Add a policy directory monitor

This change adds a PolicyDirectoryMonitor subprocess that can be
used by the server to continuously monitor and load operation
policies from the configured operation policy directory. The
monitor tracks policy file modifications, file creation, and file
deletion, restoring legacy policies from existing policy files
should the current file backing a policy get deleted. Changes to
existing policies are detected and updated as soon as the backing
policy file is saved to disk.

An extensive unit test is included to exercise the different
operating conditions the monitor may encounter.

kmip/services/server/monitor.py

@@ -0,0 +1,162 @@
+# Copyright (c) 2018 The Johns Hopkins University/Applied Physics Laboratory
+# All Rights Reserved.
+#
+# 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 logging
+import multiprocessing
+import os
+import signal
+import time
+
+from kmip.core import policy as operation_policy
+
+
+def get_json_files(p):
+    """
+    Scan the provided policy directory for all JSON policy files.
+    """
+    f = [os.path.join(p, x) for x in os.listdir(p) if x.endswith(".json")]
+    return sorted(f)
+
+
+class PolicyDirectoryMonitor(multiprocessing.Process):
+    """
+    A file monitor that tracks modifications made within the policy directory.
+    """
+
+    def __init__(self, policy_directory, policy_store):
+        """
+        Set up the file monitor with the policy directory to track.
+
+        Args:
+            policy_directory (string): The system path of the policy directory
+                that should be monitored. Required.
+            policy_store (DictProxy): A dictionary proxy created by the server
+                multiprocessing resource manager. Used to store and share the
+                policy information across server processes and threads.
+                Required.
+        """
+        super(PolicyDirectoryMonitor, self).__init__()
+
+        self.halt_trigger = multiprocessing.Event()
+        self.policy_directory = policy_directory
+
+        self.file_timestamps = None
+        self.policy_cache = None
+        self.policy_files = None
+        self.policy_map = None
+        self.policy_store = policy_store
+
+        self.reserved_policies = ['default', 'public']
+
+        def interrupt_handler(trigger, frame):
+            self.stop()
+        signal.signal(signal.SIGINT, interrupt_handler)
+        signal.signal(signal.SIGTERM, interrupt_handler)
+
+        self.logger = logging.getLogger("kmip.server.monitor")
+        self.initialize_tracking_structures()
+
+    def stop(self):
+        self.halt_trigger.set()
+
+    def run(self):
+        """
+        Start monitoring operation policy files.
+        """
+        self.initialize_tracking_structures()
+
+        self.logger.info("Starting up the operation policy file monitor.")
+        while not self.halt_trigger.is_set():
+            time.sleep(1)
+
+            policy_files = get_json_files(self.policy_directory)
+            for f in set(policy_files) - set(self.policy_files):
+                self.file_timestamps[f] = 0
+            for f in set(self.policy_files) - set(policy_files):
+                self.logger.info("Removing policies for file: {}".format(f))
+                self.file_timestamps.pop(f, None)
+                for p in self.policy_cache.keys():
+                    self.disassociate_policy_and_file(p, f)
+                for p in [k for k, v in self.policy_map.items() if v == f]:
+                    self.restore_or_delete_policy(p)
+            self.policy_files = policy_files
+
+            for f in sorted(self.file_timestamps.keys()):
+                t = os.path.getmtime(f)
+                if t > self.file_timestamps[f]:
+                    self.logger.info("Loading policies for file: {}".format(f))
+                    self.file_timestamps[f] = t
+                    old_p = [k for k, v in self.policy_map.items() if v == f]
+                    try:
+                        new_p = operation_policy.read_policy_from_file(f)
+                    except ValueError:
+                        self.logger.error("Failure loading file: {}".format(f))
+                        self.logger.debug("", exc_info=True)
+                        continue
+                    for p in new_p.keys():
+                        self.logger.info("Loading policy: {}".format(p))
+                        if p in self.reserved_policies:
+                            self.logger.warning(
+                                "Policy '{}' overwrites a reserved policy and "
+                                "will be thrown out.".format(p)
+                            )
+                            continue
+                        if p in sorted(self.policy_store.keys()):
+                            self.logger.debug(
+                                "Policy '{}' overwrites an existing "
+                                "policy.".format(p)
+                            )
+                            if f != self.policy_map.get(p):
+                                self.policy_cache.get(p).append(
+                                    (
+                                        time.time(),
+                                        self.policy_map.get(p),
+                                        self.policy_store.get(p)
+                                    )
+                                )
+                        else:
+                            self.policy_cache[p] = []
+                        self.policy_store[p] = new_p.get(p)
+                        self.policy_map[p] = f
+                    for p in set(old_p) - set(new_p.keys()):
+                        self.disassociate_policy_and_file(p, f)
+                        self.restore_or_delete_policy(p)
+        self.logger.info("Stopping the operation policy file monitor.")
+
+    def initialize_tracking_structures(self):
+        self.file_timestamps = {}
+        self.policy_cache = {}
+        self.policy_files = []
+        self.policy_map = {}
+
+        for k in self.policy_store.keys():
+            self.policy_store.pop(k, None)
+
+    def disassociate_policy_and_file(self, policy, file_name):
+        c = self.policy_cache.get(policy, [])
+        for i in [c.index(e) for e in c if e[1] == file_name][::-1]:
+            c.pop(i)
+
+    def restore_or_delete_policy(self, policy):
+        c = self.policy_cache.get(policy, [])
+        if len(c) == 0:
+            self.logger.info("Removing policy: {}".format(policy))
+            self.policy_store.pop(policy, None)
+            self.policy_map.pop(policy, None)
+            self.policy_cache.pop(policy, None)
+        else:
+            e = c.pop()
+            self.policy_store[policy] = e[2]
+            self.policy_map[policy] = e[1]