Re: Sandboxing a module that clutters the global environment

[alloyed@...]

On 10/5/2016 6:31 AM, tyrondis wrote:

> Hi *,
>
> I have a 3rd party module that operates and maintains its state in the 
> global environment.
> Is there anyway I can load this module into a custom context table, so 
> that it uses that table as its _G? I want to be able to have multiple 
> instances of that module, which is currently not possible because of 
> its “Singleton” nature.
>
> I could also refactor the 3rd part module but I want to have it 
> untouched to make it easier to apply potential patches to it.
>
> Thanks
> Tyr

I've done something like this to run multiple luarocks commands from a 
single lua state.
Relevant functions:
https://git.io/vPcIG
https://git.io/vPcIW

This was a high-touch process: I actually stuck a breakpoint in the 
middle of luarocks so I could inspect the environment to see exactly 
what exactly I needed to shim and what I didn't.

Once I knew that (in my case _G and package.loaded) I used a simple 
shim:

t = setmetatable({}, {__index=old_t})

Table reads should behave the same, but every time a table gets written 
to, the write goes into the shim instead of the old table. This is 
shallow, so something like `t.a.b` would leak back into the original 
t.a, but this is fine for me since luarocks doesn't do anything 
particularly silly.

I use Lua 5.1's setfenv to apply the new environment, but _ENV can be 
used to similar effect on 5.2/5.3:
http://leafo.net/guides/setfenv-in-lua52-and-above.html