Fix edge case with relative SMP URLs

[raphaelm]

This fixes an issue observed in the wild with the following NAPTR record:

100 10 "U" "Meta:SMP" "!.*!https://smp.service.afasonline.com/smp!" .

which needs to be resolved to https://smp.service.afasonline.com/smp/iso6523-actorid-upis:: not https://smp.service.afasonline.com/iso6523-actorid-upis::

Unfortunately, the spec seems a little fuzzy on this.

[arj03]

I don't understand the comment at all :)

The URL should be used as defined right? https://smp.service.afasonline.com/smp is different from https://smp.service.afasonline.com/smp/. Oxalis used specifically as4 and not as4/

[raphaelm]

Yes, the URL should be used as defined, it's about how it's combined. So if DNS says

100 10 "U" "Meta:SMP" "!.*!https://smp.service.afasonline.com/smp!" .

do we need

a) https://smp.service.afasonline.com/smpiso6523-actorid-upis::$participant
b) https://smp.service.afasonline.com/smp/iso6523-actorid-upis::$participant
c) https://smp.service.afasonline.com/iso6523-actorid-upis::$participant

The current code tries to reach (c), which does not work. With this PR, it uses (b), because the / at the end helps Python's urljoin that this is supposed to be a path. Simple concatenation would yield (a), which I think is also wrong.

[raphaelm]

I had introduced the urljoin() in #17 since I had seem some NAPTR records contain /smp/ and then it would previously cause a // in the URL which did not work.

We could probably also go for:

    return result.rstrip("/") + "/iso6523-actorid-upis::" + participant_id

[arj03]

Thanks, I've applied the last one. Will do a release now.

[raphaelm]

Thank you!