On 03/16/19 16:55, Tom Lane wrote: > What do you think of the idea I just posted about parsing off the DOCTYPE > thing for ourselves, and not letting libxml see it?
The principled way of doing that would be to pre-parse to find a DOCTYPE, and if there is one, leave it there and parse the input as we do for 'document'. Per XML, if there is a DOCTYPE, the document must satisfy the 'document' syntax requirements, and per SQL/XML:2006-and-later, 'content' is a proper superset of 'document', so if we were asked for 'content' and can successfully parse it as 'document', we're good, and if we see a DOCTYPE and yet it incurs a parse error as 'document', well, that's what needed to happen. The DOCTYPE can appear arbitrarily far in, but the only things that can precede it are the XML decl, whitespace, XML comments, and XML processing instructions. None of those things nest, so the preceding stuff makes a regular language, and a regular expression that matches any amount of that stuff ending in <!DOCTYPE would be enough to detect that the parse should be shunted off to get 'document' treatment. The patch I submitted essentially relies on libxml to do that same parsing up to that same point and detect the error, so it would add no upfront cost in the majority of cases that aren't this corner one. But keeping a little compiled regex around and testing the input with that would hardly break the bank, either. Regards, -Chap
