Re: pass a FILE* from C to Lua

[Rena <hyperhacker@...>]

On 2013-02-21 9:27 PM, "Finn Wilcox" <finnw@firecloudsw.co.uk> wrote:
>
> On 22/02/2013 01:45, mlepage@antimeta.com wrote:
> > I would look at the source for the file lib and see what it expects.
> > I am guessing a userdata with metatable. If you can make the same
> > sort of object, it should Just Work.
> >
> Yes, in the three implementations I have looked at so far, it is always
> a userdata, and the payload always starts with a FILE*
>
> But after that, it varies depending on the implementation:
> - Lua 5.2 has a pointer to a close function following the FILE* in the
> payload
> - Lua 5.1 keeps the close function pointer in the uservalue (the payload
> contains only the FILE*)
> - LuaJIT 2.0 adds an enum to the payload instead of a function pointer.
>  It also has a tag in the header indicating that this userdata is a file
> (which you cannot fake using lua_newuserdata.)
>
> Maybe it is still possible to make this work in all 3 versions?
>
> For example, you could open a dummy file on the Lua side (tmpfile or
> /dev/null) then replace the FILE* with the supplied one and close the
> original.
>
> Or use a combination of fileno and fdup2, to keep the same FILE* but
> replace the underlying FD.
>

I thought Lua 5.2 added some way to do this?