Re: [Qemu-devel] [PATCH] Hack qmp.py to support reading a JSON multi-line response

[Luiz Capitulino <lcapitulino@redhat.com>]

On Mon, 20 Aug 2012 15:01:37 +0100
"Daniel P. Berrange" <berrange@redhat.com> wrote:

> From: "Daniel P. Berrange" <berrange@redhat.com>
> 
> The qmp-shell code assumes the JSON response is only on a single
> line. If the QEMU monitor is configured in "pretty print" mode
> the JSON response can be multi-line. The basic Python JSON APIs
> do not appear to support a streaming mode, so the simple hack
> here is to try parsing a line, and if it fails, then read another
> line, append it, and try parsing again. Keep reading lines until
> we can successfully parse
> 
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
>  QMP/qmp.py | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/QMP/qmp.py b/QMP/qmp.py
> index 36ecc1d..464a01a 100644
> --- a/QMP/qmp.py
> +++ b/QMP/qmp.py
> @@ -61,10 +61,18 @@ class QEMUMonitorProtocol:
>  
>      def __json_read(self, only_event=False):
>          while True:
> -            data = self.__sockfile.readline()
> -            if not data:
> -                return
> -            resp = json.loads(data)
> +            data = ""
> +            while True:
> +                moredata = self.__sockfile.readline()
> +                if not moredata:
> +                    return
> +                data = data + moredata
> +                try:
> +                    resp = json.loads(data)
> +                    break
> +                except ValueError:
> +                    pass
> +

I'm reluctant about this, because it makes it impossible to detect bad
json from qemu (not that qmp-shell handles this gracefully today).

At the same time I can't think of anything simpler than your hack. What
about calling json.loads() when closing } matches the number of opening ones?
QMP responses are always dictionaries.

>              if 'event' in resp:
>                  self.__events.append(resp)
>                  if not only_event: