Hello ruby-ffi group,
hopefully, some FFI wizard can help me with this rather unusual
function definition.

I try to access the OPSEC API with Ruby FFI. OPSEC is a collection of
C libraries to access CheckPoint firewalls and it is very C indeed.

So, I ran into a problem of giving a pointer to a callback function
inside a varargs parameter list, but let me explain a little bit.


To setup an OPSEC entity the API provides the opsec_init_entity
function like this:

OpsecEntity *opsec_init_entity (OpsecEnv *env, OpsecEntityType
*entity_type, ...);

so this resolves to the following RubyFFI definition:

module Opsec
  extend FFI::Library
  ffi_lib 'opsec'

  typedef :pointer, :opsec_entity
  attach_function :opsec_init_entity,
[:opsec_env, :pointer, :int, :varargs], :opsec_entity
end

The varargs is a list of attributes and their values and finally
ending with a NULL. The attribute is just an integer, the value
depends on the attribute and can be an integer, a CHAR * or a handler.
As with FFI you need to give the type for every parameter in
a :varargs, invoking this function would look something like this:

server = opsec_init_entity opsec_env, objptr, :int,
OPSEC_ENTITY_NAME, :string, "lea_server", :int, 0

and it works! Isn't FFI just great?


But it is also needed to provide callbacks here. This is how it looks
like in C:

int LeaStartHandler(OpsecSession *);
pClient = opsec_init_entity(pEnv, LEA_CLIENT,
OPSEC_SESSION_START_HANDLER, LeaStartHandler, OPSEC_EOL);

In Ruby callbacks are Procs or Lambdas, but how do I get them into the
function call described here with <callback>?

client = opsec_init_entity opsec_env, objptr, :int,
OPSEC_SESSION_START_HANDLER, :callback, <callback>, :int, 0

Does anybody know a way to give a pointer to a Proc into this function
call? Any hint is appreciated.

-aaalex