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Re: [Qemu-devel] [RFC PATCH] qmp.py: Fix exception parsing partial JSON
From: |
Daniel P . Berrangé |
Subject: |
Re: [Qemu-devel] [RFC PATCH] qmp.py: Fix exception parsing partial JSON |
Date: |
Wed, 6 Jun 2018 18:01:17 +0100 |
User-agent: |
Mutt/1.9.5 (2018-04-13) |
On Wed, Jun 06, 2018 at 01:53:19PM -0300, Philippe Mathieu-Daudé wrote:
> The readline() call returns partial data.
> Keep appending until the JSON buffer is complete.
>
> This fixes:
>
> $ scripts/qmp/qmp-shell -v -p /tmp/qmp.sock
> Traceback (most recent call last):
> File "scripts/qmp/qmp-shell", line 456, in <module>
> main()
> File "scripts/qmp/qmp-shell", line 441, in main
> qemu.connect(negotiate)
> File "scripts/qmp/qmp-shell", line 284, in connect
> self._greeting = super(QMPShell, self).connect(negotiate)
> File "scripts/qmp/qmp.py", line 143, in connect
> return self.__negotiate_capabilities()
> File "scripts/qmp/qmp.py", line 71, in __negotiate_capabilities
> greeting = self.__json_read()
> File "scripts/qmp/qmp.py", line 85, in __json_read
> resp = json.loads(data)
> File "/usr/lib/python2.7/json/__init__.py", line 339, in loads
> return _default_decoder.decode(s)
> File "/usr/lib/python2.7/json/decoder.py", line 364, in decode
> obj, end = self.raw_decode(s, idx=_w(s, 0).end())
> File "/usr/lib/python2.7/json/decoder.py", line 380, in raw_decode
> obj, end = self.scan_once(s, idx)
> ValueError: Expecting object: line 1 column 3 (char 2)
>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
> Daniel suggested this is due to blocking i/o.
>
> I'm sure there is a nicer/more pythonic way to do this, but this works for me,
> sorry :)
>
> scripts/qmp/qmp.py | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/scripts/qmp/qmp.py b/scripts/qmp/qmp.py
> index 5c8cf6a056..e8b55dfcc4 100644
> --- a/scripts/qmp/qmp.py
> +++ b/scripts/qmp/qmp.py
> @@ -78,11 +78,16 @@ class QEMUMonitorProtocol(object):
> raise QMPCapabilitiesError
>
> def __json_read(self, only_event=False):
> + data = ""
> while True:
> - data = self.__sockfile.readline()
> - if not data:
> + tmp = self.__sockfile.readline()
> + if not tmp:
> return
> - resp = json.loads(data)
> + data += tmp
> + try:
> + resp = json.loads(data)
> + except ValueError:
> + continue
Downside is that we'll blindly loop if QEMU ever sends
malformed data, but given the use context of this QMP
shell that's not too serious.
> if 'event' in resp:
> self.logger.debug("<<< %s", resp)
> self.__events.append(resp)
If we get an event, we'll continue on the loop and append
to 'data' again, so you must blank out data to "" after
json.loads() succeeeds.
Regards,
Daniel
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