feat: reduce denial of service protection overhead (#1157)

src/zeroconf/_handlers.py

@@ -133,23 +133,6 @@ def _add_answers_additionals(out: DNSOutgoing, answers: _AnswerWithAdditionalsTy
                 sending.add(additional)
 
 
-def sanitize_incoming_record(record: DNSRecord) -> None:
-    """Protect zeroconf from records that can cause denial of service.
-
-    We enforce a minimum TTL for PTR records to avoid
-    ServiceBrowsers generating excessive queries refresh queries.
-    Apple uses a 15s minimum TTL, however we do not have the same
-    level of rate limit and safe guards so we use 1/4 of the recommended value.
-    """
-    if record.ttl and record.ttl < _DNS_PTR_MIN_TTL and isinstance(record, DNSPointer):
-        log.debug(
-            "Increasing effective ttl of %s to minimum of %s to protect against excessive refreshes.",
-            record,
-            _DNS_PTR_MIN_TTL,
-        )
-        record.set_created_ttl(record.created, _DNS_PTR_MIN_TTL)
-
-
 class _QueryResponse:
     """A pair for unicast and multicast DNSOutgoing responses."""
 
@@ -420,14 +403,26 @@ def async_updates_from_response(self, msg: DNSIncoming) -> None:
         threadsafe.
         """
         updates: List[RecordUpdate] = []
-        address_adds: List[DNSAddress] = []
+        address_adds: List[DNSRecord] = []
         other_adds: List[DNSRecord] = []
         removes: Set[DNSRecord] = set()
         now = msg.now
         unique_types: Set[Tuple[str, int, int]] = set()
 
         for record in msg.answers:
-            sanitize_incoming_record(record)
+            # Protect zeroconf from records that can cause denial of service.
+            #
+            # We enforce a minimum TTL for PTR records to avoid
+            # ServiceBrowsers generating excessive queries refresh queries.
+            # Apple uses a 15s minimum TTL, however we do not have the same
+            # level of rate limit and safe guards so we use 1/4 of the recommended value.
+            if record.ttl and record.type == _TYPE_PTR and record.ttl < _DNS_PTR_MIN_TTL:
+                log.debug(
+                    "Increasing effective ttl of %s to minimum of %s to protect against excessive refreshes.",
+                    record,
+                    _DNS_PTR_MIN_TTL,
+                )
+                record.set_created_ttl(record.created, _DNS_PTR_MIN_TTL)
 
             if record.unique:  # https://tools.ietf.org/html/rfc6762#section-10.2
                 unique_types.add((record.name, record.type, record.class_))
@@ -437,7 +432,7 @@ def async_updates_from_response(self, msg: DNSIncoming) -> None:
                 if maybe_entry is not None:
                     maybe_entry.reset_ttl(record)
                 else:
-                    if isinstance(record, DNSAddress):
+                    if record.type in _ADDRESS_RECORD_TYPES:
                         address_adds.append(record)
                     else:
                         other_adds.append(record)