DataDumper is a Lua table serialization, slow but mostly complete

DataDumper.lua

--[[ DataDumper.lua
Copyright (c) 2007 Olivetti-Engineering SA

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.
]]

local dumplua_closure = [[
local closures = {}
local function closure(t) 
  closures[#closures+1] = t
  t[1] = assert(loadstring(t[1]))
  return t[1]
end

for _,t in pairs(closures) do
  for i = 2,#t do 
    debug.setupvalue(t[1], i-1, t[i]) 
  end 
end
]]

local lua_reserved_keywords = {
  'and', 'break', 'do', 'else', 'elseif', 'end', 'false', 'for', 
  'function', 'if', 'in', 'local', 'nil', 'not', 'or', 'repeat', 
  'return', 'then', 'true', 'until', 'while' }

local function keys(t)
  local res = {}
  local oktypes = { stringstring = true, numbernumber = true }
  local function cmpfct(a,b)
    if oktypes[type(a)..type(b)] then
      return a < b
    else
      return type(a) < type(b)
    end
  end
  for k in pairs(t) do
    res[#res+1] = k
  end
  table.sort(res, cmpfct)
  return res
end

local c_functions = {}
for _,lib in pairs{'_G', 'string', 'table', 'math', 
    'io', 'os', 'coroutine', 'package', 'debug'} do
  local t = _G[lib] or {}
  lib = lib .. "."
  if lib == "_G." then lib = "" end
  for k,v in pairs(t) do
    if type(v) == 'function' and not pcall(string.dump, v) then
      c_functions[v] = lib..k
    end
  end
end

function DataDumper(value, varname, fastmode, ident)
  local defined, dumplua = {}
  -- Local variables for speed optimization
  local string_format, type, string_dump, string_rep = 
        string.format, type, string.dump, string.rep
  local tostring, pairs, table_concat = 
        tostring, pairs, table.concat
  local keycache, strvalcache, out, closure_cnt = {}, {}, {}, 0
  setmetatable(strvalcache, {__index = function(t,value)
    local res = string_format('%q', value)
    t[value] = res
    return res
  end})
  local fcts = {
    string = function(value) return strvalcache[value] end,
    number = function(value) return value end,
    boolean = function(value) return tostring(value) end,
    ['nil'] = function(value) return 'nil' end,
    ['function'] = function(value) 
      return string_format("loadstring(%q)", string_dump(value)) 
    end,
    userdata = function() error("Cannot dump userdata") end,
    thread = function() error("Cannot dump threads") end,
  }
  local function test_defined(value, path)
    if defined[value] then
      if path:match("^getmetatable.*%)$") then
        out[#out+1] = string_format("s%s, %s)\n", path:sub(2,-2), defined[value])
      else
        out[#out+1] = path .. " = " .. defined[value] .. "\n"
      end
      return true
    end
    defined[value] = path
  end
  local function make_key(t, key)
    local s
    if type(key) == 'string' and key:match('^[_%a][_%w]*$') then
      s = key .. "="
    else
      s = "[" .. dumplua(key, 0) .. "]="
    end
    t[key] = s
    return s
  end
  for _,k in ipairs(lua_reserved_keywords) do
    keycache[k] = '["'..k..'"] = '
  end
  if fastmode then 
    fcts.table = function (value)
      -- Table value
      local numidx = 1
      out[#out+1] = "{"
      for key,val in pairs(value) do
        if key == numidx then
          numidx = numidx + 1
        else
          out[#out+1] = keycache[key]
        end
        local str = dumplua(val)
        out[#out+1] = str..","
      end
      if string.sub(out[#out], -1) == "," then
        out[#out] = string.sub(out[#out], 1, -2);
      end
      out[#out+1] = "}"
      return "" 
    end
  else 
    fcts.table = function (value, ident, path)
      if test_defined(value, path) then return "nil" end
      -- Table value
      local sep, str, numidx, totallen = " ", {}, 1, 0
      local meta, metastr = (debug or getfenv()).getmetatable(value)
      if meta then
        ident = ident + 1
        metastr = dumplua(meta, ident, "getmetatable("..path..")")
        totallen = totallen + #metastr + 16
      end
      for _,key in pairs(keys(value)) do
        local val = value[key]
        local s = ""
        local subpath = path
        if key == numidx then
          subpath = subpath .. "[" .. numidx .. "]"
          numidx = numidx + 1
        else
          s = keycache[key]
          if not s:match "^%[" then subpath = subpath .. "." end
          subpath = subpath .. s:gsub("%s*=%s*$","")
        end
        s = s .. dumplua(val, ident+1, subpath)
        str[#str+1] = s
        totallen = totallen + #s + 2
      end
      if totallen > 80 then
        sep = "\n" .. string_rep("  ", ident+1)
      end
      str = "{"..sep..table_concat(str, ","..sep).." "..sep:sub(1,-3).."}" 
      if meta then
        sep = sep:sub(1,-3)
        return "setmetatable("..sep..str..","..sep..metastr..sep:sub(1,-3)..")"
      end
      return str
    end
    fcts['function'] = function (value, ident, path)
      if test_defined(value, path) then return "nil" end
      if c_functions[value] then
        return c_functions[value]
      elseif debug == nil or debug.getupvalue(value, 1) == nil then
        return string_format("loadstring(%q)", string_dump(value))
      end
      closure_cnt = closure_cnt + 1
      local res = {string.dump(value)}
      for i = 1,math.huge do
        local name, v = debug.getupvalue(value,i)
        if name == nil then break end
        res[i+1] = v
      end
      return "closure " .. dumplua(res, ident, "closures["..closure_cnt.."]")
    end
  end
  function dumplua(value, ident, path)
    return fcts[type(value)](value, ident, path)
  end
  if varname == nil then
    varname = "return "
  elseif varname:match("^[%a_][%w_]*$") then
    varname = varname .. " = "
  end
  if fastmode then
    setmetatable(keycache, {__index = make_key })
    out[1] = varname
    table.insert(out,dumplua(value, 0))
    return table.concat(out)
  else
    setmetatable(keycache, {__index = make_key })
    local items = {}
    for i=1,10 do items[i] = '' end
    items[3] = dumplua(value, ident or 0, "t")
    if closure_cnt > 0 then
      items[1], items[6] = dumplua_closure:match("(.*\n)\n(.*)")
      out[#out+1] = ""
    end
    if #out > 0 then
      items[2], items[4] = "local t = ", "\n"
      items[5] = table.concat(out)
      items[7] = varname .. "t"
    else
      items[2] = varname
    end
    return table.concat(items)
  end
end

This is basically a copy from http://lua-users.org/wiki/DataDumper

Here is one of the multiple ways to implement the serialization of a table. See http://lua-users.org/wiki/TableSerialization for a list of many other solutions. This version is written for Lua 5.1 and is quite long, because it tries to be as generic as possible and to keep its output string human readable. The drawback is that it is not the fastest one, mainly because it returns a string and does not write to a temporarily file. Still, there is a "fast" mode with fewer features, when execution time (or memory) is important. The function is copyrighted on MIT license, so is is free to use even in a commercial product.

DataDumper consists of a single Lua function, which could easily be put in a separate module or integrated into a bigger one. The function has four parameters, but only the first one is mandatory. It always returns a string value, which is valid Lua code. Simply executing this chunk will import back to a variable the complete structure of the original variable. For simple structures, there is only one Lua instruction like a table constructor, but some more complex features will output a script with more instructions.

All the following language features are supported:

* Simple Lua types: nil, boolean, number, string
* Tables are dumped recursively
* Table metatables are also dumped recursively
* Simple Lua functions (no upvalue) are dumped with loadstring
* Lua closures with upvalues are also supported, using the debug library!
* Known C functions are output using their original name
* Complex tables structures with internal references are supported 

What is not supported since it seems to be impossible, are these types:

* Both light and full userdata
* Coroutines
* Other C functions 

Here is the function declaration:

function DataDumper(value[, varname, fastmode, indent])

* value can be of any supported type
* varname: optional variable name. Depending on its form, the output will look like:
      o nil: "return value"
      o identifier: "varname = value"
      o other: "varname".."value" 
* fastmode is a boolean value:
      o true: optimizes for speed. Metatables, closures, C functions and references are not supported. Returns a code chunk without any space or new line!
      o false: supports all advanced features and favors readable code with good indentation. 
* indent: the number of additional indentation level. Default is 0.