Discovery URL querying functions

The existing discovery mechanism is geared around allowing users to
create appropriate client objects. It does not provide any means to
query version responses to determine the URLs of available versions.
This patch adds url_for (similar to the functions available on service
catalog) and data_for functions that can do lower level queries for
URLs and version response data.

Because of the client creation functionality the existing discover.py
cannot be imported from within keystoneclient due to cyclical dependency
resolution. The querying functions are therefore added to a private
keystoneclient file and exposed to the original Discover object via
inheritance. This private object can then be used within the
keystoneclient library.

Blueprint: endpoint-version-query
Change-Id: I7e1891536289c57ad3fbe8ef1c6e50b7344d83d5

1 files changed, 252 insertions, 0 deletions

diff --git a/keystoneclient/_discover.py b/keystoneclient/_discover.py
new file mode 100644
index 0000000..4891f27
--- /dev/null
+++ b/keystoneclient/_discover.py
@@ -0,0 +1,252 @@
+# 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.
+
+"""The passive components to version discovery.
+
+The Discover object in discover.py contains functions that can create objects
+on your behalf. These functions are not usable from within the keystoneclient
+library because you will get dependency resolution issues.
+
+The Discover object in this file provides the querying components of Discovery.
+This includes functions like url_for which allow you to retrieve URLs and the
+raw data specified in version discovery responses.
+"""
+
+import logging
+
+from keystoneclient import exceptions
+
+
+_LOGGER = logging.getLogger(__name__)
+
+
+def get_version_data(session, url):
+    """Retrieve raw version data from a url."""
+    headers = {'Accept': 'application/json'}
+
+    resp = session.get(url, headers=headers)
+
+    try:
+        body_resp = resp.json()
+    except ValueError:
+        pass
+    else:
+        # In the event of querying a root URL we will get back a list of
+        # available versions.
+        try:
+            return body_resp['versions']['values']
+        except (KeyError, TypeError):
+            pass
+
+        # Most servers don't have a 'values' element so accept a simple
+        # versions dict if available.
+        try:
+            return body_resp['versions']
+        except KeyError:
+            pass
+
+        # Otherwise if we query an endpoint like /v2.0 then we will get back
+        # just the one available version.
+        try:
+            return [body_resp['version']]
+        except KeyError:
+            pass
+
+    err_text = resp.text[:50] + '...' if len(resp.text) > 50 else resp.text
+    msg = 'Invalid Response - Bad version data returned: %s' % err_text
+    raise exceptions.DiscoveryFailure(msg)
+
+
+def normalize_version_number(version):
+    """Turn a version representation into a tuple."""
+
+    # trim the v from a 'v2.0' or similar
+    try:
+        version = version.lstrip('v')
+    except AttributeError:
+        pass
+
+    # if it's an integer or a numeric as a string then normalize it
+    # to a string, this ensures 1 decimal point
+    try:
+        num = float(version)
+    except Exception:
+        pass
+    else:
+        version = str(num)
+
+    # if it's a string (or an integer) from above break it on .
+    try:
+        return tuple(map(int, version.split('.')))
+    except Exception:
+        pass
+
+    # last attempt, maybe it's a list or iterable.
+    try:
+        return tuple(map(int, version))
+    except Exception:
+        pass
+
+    raise TypeError('Invalid version specified: %s' % version)
+
+
+def version_match(required, candidate):
+    """Test that an available version is a suitable match for a required
+    version.
+
+    To be suitable a version must be of the same major version as required
+    and be at least a match in minor/patch level.
+
+    eg. 3.3 is a match for a required 3.1 but 4.1 is not.
+
+    :param tuple required: the version that must be met.
+    :param tuple candidate: the version to test against required.
+
+    :returns bool: True if candidate is suitable False otherwise.
+    """
+    # major versions must be the same (e.g. even though v2 is a lower
+    # version than v3 we can't use it if v2 was requested)
+    if candidate[0] != required[0]:
+        return False
+
+    # prevent selecting a minor version less than what is required
+    if candidate < required:
+        return False
+
+    return True
+
+
+class Discover(object):
+
+    CURRENT_STATUSES = ('stable', 'current', 'supported')
+    DEPRECATED_STATUSES = ('deprecated',)
+    EXPERIMENTAL_STATUSES = ('experimental',)
+
+    def __init__(self, session, url):
+        self._data = get_version_data(session, url)
+
+    def raw_version_data(self, allow_experimental=False,
+                         allow_deprecated=True, allow_unknown=False):
+        """Get raw version information from URL.
+
+        Raw data indicates that only minimal validation processing is performed
+        on the data, so what is returned here will be the data in the same
+        format it was received from the endpoint.
+
+        :param bool allow_experimental: Allow experimental version endpoints.
+        :param bool allow_deprecated: Allow deprecated version endpoints.
+        :param bool allow_unknown: Allow endpoints with an unrecognised status.
+
+        :returns list: The endpoints returned from the server that match the
+                       criteria.
+        """
+        versions = []
+        for v in self._data:
+            try:
+                status = v['status']
+            except KeyError:
+                _LOGGER.warning('Skipping over invalid version data. '
+                                'No stability status in version.')
+                continue
+
+            status = status.lower()
+
+            if status in self.CURRENT_STATUSES:
+                versions.append(v)
+            elif status in self.DEPRECATED_STATUSES:
+                if allow_deprecated:
+                    versions.append(v)
+            elif status in self.EXPERIMENTAL_STATUSES:
+                if allow_experimental:
+                    versions.append(v)
+            elif allow_unknown:
+                versions.append(v)
+
+        return versions
+
+    def version_data(self, **kwargs):
+        """Get normalized version data.
+
+        Return version data in a structured way.
+
+        :returns list(dict): A list of version data dictionaries sorted by
+                             version number. Each data element in the returned
+                             list is a dictionary consisting of at least:
+
+          :version tuple: The normalized version of the endpoint.
+          :url str: The url for the endpoint.
+          :raw_status str: The status as provided by the server
+        """
+        data = self.raw_version_data(**kwargs)
+        versions = []
+
+        for v in data:
+            try:
+                version_str = v['id']
+            except KeyError:
+                _LOGGER.info('Skipping invalid version data. Missing ID.')
+                continue
+
+            try:
+                links = v['links']
+            except KeyError:
+                _LOGGER.info('Skipping invalid version data. Missing links')
+                continue
+
+            version_number = normalize_version_number(version_str)
+
+            for link in links:
+                try:
+                    rel = link['rel']
+                    url = link['href']
+                except (KeyError, TypeError):
+                    _LOGGER.info('Skipping invalid version link. '
+                                 'Missing link URL or relationship.')
+                    continue
+
+                if rel.lower() == 'self':
+                    break
+            else:
+                _LOGGER.info('Skipping invalid version data. '
+                             'Missing link to endpoint.')
+                continue
+
+            versions.append({'version': version_number,
+                             'url': url,
+                             'raw_status': v['status']})
+
+        versions.sort(key=lambda v: v['version'])
+        return versions
+
+    def data_for(self, version, **kwargs):
+        """Return endpoint data for a specific version.
+
+        :returns dict: the endpoint data for a URL that matches the required
+                       version (the format is described in version_data)
+                       or None if no match.
+        """
+        version = normalize_version_number(version)
+        version_data = self.version_data(**kwargs)
+
+        for data in reversed(version_data):
+            if version_match(version, data['version']):
+                return data
+
+        return None
+
+    def url_for(self, version, **kwargs):
+        """Get the endpoint url for a required version.
+
+        :returns str: The url for the specified version or None if no match.
+        """
+        data = self.data_for(version, **kwargs)
+        return data['url'] if data else None