Adds APIVersionRequest class for API Microversions

Adds the APIVersionRequest class which handles converting the API
version requested from a request header string and supplies
comparison and matching methods used by microversions and REST
API code to determine what code paths to take.

Partially implements blueprint api-microversions

Change-Id: Ic75d36fc0d27b615e70e1fe56c1626e9e501b1d6

nova/api/openstack/api_version_request.py

@@ -0,0 +1,76 @@
+# Copyright 2014 IBM Corp.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import re
+
+from nova import exception
+
+
+class APIVersionRequest(object):
+    """This class represents an API Version Request with convenience
+    methods for manipulation and comparison of version
+    numbers that we need to do to implement microversions.
+    """
+
+    def __init__(self, version_string=None):
+        """Create an API version request object."""
+        self.ver_major = None
+        self.ver_minor = None
+
+        if version_string is not None:
+            match = re.match(r"^([1-9]\d*)\.([1-9]\d*|0)$",
+                             version_string)
+            if match:
+                self.ver_major = int(match.group(1))
+                self.ver_minor = int(match.group(2))
+            else:
+                raise exception.InvalidAPIVersionString(version=version_string)
+
+    def __str__(self):
+        return ("API Version Request Major: %s, Minor: %s"
+                % (self.ver_major, self.ver_minor))
+
+    def is_null(self):
+        return self.ver_major is None and self.ver_minor is None
+
+    def __cmp__(self, other):
+        if not isinstance(other, APIVersionRequest):
+            raise TypeError
+        return cmp((self.ver_major, self.ver_minor),
+                   (other.ver_major, other.ver_minor))
+
+    def matches(self, min_version, max_version):
+        """Returns whether the version object represents a version
+        greater than or equal to the minimum version and less than
+        or equal to the maximum version.
+
+        @param min_version: Minimum acceptable version.
+        @param max_version: Maximum acceptable version.
+        @returns: boolean
+
+        If min_version is null then there is no minimum limit.
+        If max_version is null then there is no maximum limit.
+        If self is null then raise ValueError
+        """
+
+        if self.is_null():
+            raise ValueError
+        if max_version.is_null() and min_version.is_null():
+            return True
+        elif max_version.is_null():
+            return min_version <= self
+        elif min_version.is_null():
+            return self <= max_version
+        else:
+            return min_version <= self <= max_version