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fix: avoid querying to refresh types in the ServiceBrowser when they are seen after scheduling #1171

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bdraco wants to merge 4 commits into from
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fix: avoid querying to refresh types in the ServiceBrowser when they are seen after scheduling #1171

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1bff201
fix: avoid querying to refresh types in the ServiceBrowser when they …
bdraco May 4, 2023
1b52e2b
fix: speed up since its threadsafe
bdraco May 4, 2023
cc2cb7f
fix: only start checking when we hit the backoff limit
bdraco May 4, 2023
a60f216
Merge branch 'master' into refresh_too_soon
bdraco Jun 5, 2023
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23 changes: 21 additions & 2 deletions src/zeroconf/_services/browser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,7 @@
cast,
)

from .._cache import DNSCache
from .._dns import DNSPointer, DNSQuestion, DNSQuestionType, DNSRecord
from .._logger import log
from .._protocol.outgoing import DNSOutgoing
Expand Down Expand Up @@ -69,6 +70,8 @@
# https://datatracker.ietf.org/doc/html/rfc6762#section-5.2
_FIRST_QUERY_DELAY_RANDOM_INTERVAL = (20, 120) # ms

_BROWSER_BACKOFF_LIMIT_MS = _BROWSER_BACKOFF_LIMIT * 1000

_ON_CHANGE_DISPATCH = {
ServiceStateChange.Added: "add_service",
ServiceStateChange.Removed: "remove_service",
Expand Down Expand Up @@ -198,6 +201,7 @@ class QueryScheduler:

def __init__(
self,
cache: DNSCache,
types: Set[str],
delay: int,
first_random_delay_interval: Tuple[int, int],
Expand All @@ -207,6 +211,7 @@ def __init__(
self._next_time: Dict[str, float] = {}
self._first_random_delay_interval = first_random_delay_interval
self._delay: Dict[str, float] = {check_type_: delay for check_type_ in self._types}
self._cache = cache

def start(self, now: float) -> None:
"""Start the scheduler."""
Expand Down Expand Up @@ -251,9 +256,23 @@ def process_ready_types(self, now: float) -> List[str]:
if due > now:
continue

if self._delay[type_] == _BROWSER_BACKOFF_LIMIT_MS:
# Once we reach the backoff limit, we have a primed cache. If there are
# no stale PTR records because the record came in after we scheduled the
# query, we can reschedule the query to happen later.
next_refresh_time_by_record = [
record.get_expiration_time(_EXPIRE_REFRESH_TIME_PERCENT)
for record in self._cache.async_all_by_details(type_, _TYPE_PTR, _CLASS_IN)
]
if next_refresh_time_by_record:
recalculated_next_time = min(next_refresh_time_by_record)
if recalculated_next_time > now:
self._next_time[type_] = recalculated_next_time
continue

ready_types.append(type_)
self._next_time[type_] = now + self._delay[type_]
self._delay[type_] = min(_BROWSER_BACKOFF_LIMIT * 1000, self._delay[type_] * 2)
self._delay[type_] = min(_BROWSER_BACKOFF_LIMIT_MS, self._delay[type_] * 2)

return ready_types

Expand Down Expand Up @@ -301,7 +320,7 @@ def __init__(
self.question_type = question_type
self._pending_handlers: Dict[Tuple[str, str], ServiceStateChange] = {}
self._service_state_changed = Signal()
self.query_scheduler = QueryScheduler(self.types, delay, _FIRST_QUERY_DELAY_RANDOM_INTERVAL)
self.query_scheduler = QueryScheduler(zc.cache, self.types, delay, _FIRST_QUERY_DELAY_RANDOM_INTERVAL)
self.done = False
self._first_request: bool = True
self._next_send_timer: Optional[asyncio.TimerHandle] = None
Expand Down
4 changes: 3 additions & 1 deletion tests/services/test_browser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@
current_time_millis,
millis_to_seconds,
)
from zeroconf._cache import DNSCache
from zeroconf._services import ServiceStateChange
from zeroconf._services.browser import ServiceBrowser
from zeroconf._services.info import ServiceInfo
Expand Down Expand Up @@ -991,7 +992,8 @@ async def test_generate_service_query_suppress_duplicate_questions():
async def test_query_scheduler():
delay = const._BROWSER_TIME
types_ = {"_hap._tcp.local.", "_http._tcp.local."}
query_scheduler = _services_browser.QueryScheduler(types_, delay, (0, 0))
cache = DNSCache()
query_scheduler = _services_browser.QueryScheduler(cache, types_, delay, (0, 0))
Comment on lines 993 to +996

@bdraco bdraco May 4, 2023

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We need another query scheduler test that interacts with a populated DNSCache before we can merge this


now = current_time_millis()
query_scheduler.start(now)
Expand Down