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Date: Thu, 17 Dec 2009 17:19:27 -0200
From: Luiz Capitulino <lcapitulino@redhat.com>
Subject: Re: [Qemu-devel] QMP's success response
Message-ID: <20091217171927.0aa4d242@doriath>
In-Reply-To: <20091217190918.GB362@shareable.org>
References: <20091217154147.22845395@doriath>
	<20091217190918.GB362@shareable.org>
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To: Jamie Lokier <jamie@shareable.org>
Cc: aliguori@linux.vnet.ibm.com, avi@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com

On Thu, 17 Dec 2009 19:09:18 +0000
Jamie Lokier <jamie@shareable.org> wrote:

> Luiz Capitulino wrote:
> > 
> >  Hi there,
> > 
> >  Currently, when a regular command doesn't have any data to output,
> > QMP will emit:
> > 
> > { "return": "OK" }
> > 
> >  I thought this was a good idea because it has a clear meaning. Silly me,
> > this is optimized for humans, but for machines it introduces the problem
> > that such commands can't be changed to return values.
> > 
> >  I'm not sure this is will ever happen, but to stay safe a better way
> > would be to return an empty dict, like this:
> > 
> > { "return": {} }
> 
> Logically, it would be { "return": null }. 

 In practice it brings the same problem.

> What if future return value is actually an empty dict? ;-)

 This is compatible and has the same end result.

>  E.g. from an enumeration command,  where the enumerated set is empty.

 Either, the command could return the empty dict or a dict
containing a "enum" key, which would be emitted like:

{ "result": { "enum": {} } }