Extract quorum-size calculation to utility method.

The behavior's the same as before; this just makes the code (IMHO) a
little easier to read.

Change-Id: Ie54d836d81af7410057219f60b72b840c9ce51b9

swift/common/utils.py

@@ -1856,6 +1856,14 @@ def public(func):
     return wrapped
 
 
+def quorum_size(n):
+    """
+    Number of successful backend requests needed for the proxy to consider
+    the client request successful.
+    """
+    return (n // 2) + 1
+
+
 def rsync_ip(ip):
     """
     Transform ip string to an rsync-compatible form

swift/proxy/controllers/base.py

@@ -37,7 +37,8 @@ from eventlet.timeout import Timeout
 
 from swift.common.wsgi import make_pre_authed_env
 from swift.common.utils import normalize_timestamp, config_true_value, \
-    public, split_path, list_from_csv, GreenthreadSafeIterator
+    public, split_path, list_from_csv, GreenthreadSafeIterator, \
+    quorum_size
 from swift.common.bufferedhttp import http_connect
 from swift.common.exceptions import ChunkReadTimeout, ConnectionTimeout
 from swift.common.http import is_informational, is_success, is_redirection, \
@@ -749,7 +750,7 @@ class Controller(object):
             for hundred in (HTTP_OK, HTTP_MULTIPLE_CHOICES, HTTP_BAD_REQUEST):
                 hstatuses = \
                     [s for s in statuses if hundred <= s < hundred + 100]
-                if len(hstatuses) > len(statuses) / 2:
+                if len(hstatuses) >= quorum_size(len(statuses)):
                     status = max(hstatuses)
                     status_index = statuses.index(status)
                     resp.status = '%s %s' % (status, reasons[status_index])

swift/proxy/controllers/obj.py

@@ -37,7 +37,8 @@ from eventlet.queue import Queue
 from eventlet.timeout import Timeout
 
 from swift.common.utils import ContextPool, normalize_timestamp, \
-    config_true_value, public, json, csv_append, GreenthreadSafeIterator
+    config_true_value, public, json, csv_append, GreenthreadSafeIterator, \
+    quorum_size
 from swift.common.bufferedhttp import http_connect
 from swift.common.constraints import check_metadata, check_object_creation, \
     CONTAINER_LISTING_LIMIT, MAX_FILE_SIZE, MAX_BUFFERED_SLO_SEGMENTS
@@ -1016,11 +1017,12 @@ class ObjectController(Controller):
                        req.path_info, nheaders, self.app.logger.thread_locals)
 
         conns = [conn for conn in pile if conn]
-        if len(conns) <= len(nodes) / 2:
+        min_conns = quorum_size(len(nodes))
+        if len(conns) < min_conns:
             self.app.logger.error(
                 _('Object PUT returning 503, %(conns)s/%(nodes)s '
                   'required connections'),
-                {'conns': len(conns), 'nodes': len(nodes) // 2 + 1})
+                {'conns': len(conns), 'nodes': min_conns})
             return HTTPServiceUnavailable(request=req)
         bytes_transferred = 0
         try:
@@ -1047,11 +1049,11 @@ class ObjectController(Controller):
                                 if chunked else chunk)
                         else:
                             conns.remove(conn)
-                    if len(conns) <= len(nodes) / 2:
+                    if len(conns) < min_conns:
                         self.app.logger.error(_(
                             'Object PUT exceptions during'
                             ' send, %(conns)s/%(nodes)s required connections'),
-                            {'conns': len(conns), 'nodes': len(nodes) / 2 + 1})
+                            {'conns': len(conns), 'nodes': min_conns})
                         return HTTPServiceUnavailable(request=req)
                 for conn in conns:
                     if conn.queue.unfinished_tasks:

test/unit/common/test_utils.py

@@ -1126,6 +1126,15 @@ log_name = %(yarr)s'''
         self.assertFalse(utils.streq_const_time('a', 'aaaaa'))
         self.assertFalse(utils.streq_const_time('ABC123', 'abc123'))
 
+    def test_quorum_size(self):
+        expected_sizes = {1: 1,
+                          2: 2,
+                          3: 2,
+                          4: 3,
+                          5: 3}
+        got_sizes = dict([(n, utils.quorum_size(n)) for n in expected_sizes])
+        self.assertEqual(expected_sizes, got_sizes)
+
     def test_rsync_ip_ipv4_localhost(self):
         self.assertEqual(utils.rsync_ip('127.0.0.1'), '127.0.0.1')