old lua sandboxing code

sandbox.lua

require "task"

function dothebox( )

	local makeReadOnly = function( t )
		proxy = {}
		mt = {}
			mt.__metatable = "None of your business!"
			mt.__index = t
			mt.__newindex = 	function( t, k, v )
									error( "Can not edit protected tables!" )
								end

		setmetatable( proxy, mt )
		return proxy
	end

	local protectedTables =
	{
		"os",
		"bit",
		"table",
		"string",
		"math",
		"coroutine",
		"tostring",
		"print",
		"pairs",
		"next",
		"ipairs",
		"assert",
		"_VERSION",
		"_G"
	}

	local makeProtected = function( t )
		proxy = {}
		mt = {}
			mt.__metatable = "None of your business!"
			mt.__index = t
			mt.__newindex = 	function( tab, key, val )
									for _, prot in pairs( protectedTables ) do
										if key == prot then
											error( "Can not edit protected tables!", 2 )
										end
									end
									--tab[key] = val   -- update original table
									rawset( tab, key, val )
								end

		setmetatable( proxy, mt )
		return proxy
	end

	local env = {}

	env._G = makeProtected( env )

	env._VERSION = _VERSION

	env.assert = assert
	env.ipairs = ipairs
	env.next = next
	env.pairs = pairs

	local toPrint = nil

	env.print = function(...)
					local s = ""

					if arg.n > 1 then
						s = arg[1]
						arg.n = nil
						arg[1] = nil
						for k, v in pairs( arg ) do
							s = s .. ", " .. tostring( v )
						end
					else
						s = arg[1]
					end

					if toPrint then
						toPrint = toPrint .. ", " .. s
					else
						toPrint = s
					end

				end

	env.tonumber = tonumber
	env.tostring = tostring
	env.setmetatable = setmetatable
	env.getmetatable = getmetatable
	env.type = type

	env.coroutine = makeReadOnly( coroutine )
	env.math = makeReadOnly( math )
	env.string = makeReadOnly( string )
	env.table = makeReadOnly( table	)
	env.bit = makeReadOnly( bit )

	env.os = os
	env.os.execute = nil
	env.os.exit = nil
	env.os.getenv = nil
	env.os.remove = nil
	env.os.rename = nil
	env.os.setlocale = nil
	env.os.tmpname = nil
	env.os = makeReadOnly( env.os )

	env = makeProtected( env )

	local ret_num_args = function(...) return { n = select( "#", ... ), ... } end

	local main_id = arg[1]

	while true do
		local code, flag, rc =  task.receive( 50 )

		if rc == 0 then
			local func, err = loadstring( "return " .. code );
			if not func then
				func, err = loadstring( code );
			end
			if not func then
				task.post( main_id, err, 0 );
			else
				setfenv( func, env )
				local args = ret_num_args( pcall( func ) )

				if not toPrint then
					if args.n > 1 then
						local num = args.n
						args.n = nil --  should remove the number of args and the true/false entry
						args[1] = nil

						res = ""
						if #args > 1 then
							for i = 2, num, 1 do
								res = res .. " " .. tostring( args[i] )
							end
						else
							res = tostring( args[3] )
						end

						task.post( main_id, res, 0 )
					else
						task.post( main_id, "executed...", 0 )
					end
				else

					res = tostring( toPrint )
					toPrint = nil

					task.post( main_id, res, 0 )
				end
			end
		end

	end

end

main_id = task.id()
tsk = task.create( "=" .. string.dump( dothebox ), { main_id } )

function sandbox( code )

	if not task.isrunning( tsk ) then
		tsk = task.create( "=" .. string.dump( dothebox ), { main_id } )
		if tsk < 0 then return nil end
	end

	task.post( tsk, code, 0 )

	local msg, flag, rc = task.receive( 5000 )
	if rc == 0 then
		return msg
	elseif rc == -2 then
		task.cancel( tsk )
		return "ERROR: Script execution time of 5s exceeded!"
	end

end