diff options
Diffstat (limited to 'synapse/http/federation/well_known_resolver.py')
| -rw-r--r-- | synapse/http/federation/well_known_resolver.py | 82 |
1 files changed, 60 insertions, 22 deletions
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() |