Re: possible encoding issues with libxml2 functions

On Sun, Aug 20, 2017 at 10:37:10PM +0200, Pavel Stehule wrote:
> > We have xpath-bugfix.patch and xpath-parsing-error-fix.patch. Both are
> > equivalent under supported use cases (xpath in UTF8 databases). Among
> > non-supported use cases, they each make different things better and
> > different
> > things worse. We should prefer to back-patch the version harming fewer
> > applications. I expect non-ASCII data is more common than xml declarations
> > with "encoding" attribute, so xpath-bugfix.patch will harm fewer
> > applications.
> >
> > Having said that, I now see a third option. Condition this thread's
> > patch's
> > effects on GetDatabaseEncoding()==PG_UTF8. That way, we fix supported
> > cases,
> > and we remain bug-compatible in unsupported cases. I think that's better
> > than
> > the other options discussed so far. If you agree, please send a patch
> > based
> > on xpath-bugfix.patch with the GetDatabaseEncoding()==PG_UTF8 change and
> > the
> > two edits I described earlier.
> >
>
> I am sorry - too long day today. Do you think some like
>
> diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
> index 24229c2dff..9fd6f3509f 100644
> --- a/src/backend/utils/adt/xml.c
> +++ b/src/backend/utils/adt/xml.c
> @@ -3914,7 +3914,14 @@ xpath_internal(text *xpath_expr_text, xmltype *data,
> ArrayType *namespaces,
> if (ctxt == NULL || xmlerrcxt->err_occurred)
> xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
> "could not allocate parser context");
> - doc = xmlCtxtReadMemory(ctxt, (char *) string, len, NULL, NULL, 0);
> +
> + /*
> + * Passed XML is always in server encoding. When server encoding
> + * is UTF8, we can pass this information to libxml2 to ignore
> + * possible invalid encoding declaration in XML document.
> + */
> + doc = xmlCtxtReadMemory(ctxt, (char *) string, len, NULL,
> + GetDatabaseEncoding() == PG_UTF8 ? "UTF-8" : NULL, 0);
> if (doc == NULL || xmlerrcxt->err_occurred)
> xml_ereport(xmlerrcxt, ERROR, ERRCODE_INVALID_XML_DOCUMENT,
> "could not parse XML document");

No, that doesn't match my description above. I don't see a way to clarify the
description. Feel free to try again. Alternately, if you wait, I will
eventually construct the patch I described.