response is not correct for no records

[rerowep]

If we have no records the <ListRecords> opening tag is missing.

<?xml version=\'1.0\' encoding=\'UTF-8\'?>
<?xml-stylesheet type="text/xsl" href="/static/xsl/oai.xsl"?>
<OAI-PMH xmlns="http://www.openarchives.org/OAI/2.0/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/ http://www.openarchives.org/OAI/2.0/OAI-PMH.xsd">
  <responseDate>2020-06-02T23:00:28Z</responseDate>
  <request until="2020-06-02T23:00:28+00:00Z" from_="2020-06-02T06:00:00+00:00Z" metadataPrefix="marc21" verb="ListRecords">
    https://localhost:5000/oai2d
  </request>
  
  <ListRecords/>
</OAI-PMH>

[wgresshoff]

<ListRecords/> is an opening and closing tag at the same time. But in my opinion, if the response of ListRecords is empty, the should be no <ListRecords> tag at all but
<error code="noRecordsMatch"/> instead. But this is surely open for discussion, the spec is not so clear about it.

[pronguen]

If there are no records to be returned, the OAI provider should not send ListRecords response with empty contents, but noRecordsMatch error message.
Please see "Error and Exception Conditions" section in: http://www.openarchives.org/OAI/openarchivesprotocol.html#ErrorConditions

We are using Ex-libris Primo, a java client very common and often used in libraries, and it does not understand an empty ListRecords tag. Python clients seem therefore to understand such a response.

[jesusbagpuss]

This issue has just been reported on the OAI-PMH Google group.

A zenodo repository was failing it's validation, as the set chosen to validate against (in their case, the openaire set) didn't contain any records, but output an empty <ListIdentifiers/> element rather than the expected <error code="noRecordsMatch"/>.

Currently they are unable to register their OAI-PMH endpoint.