Re: [Xen-devel] [PATCH] [Xend] host.get_log() : clean log of non-printable characters

[Stefan Berger <stefanb@xxxxxxxxxx>]

xen-devel-bounces@xxxxxxxxxxxxxxxxxxx wrote on 11/15/2007
09:38:37 AM:

> Stefan Berger writes ("[Xen-devel] [PATCH] [Xend] host.get_log()
: 
> clean log of non-printable characters"):
> > When retrieving the log via host.get_log() the python parser
on the
> > receiving side gets upset about non-printable characters ("\b").
Those
> > stem from libxc/xc_domain_restore:xc_domain_restore().
> 
> It is a shame that we are forced into writing a lossy log retrieval
> method by braindamage in XMLRPC and XML 1.0.  Perhaps we should
in
> future think about a get_log_lossless function which uses a binary
> encoding.  It'd have to be base64 :-/.
> 
> > -        return xen_api_success(log_buffer)
> > +        i = 0
> > +        res = ""
> > +        while i < len(log_buffer):
> > +            c = ord(log_buffer[i])
> > +            if (c < 32 or c
> 126) and (c < 10 or c > 13):
> > +                res
+= " "
> > +            else:
> > +                res
+= log_buffer[i]
> > +            i += 1
> > +        return xen_api_success(res)
> 
> This is a strange way of doing things and will be quite slow.

I agree. log_buffer[i] = ' ' unfortunately does not
wokr with python. The solution you show below is 
probably the right one.

   Stefan

> It's also wrong in that it replaces tabs.
> 
> In theory it would be best to try to map away all Unicode characters
> which are not in XML 1.0's Char.  However, this would involve
> explicitly interpreting the logfile as UTF-8 and it's not clear to
me
> that it always is.  If it isn't, it's probably better to let
the
> caller get whatever the logfile byte string is and hope they don't
> choke - at least until we know under what circumstances this arises.
> 
> So it's better just to map away the character we know is causing
> problems.  \r will be OK because it's allowed in XML as an encoding
of
> newline, which will do.  I've chosen below to replace \f as well
since
> I suspect they may appear at some point.
> 
> Ian.
> 
> diff -r ba69fe2dce91 tools/python/xen/xend/XendAPI.py
> --- a/tools/python/xen/xend/XendAPI.py   Tue Nov 13 20:13:50
2007 +0000
> +++ b/tools/python/xen/xend/XendAPI.py   Thu Nov 15 14:32:33
2007 +0000
> @@ -994,6 +994,8 @@ class XendAPI(object):
>      def host_get_log(self, session, host_ref):
>          log_file = open(XendLogging.getLogFilename())
>          log_buffer = log_file.read()
> +        log_buffer = log_buffer.replace('\b','
')
> +        log_buffer = log_buffer.replace('\f','\n')
>          return xen_api_success(log_buffer)
>  
>      def host_send_debug_keys(self, _, host_ref, keys):
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel