incorrect RPCVersionCapError message

RPCVersionCapError: Requested message version, 3.23 is too high. It needs to be lower than the specified version cap 4.0.

huh? 3.23 > 4.0?!

but reading the code, specifically version_is_compatible() in oslo_messaging/_utils.py, the actual problem is a difference in major version numbers (as major versions, eg 3 and 4, are assumed to be incompatible).

the RPCVersionCapError exception is only raised in the oslo.messaging code base when oslo_messaging._utils.version_is_compatible is false and that only happens when major versions differ and requested message minor and revision versions are less than specified version cap minor and revision versions (evaluated in that order). i suggest that the current algorithm be reflected in the exception (and log) message.

if RPCVersionCapError is intended to communicate generic version incompatibility (broader than the algorithm implemented in version_is_compatible; ie don't create dependency between RPCVersionCapError message and version_is_compatible algorithm which reside in two different files and are not explicitly tied to one another), then maybe the message needs to be generalized to "Requested message version, X is incompatible with the specified version cap Y" (and not dive into the, potentially incorrect or bound-to-change-in-the-future, details).