diff --git a/synapse/http/endpoint.py b/synapse/http/endpoint.py
index 4341ded96a..a9e024a415 100644
--- a/synapse/http/endpoint.py
+++ b/synapse/http/endpoint.py
@@ -17,7 +17,7 @@ from twisted.internet.endpoints import SSL4ClientEndpoint, TCP4ClientEndpoint
from twisted.internet import defer
from twisted.internet.error import ConnectError
from twisted.names import client, dns
-from twisted.names.error import DNSNameError
+from twisted.names.error import DNSNameError, DomainError
import collections
import logging
@@ -27,6 +27,14 @@ import random
logger = logging.getLogger(__name__)
+SERVER_CACHE = {}
+
+
+_Server = collections.namedtuple(
+ "_Server", "priority weight host port"
+)
+
+
def matrix_federation_endpoint(reactor, destination, ssl_context_factory=None,
timeout=None):
"""Construct an endpoint for the given matrix destination.
@@ -73,10 +81,6 @@ class SRVClientEndpoint(object):
Implements twisted.internet.interfaces.IStreamClientEndpoint.
"""
- _Server = collections.namedtuple(
- "_Server", "priority weight host port"
- )
-
def __init__(self, reactor, service, domain, protocol="tcp",
default_port=None, endpoint=TCP4ClientEndpoint,
endpoint_kw_args={}):
@@ -101,32 +105,8 @@ class SRVClientEndpoint(object):
@defer.inlineCallbacks
def fetch_servers(self):
- try:
- answers, auth, add = yield client.lookupService(self.service_name)
- except DNSNameError:
- answers = []
-
- if (len(answers) == 1
- and answers[0].type == dns.SRV
- and answers[0].payload
- and answers[0].payload.target == dns.Name('.')):
- raise ConnectError("Service %s unavailable", self.service_name)
-
- self.servers = []
self.used_servers = []
-
- for answer in answers:
- if answer.type != dns.SRV or not answer.payload:
- continue
- payload = answer.payload
- self.servers.append(self._Server(
- host=str(payload.target),
- port=int(payload.port),
- priority=int(payload.priority),
- weight=int(payload.weight)
- ))
-
- self.servers.sort()
+ self.servers = yield resolve_service(self.service_name)
def pick_server(self):
if not self.servers:
@@ -170,3 +150,64 @@ class SRVClientEndpoint(object):
)
connection = yield endpoint.connect(protocolFactory)
defer.returnValue(connection)
+
+
+@defer.inlineCallbacks
+def resolve_service(service_name, dns_client=client, cache=SERVER_CACHE):
+ servers = []
+
+ try:
+ try:
+ answers, _, _ = yield dns_client.lookupService(service_name)
+ except DNSNameError:
+ defer.returnValue([])
+
+ if (len(answers) == 1
+ and answers[0].type == dns.SRV
+ and answers[0].payload
+ and answers[0].payload.target == dns.Name('.')):
+ raise ConnectError("Service %s unavailable", service_name)
+
+ for answer in answers:
+ if answer.type != dns.SRV or not answer.payload:
+ continue
+
+ payload = answer.payload
+
+ host = str(payload.target)
+
+ try:
+ answers, _, _ = yield dns_client.lookupAddress(host)
+ except DNSNameError:
+ continue
+
+ ips = [
+ answer.payload.dottedQuad()
+ for answer in answers
+ if answer.type == dns.A and answer.payload
+ ]
+
+ for ip in ips:
+ servers.append(_Server(
+ host=ip,
+ port=int(payload.port),
+ priority=int(payload.priority),
+ weight=int(payload.weight)
+ ))
+
+ servers.sort()
+ cache[service_name] = list(servers)
+ except DomainError as e:
+ # We failed to resolve the name (other than a NameError)
+ # Try something in the cache, else rereaise
+ cache_entry = cache.get(service_name, None)
+ if cache_entry:
+ logger.warn(
+ "Failed to resolve %r, falling back to cache. %r",
+ service_name, e
+ )
+ servers = list(cache_entry)
+ else:
+ raise e
+
+ defer.returnValue(servers)
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