Reorganizing message payload code

This change is primarily a reorganization of the message payload code
originally found in kmip/core/messages/operations.py. The code from that
module has been moved to a new package, kmip.core.messages.payloads, and
split into separate modules according to each supported KMIP operation.

The surrounding KMIP codebase has been updated to use the new package
structure and a placeholder test suite has been put in place for future
tests. This change does NOT include test cases as these would primarily
be a refactoring from the current test suite found in
kmip/tests/core/messages/test_messages.py and that work has not been
done yet.

kmip/core/messages/payloads/locate.py

@@ -0,0 +1,138 @@
+# Copyright (c) 2014 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.
+
+from kmip.core import attributes
+from kmip.core import enums
+from kmip.core.enums import Tags
+
+from kmip.core.objects import Attribute
+
+from kmip.core.primitives import Struct
+from kmip.core.primitives import Enumeration
+from kmip.core.primitives import Integer
+
+from kmip.core.utils import BytearrayStream
+
+
+class LocateRequestPayload(Struct):
+
+    # 9.1.3.2.33
+    class ObjectGroupMember(Enumeration):
+        ENUM_TYPE = enums.ObjectGroupMember
+
+        def __init__(self, value=None):
+            super(self.__class__, self).__init__(value,
+                                                 Tags.OBJECT_GROUP_MEMBER)
+
+    class MaximumItems(Integer):
+        def __init__(self, value=None):
+            super(self.__class__, self).__init__(value,
+                                                 Tags.MAXIMUM_ITEMS)
+
+    # 9.1.3.3.2
+    class StorageStatusMask(Enumeration):
+        ENUM_TYPE = enums.StorageStatusMask
+
+        def __init__(self, value=None):
+            super(self.__class__, self).__init__(value,
+                                                 Tags.STORAGE_STATUS_MASK)
+
+    def __init__(self, maximum_items=None, storage_status_mask=None,
+                 object_group_member=None, attributes=None):
+        super(self.__class__, self).__init__(enums.Tags.REQUEST_PAYLOAD)
+        self.maximum_items = maximum_items
+        self.storage_status_mask = storage_status_mask
+        self.object_group_member = object_group_member
+        self.attributes = attributes or []
+        self.validate()
+
+    def read(self, istream):
+        super(self.__class__, self).read(istream)
+        tstream = BytearrayStream(istream.read(self.length))
+        if self.is_tag_next(Tags.MAXIMUM_ITEMS, tstream):
+            self.maximum_items = LocateRequestPayload.MaximumItems()
+            self.maximum_items.read()
+        if self.is_tag_next(Tags.STORAGE_STATUS_MASK, tstream):
+            self.storage_status_mask = LocateRequestPayload.StorageStatusMask()
+            self.storage_status_mask.read()
+        if self.is_tag_next(Tags.OBJECT_GROUP_MEMBER, tstream):
+            self.object_group_member = LocateRequestPayload.ObjectGroupMember()
+            self.object_group_member.read(tstream)
+        while self.is_tag_next(Tags.ATTRIBUTE, tstream):
+            attr = Attribute()
+            attr.read(tstream)
+            self.attributes.append(attr)
+
+        self.validate()
+
+    def write(self, ostream):
+        tstream = BytearrayStream()
+        if self.maximum_items is not None:
+            self.maximum_items.write(tstream)
+        if self.storage_status_mask is not None:
+            self.storage_status_mask.write(tstream)
+        if self.attributes is not None:
+            for a in self.attributes:
+                a.write(tstream)
+
+        # Write the length and value of the request payload
+        self.length = tstream.length()
+        super(self.__class__, self).write(ostream)
+        ostream.write(tstream.buffer)
+
+    def validate(self):
+        self._validate()
+
+    def _validate(self):
+        # TODO Finish implementation.
+        pass
+
+
+class LocateResponsePayload(Struct):
+
+    def __init__(self, unique_identifiers=[]):
+        super(self.__class__, self).__init__(enums.Tags.RESPONSE_PAYLOAD)
+        self.unique_identifiers = unique_identifiers or []
+        self.validate()
+
+    def read(self, istream):
+        super(self.__class__, self).read(istream)
+        tstream = BytearrayStream(istream.read(self.length))
+
+        while self.is_tag_next(Tags.UNIQUE_IDENTIFIER, tstream):
+            ui = attributes.UniqueIdentifier()
+            ui.read(tstream)
+            self.unique_identifiers.append(ui)
+
+        self.is_oversized(tstream)
+        self.validate()
+
+    def write(self, ostream):
+        tstream = BytearrayStream()
+
+        for ui in self.unique_identifiers:
+            ui.write(tstream)
+
+        # Write the length and value of the request payload
+        self.length = tstream.length()
+        super(self.__class__, self).write(ostream)
+        ostream.write(tstream.buffer)
+
+    def validate(self):
+        self.__validate()
+
+    def __validate(self):
+        # TODO Finish implementation.
+        pass