From b834e312a3232e971bc622111acee5ff002a836c Mon Sep 17 00:00:00 2001
From: Prashant Mital <prashantmital@gmail.com>
Date: Fri, 14 Jun 2019 13:24:55 -0700
Subject: [PATCH] PYTHON-1872 Fix SrvMonitor related test failures

---
 pymongo/monitor.py       | 17 ++++++++++-------
 test/test_srv_polling.py | 36 ++++++++++++++++++++++++++++--------
 2 files changed, 38 insertions(+), 15 deletions(-)

diff --git a/pymongo/monitor.py b/pymongo/monitor.py
index d77d4e450..23af967ff 100644
--- a/pymongo/monitor.py
+++ b/pymongo/monitor.py
@@ -204,6 +204,7 @@ class SrvMonitor(MonitorBase):
         The Topology is weakly referenced.
         """
         self._settings = topology_settings
+        self._seedlist = self._settings._seeds
         self._fqdn = self._settings.fqdn
 
         # We strongly reference the executor and it weakly references us via
@@ -228,12 +229,14 @@ class SrvMonitor(MonitorBase):
         self._topology = weakref.proxy(topology, executor.close)
 
     def _run(self):
-        try:
-            self._seedlist = self._get_seedlist()
-            self._topology.on_srv_update(self._seedlist)
-        except ReferenceError:
-            # Topology was garbage-collected.
-            self.close()
+        seedlist = self._get_seedlist()
+        if seedlist:
+            self._seedlist = seedlist
+            try:
+                self._topology.on_srv_update(self._seedlist)
+            except ReferenceError:
+                # Topology was garbage-collected.
+                self.close()
 
     def _get_seedlist(self):
         """Poll SRV records for a seedlist.
@@ -251,7 +254,7 @@ class SrvMonitor(MonitorBase):
             # - SRV records must be rescanned every heartbeatFrequencyMS
             # - Topology must be left unchanged
             self.request_check()
-            return self._seedlist
+            return None
         else:
             self._executor.update_interval(
                 max(ttl, common.MIN_SRV_RESCAN_INTERVAL))
diff --git a/test/test_srv_polling.py b/test/test_srv_polling.py
index 6794e8e54..e7d62ca00 100644
--- a/test/test_srv_polling.py
+++ b/test/test_srv_polling.py
@@ -23,6 +23,7 @@ sys.path[0:0] = [""]
 import pymongo
 
 from pymongo import common
+from pymongo.errors import ConfigurationError
 from pymongo.srv_resolver import _HAVE_DNSPYTHON
 from pymongo.mongo_client import MongoClient
 from test import client_knobs, unittest
@@ -91,6 +92,14 @@ class TestSRVPolling(unittest.TestCase):
         if not _HAVE_DNSPYTHON:
             raise unittest.SkipTest("SRV polling tests require the dnspython "
                                     "module")
+        # Patch timeouts to ensure short rescan SRV interval.
+        self.client_knobs = client_knobs(
+            heartbeat_frequency=WAIT_TIME, min_heartbeat_interval=WAIT_TIME,
+            events_queue_frequency=WAIT_TIME)
+        self.client_knobs.enable()
+
+    def tearDown(self):
+        self.client_knobs.disable()
 
     def get_nodelist(self, client):
         return client._topology.description.server_descriptions().keys()
@@ -122,7 +131,7 @@ class TestSRVPolling(unittest.TestCase):
             1, "resolver was never called")
         return True
 
-    def _run_scenario(self, dns_response, expect_change):
+    def run_scenario(self, dns_response, expect_change):
         if callable(dns_response):
             dns_resolver_response = dns_response
         else:
@@ -149,13 +158,6 @@ class TestSRVPolling(unittest.TestCase):
                     count_resolver_calls=count_resolver_calls):
                 assertion_method(expected_response, mc)
 
-    def run_scenario(self, dns_response, expect_change):
-        # Patch timeouts to ensure short rescan SRV interval.
-        with client_knobs(heartbeat_frequency=WAIT_TIME,
-                          min_heartbeat_interval=WAIT_TIME,
-                          events_queue_frequency=WAIT_TIME):
-            self._run_scenario(dns_response, expect_change)
-
     def test_addition(self):
         response = self.BASE_SRV_RESPONSE[:]
         response.append(
@@ -196,6 +198,24 @@ class TestSRVPolling(unittest.TestCase):
         response = []
         self.run_scenario(response, False)
 
+    def _test_recover_from_initial(self, response_callback):
+        with SRVPollingKnobs(
+                ttl_time=WAIT_TIME, min_srv_rescan_interval=WAIT_TIME,
+                dns_resolver_nodelist_response=response_callback,
+                count_resolver_calls=True):
+            mc = MongoClient(self.CONNECTION_STRING)
+            self.assert_nodelist_nochange(self.BASE_SRV_RESPONSE, mc)
+
+    def test_recover_from_initially_empty_seedlist(self):
+        def empty_seedlist():
+            return []
+        self._test_recover_from_initial(empty_seedlist)
+
+    def test_recover_from_initially_erroring_seedlist(self):
+        def erroring_seedlist():
+            raise ConfigurationError
+        self._test_recover_from_initial(erroring_seedlist)
+
 
 if __name__ == '__main__':
     unittest.main()