[jira] [Updated] (DAFFODIL-3074) stringAsXML always creates empty elements

["Steve Lawrence (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/DAFFODIL-3074?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Steve Lawrence updated DAFFODIL-3074:
-------------------------------------
    Fix Version/s: 4.2.0

> stringAsXML always creates empty elements
> -----------------------------------------
>
>                 Key: DAFFODIL-3074
>                 URL: https://issues.apache.org/jira/browse/DAFFODIL-3074
>             Project: Daffodil
>          Issue Type: Bug
>          Components: Back End
>            Reporter: Steve Lawrence
>            Priority: Major
>              Labels: beginner
>             Fix For: 4.2.0
>
>
> When using the stringAsXml feature, if the input XML contains something like <foo></foo>, this will be written to the infoset as <foo />, i.e. a self-closing empty element. Although stringAsXml does not guarantee that it will not change the XML in some way, where possible we try to keep the XML exactly the same. It would be nice if we could maintain empty vs non-empty elements as well.
> The issue seems to be that when the XMLStreamReader sees START_ELEMENT and END_ELEMENT events, we call writeStartElement() and writeEndElement() functions respectively:
> https://github.com/apache/daffodil/blob/main/daffodil-core/src/main/scala/org/apache/daffodil/runtime1/infoset/XMLTextInfosetInputter.scala#L145-L159
> And it seems Woodstox auto collapses elements with no content into empty elements (e.g. <foo />).
> The normal XMLStreamReader and XMLStreamWriter API's do not seem to have a way to really control this--the XMLStreamReader sees the same START/END events regardless if the element is empty or not. And the XMLStreamWriter does not have a way to specify if an element should be written as empty or not. 
> But I think the Woodstox XMLStreamReader2 and XMLStreamWriter2 API's do provide enough information. Based on the API and skimming code, I think these are the changes that need to be made, though they haven't been tested:
> 1. In the XMLTextInfosetInputter and XMLTextInfosetOutputter, when we call createXMLStreamReader or createXMLStreamWriter, we cast the result to the Woodstox XMLStreamReader2 and XMLStreamWriter2 interfaces. This gives us access to the additional API functions we need.
> 2. Modify the writeXMLStreamEvent in XMLTextInfosetInputter so that the START_ELEMENT logic is something like this:
> {code:scala}
> if (xsr.isEmptyElement()) {
>   xsw.writeEmptyElement(...)
> } else {
>   xsw.writeStartElement(...)
> }
> ... // existing namespace/attribute code
> if (xsr.isEmptyElement()) {
>   xsr.next() // skip the END_ELEMENT event since writeEmptyElement ends the element
> }
> {code}
> So we call writeEmptyElement or writeStartElement depending on if the the element is empty or not. And if the element is empty, then we also call xsr.next() to skip the END_ELEMENT event to avoid calling writeEndElement for it.
> 3. Modify  the END_ELEMENT logic so it calls xsw.writeFullEndElement() instead of xsw.writeEndElement(). This forces it to write both the opening and closing tag.
> So now END_ELEMENT ensures we always write an opening and closing tag, and START_ELEMENT handles the case where the element is empty and ensures END_ELEMENT is skipped.
>  



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