[Part 3 of #205] Added utils for k8s model verification

kubespawner/utils.py

@@ -2,7 +2,7 @@
 Misc. general utility functions, not tied to Kubespawner directly
 """
 import hashlib
-
+import copy
 
 def generate_hashed_slug(slug, limit=63, hash_length=6):
     """
@@ -27,3 +27,130 @@ def generate_hashed_slug(slug, limit=63, hash_length=6):
         prefix=slug[:limit - hash_length - 1],
         hash=slug_hash[:hash_length],
     ).lower()
+
+
+def update_k8s_model(target, changes, logger=None, target_name=None):
+    """
+    Takes a model instance such as V1PodSpec() and updates it with another
+    model, which is allowed to be a dict or another model instance of the same
+    type. The logger is used to warn if any truthy value in the target is is
+    overridden. The target_name parameter can for example be "extra_pod_config",
+    allowing the logger to write out something more meaningful to the user.
+    """
+    model_type = type(target)
+    if not hasattr(target, 'attribute_map'):
+        raise AttributeError("Attribute 'target' ({}) must be an object (such as 'V1PodSpec') with an attribute 'attribute_map'.".format(model_type.__name__))
+    if not isinstance(changes, model_type) and not isinstance(changes, dict):
+        raise AttributeError("Attribute 'changes' ({}) must be an object of the same type as 'target' ({}) or a 'dict'.".format(type(changes).__name__, model_type.__name__))
+
+    changes_dict = _get_k8s_model_dict(model_type, changes)
+    for key, value in changes_dict.items():
+        if key not in target.attribute_map:
+            raise ValueError("The attribute 'changes' ({}) contained '{}' not modeled by '{}'.".format(type(changes).__name__, key, model_type.__name__))
+
+
+        # If changes are passed as a dict, they will only have a few keys/value
+        # pairs representing the specific changes. If the changes parameter is a
+        # model instance on the other hand, the changes parameter will have a
+        # lot of default values as well. These default values, which are also
+        # falsy, should not use to override the target's values.
+        if isinstance(changes, dict) or value:
+            if getattr(target, key):
+                if logger and target_name:
+                    logger.warning("Overriding KubeSpawner.{}'s value '{}' with '{}'.".format(target_name, getattr(target, key), value))
+            setattr(target, key, value)
+
+    return target
+
+def get_k8s_model(model_type, model_dict):
+    """
+    Returns an instance of type specified model_type from an model instance or
+    represantative dictionary.
+    """
+    model_dict = copy.deepcopy(model_dict)
+
+    if isinstance(model_dict, model_type):
+        return model_dict
+    elif isinstance(model_dict, dict):
+        # convert the dictionaries camelCase keys to snake_case keys
+        _map_dict_keys_to_model_attributes(model_type, model_dict)
+        # use the dictionary keys to initialize a model of given type
+        return model_type(**model_dict)
+    else:
+        raise AttributeError("Expected object of type 'dict' (or '{}') but got '{}'.".format(model_type.__name__, type(model_dict).__name__))
+
+def _get_k8s_model_dict(model_type, model):
+    """
+    Returns a dictionary representation of a provided model type
+    """
+    model = copy.deepcopy(model)
+
+    if isinstance(model, model_type):
+        return model.to_dict()
+    elif isinstance(model, dict):
+        return _map_dict_keys_to_model_attributes(model_type, model)
+    else:
+        raise AttributeError("Expected object of type '{}' (or 'dict') but got '{}'.".format(model_type.__name__, type(model).__name__))
+
+def _map_dict_keys_to_model_attributes(model_type, model_dict):
+    """
+    Maps a dict's keys to the provided models attributes using its attribute_map
+    attribute. This is (always?) the same as converting camelCase to snake_case.
+    Note that the function will not influence nested object's keys.
+    """
+
+    # it is important to iterate over a copy of the dictionaries keys, as they
+    # will be updated in the loop
+    for key in list(model_dict.keys()):
+        model_dict[_get_k8s_model_attribute(model_type, key)] = model_dict.pop(key)
+
+    return model_dict
+
+def _get_k8s_model_attribute(model_type, field_name):
+    """
+    Takes a model type and a Kubernetes API resource field name (such as
+    "serviceAccount") and returns a related attribute name (such as
+    "service_account") to be used with  kubernetes.client.models objects. It is
+    impossible to prove a negative but it seems like it is always a question of
+    making camelCase to snake_case but by using the provided 'attribute_map' we
+    also ensure that the fields actually exist.
+
+    Example of V1PodSpec's attribute_map:
+    {
+        'active_deadline_seconds': 'activeDeadlineSeconds',
+        'affinity': 'affinity',
+        'automount_service_account_token': 'automountServiceAccountToken',
+        'containers': 'containers',
+        'dns_policy': 'dnsPolicy',
+        'host_aliases': 'hostAliases',
+        'host_ipc': 'hostIPC',
+        'host_network': 'hostNetwork',
+        'host_pid': 'hostPID',
+        'hostname': 'hostname',
+        'image_pull_secrets': 'imagePullSecrets',
+        'init_containers': 'initContainers',
+        'node_name': 'nodeName',
+        'node_selector': 'nodeSelector',
+        'priority': 'priority',
+        'priority_class_name': 'priorityClassName',
+        'restart_policy': 'restartPolicy',
+        'scheduler_name': 'schedulerName',
+        'security_context': 'securityContext',
+        'service_account': 'serviceAccount',
+        'service_account_name': 'serviceAccountName',
+        'subdomain': 'subdomain',
+        'termination_grace_period_seconds': 'terminationGracePeriodSeconds',
+        'tolerations': 'tolerations',
+        'volumes': 'volumes'
+    }
+    """
+    # if we get "service_account", return
+    if field_name in model_type.attribute_map:
+        return field_name
+
+    # if we get "serviceAccount", then return "service_account"
+    for key, value in model_type.attribute_map.items():
+        if value == field_name:
+            return key
+    else:
+        raise ValueError("'{}' did not have an attribute matching '{}'".format(model_type.__name__, field_name))

tests/test_utils.py

@@ -0,0 +1,96 @@
+import copy
+from kubespawner.utils import get_k8s_model, update_k8s_model, _get_k8s_model_attribute
+from kubernetes.client.models import (
+    V1PodSpec, V1SecurityContext, V1Container, V1Capabilities, V1Lifecycle
+)
+
+class MockLogger(object):
+    """Trivial class to store logs for inspection after a test run."""
+
+    def __init__(self):
+        self.warning_count = 0
+
+    def warning(self, message):
+        """Remembers the most recent warning."""
+        self.most_recent_warning = message
+        self.warning_count += 1
+
+
+def test__get_k8s_model_attribute():
+    """Verifies fundamental behavior"""
+    assert _get_k8s_model_attribute(V1PodSpec, "service_account") == "service_account"
+    assert _get_k8s_model_attribute(V1PodSpec, "serviceAccount") == "service_account"
+
+def test_update_k8s_model():
+    """Ensure update_k8s_model does what it should. The test is first updating
+    attributes using the function and then and manually verifies that the
+    correct changes have been made."""
+    manually_updated_target = V1Container(
+        name="mock_name",
+        image="mock_image",
+        command=['iptables'],
+        security_context=V1SecurityContext(
+            privileged=True,
+            run_as_user=0,
+            capabilities=V1Capabilities(add=['NET_ADMIN'])
+        )
+    )
+    target = copy.deepcopy(manually_updated_target)
+    source = {"name": "new_mock_name"}
+    update_k8s_model(target, source)
+
+    manually_updated_target.name = "new_mock_name"
+
+    assert target == manually_updated_target
+
+def test_update_k8s_models_logger_warning():
+    """Ensure that the update_k8s_model function uses the logger to warn about
+    overwriting previous values."""
+    target = V1Container(
+        name="mock_name"
+    )
+    source = {"name": "new_mock_name", "image_pull_policy": "Always"}
+    mock_locker = MockLogger()
+    update_k8s_model(target, source, logger=mock_locker, target_name="test-runner")
+
+    assert mock_locker.most_recent_warning.find("KubeSpawner.test-runner's value 'mock_name' with 'new_mock_name'")
+    assert mock_locker.warning_count == 1
+
+
+def test_get_k8s_model():
+    """Thest that passing either a kubernetes.client.models object or as a
+    dictionary to representing it get_k8s_model should work."""
+    # verify get_k8s_model for when passing dict objects
+    v1_lifecycle_from_dict = get_k8s_model(
+        V1Lifecycle,
+        {
+            'preStop': {
+                'exec': {
+                    'command': ['/bin/sh', 'test']
+                }
+            }
+        },
+    )
+
+    assert isinstance(v1_lifecycle_from_dict, V1Lifecycle)
+    assert v1_lifecycle_from_dict.to_dict() == {
+        'post_start': None,
+        'pre_stop': {
+            'exec': {
+                'command': ['/bin/sh', 'test']
+            }
+        },
+    }
+
+    # verify get_k8s_model for when passing model objects
+    v1_lifecycle_from_model_object = get_k8s_model(V1Lifecycle, v1_lifecycle_from_dict)
+
+    assert isinstance(v1_lifecycle_from_model_object, V1Lifecycle)
+    assert v1_lifecycle_from_model_object.to_dict() == {
+        'post_start': None,
+        'pre_stop': {
+            'exec': {
+                'command': ['/bin/sh', 'test']
+            }
+        },
+    }