Add primitive Redfish task monitor

This commit adds simple Redfish task monitor. We could eventually
migrate to sushy's built-in task monitor once it becomes available.

requirements.txt

@@ -3,5 +3,6 @@
 # process, which may cause wedges in the gate later.
 
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
+python-dateutil>=2.7.0 # BSD
 six>=1.10.0 # MIT
 sushy # Apache-2.0

sushy_oem_dellemc/asynchronous.py

@@ -0,0 +1,53 @@
+# 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 datetime import datetime
+from datetime import timedelta
+import logging
+import time
+
+from dateutil import parser
+import sushy
+
+LOG = logging.getLogger(__name__)
+
+
+def _to_datetime(retry_after_str):
+    if retry_after_str.isdigit():
+        # Retry-After: 120
+        return datetime.now() + timedelta(seconds=int(retry_after_str))
+    else:
+        # Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
+        return parser.parse(retry_after_str)
+
+
+def http_call(conn, method, *args, **kwargs):
+    handle = getattr(conn, method.lower())
+
+    response = handle(*args, **kwargs)
+
+    while response.status_code == 202:
+        location = response.headers.get('location')
+        retry_after = response.headers.get('retry-after')
+        retry_after = _to_datetime(retry_after)
+
+        time.sleep(max(0, retry_after - datetime.now()))
+
+        response = conn.get(location)
+
+    if response.status_code >= 400:
+        raise sushy.exceptions.ExtensionError(
+            error='HTTP %s with args %s, kwargs %s failed '
+                  'with code %s' % (method.upper(), args, kwargs,
+                                    response.status_code))
+
+    return response

sushy_oem_dellemc/resources/manager/manager.py

@@ -17,6 +17,8 @@ from sushy.resources import base
 from sushy.resources import common
 from sushy.resources.oem import base as oem_base
 
+from sushy_oem_dellemc import asynchronous
+
 LOG = logging.getLogger(__name__)
 
 
@@ -90,20 +92,15 @@ class DellManagerExtension(oem_base.OEMResourceBase):
         # TODO (etingof): figure out if on-time or persistent boot can at
         # all be implemented via this OEM call
 
-        response = self._conn.post(
-            self.import_system_configuration_uri, data=magic_saucer)
-
-        if response.status_code != 202:
-            raise sushy.exceptions.ExtensionError(
-                error='Dell OEM action ImportSystemConfiguration fails '
-                      'with code %s' % response.status_code)
+        response = asynchronous.http_call(
+            self._conn, 'post',
+            self.import_system_configuration_uri,
+            data=magic_saucer)
 
         LOG.info("Set boot device to %(device)s via "
                  "Dell OEM magic spell", {'device': device})
 
-        # TODO(etingof): extract iDRAC task ID which looks like r"JID_.+?,"
-
-        # TODO(etingof): poll Redfish TaskService to see when task is completed
+        return response
 
 
 def get_extension(*args, **kwargs):