Versioning

The UMA standard provides a method for version negotiation as part of the initial LnurlpRequest. UMA versions include major and minor components in the format <major>.<minor> (eg. 1.2). Minor version bumps are non-breaking, but may contain minor new optional features. Major version bumps include breaking changes. If a VASP only supports versions 1.X, they may not be able to talk to a VASP on version 2.X. The version negotiation flow is as follows:

The UMA SDK handles a lot of the heavy lifting for you here. On the receiving VASP side, when trying to parse the LnurlpRequest, you'll get an error if the sending VASP's specified protocol version is incompatible with the SDK version you're using. You can then return a 412 status code.

# Using flask
from flask import Response

try:
  request = uma.parse_lnurlp_request(request_url)
except uma.UnsupportedVersionException as ex:
  return Response(ex.to_json(), status=412, mimetype='application/json')

On the sending VASP side, you'll need to look out for a 412 status code response to the LnurlpRequest and then can use the SDK's helpers to retry with an appropriate new version code.

supported_major_versions = uma.get_supported_major_versions_from_error(error_json)
highest_supported_version = uma.select_highest_supported_version(supported_major_versions)
if not highest_supported_version:
  # TODO: Handle the error. You don't support any of the other VASP's versions
  return

lnurlp_request = uma.create_lnurlp_request_url(
  signing_private_key,
  receiver_address,
  vasp_domain,
  True,  # is_subject_to_travel_rule
  highest_supported_version,  # uma_version_override
)

If the sending VASP does not support any of the receiving VASP's protocol versions, the LnurlpRequest fails and the protocol cannot continue.