clarifying CQL2-based responses and paging links

[tomkralidis]

When an OGC API - Features server processes an .../items query which has, for example, a CQL2 JSON payload, how can next and/or prev links provide paging with the same results in paging fashion?

Options:

1. encode CQL2 JSON as CQL2 TEXT in a next/prev link
2. add additional properties to a link object to capture/preserve POST semantics
3. other options?

cc @pvretano @cportele

Related: geopython/pycsw#1182

[cportele]

@tomkralidis

items does not support queries as payloads (according to the standard, APIs can of course support POST/QUERY on items for queries), but the same issue applies to ad-hoc queries on the search endpoint.

In ldproxy we have a related issue: ldproxy/ldproxy#906. The two options that we see are:

• Extending the link object to support other HTTP methods and a payload;
• Temporarily store such queries on the server and use opaque next links (effectively make these unpublished-short-term-stored-queries).

[tomkralidis]

Thanks @cportele. I would advocate for extending the link object, as it can ensure full transparency of a paging workflow (albeit adding more machinery to a client), as well as not introduce the need for a server to manage stored queries per se.

[cportele]

@tomkralidis

Opaque next links would be the better solution as they are already covered by the specifications and they use standard RFC 8288 web links. That is, there is no need for client changes.

In general, all links should still work in clients that only know about RFC 8288, to avoid surprises by links that result in 4xx or 5xx responses. So probably an extended link that supports POST with payloads would require yet another category beside "link" and "link template" (like "link with payload").

For cases where opaque "next" links cannot be implemented in a server an extended link object may be the best solution, if it is realistic to expect that clients can handle them.

I looked at STAC API and they support both opaque next links (like OGC API Features does) and also specify an extended link object for other methods and requests with payload: https://github.com/radiantearth/stac-api-spec/tree/main/item-search#pagination