Gracefully handle the ring file not found error.

Change-Id: I35c33f3938709d5d9a9a55640a503f186df9a965
Signed-off-by: Mohammed Junaid <junaid@redhat.com>
Reviewed-on: http://review.gluster.org/5368
Reviewed-by: Luis Pabon <lpabon@redhat.com>
Tested-by: Luis Pabon <lpabon@redhat.com>

gluster/swift/common/ring.py

@@ -13,6 +13,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import os
+import errno
 from ConfigParser import ConfigParser
 from swift.common.ring import ring
 from swift.common.utils import search_tree
@@ -39,12 +41,20 @@ if not reseller_prefix.endswith('_'):
 
 class Ring(ring.Ring):
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, serialized_path, *args, **kwargs):
         self.false_node = {'zone': 1, 'weight': 100.0, 'ip': '127.0.0.1',
                            'id': 0, 'meta': '', 'device': 'volume_not_in_ring',
                            'port': 6012}
         self.account_list = []
-        ring.Ring.__init__(self, *args, **kwargs)
+
+        ring_file = os.path.join(serialized_path, kwargs['ring_name']
+                                 + '.ring.gz')
+        if not os.path.exists(ring_file):
+            raise OSError(errno.ENOENT, 'No such file or directory',
+                          'ring files do not exists under %s, '
+                          'aborting proxy-server start.' % serialized_path)
+
+        ring.Ring.__init__(self, serialized_path, *args, **kwargs)
 
     def _get_part_nodes(self, part):
         seen_ids = set()

test/unit/common/test_ring.py

@@ -14,6 +14,7 @@
 # limitations under the License.
 
 import os
+import errno
 import unittest
 import gluster.swift.common.constraints
 import swift.common.utils
@@ -66,3 +67,15 @@ class TestRing(unittest.TestCase):
     def test_invalid_partition(self):
         nodes = self.ring.get_part_nodes(0)
         self.assertEqual(nodes[0]['device'], 'volume_not_in_ring')
+
+    def test_ring_file_enoent(self):
+        swiftdir = os.path.join(os.getcwd(), "common", "data")
+        try:
+            self.ring = Ring(swiftdir, ring_name='obj')
+        except OSError as ose:
+            if ose.errno == errno.ENOENT:
+                pass
+            else:
+                self.fail('ENOENT expected, %s received.' %ose.errno)
+        else:
+            self.fail('OSError expected.')