Does Libvirt's json parser support single quoted string in qmp json string?

Daniel P. Berrangé berrange at
Tue Feb 4 09:21:30 UTC 2020

On Tue, Feb 04, 2020 at 09:11:27AM +0100, Markus Armbruster wrote:
> Eric Blake <eblake at> writes:
> > [adding Markus]
> >
> > On 2/3/20 4:13 AM, Daniel P. Berrangé wrote:
> >> On Fri, Jan 31, 2020 at 06:44:42AM -0600, Eric Blake wrote:
> >>> On 1/31/20 4:38 AM, Peter Luo wrote:
> >>>
> >>>> error: internal error: cannot parse json {"execute": "block-commit", "arguments": { "device": "drive-virtio-disk2", "job-id": "job100", "base":'json:{"encrypt.key-secret":"vol-38973xjl.secret","driver":"qcow2","file":{"driver":"file","filename":"/pitrix/data/container/vol-38973xjl.img"}}', "top": "/pitrix/data/container/vol-38973xjl_ss-2tw7v0mm.img"}}: lexical error: invalid char in json text.
> >>>>
> >>>>             , "job-id": "job100", "base":'json:{"encrypt.key-secret":"vo
> >>>>
> >>>>                        (right here) ------^
> >>>>
> >>>
> >>> qemu's QMP language has an extension where it accepts 'string' in addition
> >>> to the JSON "string".  But it uses a hand-rolled parser, so it can do
> >>> whatever it wants.
> >>
> >> Can we deprecate & remove this extension in QEMU ?


> >> On the flip side, if we're going to support extensions like single quoting,
> >> then we should make it clear to applications that this is not really JSON
> >> and that they need to provide an impl that is 100% matching QEMU's dialect.
> >> This effectively means they need just import a copy of QEMU's code.
> To the best of my knowledge, the JSON parser interprets any valid strict
> JSON input in accordance to RFC 8259.  In other words, you don't notice
> the extensions unless you use them, or rely on invalid strict JSON to be
> rejected.
> Peter Luo's input uses one of QEMU's JSON parser's extensions like this:
>     "base":'json:{...}'
> This is not valid strict JSON.  Libvirt's JSON parser doesn't accept it.
> The problem is not presence of extensions in QEMU, it's the use of these
> extensions in input for libvirt.  Removing the extensions from QEMU will
> not affect the error.  Removing their use from the input will.

The issue that I see is that QEMU accepts this input string when it
parsers JSON provided by the user.  This in turn means the user has
an expectation that other tools based on QEMU will accept this exact
same document. This is not the case because the other tools are
using a stricter impl of JSON. 

IOW QEMU's extensions have mislead the users into believing their 
JSON input is valid for any tool based on QEMU. 

Thus overall I think it would be beneficial for any places where
QEMU accepts JSON from external users or apps, to be restricted to
common JSON syntax only, without any QEMU specific extensions.

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