Problem with the client-side ("serviceprovider") implementation of ListRecords

[landreev]

It appears that harvesting via ListRecords is broken. The reason we never noticed is that Dataverse OAI client hasn't been using it, relying instead on making a ListIdentifiers call, then calling GetRecord for each non-deleted identifier. I am however working on adding support for harvesting via ListRecords as well, optionally.

To skip directly to the punchline, I believe all it is is this line:

xoai/xoai-service-provider/src/main/java/io/gdcc/xoai/serviceprovider/parsers/MetadataParser.java

Line 34 in 7584005

reader.next(elementName(localPart(equalTo("metadata"))));

The problem being that the <metadata> tag in question has already been parsed by the RecordParser before this parser has been called, here:

xoai/xoai-service-provider/src/main/java/io/gdcc/xoai/serviceprovider/parsers/RecordParser.java

Line 48 in 7584005

reader.next(elementName(localPart(equalTo("metadata")))).next(aStartElement());

A larger fragment:

xoai/xoai-service-provider/src/main/java/io/gdcc/xoai/serviceprovider/parsers/RecordParser.java

Lines 48 to 60 in 7584005

	reader.next(elementName(localPart(equalTo("metadata")))).next(aStartElement());
	String content = reader.retrieveCurrentAsString();
	ByteArrayInputStream inputStream =
	new ByteArrayInputStream(content.getBytes(StandardCharsets.UTF_8));
	XSLPipeline pipeline =
	new XSLPipeline(inputStream, true)
	.apply(context.getMetadataTransformer(metadataPrefix));
	if (context.hasTransformer()) pipeline.apply(context.getTransformer());
	try {
	record.withMetadata(new Metadata(new MetadataParser().parse(pipeline.process())));
	} catch (TransformerException e) {

In other words, when it's trying to parse this fragment of a ListRecords response:

<metadata>
<oai_dc:dc xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
<dc:title>This is my test dataset</dc:title>
<dc:identifier>https://doi.org/10.5072/FK2/U6AEZM</dc:identifier>
<dc:creator>Castro, Eleni</dc:creator>
<dc:publisher>Demo Dataverse</dc:publisher>
<dc:description>This is my dataset</dc:description>
<dc:subject>Social Sciences</dc:subject>
<dc:subject>Test</dc:subject>
<dc:date>2015-04-20</dc:date>
<dc:contributor>Admin, Dataverse</dc:contributor>
</oai_dc:dc>
</metadata>

the content String in line 49 above will only contain the <oai_dc:dc ...> ... </oai_dc:dc> part, and that's where the next parser bombs with

java.util.NoSuchElementException null
StackTrace: 
com.ctc.wstx.evt.WstxEventReader.throwEndOfInput(WstxEventReader.java:511)
com.ctc.wstx.evt.WstxEventReader.nextEvent(WstxEventReader.java:270)
io.gdcc.xoai.xmlio.XmlReader.next(XmlReader.java:129)
io.gdcc.xoai.serviceprovider.parsers.MetadataParser.parse(MetadataParser.java:34)
io.gdcc.xoai.serviceprovider.parsers.RecordParser.parse(RecordParser.java:60)
io.gdcc.xoai.serviceprovider.parsers.ListRecordsParser.next(ListRecordsParser.java:5
8)
io.gdcc.xoai.serviceprovider.handler.ListRecordHandler.nextIteration(ListRecordHandl
er.java:67)
io.gdcc.xoai.serviceprovider.lazy.ItemIterator.hasNext(ItemIterator.java:31)
io.gdcc.xoai.serviceprovider.lazy.ItemIterator.<init>(ItemIterator.java:22)
io.gdcc.xoai.serviceprovider.ServiceProvider.listRecords(ServiceProvider.java:73)
edu.harvard.iq.dataverse.harvest.client.oai.OaiHandler.runListRecords(OaiHandler.java:266)
edu.harvard.iq.dataverse.harvest.client.HarvesterServiceBean.harvestOAIviaListRecords(HarvesterServiceBean.java:289)

The fix appears to be as simple as commenting out line 34 in MetadataParser.java 😄.
But it would sound prudent to add a test or two that would attempt to parse some example fragments.

[landreev]

Hmm, I actually don't understand what's going on - looking at the existing RecordParser tests, I don't really get how they are passing.

[landreev]

Ok, I see, the tests are passing because of
context = new Context().withMetadataTransformer("oai_dc", KnownTransformer.OAI_DC);
in the test setup.

[landreev]

@poikilotherm I want to close this issue, since I opened it based on not understanding how that parser was supposed to work. (I warned upfront that that was a possibility)
But can I keep it open for just a little longer, just to understand what's going on there.
Am I reading it correctly, that XOAI can only harvest metadata for which it has a to_xoai xsl transform?

(as you can see, Dataverse hasn't been using this parser at all)

[landreev]

I may ask for, and/or make a PR adding an extra feature to record processing.