From: Oliver <python152@...>
Date: 2007-07-17T11:55:36+09:00
Subject: ruby extension help

hi, folks -

I am working on a ruby extension for an existing C library, and ran
into difficulties due to a "unique" data structure (unique in the
sense that I didn't find any examples to follow).

I've posted a similar help message on comp.language.ruby, but didn't
get a clear answer, hopefully this will reach a wider developer
community and I appreciate your help.

=== background

The C library I am working on has a so-called dynamic command dispatch
structure, it is basically a hook meant for accommodating a set of
user-provided call back functions. It is defined as follows:

/* command dispatch structure */
typedef int (*proxy_cmd)(int trans_id, int nargs, char **args);

struct proxy_commands {
        int                         cmd_base;
        int                         cmd_size;
        proxy_cmd *       cmd_funcs;
};

typedef struct proxy_commands   proxy_commands;

/* end of definition */


=== C usage

Under normal case, a C library user will supply the following
structure and make use of above structure.

int my_init(server,port) { ... }
int my_connect( ... ) { ...}

/* put all function pointer into array */
proxy_cmd cmds[] = {
   my_init,
   my_connect,
   my_finish,
   ...
};


/* and then fill in the required structure */

proxy_commands mytabs = {
    CMD_BASE;
    sizeof(cmds)/sizeof(proxy_cmd),
    cmds

}

/* finally, they can call a library API to register these functions */

register(&mytabs)


=== Ruby extension

Now, when I try to wrap above structure in ruby, I am facing a
dilemma: for the call back function that a C user need to supply, I
want the flexibility to allow user to write those call back functions
in Ruby. Otherwise, they will have to write a mixture of ruby and C to
use a C library, which is kind of awkward.

To support writing these call backs in Ruby, that means in the wrapper
code, I need to "map" those Ruby functions into C, somehow, and fill
in the required structure such as I did in "mytabs", is this correct
steps to follow? and how do I do that?

I am hoping ruby code of using the library will be something like
this, but I don't know if it is possible at all:

def my_init(server, port) { ... } end
def my_connect(...) { ... } end

funcs = [my_init, my_connect]
foo = Proxy.new
foo.register(funcs)

or something like that.

I know this is a convoluted case, and probably too much details to
follow. Let me know if this needs any clarification. Any pointer or
help is much appreciated.

Thanks

Oliver