Re: Extending Lua-RPC: questions about handling index and call events

[Geoff Leyland <geoff_leyland@...>]

Hi,

That's a tough one - how would you handle


remote_cos = handle.math.cos
res = remote_cos(3.1)

or

table_I_want_transferred_in_its_entirety_now = handle.a_table

Can you work out a user's intentions without extra syntax?

You could obviously have some kind of evaluate function:

res = rpc.evaluate(handle.sometable.entry)

but I guess you're trying to avoid that because you didn't mention  
it?  Would lazy evaluation work?  You could not do anything until the  
object is used by a __call, __tostring, __add or some other  
metamethod.  There would be the usual problem with comparison  
operators, but it would work some of the time I think.

Cheers,
Geoff

On 4/06/2009, at 4:45 AM, James Snyder wrote:

> Hi -
>
> I've been working on adding some features to Russell Smith's Lua-RPC  
> (http://q12.org/lua/index.html), which I've started putting up on  
> GitHub here (functional, but not yet at a release stage: http://github.com/jsnyder/luarpc/) 
> .  It works by having a server listen for incoming requests for  
> function calls.  When one comes in it executes it and handles the  
> return of data from the called function back to the client machine.   
> The client side is slightly more interesting, when one successfully  
> connects to a server, one gets a handle userdata, which has an  
> __index metatable.  When the table is indexed, a helper userdata is  
> created with a __call metatable.  If this helper is called, the  
> function name is transmitted to the remote Lua state and pcalled  
> with a custom error handler.  Depending on how things complete;  
> results or error handling information are passed back to the client  
> that initiated the call.
>
> This works fairly well, but I would like to extend it so that in  
> addition to calls to global functions, one could also call functions  
> registered on tables, as well as just index remote variables or  
> table entries to be able to inspect the remote state without having  
> to send a function over to do that.
>
> As it stands, one can do things like:
> handle = rpc.connect()
> res = handle.tostring(3.15)
>
> The number 3.15 goes out to the server, the server does the  
> tostring, and the resulting string is passed back to the client on  
> the stack.
>
> Now to the question:
> I'd like to be able to do things like:
> res = handle.math.cos(3.1)
>
> or:
>
> res = handle.sometable.someentry
>
> and have the former perform the operation on the remote machine,  
> with a result returned, or the latter give me what was in someentry  
> on the remote machine.  What I'm unsure of however is how to know  
> whether the sequence will end with gettable or call before  
> returning.  Any suggestions on how to structure that to work for  
> either situation?  It would be quite neat to be able to essentially  
> work with a remote Lua environment just by prepending the handle.
>
> Thanks in advance :-)
>
>
> --
> James Snyder
> Biomedical Engineering
> Northwestern University
> jbsnyder@fanplastic.org
> http://fanplastic.org/key.txt
> ph: (847) 448-0386