Correct RPCVersionCapError message

This change adjusts the exception message to be more in line with the
version compatibility algorithm so as to accurately portray the
problem to the log recipient.

The RPCVersionCapError message can be grossly incorrect when the
requested message's major version is lower than the specified version
cap's major version, declaring the requested message version as too
high, when the real error is that the major versions differ (as major
versions are assumed to be incompatible).

Example:

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

Change-Id: Iceef999ed385f2ba77449c568127f50f83d47196
Closes-Bug: 1468525

1 files changed, 4 insertions, 2 deletions

diff --git a/oslo_messaging/rpc/client.py b/oslo_messaging/rpc/client.py
index 3ea7034..3b05785 100644
--- a/oslo_messaging/rpc/client.py
+++ b/oslo_messaging/rpc/client.py
@@ -63,8 +63,10 @@ class RPCVersionCapError(exceptions.MessagingException):
     def __init__(self, version, version_cap):
         self.version = version
         self.version_cap = version_cap
-        msg = ("Requested message version, %(version)s is too high. It needs "
-               "to be lower than the specified version cap %(version_cap)s." %
+        msg = ("Requested message version, %(version)s is incompatible.  It "
+               "needs to be equal in major version and less than or equal "
+               "in minor version as the specified version cap "
+               "%(version_cap)s." %
                dict(version=self.version, version_cap=self.version_cap))
         super(RPCVersionCapError, self).__init__(msg)