Add new records first in cache entry instead of last (python-zeroconf#110)

* Add new records first in cache entry instead of last

* Added DNSCache unit test

Author: emontnemery

test_zeroconf.py

@@ -497,6 +497,19 @@ def test_incoming_ipv6(self):
         pass
 
 
+class TestDNSCache(unittest.TestCase):
+
+    def test_order(self):
+        record1 = r.DNSAddress('a', r._TYPE_SOA, r._CLASS_IN, 1, b'a')
+        record2 = r.DNSAddress('a', r._TYPE_SOA, r._CLASS_IN, 1, b'b')
+        cache = r.DNSCache()
+        cache.add(record1)
+        cache.add(record2)
+        entry = r.DNSEntry('a', r._TYPE_SOA, r._CLASS_IN)
+        cached_record = cache.get(entry)
+        self.assertEqual(cached_record, record2)
+
+
 class ServiceTypesQuery(unittest.TestCase):
 
     def test_integration_with_listener(self):

zeroconf.py

@@ -1014,7 +1014,8 @@ def __init__(self):
 
     def add(self, entry):
         """Adds an entry"""
-        self.cache.setdefault(entry.key, []).append(entry)
+        # Insert first in list so get returns newest entry
+        self.cache.setdefault(entry.key, []).insert(0, entry)
 
     def remove(self, entry):
         """Removes an entry"""