[s-xml-rpc-devel] Defining remote functions

[Sven Van Caekenberghe]

On 17 Jun 2004, at 20:20, Frédéric Brunel wrote:

> Hi,
>
> By googling the Web for an XML-RPC implementation in Common Lisp, I 
> found S-XML-RPC and other one for Corman Lisp.  I'm glad that 
> S-XML-RPC is now part of Common-Lisp.net.
>
> By the way, looking at the Corman Lisp API for XML-RPC, I found 
> interesting that it have the ability to define a standard function 
> embedding an XML-RPC call.  How about implementing this kind of thing 
> in S-XML-RPC?  I wrote the following lines of code:
>
> (defmacro define-xmlrpc-method (name args &key url method)
>   `(defun ,name ,args
>      (xml-rpc-call (encode-xml-rpc-call ,method , at args)
>        :url ,(puri:uri-path url)
>        :host ,(puri:uri-host url)
>        :port ,(cond ((puri:uri-port url)) (t 80)))))
>
> (define-xmlrpc-method get-state-name (state)
>   :url #u"http://betty.userland.com/RPC2"
>   :method "examples.getStateName")
>
> (define-xmlrpc-method get-time ()
>   :url #u"http://time.xmlrpc.com/RPC2"
>   :method "currentTime.getCurrentTime")
>
> ? (get-state-name 41)
> "South Dakota"
>
> ? (get-time)
> #<XML-RPC-TIME 20040617T10:47:31>
>
> I rely on the great PURI package to parse URL.  Quite straightforward.

I do like the general idea, maybe we could add the macro to 
extension.lisp - I would like to have some more time to think over all 
possible implications.

> Of course, we should also wrap and unwrap some type convertions not to 
> see anything about the XML-RPC types.  I guess the function should 
> also accept HASHTABLEs to be converted in XML-RPC structs.
>
> What do you think?

There is a kind of problem with xml-rpc concering type conversions: 
xml-rpc itself supports only a limited number of types with no 
possibility to annotate them. I you want automatic conversions (like we 
have implemented it now), this will only take you one part of the way: 
for example, now cl sequences (lists and vectors) map to xml-rpc 
arrays, but when you get back an xml-rpc array you always get a list. 
Mapping cl structs, clos objects and hashtables to xml-rpc structs 
would work, but there would only be one return type.

The alternative (which is a lot more verbose) would be explicitely 
specify the xml-rpc call signature so that more complex (and usefull) 
conversions could be done (much like ffi). You could then say for 
example that a certain clos object is expected and converted to and 
from an xml-rpc struct. But this would then need to be extended to 
composite types, like arrays of a certain element type, or member types 
for slots ...

All this could be a very interesting and usefull extension. But one of 
the strengths of xml-rpc is its simplicity, especially in a dynamic 
language like lisp.

> -- 
> Frederic Brunel

Thanks for the feedback, frederic,

Sven