StAXEncoder.writeAttribute() putting attributes on wrong element?

[jsbiff]

In the following code, if xmlw is a normal StAX XMLStreamWriter object, the xhtml comes out correctly, that is, with the "rel" and "href" attributes attached to the "link" element:

       xmlw.writeStartElement("head");
	xmlw.writeEmptyElement("link");
	xmlw.writeAttribute("rel", "stylesheet");
	xmlw.writeAttribute("href", "css/xmlwriter01.css");
	xmlw.writeStartElement("title");
	xmlw.writeCharacters(title);
	xmlw.writeEndElement();
	xmlw.writeEndElement();

I ran this program (there's more to it - like setting encoding and fidelity options on the factory object - including the option EncodingOptions.INCLUDE_OPTIONS so that the resulting Exi file would have the options needed to decode it) , again, but this time I had xmlw setup as a StAXEncoder object, to write out the xhtml as an exi file.

I then used the exificient-gui program to decode to an XML file, and what I discovered is that the two attributes that should have been on the "link" element, ended up on the element AFTER the link element (which was a "title" element).

I think this might be a bug?

[danielpeintner]

I think the problem is that the current implementation assumes that the following line

xmlw.writeEmptyElement("link");

is a start element followed by an end element.
Hence, no attributes.

see

exificient/src/main/java/com/siemens/ct/exi/main/api/stream/StAXEncoder.java

Lines 618 to 622 in 6c16b06

	public void writeEmptyElement(String prefix, String localName,
	String namespaceURI) throws XMLStreamException {
	this.writeStartElement(prefix, localName, namespaceURI);
	this.writeEndElement();
	}

If I get your message (code snippet) right, it might be possible that in StAX terms an empty element might have attributes, right?
If so the implementation of https://github.com/EXIficient/exificient/blob/master/src/main/java/com/siemens/ct/exi/main/api/stream/StAXEncoder.java is not correct.

Note: a workaround would be to use the following sequence.

xmlw.writeStartElement("head");
xmlw.writeStartElement("link");
xmlw.writeAttribute("rel", "stylesheet");
xmlw.writeAttribute("href", "css/xmlwriter01.css");
xmlw.writeEndElement(); // link
xmlw.writeStartElement("title");
xmlw.writeCharacters(title);
xmlw.writeEndElement(); // title
xmlw.writeEndElement(); // head

[jsbiff]

@danielpeintner "If I get your message (code snippet) right, it might be possible that in StAX terms an empty element might have attributes, right?"

That sounds about right. Yes, I could do a non-empty element, but, yes, StAX allows to add attributes to an empty element - because an empty element is still allowed to have attributes. It would end up looking, in standard xml text serialization, as:

<link rel="stylesheet" href="css/xmlwriter01.css" />

The "end" of the element seems to happen automatically in the JDK implementation, when a non-attribute event happens after a writeEmptyElement. So, in this example, when xmlw.writeStartElement("title"); is run, the empty element gets closed. I would expect "characters", "PCData" or "EndElement" events to also signal the end of the empty element (note that if an empty element is followed by an endelement, I don't think the endelement closes the empty element - rather it would close the parent element of the empty element; the reason I think this is, that as an experiment, I tried adding a writeEndElement after my empty element, and this caused a cascade error later in the app, when it got to the very last writeEndElement for the "html" element - the error indicated there was no element to close).

The interesting thing here is, if I take that text serialization from my program, encode it to exi with exificient-gui, then decode it again to xml, it preserves the link as an empty element with attributes. I guess that probably the exificient-gui app uses a different API like the SAX writer, which handles empty elements correctly.

So, in summary, yes, I think you've identified this correctly as a bug in StAXEncoder.java.

[danielpeintner]

Please take a look at #44
It should fix the issue.

[jsbiff]

@danielpeintner I tried to test this. I'm still seeing the errant resulting xml file after decoding with exificient gui.

Update: I realized that after cloning, I was supposed to switch to the issue-43 branch, and had not. I just did that, and am rebuilding exificient now. Will retest.

Update2: Success! After I switched to the correct branch ( 🤦🏻 ), rebuilt exificient, and tested again, I'm now getting CORRECT behavior - the attributes are attached to the empty 'link' element and not the following 'title' element.