Sandboxing Kawa

[Per Bothner]

1. Is it possible to restrict the initially available symbols in a
kawa.standard.Scheme instance to a tiny core subset (such as lambda,
if, define, begin, etc)? A default Scheme instance in Kawa has 807
symbols in the environment.

The default Kawa environment is defined by the (two) calls to
loadClass("kawa.lib.kawa.base", xxx) in kawa/standard/Scheme.java.
So all of the initially visible names are defined by kawa.lib.kawa.base
(defined in kawa/lib/kawa/base.scm). So you can replace kawa.lib.kawa.base
to a "smaller" initial library.

I suggested creating sub-classes of kawa.standard,Scheme and
kawa.standard.SchemeCompilation.

In addition you need to override checkDefaultBinding from
SchemeCompilation. The easiest and most reliable is just have it return null.

2. Is it possible to restrict the interpreter to only working with a
single java.nio.file.FileSystem? I'd like it if any attempt to do I/O
went through a given filesystem instance. I don't mind if I have to
implement my own I/O library to do this.
3. Is it possible to restrict the classes that the interpreter is
allowed to access or import? For example, right now nothing stops the
someone from writing (java.lang.System:exit 0).

Both of these require disabling "backdoors" to Java classes, methods,
fields. Overriding ,checkDefaultBidning and maybe the colon
operator should do that.