Esoteric QMP specification questions of dubious importance

[John Snow <jsnow@redhat.com>]

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I'm writing a "fake" QMP server for the purposes of creating unit tests for
the python QMP library. In doing so, I am left with some esoteric questions:


(1) qemu-spec.txt, section 2.4.2, "error":

The format of an "error response" is:

> { "error": { "class": json-string, "desc": json-string }, "id":
json-value }

For the purposes of naming internal types in the QMP library, does the
"error" object value have a canonical type name? It's not defined in QAPI
that I can see.


(2) qemu-spec.txt, section 2.2 "Server Greeting":

The greeting message format is:

> { "QMP": { "version": json-object, "capabilities": json-array } }
>
> Where,
>
> - The "version" member contains the Server's version information (the
format
>  is the same of the query-version command)

The layout of the "version" object is not specified in the spec itself,
though it does ask you to refer to the query-version command.
Hypothetically, is an alternate implementation of QMP in a binary that is
*not* QEMU allowed to change the layout of the "version" object (so long as
it matched whatever format it had for a "query-version" command, also not
mandated by the spec), or must it *always* conform to this precise layout?

(qapi/control.json):

> { 'struct': 'VersionInfo',
>    'data': {'qemu': 'VersionTriple', 'package': 'str'} }

If so, what should such a hypothetical client that is *not* QEMU do here?
What version does it report for the "qemu" VersionTriple member? Can I
report 0.0.0?


(3) Does the qmp-spec technically mandate any commands being available?

I believe that qmp_capabilities is definitively a requirement of the spec,
but what about query-commands, query-version, or quit? Are they technically
requirements of the QMP spec, or just requirements of QEMU?


Weird questions, I know.
--js

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