views: signposting: fix: fallback to level 2 linkset if collections size too big to control link header size

[ptamarit]

• Bug fixes FAIR signposting level 1 support (HTTP Link headers & link rel item) invenio-app-rdm#2937
  • On a deployed environment, causing nginx to throw a generic 502 Bad Gateway.
• Fails on deployed setups with nginx since there is a limit on the size of the HTTP headers

[ptamarit]

This is a bit of an arbitrary limit:

• For author, we only include the ORCID URL, so the length is under control
• For item, filenames have a limit of 255 characters, so we should test on a deployed environment with filenames of this length
• For license, custom ones can have very long URLs (I tried with 5000 characters), since the marshmallow URL validator does not check for length, so this might be a big problem

[slint]

It's fine in this case to have the "magic" 5, since passing config to the serializers from the app is quite cumbersome (and breaks the assumption that serializers don't depend on Flask application context).

[slint]

LGTM, and thanks for the nice tests :)

[ptamarit]

Another way of avoid this problem is to configure nginx to allow for bigger response headers with:

    # Allow for larger HTTP response headers for FAIR signposting
    # level 1 support (see invenio-app-rdm#2937)
    uwsgi_buffers 8 16k;
    uwsgi_buffer_size 16k;