Re: [xml] question regarding error reporting

[Mark Vakoc <thevakoc-xml yahoo com>]

> > ...
> >   if ((channel == xmlParserError) ||
> >         (channel == xmlParserWarning) ||
> >     (channel == xmlParserValidityError) ||
> >     (channel == xmlParserValidityWarning))
> >     xmlReportError(to, ctxt, str, NULL, NULL);
> >     else if ((channel == (xmlGenericErrorFunc) fprintf) ||
> >              (channel == xmlGenericErrorDefaultFunc))
> >     xmlReportError(to, ctxt, str, channel, data);
> >     else
> >     channel(data, "%s", str);
> > ...

> > Is there a reason that xmlReportError isn't called regardless of what error
> > handler channel points to?
>
>   I think that the point was to make a single callback in case a structured
> error handler has been set-up (xmlReportError makes at least 2 calls IIRC).
> The expectation is that the structured error handler will find informations
> like the source file and line number from data or the global error variable.
> I.e. fprintf is not a structured error reporting mechanism, it's string
> based,
> so it can be called multiple times for one error, on the other hand the user
> callback is structured and should be called only once per error. I think it's
> the reason for this dichotomy.

Hmmm... fprintf isn't a stuctured error handler, but neither is channel.  I
believe by the time this segment is reached the search for a structured error
handler to report the message has been exhausted and there doesn't seem to be a
means to use custom structured error handlers within relaxng validation.  As
such there seems to be a "information penalty" when when using custom error
handlers and the error domain isn't parsing or validating (those seem to be
handled specially).

So if I understand your explanation correctly the goal is to only call channel
once per xmlRaiseError call unless the handler happens to be fprintf (as such
libxml2 knows that it is not a problem call it repeatedly per call to
__xmlRaiseError)?  If so perhaps __xmlRaiseError can instead call
xmlReportError2 that would emulate xmlReportError only building the output to a
string then calling channel just once?