Re: [Qemu-devel] [PATCH v4 2/4] scripts: qmp-shell: Expand support for QMP expressions

[John Snow]

On 04/29/2015 03:25 PM, Eric Blake wrote:
> On 04/29/2015 01:14 PM, 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", "False" and "None" literals instead
> > of JSON's equivalent true, false, and null 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.
> >
> > 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.
> >
> > Signed-off-by: John Snow <address@hidden>
> > ---
> >   scripts/qmp/qmp-shell | 63 ++++++++++++++++++++++++++++++++++++++-------------
> >   1 file changed, 47 insertions(+), 16 deletions(-)
>
> > +class FuzzyJSON(ast.NodeTransformer):
> > +    '''This extension of ast.NodeTransformer filters literal "true/false/null"
> > +    values in an AST and replaces them by proper "True/False/None" values that
> > +    Python can properly evaluate.'''
> > +    def visit_Name(self, node):
> > +        if node.id == 'true':
> > +            node.id = 'True'
> > +        if node.id == 'false':
> > +            node.id = 'False'
> > +        if node.id == 'null':
> > +            node.id = 'None'
> > +        return node
>
> Cute!

;)

> Reviewed-by: Eric Blake <address@hidden>

So the only remaining crime I am aware of is that when specifying 
key=val pairs without hoping for a favorable QMP deserialization is that 
we still accept e.g. "TrUe" and "FaLSe" and so on.

Patch 4 tries to make amends by explicitly converting objects back to 
strict JSON and printing that out for the user (if they supplied -v) so 
we can observe what conversions qmp-shell made for us to make things nice.

And I think I'm done playing with this for now. If I go any further, 
there's bound to be flex and bison files in the tree!

--js