Re: Constructing protected environments
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- Subject: Re: Constructing protected environments
- From: Eva Schmidt <es@...>
- Date: 2007年12月27日 09:46:08 +0100
Hi Jorge,
I'm not sure if there is a better way for doing so, but I solved the same
problem that way:
1.) Call a handle_data function within the read() function of the socket:
local s, error = client_socket:receive("*l")
handle_data (s)
2.) Define your own environment within the handle function:
local env = {}
... and bind the functions you want to be allowed ...
env.print = print -- print function in environment is the Lua builtin printing
function
...
3.) Call loadstring () and assign the resulting function to a variable. Don't
execute directly. Instead, call a helping function try_call which sets the
environment and calls pcall:
result, error = loadstring (s)
if not error then
try_call (result, env)
return
end
-----
function try_call (result, env)
setfenv (result, env)
-- check if result() is a valid function
if not pcall (result) then
print ("Error!")
return false
end
return true
end
After setfenv () the function result knows *only* the functions and variables in
env. The pcall () executes the function. This is what happens by
loadstring(s)()
I hope that helps :-)
Cheers,
Eva
Jorge Visca wrote:
Hi to everyone.
My (lua) program gets a chunk trough the network, and loads it with
loadstring. I provide a set of functions for this piece of code, and i
want to call some functions it declares. PiL recommends building a
protected environment for those cases. I guess it must be done using
scoping and redefining variables, and I was wondering what's the correct
method for that.
Is there a good example somewhere?
Thanks in advance,
Jorge