xcube serve failing to open cubes (sometimes silently)

[mdespriee]

Describe the bug

I'm evaluating xcube for a range of use-cases, like displaying a cube built from a sequence of geotiffs, or displaying an ECMWF model output like this one.

So far, my main struggle is when xcube serve refuses to load a cube (considered valid by xcube verify) and most of the time, the problem is silent (despite -vvv).

I manage to identify one cause, around type of dimension attributes:

• in the ECMWF data mentioned above, some attributes are int64. This causes this exception: TypeError: Object of type int64 is not JSON serializable.
• In another situation, I had the attribute valid_range being converted to a np.array by the to_netcdf() operation. This caused this line to fail.

Besides these 2 causes, I would strongly suggest to make the cube loading much more verbose, so we can pinpoint issues.

Additional context

xcube version 1.2.0

[AliceBalfanz]

@mdespriee thank you for reporting! Would you like to start wroking on this issue yourself and create a PR? Looks like you have been looking closer into the code while debugging already :)