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Re: [Qemu-devel] [PATCH] Hack qmp.py to support reading a JSON multi-lin
From: |
Luiz Capitulino |
Subject: |
Re: [Qemu-devel] [PATCH] Hack qmp.py to support reading a JSON multi-line response |
Date: |
Mon, 20 Aug 2012 15:28:01 -0300 |
On Mon, 20 Aug 2012 19:25:02 +0100
"Daniel P. Berrange" <address@hidden> wrote:
> On Mon, Aug 20, 2012 at 03:03:11PM -0300, Luiz Capitulino wrote:
> > On Mon, 20 Aug 2012 15:01:37 +0100
> > "Daniel P. Berrange" <address@hidden> wrote:
> >
> > > From: "Daniel P. Berrange" <address@hidden>
> > >
> > > 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 <address@hidden>
> > > ---
> > > 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).
>
> Yeah, it is slightly unpleasant.
>
> > 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.
>
> How about making multi-line processing an optional feature, by adding
> a '-m' flag to qmp-shell. That way we still get error checking by
> default
Good idea.
>
>
> Daniel