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Re: [Qemu-devel] [RFC PATCH v3 11/11] QMP/qmp.py: set locale for excepti

From: Tomoki Sekiyama
Subject: Re: [Qemu-devel] [RFC PATCH v3 11/11] QMP/qmp.py: set locale for exceptions to display non-ascii messages correctly
Date: Fri, 24 May 2013 18:55:21 +0000

On 5/23/13 8:30 , "Stefan Hajnoczi" <address@hidden> wrote:

>On Tue, May 21, 2013 at 11:34:16AM -0400, Tomoki Sekiyama wrote:
>> qemu-ga in Windows may return error message with multibyte characters
>> when the guest OS language is set to other than English. To display such
>> messages correctly, this encodes the message based on the locale
>> Signed-off-by: Tomoki Sekiyama <address@hidden>
>> ---
>>  QMP/qmp.py |    4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>> diff --git a/QMP/qmp.py b/QMP/qmp.py
>> index c551df1..ee21819 100644
>> --- a/QMP/qmp.py
>> +++ b/QMP/qmp.py
>> @@ -11,6 +11,7 @@
>>  import json
>>  import errno
>>  import socket
>> +import locale
>>  class QMPError(Exception):
>>      pass
>> @@ -133,7 +134,8 @@ class QEMUMonitorProtocol:
>>      def command(self, cmd, **kwds):
>>          ret = self.cmd(cmd, kwds)
>>          if ret.has_key('error'):
>> -            raise Exception(ret['error']['desc'])
>> +            enc = locale.getpreferredencoding()
>> +            raise Exception(ret['error']['desc'].encode(enc))
>You should not need to explicitly encode the error descriptor.  The
>error description should be UTF-8 on the wire and a Unicode Python
>string in this script.
>I think the real problem is:
>1. Guest qga is writing strings in local encoding onto the wire.

The error description Guest qga writes is encoded like:

  {"error": {"class": "GenericError", "desc": "\u64CD\u4F5C\u306F..."}}

I feel this is correct (\u64CD is a correct representation of single
character in Unicode).

>2. qmp.py isn't UTF-8-decoding strings received over the wire.

And qmp.py can decode this correctly, and ret['error']['desc'] is
Unicode Python string.

The problem looks like in python Exception, that cannot print out
the message at all if it contains non-ascii Unicode string:

% python

>>> raise Exception(u"abc")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
Exception: abc

>>> raise Exception(u"abcü")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>

while the "print" doesn't have this issue:

>>> print(u"abcü")

>Either or both bugs could be present.  Once they are fixed you shouldn't
>see encoding problems.

Anyway, as I understood this patch for qmp.py is not correct way to fix
this issue, I'm going to drop it from the series.


Tomoki Sekiyama

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