feat: avoid decoding known answers if we have no answers to give (#1308)

src/zeroconf/_core.py

@@ -577,15 +577,17 @@ def handle_assembled_query(
     ) -> None:
         """Respond to a (re)assembled query.
 
-        If the protocol recieved packets with the TC bit set, it will
+        If the protocol received packets with the TC bit set, it will
         wait a bit for the rest of the packets and only call
         handle_assembled_query once it has a complete set of packets
         or the timer expires. If the TC bit is not set, a single
         packet will be in packets.
         """
-        now = packets[0].now
         ucast_source = port != _MDNS_PORT
         question_answers = self.query_handler.async_response(packets, ucast_source)
+        if not question_answers:
+            return
+        now = packets[0].now
         if question_answers.ucast:
             questions = packets[0].questions
             id_ = packets[0].id

src/zeroconf/_handlers/answers.py

@@ -59,6 +59,14 @@ def __init__(
         self.mcast_aggregate = mcast_aggregate
         self.mcast_aggregate_last_second = mcast_aggregate_last_second
 
+    def __repr__(self) -> str:
+        """Return a string representation of this QuestionAnswers."""
+        return (
+            f'QuestionAnswers(ucast={self.ucast}, mcast_now={self.mcast_now}, '
+            f'mcast_aggregate={self.mcast_aggregate}, '
+            f'mcast_aggregate_last_second={self.mcast_aggregate_last_second})'
+        )
+
 
 class AnswerGroup:
     """A group of answers scheduled to be sent at the same time."""

src/zeroconf/_handlers/multicast_outgoing_queue.py

@@ -77,7 +77,7 @@ def async_add(self, now: _float, answers: _AnswerWithAdditionalsType) -> None:
             # If we calculate a random delay for the send after time
             # that is less than the last group scheduled to go out,
             # we instead add the answers to the last group as this
-            # allows aggregating additonal responses
+            # allows aggregating additional responses
             last_group = self.queue[-1]
             if send_after <= last_group.send_after:
                 last_group.answers.update(answers)
@@ -116,7 +116,7 @@ def async_ready(self) -> None:
             # be sure we schedule them to go out later
             loop.call_at(loop.time() + millis_to_seconds(self.queue[0].send_after - now), self.async_ready)
 
-        if answers:
+        if answers:  # pragma: no branch
             # If we have the same answer scheduled to go out, remove them
             self._remove_answers_from_queue(answers)
             zc.async_send(construct_outgoing_multicast_answers(answers))

src/zeroconf/_handlers/query_handler.pxd

@@ -18,6 +18,23 @@ cdef cython.set _ADDRESS_RECORD_TYPES
 cdef object IPVersion, _IPVersion_ALL
 cdef object _TYPE_PTR, _CLASS_IN, _DNS_OTHER_TTL
 
+cdef unsigned int _ANSWER_STRATEGY_SERVICE_TYPE_ENUMERATION
+cdef unsigned int _ANSWER_STRATEGY_POINTER
+cdef unsigned int _ANSWER_STRATEGY_ADDRESS
+cdef unsigned int _ANSWER_STRATEGY_SERVICE
+cdef unsigned int _ANSWER_STRATEGY_TEXT
+
+cdef list _EMPTY_SERVICES_LIST
+cdef list _EMPTY_TYPES_LIST
+
+cdef class _AnswerStrategy:
+
+    cdef public DNSQuestion question
+    cdef public unsigned int strategy_type
+    cdef public list types
+    cdef public list services
+
+
 cdef class _QueryResponse:
 
     cdef bint _is_probe
@@ -53,24 +70,30 @@ cdef class QueryHandler:
     cdef QuestionHistory question_history
 
     @cython.locals(service=ServiceInfo)
-    cdef _add_service_type_enumeration_query_answers(self, cython.dict answer_set, DNSRRSet known_answers)
+    cdef _add_service_type_enumeration_query_answers(self, list types, cython.dict answer_set, DNSRRSet known_answers)
 
     @cython.locals(service=ServiceInfo)
-    cdef _add_pointer_answers(self, str lower_name, cython.dict answer_set, DNSRRSet known_answers)
+    cdef _add_pointer_answers(self, list services, cython.dict answer_set, DNSRRSet known_answers)
 
     @cython.locals(service=ServiceInfo, dns_address=DNSAddress)
-    cdef _add_address_answers(self, str lower_name, cython.dict answer_set, DNSRRSet known_answers, cython.uint type_)
+    cdef _add_address_answers(self, list services, cython.dict answer_set, DNSRRSet known_answers, cython.uint type_)
 
     @cython.locals(question_lower_name=str, type_=cython.uint, service=ServiceInfo)
-    cdef cython.dict _answer_question(self, DNSQuestion question, DNSRRSet known_answers)
+    cdef cython.dict _answer_question(self, DNSQuestion question, unsigned int strategy_type, list types, list services, DNSRRSet known_answers)
 
     @cython.locals(
         msg=DNSIncoming,
+        msgs=list,
+        strategy=_AnswerStrategy,
         question=DNSQuestion,
         answer_set=cython.dict,
         known_answers=DNSRRSet,
         known_answers_set=cython.set,
+        is_unicast=bint,
         is_probe=object,
-        now=object
+        now=float
     )
     cpdef async_response(self, cython.list msgs, cython.bint unicast_source)
+
+    @cython.locals(name=str, question_lower_name=str)
+    cdef _get_answer_strategies(self, DNSQuestion question)