Re: [xml-dev] External subset processing by browsers

["Andrew Welch" <andrew.j.welch@gmail.com>]

Hi Elliotte,

2008/12/5 Elliotte Rusty Harold <elharo@metalab.unc.edu>:
> Firefox. There are two separate issues here:
>
> 1. Whether Firefox should read the external DTD subset.
> 2. How it should treat unrecognized entities when it doesn't read the
> external subset.
>
> Let me check the spec, but my recollection is that if the external DTD
> subset is not read, unrecognized entities are not a fatal error.

I have a similar issue, for example there are some RSS feeds which
contain entity references but no doctype:

<foo>foo &euro; bar</foo>

I was trying the handle them by supplying a LexicalHandler (to trap
and convert them to numeric refs), and setting a few Xerces features,
but it always throws an exception for it before the startEntity event.

Sample code (using Xerces 2.9.0):

public class Test extends XMLFilterImpl implements LexicalHandler {

    public static void main(String... args) throws Exception {
        new Test();
    }

    public Test() throws Exception {

        String xml = "<foo>foo &euro; bar</foo>";

        XMLReader xmlReader =
XMLReaderFactory.createXMLReader("org.apache.xerces.parsers.SAXParser");
        xmlReader.setProperty("http://xml.org/sax/properties/lexical-handler";,
this);
        xmlReader.setFeature("http://apache.org/xml/features/scanner/notify-char-refs";,
true);
        xmlReader.setFeature("http://apache.org/xml/features/validation/unparsed-entity-checking";,
false);
        xmlReader.setFeature("http://xml.org/sax/features/external-parameter-entities";,
false);
        xmlReader.setEntityResolver(this);
        xmlReader.parse(new InputSource(new StringReader(xml)));
    }

    @Override
    public void startDocument() throws SAXException {
        super.startDocument();
    }

   public void startEntity(String name) throws SAXException {
       System.out.println("Start ent: " + name);
    }

    public void endEntity(String name) throws SAXException { }
    public void startCDATA() throws SAXException { }
    public void endCDATA() throws SAXException {  }
    public void startDTD(String name, String publicId, String
systemId) throws SAXException { }
    public void endDTD() throws SAXException { }
    public void comment(char[] ch, int start, int length) throws
SAXException { }
}

The output when running this is:

[Fatal Error] :1:16: The entity "euro" was referenced, but not declared.
Exception in thread "main" org.xml.sax.SAXParseException: The entity
"euro" was referenced, but not declared.
        at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
        at Test.<init>(Test.java:37)


It would be really nice to handle this non-well-formed input using XML
tools without resorting to a regex replace across every feed... I'm
not sure it's possible but the features make it seem like it should be
- any ideas?


thanks
-- 
Andrew Welch
http://andrewjwelch.com
Kernow: http://kernowforsaxon.sf.net/