Re: [Qemu-devel] [PATCH v2 2/4] scripts: qmp-shell: Expand support for QMP expressions

[Eric Blake]

On 04/22/2015 10:21 AM, John Snow wrote:
> This includes support for [] expressions, single-quotes in
> QMP expressions (which is not strictly a part of JSON), and
> the ability to use "True" or "False" literals instead of
> JSON's lowercased 'true' and 'false' literals.
> 
> qmp-shell currently allows you to describe values as
> JSON expressions:
> key={"key":{"key2":"val"}}
> 
> But it does not currently support arrays, which are needed
> for serializing and deserializing transactions:
> key=[{"type":"drive-backup","data":{...}}]
> 
> qmp-shell also only currently accepts doubly quoted strings
> as-per JSON spec, but QMP allows single quotes.
> 
> Lastly, python allows you to utilize "True" or "False" as
> boolean literals, but JSON expects "true" or "false". Expand
> qmp-shell to allow the user to type either, converting to the
> correct type.

Well, when easy to do.  See below for more discussion...

> 
> As a consequence of the above, the key=val parsing is also improved
> to give better error messages if a key=val token is not provided.
> 
> CAVEAT: The parser is still extremely rudimentary and does not
> expect to find spaces in {} nor [] expressions. This patch does
> not improve this functionality.

If someone cares about this, they can fix it later.  As I said in the v1
review, qmp-shell is mostly for debugging and testsuites, and we can
live with the caveats for now.

> 
> Signed-off-by: John Snow <address@hidden>
> ---
>  scripts/qmp/qmp-shell | 44 ++++++++++++++++++++++++++++----------------
>  1 file changed, 28 insertions(+), 16 deletions(-)

As far as I can tell, this makes qmp-shell strictly more useful, so I
have no qualms giving:

Reviewed-by: Eric Blake <address@hidden>

> 
> diff --git a/scripts/qmp/qmp-shell b/scripts/qmp/qmp-shell
> index a9632ec..4cdcb6c 100755
> --- a/scripts/qmp/qmp-shell
> +++ b/scripts/qmp/qmp-shell
> @@ -88,23 +88,35 @@ class QMPShell(qmp.QEMUMonitorProtocol):
>          # clearing everything as it doesn't seem to matter
>          readline.set_completer_delims('')
>  
> +    def __parse_value(self, val):
> +        try:
> +            return int(val)
> +        except ValueError:
> +            pass
> +
> +        if val.lower() == 'true':
> +            return True
> +        if val.lower() == 'false':
> +            return False

...as promised earlier,

This allows param=tRuE (neither JSON nor Python), but that's a minor
price to pay to get both param=true (param=JSON style) and param=True
(param=Python style) to work.  Meanwhile...

> +        if val.startswith(('{', '[')):
> +            try:
> +                return json.loads(val)

This statement accepts param=JSON style, as in:
 param={ "foo":true }
but it rejects (as invalid JSON):
 param={ 'foo':true }
 param={ "foo":True }
 param={ 'foo':True }

> +            except ValueError:
> +                pass
> +            try:
> +                return ast.literal_eval(val)

And this statement accepts param=Python style, as in:
 param={ "foo":True }
 param={ 'foo':True }
but it rejects (as invalid Python):
 param={ "foo":true }
 param={ 'foo':true }

Of those four combinations, QMP accepts:
 param={ "foo":true }
 param={ 'foo':true }
while rejecting:
 param={ "foo":True }
 param={ 'foo':True }

So among the four combinations of single/double quoting vs upper/lower
casing of boolean literals, qmp-shell now accepts three variants, but we
have a case that QMP accepts but qmp-shell rejects (single quotes mixed
with lower-case true).

Not the end of the world (again, if someone wants all four cases to work
in qmp-shell and/or QMP proper, they can provide a patch later to
further enhance things).  But maybe worth expanding that CAVEAT in the
commit message to acknowledge the issues.

At any rate, doesn't affect my R-b given above.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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