Fix StatsD tests to not use real DNS

In common/test_utils.py, TestStatsdLogging had the majority of its
test cases calling the real socket.getaddrinfo(), which uses real
DNS. This is very slightly slower than using a mock getaddrinfo() when
the machine running the tests has functioning DNS, but on a machine
with no network connection at all, the tests are excruciatingly slow
due to timeouts.

This commit mocks things out as appropriate. There's still one user of
the real getaddrinfo(), but it's for ::1, so that's just local
resolution based on /etc/hosts.

Timing numbers for "./.unittests test.unit.common.test_utils:TestStatsdLogging":

 * network, without this patch: 1.8s
 * no network, without this patch: 221.2s (ouch)
 * network, with this patch: 1.1s
 * no network, with this patch: 1.1s

Change-Id: I1a2d6f24fc9bb928894fb1fd8383516250e29e0c

test/unit/common/test_utils.py

@@ -3613,6 +3613,28 @@ class TestFileLikeIter(unittest.TestCase):
 
 
 class TestStatsdLogging(unittest.TestCase):
+    def setUp(self):
+
+        def fake_getaddrinfo(host, port, *args):
+            # this is what a real getaddrinfo('localhost', port,
+            # socket.AF_INET) returned once
+            return [(socket.AF_INET,      # address family
+                     socket.SOCK_STREAM,  # socket type
+                     socket.IPPROTO_TCP,  # socket protocol
+                     '',                  # canonical name,
+                     ('127.0.0.1', port)),  # socket address
+                    (socket.AF_INET,
+                     socket.SOCK_DGRAM,
+                     socket.IPPROTO_UDP,
+                     '',
+                     ('127.0.0.1', port))]
+
+        self.real_getaddrinfo = utils.socket.getaddrinfo
+        self.getaddrinfo_patcher = mock.patch.object(
+            utils.socket, 'getaddrinfo', fake_getaddrinfo)
+        self.mock_getaddrinfo = self.getaddrinfo_patcher.start()
+        self.addCleanup(self.getaddrinfo_patcher.stop)
+
     def test_get_logger_statsd_client_not_specified(self):
         logger = utils.get_logger({}, 'some-name', log_route='some-route')
         # white-box construction validation
@@ -3699,10 +3721,16 @@ class TestStatsdLogging(unittest.TestCase):
         # We have to check the given hostname or IP for IPv4/IPv6 on logger
         # instantiation so we don't call getaddrinfo() too often and don't have
         # to call bind() on our socket to detect IPv4/IPv6 on every send.
-        logger = utils.get_logger({
-            'log_statsd_host': '::1',
-            'log_statsd_port': '9876',
-        }, 'some-name', log_route='some-route')
+        #
+        # This test uses the real getaddrinfo, so we patch over the mock to
+        # put the real one back. If we just stop the mock, then
+        # unittest.exit() blows up, but stacking real-fake-real works okay.
+        with mock.patch.object(utils.socket, 'getaddrinfo',
+                               self.real_getaddrinfo):
+            logger = utils.get_logger({
+                'log_statsd_host': '::1',
+                'log_statsd_port': '9876',
+            }, 'some-name', log_route='some-route')
         statsd_client = logger.logger.statsd_client
 
         self.assertEqual(statsd_client._sock_family, socket.AF_INET6)
@@ -3712,10 +3740,12 @@ class TestStatsdLogging(unittest.TestCase):
         self.assertEqual(got_sock.family, socket.AF_INET6)
 
     def test_bad_hostname_instantiation(self):
-        logger = utils.get_logger({
-            'log_statsd_host': 'i-am-not-a-hostname-or-ip',
-            'log_statsd_port': '9876',
-        }, 'some-name', log_route='some-route')
+        with mock.patch.object(utils.socket, 'getaddrinfo',
+                               side_effect=utils.socket.gaierror("whoops")):
+            logger = utils.get_logger({
+                'log_statsd_host': 'i-am-not-a-hostname-or-ip',
+                'log_statsd_port': '9876',
+            }, 'some-name', log_route='some-route')
         statsd_client = logger.logger.statsd_client
 
         self.assertEqual(statsd_client._sock_family, socket.AF_INET)
@@ -3730,10 +3760,24 @@ class TestStatsdLogging(unittest.TestCase):
         # IP address in the configuration is fixed.
 
     def test_sending_ipv6(self):
-        logger = utils.get_logger({
-            'log_statsd_host': '::1',
-            'log_statsd_port': '9876',
-        }, 'some-name', log_route='some-route')
+        def fake_getaddrinfo(host, port, *args):
+            # this is what a real getaddrinfo('::1', port,
+            # socket.AF_INET6) returned once
+            return [(socket.AF_INET6,
+                     socket.SOCK_STREAM,
+                     socket.IPPROTO_TCP,
+                     '', ('::1', port, 0, 0)),
+                    (socket.AF_INET6,
+                     socket.SOCK_DGRAM,
+                     socket.IPPROTO_UDP,
+                     '',
+                     ('::1', port, 0, 0))]
+
+        with mock.patch.object(utils.socket, 'getaddrinfo', fake_getaddrinfo):
+            logger = utils.get_logger({
+                'log_statsd_host': '::1',
+                'log_statsd_port': '9876',
+            }, 'some-name', log_route='some-route')
         statsd_client = logger.logger.statsd_client
 
         fl = FakeLogger()