[webkit-dev] Writing a new XML parser with no external libraries

[Eric Seidel]

That was done, long ago.  You can find the old patches in our svn history. :)

On Tue, Jun 28, 2011 at 6:44 PM, Wyatt Carss <wcarss at google.com> wrote:
> If that were all, would it be possible to patch libxml2 to use UTF-16? That
> might be less of an undertaking than writing a new xml library, but that
> could just be my youthful naivety..
>
> On Tue, Jun 28, 2011 at 6:36 PM, Jeffrey Pfau <jpfau at apple.com> wrote:
>>
>> I don't know all of the problems libxml2 has, but one of the ones I've
>> heard is that WebCore uses UTF-16 internally, and libxml2 uses UTF-8, so the
>> data is perpetually converted between the two formats--and this is slow. If
>> there are any other big ones, I haven't been told them, only that it would
>> be good to have a replacement.
>>
>> Jeffrey Pfau
>>
>> On Jun 28, 2011, at 6:30 PM, Dirk Pranke wrote:
>>
>> > Can you expand a bit more on "using libxml2 exposes its own share of
>> > problems"?
>> >
>> > -- Dirk
>> >
>> > On Tue, Jun 28, 2011 at 6:12 PM, Jeffrey Pfau <jpfau at apple.com> wrote:
>> >> Currently, WebCore uses libxml2, or, if available, QtXml to parse
>> >> incoming XML. However, QtXml isn't always available, and using libxml2
>> >> exposes its own share of problems. As such, I'm undertaking writing an XML
>> >> parser that uses no external libraries.
>> >>
>> >> The first step to doing this is to add a new flag that switches off the
>> >> other two parsers. As the parsers are already independent and can be
>> >> switched between by checking USE(QXMLSTREAM), I am adding USE(LIBXML2)
>> >> checks, replacing the #else conditionals, and also a new ENABLE check,
>> >> tentatively called NEW_XML (although names such as NATIVE_XML or XML_NATIVE,
>> >> etc, may be more appropriate).
>> >>
>> >> As there will probably be a new slew of files pertaining to XML
>> >> parsing, I will put these files in WebCore/xml/parser, and move the existing
>> >> XMLDocumentParser* file into this new directory. As far as I know, the
>> >> placement of these files in WebCore/dom/ is legacy, and, assuming the build
>> >> on each platform is changed, it makes sense to move them.
>> >>
>> >> Once all the files are in a logical place, I plan to make a new file
>> >> for a skeleton of the new XMLDocumentParser, at least to get it to link
>> >> until a real one is in place, even if the XML parser at that point is just a
>> >> data sink.
>> >>
>> >> From there, I plan to copy and modify a good chunk of the lower level
>> >> HTML tokenization and parsing code, and make changes as necessary to make it
>> >> work on generalized XML, at least until I can generalize the common code in
>> >> such a way that the HTML and XML tokenizers can be subclasses and use common
>> >> code. I'd probably do the refactoring at the end.
>> >>
>> >> I'm still exploring the existing parsing code, but I'd probably work my
>> >> way up from there. I've read a lot of the XML 1.0 spec in preparation, as
>> >> well, but it doesn't have much on implementation itself. If QtWebKit or
>> >> parsing people have any comments, concerns, or help, I'd be more than
>> >> willing to listen--I'm just starting here, and I'm not completely familiar
>> >> with the codebase.
>> >>
>> >> Although no code is checked in so far, I've started on this list
>> >> already and have gotten as far as the new flags, a skeleton
>> >> XMLDocumentParserNew.cpp, and making a tokenizer that compiles and links,
>> >> but is completely untested.
>> >>
>> >> Jeffrey Pfau
>> >> _______________________________________________
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>> >> webkit-dev at lists.webkit.org
>> >> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
>> >>
>>
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