Re: [opendemo-devel] Perfomance.

[Dr. U. G. <Uwe...@ph...>]

Hello!

> I come to the conclusion, that I first have to look at and understand all the
> typical uses of all the fb* functions.
I found a possible buffer overrun in the code:

libs/od_xml_read.c/xmlParseCharacters()
reads characters up to the first processing character (<,&) and 
discards any whitespaces up to the first real character.

The main point is
firstChar = -1;
for (len = 0; ; len++) {
	c = fbReadChar(doc.fb, len);
	if (c == '<' || c == '&')
		break;
	...
	if (!IS_BLANK(c) && firstChar == -1)
		firstChar = len;
}
So we have now len bytes checked and at the position firstChar 
(firstChar <= len) ends the whitespaces.

If we had only 'len' whitespaces, these 'len' bytes will be ignored:
        if (firstChar == -1) {
                if (doc.sax && doc.sax->ignorableWhitespace)
                        doc.sax->ignorableWhitespace(doc.userData,
                                mbGetBuffer(doc.fb->mb) + doc.fb->offset, len);
        }
        else {
But if we had also real data, we do something strange:
                if (doc.sax && doc.sax->characters)
                        doc.sax->characters(doc.userData,
                                mbGetBuffer(doc.fb->mb) + doc.fb->offset + firstChar, len);
        }
This would mean, we have len characters after the firstChar position.
I think, this must be:
	else {
		/*
			ignorable whitespace comes only between 2 tags,
			so we have no doc.sax->ignorableWhitespace() call here.
		*/
		/* after the white-spaces come only len-firstChar characters */
                if (doc.sax && doc.sax->characters)
                        doc.sax->characters(doc.userData,
                                mbGetBuffer(doc.fb->mb) + doc.fb->offset + firstChar, len - firstChar);
	}
This problem never arose, because the ODQ3A files contain no simple characters
but only XML tags and everything is in attributes.

I'll read the code a bit further, maybe I find something more. I intend to
implement some ring-buffer code tomorrow and 'll fix this one too.

Bye, Uwe