diff options
Diffstat (limited to 'synapse/http/endpoint.py')
| -rw-r--r-- | synapse/http/endpoint.py | 128 |
1 files changed, 108 insertions, 20 deletions
diff --git a/synapse/http/endpoint.py b/synapse/http/endpoint.py index d8923c9abb..a97532162f 100644 --- a/synapse/http/endpoint.py +++ b/synapse/http/endpoint.py @@ -12,6 +12,7 @@ # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. +import socket from twisted.internet.endpoints import HostnameEndpoint, wrapClientTLS from twisted.internet import defer, reactor @@ -30,7 +31,10 @@ logger = logging.getLogger(__name__) SERVER_CACHE = {} - +# our record of an individual server which can be tried to reach a destination. +# +# "host" is actually a dotted-quad or ipv6 address string. Except when there's +# no SRV record, in which case it is the original hostname. _Server = collections.namedtuple( "_Server", "priority weight host port expires" ) @@ -219,9 +223,10 @@ class SRVClientEndpoint(object): return self.default_server else: raise ConnectError( - "Not server available for %s" % self.service_name + "No server available for %s" % self.service_name ) + # look for all servers with the same priority min_priority = self.servers[0].priority weight_indexes = list( (index, server.weight + 1) @@ -231,11 +236,22 @@ class SRVClientEndpoint(object): total_weight = sum(weight for index, weight in weight_indexes) target_weight = random.randint(0, total_weight) - for index, weight in weight_indexes: target_weight -= weight if target_weight <= 0: server = self.servers[index] + # XXX: this looks totally dubious: + # + # (a) we never reuse a server until we have been through + # all of the servers at the same priority, so if the + # weights are A: 100, B:1, we always do ABABAB instead of + # AAAA...AAAB (approximately). + # + # (b) After using all the servers at the lowest priority, + # we move onto the next priority. We should only use the + # second priority if servers at the top priority are + # unreachable. + # del self.servers[index] self.used_servers.append(server) return server @@ -280,26 +296,21 @@ def resolve_service(service_name, dns_client=client, cache=SERVER_CACHE, clock=t continue payload = answer.payload - host = str(payload.target) - srv_ttl = answer.ttl - try: - answers, _, _ = yield dns_client.lookupAddress(host) - except DNSNameError: - continue + hosts = yield _get_hosts_for_srv_record( + dns_client, str(payload.target) + ) - for answer in answers: - if answer.type == dns.A and answer.payload: - ip = answer.payload.dottedQuad() - host_ttl = min(srv_ttl, answer.ttl) + for (ip, ttl) in hosts: + host_ttl = min(answer.ttl, ttl) - servers.append(_Server( - host=ip, - port=int(payload.port), - priority=int(payload.priority), - weight=int(payload.weight), - expires=int(clock.time()) + host_ttl, - )) + servers.append(_Server( + host=ip, + port=int(payload.port), + priority=int(payload.priority), + weight=int(payload.weight), + expires=int(clock.time()) + host_ttl, + )) servers.sort() cache[service_name] = list(servers) @@ -317,3 +328,80 @@ def resolve_service(service_name, dns_client=client, cache=SERVER_CACHE, clock=t raise e defer.returnValue(servers) + + +@defer.inlineCallbacks +def _get_hosts_for_srv_record(dns_client, host): + """Look up each of the hosts in a SRV record + + Args: + dns_client (twisted.names.dns.IResolver): + host (basestring): host to look up + + Returns: + Deferred[list[(str, int)]]: a list of (host, ttl) pairs + + """ + ip4_servers = [] + ip6_servers = [] + + def cb(res): + # lookupAddress and lookupIP6Address return a three-tuple + # giving the answer, authority, and additional sections of the + # response. + # + # we only care about the answers. + + return res[0] + + def eb(res, record_type): + if res.check(DNSNameError): + return [] + logger.warn("Error looking up %s for %s: %s", + record_type, host, res, res.value) + return res + + # no logcontexts here, so we can safely fire these off and gatherResults + d1 = dns_client.lookupAddress(host).addCallbacks(cb, eb) + d2 = dns_client.lookupIPV6Address(host).addCallbacks(cb, eb) + results = yield defer.DeferredList( + [d1, d2], consumeErrors=True) + + # if all of the lookups failed, raise an exception rather than blowing out + # the cache with an empty result. + if results and all(s == defer.FAILURE for (s, _) in results): + defer.returnValue(results[0][1]) + + for (success, result) in results: + if success == defer.FAILURE: + continue + + for answer in result: + if not answer.payload: + continue + + try: + if answer.type == dns.A: + ip = answer.payload.dottedQuad() + ip4_servers.append((ip, answer.ttl)) + elif answer.type == dns.AAAA: + ip = socket.inet_ntop( + socket.AF_INET6, answer.payload.address, + ) + ip6_servers.append((ip, answer.ttl)) + else: + # the most likely candidate here is a CNAME record. + # rfc2782 says srvs may not point to aliases. + logger.warn( + "Ignoring unexpected DNS record type %s for %s", + answer.type, host, + ) + continue + except Exception as e: + logger.warn("Ignoring invalid DNS response for %s: %s", + host, e) + continue + + # keep the ipv4 results before the ipv6 results, mostly to match historical + # behaviour. + defer.returnValue(ip4_servers + ip6_servers) |