Enable VuFind to query Hathi on canceled OCNs as well as current OCNs

[dbietila]

Currently, VuFind should check for Hathi availability based on current OCLC number (which is an 035 $a field). Sometimes, Hathi uses an outdated or canceled OCLC number for the record on their end. We may have these canceled OCLC numbers in our records as 035 $z fields.

Can we also check the Hathi API for matches based on the 035 $z numbers? This could be done in several ways - maybe we send all of the numbers concurrently, and maybe we check the 035 $z only when there is not a match using the 035 $a.

[bbusenius]

I looked into this and it's as I remembered. Currently VuFind does not use an API to check Hathi availability before generating the link. Instead, it just generates a link based on the MARC fields (and/or bib number) and the OCLC number. There is no checking, it just looks at the MARC and generates the link. In order to do what's being asked here, we would need to re-write all the logic to precheck using an API and generate the link asynchronously. This would be a fairly large project. I'm curious about how many bad links we generate because this has been in service for a long time.