Introspect data from Python missing return parameters

[John (J5) Palmieri]

In Python you can't know what will be returned if anything.  Sanity
checking returns I feel is the job of the caller.  If anything I would
just assume return a v which you wouldn't be able to sanity check
anyway.  

On Thu, 2005-10-06 at 20:14 +0100, Daniel P. Berrange wrote:
> I've been doing some interoperability testing of the Perl bindings, and 
> noticed a problem with the introspection data returned by Python services.
> While it provides information about the input parameters on methods, it
> omits information about the return parameters. Taking the 'example-service.py' 
> program, it returns
> 
> <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN" 
>   "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
> <node name="/SomeObject">
>   <interface name="org.freedesktop.DBus.Introspectable">
>     <method name="Introspect">
>     </method>
>   </interface>
>   <interface name="org.designfu.SampleInterface">
>     <method name="GetDict">
>     </method>
>     <method name="HelloWorld">
>       <arg name="hello_message" type="v" />
>     </method>
>     <method name="GetTuple">
>     </method>
>   </interface>
> </node>
> 
> Which is basically saying all its methods have no return value. In the Perl
> bindings I had assumed that introspection data is basically complete, or
> absent altogether. If present, I use the introspection data for return types
> to sanity the method reply contents. Hence with the return types missing, 
> the sanity checks abort the caller. 
> 
> I expect to receive something closer to:
> 
> <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
>   "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
> <node name="/SomeObject">
>   <interface name="org.freedesktop.DBus.Introspectable">
>     <method name="Introspect">
>       <arg type="s" direction="out"/>
>     </method>
>   </interface>
>   <interface name="org.designfu.SampleInterface">
>     <method name="GetDict">
>       <arg type="a{ss}" direction="out"/>
>     </method>
>     <method name="GetTuple">
>       <arg type="(ss)" direction="out"/>
>     </method>
>     <method name="HelloWorld">
>       <arg type="s" direction="in"/>
>       <arg type="as" direction="out"/>
>     </method>
>   </interface>
> </node>
> 
> 
> For weakly typed languages this isn't really too critical whether the
> return types are there or not, but strongly typed languages which 
> use introspection data to auto generate API bindings would be handicapped. 
> Thus I think it would be useful to fill out the spec on introspection
> to make it explicit about the semantics of the data provided. 
> 
>  * Is it compulsory to list all interfaces ?
>  * Is it compulsory to list all methods/signals within an interface ? 
>  * Is it compulsory to list all parameters/return types for a method ?
> 
> Personally I'd like the answer to be yes for all of those questions,
> since it makes it possible to sanity check usage in the client code
> to provide explicit & informative error messages to the programmer.
> 
> Regards,
> Dan.
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