove group separators
+  numfilter = "[^0-9%-%+eE" .. gsub(decpoint, "[%^%$%(%)%%%.%[%]%*%+%-%?]", "%%%0") .. "]+"
+end
+
+updatedecpoint()
+
+local function num2str (num)
+  return replace(fsub(tostring(num), numfilter, ""), decpoint, ".")
+end
+
+local function str2num (str)
+  local num = tonumber(replace(str, ".", decpoint))
+  if not num then
+    updatedecpoint()
+    num = tonumber(replace(str, ".", decpoint))
+  end
+  return num
+end
+
+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, state)
+  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, state)
+end
+
+local function appendcustom(res, buffer, state)
+  local buflen = state.bufferlen
+  if type (res) == 'string' then
+    buflen = buflen + 1
+    buffer[buflen] = res
+  end
+  return buflen
+end
+
+local function exception(reason, value, state, buffer, buflen, defaultmessage)
+  defaultmessage = defaultmessage or reason
+  local handler = state.exception
+  if not handler then
+    return nil, defaultmessage
+  else
+    state.bufferlen = buflen
+    local ret, msg = handler (reason, value, state, defaultmessage)
+    if not ret then return nil, msg or defaultmessage end
+    return appendcustom(ret, buffer, state)
+  end
+end
+
+function json.encodeexception(reason, value, state, defaultmessage)
+  return quotestring("<" .. defaultmessage .. ">")
+end
+
+encode2 = function (value, indent, level, buffer, buflen, tables, globalorder, state)
+  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 exception('reference cycle', value, state, buffer, buflen)
+    end
+    tables[value] = true
+    state.bufferlen = buflen
+    local ret, msg = valtojson (value, state)
+    if not ret then return exception('custom encoder failed', value, state, buffer, buflen, msg) end
+    tables[value] = nil
+    buflen = appendcustom(ret, buffer, state)
+  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 = num2str (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 exception('reference cycle', value, state, buffer, buflen)
+    end
+    tables[value] = true
+    level = level + 1
+    local isa, n = isarray (value)
+    if n == 0 and valmeta and valmeta.__jsontype == 'object' then
+      isa = false
+    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, state)
+        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 ~= nil then
+            used[k] = true
+            buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder, state)
+            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, state)
+            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, state)
+          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 exception ('unsupported type', value, state, buffer, buflen,
+      "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 {}
+  state.buffer = buffer
+  updatedecpoint()
+  local ret, msg = encode2 (value, state.indent, state.level or 0,
+                   buffer, state.bufferlen or 0, state.tables or {}, state.keyorder, state)
+  if not ret then
+    error (msg, 2)
+  elseif oldbuffer == buffer then
+    state.bufferlen = ret
+    return true
+  else
+    state.bufferlen = nil
+    state.buffer = nil
+    return concat (buffer)
+  end
+end
+
+local function loc (str, where)
+  local line, pos, linepos = 1, 1, 0
+  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
+    local sub2 = strsub (str, pos, pos + 1)
+    if sub2 == "\239\187" and strsub (str, pos + 2, pos + 2) == "\191" then
+      -- UTF-8 Byte Order Mark
+      pos = pos + 3
+    elseif sub2 == "//" then
+      pos = strfind (str, "[\n\r]", pos + 2)
+      if not pos then return nil end
+    elseif sub2 == "/*" then
+      pos = strfind (str, "*/", pos + 2)
+      if not pos then return nil end
+      pos = pos + 2
+    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 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 = str2num (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
+
+local function optionalmetatables(...)
+  if select("#", ...) > 0 then
+    return ...
+  else
+    return {__jsontype = 'object'}, {__jsontype = 'array'}
+  end
+end
+
+function json.decode (str, pos, nullval, ...)
+  local objectmeta, arraymeta = optionalmetatables(...)
+  return scanvalue (str, pos, nullval, objectmeta, arraymeta)
+end
+
+function json.use_lpeg ()
+  local g = require ("lpeg")
+
+  if g.version() == "0.11" then
+    error "due to a bug in LPeg 0.11, it cannot be used for JSON matching"
+  end
+
+  local pegmatch = g.match
+  local P, S, R = g.P, g.S, g.R
+
+  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 function ErrorUnterminatedCall (str, pos, what, state)
+    return ErrorCall (str, pos - 1, "unterminated " .. what, state)
+  end
+
+  local SingleLineComment = P"//" * (1 - S"\n\r")^0
+  local MultiLineComment = P"/*" * (1 - P"*/")^0 * P"*/"
+  local Space = (S" \n\r\t" + P"\239\187\191" + SingleLineComment + MultiLineComment)^0
+
+  local function ErrUnterminated (what)
+    return g.Cmt (g.Cc (what) * g.Carg (2), ErrorUnterminatedCall)
+  end
+
+  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"\"" + ErrUnterminated "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))/str2num
+  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 start = pos
+    local npos
+    local t, nt = {}, 0
+    repeat
+      obj, cont, npos = pegmatch (ArrayContent, str, pos, nullval, state)
+      if cont == 'end' then
+        return ErrorUnterminatedCall (str, start, "array", state)
+      end
+      pos = npos
+      if cont == 'cont' or cont == 'last' then
+        nt = nt + 1
+        t[nt] = obj
+      end
+    until cont ~= 'cont'
+    return pos, setmetatable (t, state.arraymeta)
+  end
+
+  local function parseobject (str, pos, nullval, state)
+    local obj, key, cont
+    local start = pos
+    local npos
+    local t = {}
+    repeat
+      key, obj, cont, npos = pegmatch (ObjectContent, str, pos, nullval, state)
+      if cont == 'end' then
+        return ErrorUnterminatedCall (str, start, "object", state)
+      end
+      pos = npos
+      if cont == 'cont' or cont == 'last' then
+        t[key] = obj
+      end
+    until cont ~= 'cont'
+    return pos, setmetatable (t, state.objectmeta)
+  end
+
+  local Array = P"[" * g.Cmt (g.Carg(1) * g.Carg(2), parsearray)
+  local Object = P"{" * g.Cmt (g.Carg(1) * g.Carg(2), parseobject)
+  local Value = Space * (Array + Object + SimpleValue)
+  local ExpectedValue = Value + Space * Err "value expected"
+  local ExpectedKey = String + Err "key expected"
+  local End = P(-1) * g.Cc'end'
+  local ErrInvalid = Err "invalid JSON"
+  ArrayContent = (Value * Space * (P"," * g.Cc'cont' + P"]" * g.Cc'last'+ End + ErrInvalid)  + g.Cc(nil) * (P"]" * g.Cc'empty' + End  + ErrInvalid)) * g.Cp()
+  local Pair = g.Cg (Space * ExpectedKey * Space * (P":" + Err "colon expected") * ExpectedValue)
+  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()
+  local DecodeValue = ExpectedValue * g.Cp ()
+
+  jsonlpeg.version = json.version
+  jsonlpeg.encode = json.encode
+  jsonlpeg.null = json.null
+  jsonlpeg.quotestring = json.quotestring
+  jsonlpeg.addnewline = json.addnewline
+  jsonlpeg.encodeexception = json.encodeexception
+  jsonlpeg.using_lpeg = true
+
+  function jsonlpeg.decode (str, pos, nullval, ...)
+    local state = {}
+    state.objectmeta, state.arraymeta = optionalmetatables(...)
+    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
+
+  -- cache result of this function:
+  json.use_lpeg = function () return jsonlpeg end
+  jsonlpeg.use_lpeg = json.use_lpeg
+
+  return jsonlpeg
+end
+
+if always_use_lpeg then
+  return json.use_lpeg()
+end
+
+return json
+