PYTHON-4575 Remove hostname length check

- Add test

Author: aclark4life

pymongo/asynchronous/srv_resolver.py

@@ -96,6 +96,10 @@ def __init__(
         except Exception:
             raise ConfigurationError(_INVALID_HOST_MSG % (fqdn,)) from None
         self.__slen = len(self.__plist)
+        if fqdn == self._resolve_uri(True)[0].target.to_text():
+            raise ConfigurationError(
+                "Invalid SRV host: return address is identical to SRV hostname"
+            )
 
     async def get_options(self) -> Optional[str]:
         from dns import resolver

pymongo/synchronous/srv_resolver.py

@@ -96,6 +96,10 @@ def __init__(
         except Exception:
             raise ConfigurationError(_INVALID_HOST_MSG % (fqdn,)) from None
         self.__slen = len(self.__plist)
+        if fqdn == self._resolve_uri(True)[0].target.to_text():
+            raise ConfigurationError(
+                "Invalid SRV host: return address is identical to SRV hostname"
+            )
 
     def get_options(self) -> Optional[str]:
         from dns import resolver

test/test_uri_parser.py

@@ -576,6 +576,21 @@ def test_error_when_return_address_does_not_end_with_srv_domain(self):
                 "mock_target": "test_1.evil.com",
                 "expected_error": "Invalid SRV host",
             },
+            {
+                "query": "_mongodb._tcp.localhost",
+                "mock_target": "localhost",
+                "expected_error": "Invalid SRV host",
+            },
+            {
+                "query": "_mongodb._tcp.localhost",
+                "mock_target": "localhost",
+                "expected_error": "Invalid SRV host",
+            },
+            {
+                "query": "_mongodb._tcp.mongo.local",
+                "mock_target": "mongo.local",
+                "expected_error": "Invalid SRV host",
+            },
         ]
         for case in test_cases:
             with patch("dns.resolver.resolve") as mock_resolver: