diff --git a/synapse/http/federation/well_known_resolver.py b/synapse/http/federation/well_known_resolver.py
index d2866ff67d..bb250c6922 100644
--- a/synapse/http/federation/well_known_resolver.py
+++ b/synapse/http/federation/well_known_resolver.py
@@ -44,6 +44,12 @@ WELL_KNOWN_MAX_CACHE_PERIOD = 48 * 3600
# lower bound for .well-known cache period
WELL_KNOWN_MIN_CACHE_PERIOD = 5 * 60
+# Attempt to refetch a cached well-known N% of the TTL before it expires.
+# e.g. if set to 0.2 and we have a cached entry with a TTL of 5mins, then
+# we'll start trying to refetch 1 minute before it expires.
+WELL_KNOWN_GRACE_PERIOD_FACTOR = 0.2
+
+
logger = logging.getLogger(__name__)
@@ -80,15 +86,38 @@ class WellKnownResolver(object):
Deferred[WellKnownLookupResult]: The result of the lookup
"""
try:
- result = self._well_known_cache[server_name]
+ prev_result, expiry, ttl = self._well_known_cache.get_with_expiry(
+ server_name
+ )
+
+ now = self._clock.time()
+ if now < expiry - WELL_KNOWN_GRACE_PERIOD_FACTOR * ttl:
+ return WellKnownLookupResult(delegated_server=prev_result)
except KeyError:
- # TODO: should we linearise so that we don't end up doing two .well-known
- # requests for the same server in parallel?
+ prev_result = None
+
+ # TODO: should we linearise so that we don't end up doing two .well-known
+ # requests for the same server in parallel?
+ try:
with Measure(self._clock, "get_well_known"):
result, cache_period = yield self._do_get_well_known(server_name)
- if cache_period > 0:
- self._well_known_cache.set(server_name, result, cache_period)
+ except _FetchWellKnownFailure as e:
+ if prev_result and e.temporary:
+ # This is a temporary failure and we have a still valid cached
+ # result, so lets return that. Hopefully the next time we ask
+ # the remote will be back up again.
+ return WellKnownLookupResult(delegated_server=prev_result)
+
+ result = None
+
+ # add some randomness to the TTL to avoid a stampeding herd every hour
+ # after startup
+ cache_period = WELL_KNOWN_INVALID_CACHE_PERIOD
+ cache_period += random.uniform(0, WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER)
+
+ if cache_period > 0:
+ self._well_known_cache.set(server_name, result, cache_period)
return WellKnownLookupResult(delegated_server=result)
@@ -99,40 +128,42 @@ class WellKnownResolver(object):
Args:
server_name (bytes): name of the server, from the requested url
+ Raises:
+ _FetchWellKnownFailure if we fail to lookup a result
+
Returns:
- Deferred[Tuple[bytes|None|object],int]:
- result, cache period, where result is one of:
- - the new server name from the .well-known (as a `bytes`)
- - None if there was no .well-known file.
- - INVALID_WELL_KNOWN if the .well-known was invalid
+ Deferred[Tuple[bytes,int]]: The lookup result and cache period.
"""
uri = b"https://%s/.well-known/matrix/server" % (server_name,)
uri_str = uri.decode("ascii")
logger.info("Fetching %s", uri_str)
+
+ # We do this in two steps to differentiate between possibly transient
+ # errors (e.g. can't connect to host, 503 response) and more permenant
+ # errors (such as getting a 404 response).
try:
response = yield make_deferred_yieldable(
self._well_known_agent.request(b"GET", uri)
)
body = yield make_deferred_yieldable(readBody(response))
+
+ if 500 <= response.code < 600:
+ raise Exception("Non-200 response %s" % (response.code,))
+ except Exception as e:
+ logger.info("Error fetching %s: %s", uri_str, e)
+ raise _FetchWellKnownFailure(temporary=True)
+
+ try:
if response.code != 200:
raise Exception("Non-200 response %s" % (response.code,))
parsed_body = json.loads(body.decode("utf-8"))
logger.info("Response from .well-known: %s", parsed_body)
- if not isinstance(parsed_body, dict):
- raise Exception("not a dict")
- if "m.server" not in parsed_body:
- raise Exception("Missing key 'm.server'")
+
+ result = parsed_body["m.server"].encode("ascii")
except Exception as e:
logger.info("Error fetching %s: %s", uri_str, e)
-
- # add some randomness to the TTL to avoid a stampeding herd every hour
- # after startup
- cache_period = WELL_KNOWN_INVALID_CACHE_PERIOD
- cache_period += random.uniform(0, WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER)
- return (None, cache_period)
-
- result = parsed_body["m.server"].encode("ascii")
+ raise _FetchWellKnownFailure(temporary=False)
cache_period = _cache_period_from_headers(
response.headers, time_now=self._reactor.seconds
@@ -185,3 +216,10 @@ def _parse_cache_control(headers):
v = splits[1] if len(splits) > 1 else None
cache_controls[k] = v
return cache_controls
+
+
+@attr.s()
+class _FetchWellKnownFailure(Exception):
+ # True if we didn't get a non-5xx HTTP response, i.e. this may or may not be
+ # a temporary failure.
+ temporary = attr.ib()
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