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Merge pull request #5864 from matrix-org/erikj/reliable_lookups

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Refactor MatrixFederationAgent to retry SRV.
This commit is contained in:
Erik Johnston 2019-08-27 16:54:06 +01:00 committed by GitHub
commit dfd10f5133
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7 changed files with 291 additions and 223 deletions
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1
changelog.d/5864.feature Normal file
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@ -0,0 +1 @@
Correctly retry all hosts returned from SRV when we fail to connect.

378
synapse/http/federation/matrix_federation_agent.py
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@ -14,21 +14,21 @@
# limitations under the License.
import logging
import urllib
import attr
from netaddr import IPAddress
from netaddr import AddrFormatError, IPAddress
from zope.interface import implementer
from twisted.internet import defer
from twisted.internet.endpoints import HostnameEndpoint, wrapClientTLS
from twisted.internet.interfaces import IStreamClientEndpoint
from twisted.web.client import URI, Agent, HTTPConnectionPool
from twisted.web.client import Agent, HTTPConnectionPool
from twisted.web.http_headers import Headers
from twisted.web.iweb import IAgent
from twisted.web.iweb import IAgent, IAgentEndpointFactory
from synapse.http.federation.srv_resolver import SrvResolver, pick_server_from_list
from synapse.http.federation.srv_resolver import Server, SrvResolver
from synapse.http.federation.well_known_resolver import WellKnownResolver
from synapse.logging.context import make_deferred_yieldable
from synapse.logging.context import make_deferred_yieldable, run_in_background
from synapse.util import Clock
logger = logging.getLogger(__name__)
@ -36,8 +36,9 @@ logger = logging.getLogger(__name__)
@implementer(IAgent)
class MatrixFederationAgent(object):
"""An Agent-like thing which provides a `request` method which will look up a matrix
server and send an HTTP request to it.
"""An Agent-like thing which provides a `request` method which correctly
handles resolving matrix server names when using matrix://. Handles standard
https URIs as normal.
Doesn't implement any retries. (Those are done in MatrixFederationHttpClient.)
@ -65,17 +66,19 @@ class MatrixFederationAgent(object):
):
self._reactor = reactor
self._clock = Clock(reactor)
self._tls_client_options_factory = tls_client_options_factory
if _srv_resolver is None:
_srv_resolver = SrvResolver()
self._srv_resolver = _srv_resolver
self._pool = HTTPConnectionPool(reactor)
self._pool.retryAutomatically = False
self._pool.maxPersistentPerHost = 5
self._pool.cachedConnectionTimeout = 2 * 60
self._agent = Agent.usingEndpointFactory(
self._reactor,
MatrixHostnameEndpointFactory(
reactor, tls_client_options_factory, _srv_resolver
),
pool=self._pool,
)
if _well_known_resolver is None:
_well_known_resolver = WellKnownResolver(
self._reactor,
@ -93,19 +96,15 @@ class MatrixFederationAgent(object):
"""
Args:
method (bytes): HTTP method: GET/POST/etc
uri (bytes): Absolute URI to be retrieved
headers (twisted.web.http_headers.Headers|None):
HTTP headers to send with the request, or None to
send no extra headers.
bodyProducer (twisted.web.iweb.IBodyProducer|None):
An object which can generate bytes to make up the
body of this request (for example, the properly encoded contents of
a file for a file upload). Or None if the request is to have
no body.
Returns:
Deferred[twisted.web.iweb.IResponse]:
fires when the header of the response has been received (regardless of the
@ -113,210 +112,207 @@ class MatrixFederationAgent(object):
response from being received (including problems that prevent the request
from being sent).
"""
parsed_uri = URI.fromBytes(uri, defaultPort=-1)
res = yield self._route_matrix_uri(parsed_uri)
# We use urlparse as that will set `port` to None if there is no
# explicit port.
parsed_uri = urllib.parse.urlparse(uri)
# set up the TLS connection params
# If this is a matrix:// URI check if the server has delegated matrix
# traffic using well-known delegation.
#
# XXX disabling TLS is really only supported here for the benefit of the
# unit tests. We should make the UTs cope with TLS rather than having to make
# the code support the unit tests.
if self._tls_client_options_factory is None:
tls_options = None
else:
tls_options = self._tls_client_options_factory.get_options(
res.tls_server_name.decode("ascii")
# We have to do this here and not in the endpoint as we need to rewrite
# the host header with the delegated server name.
delegated_server = None
if (
parsed_uri.scheme == b"matrix"
and not _is_ip_literal(parsed_uri.hostname)
and not parsed_uri.port
):
well_known_result = yield self._well_known_resolver.get_well_known(
parsed_uri.hostname
)
delegated_server = well_known_result.delegated_server
# make sure that the Host header is set correctly
if delegated_server:
# Ok, the server has delegated matrix traffic to somewhere else, so
# lets rewrite the URL to replace the server with the delegated
# server name.
uri = urllib.parse.urlunparse(
(
parsed_uri.scheme,
delegated_server,
parsed_uri.path,
parsed_uri.params,
parsed_uri.query,
parsed_uri.fragment,
)
)
parsed_uri = urllib.parse.urlparse(uri)
# We need to make sure the host header is set to the netloc of the
# server.
if headers is None:
headers = Headers()
else:
headers = headers.copy()
if not headers.hasHeader(b"host"):
headers.addRawHeader(b"host", res.host_header)
headers.addRawHeader(b"host", parsed_uri.netloc)
class EndpointFactory(object):
@staticmethod
def endpointForURI(_uri):
ep = LoggingHostnameEndpoint(
self._reactor, res.target_host, res.target_port
)
if tls_options is not None:
ep = wrapClientTLS(tls_options, ep)
return ep
agent = Agent.usingEndpointFactory(self._reactor, EndpointFactory(), self._pool)
res = yield make_deferred_yieldable(
agent.request(method, uri, headers, bodyProducer)
self._agent.request(method, uri, headers, bodyProducer)
)
return res
@defer.inlineCallbacks
def _route_matrix_uri(self, parsed_uri, lookup_well_known=True):
"""Helper for `request`: determine the routing for a Matrix URI
Args:
parsed_uri (twisted.web.client.URI): uri to route. Note that it should be
parsed with URI.fromBytes(uri, defaultPort=-1) to set the `port` to -1
if there is no explicit port given.
@implementer(IAgentEndpointFactory)
class MatrixHostnameEndpointFactory(object):
"""Factory for MatrixHostnameEndpoint for parsing to an Agent.
"""
lookup_well_known (bool): True if we should look up the .well-known file if
there is no SRV record.
def __init__(self, reactor, tls_client_options_factory, srv_resolver):
self._reactor = reactor
self._tls_client_options_factory = tls_client_options_factory
Returns:
Deferred[_RoutingResult]
"""
# check for an IP literal
try:
ip_address = IPAddress(parsed_uri.host.decode("ascii"))
except Exception:
# not an IP address
ip_address = None
if srv_resolver is None:
srv_resolver = SrvResolver()
if ip_address:
port = parsed_uri.port
if port == -1:
port = 8448
return _RoutingResult(
host_header=parsed_uri.netloc,
tls_server_name=parsed_uri.host,
target_host=parsed_uri.host,
target_port=port,
)
self._srv_resolver = srv_resolver
if parsed_uri.port != -1:
# there is an explicit port
return _RoutingResult(
host_header=parsed_uri.netloc,
tls_server_name=parsed_uri.host,
target_host=parsed_uri.host,
target_port=parsed_uri.port,
)
if lookup_well_known:
# try a .well-known lookup
well_known_result = yield self._well_known_resolver.get_well_known(
parsed_uri.host
)
well_known_server = well_known_result.delegated_server
if well_known_server:
# if we found a .well-known, start again, but don't do another
# .well-known lookup.
# parse the server name in the .well-known response into host/port.
# (This code is lifted from twisted.web.client.URI.fromBytes).
if b":" in well_known_server:
well_known_host, well_known_port = well_known_server.rsplit(b":", 1)
try:
well_known_port = int(well_known_port)
except ValueError:
# the part after the colon could not be parsed as an int
# - we assume it is an IPv6 literal with no port (the closing
# ']' stops it being parsed as an int)
well_known_host, well_known_port = well_known_server, -1
else:
well_known_host, well_known_port = well_known_server, -1
new_uri = URI(
scheme=parsed_uri.scheme,
netloc=well_known_server,
host=well_known_host,
port=well_known_port,
path=parsed_uri.path,
params=parsed_uri.params,
query=parsed_uri.query,
fragment=parsed_uri.fragment,
)
res = yield self._route_matrix_uri(new_uri, lookup_well_known=False)
return res
# try a SRV lookup
service_name = b"_matrix._tcp.%s" % (parsed_uri.host,)
server_list = yield self._srv_resolver.resolve_service(service_name)
if not server_list:
target_host = parsed_uri.host
port = 8448
logger.debug(
"No SRV record for %s, using %s:%i",
parsed_uri.host.decode("ascii"),
target_host.decode("ascii"),
port,
)
else:
target_host, port = pick_server_from_list(server_list)
logger.debug(
"Picked %s:%i from SRV records for %s",
target_host.decode("ascii"),
port,
parsed_uri.host.decode("ascii"),
)
return _RoutingResult(
host_header=parsed_uri.netloc,
tls_server_name=parsed_uri.host,
target_host=target_host,
target_port=port,
def endpointForURI(self, parsed_uri):
return MatrixHostnameEndpoint(
self._reactor,
self._tls_client_options_factory,
self._srv_resolver,
parsed_uri,
)
@implementer(IStreamClientEndpoint)
class LoggingHostnameEndpoint(object):
"""A wrapper for HostnameEndpint which logs when it connects"""
class MatrixHostnameEndpoint(object):
"""An endpoint that resolves matrix:// URLs using Matrix server name
resolution (i.e. via SRV). Does not check for well-known delegation.
def __init__(self, reactor, host, port, *args, **kwargs):
self.host = host
self.port = port
self.ep = HostnameEndpoint(reactor, host, port, *args, **kwargs)
Args:
reactor (IReactor)
tls_client_options_factory (ClientTLSOptionsFactory|None):
factory to use for fetching client tls options, or none to disable TLS.
srv_resolver (SrvResolver): The SRV resolver to use
parsed_uri (twisted.web.client.URI): The parsed URI that we're wanting
to connect to.
"""
def __init__(self, reactor, tls_client_options_factory, srv_resolver, parsed_uri):
self._reactor = reactor
self._parsed_uri = parsed_uri
# set up the TLS connection params
#
# XXX disabling TLS is really only supported here for the benefit of the
# unit tests. We should make the UTs cope with TLS rather than having to make
# the code support the unit tests.
if tls_client_options_factory is None:
self._tls_options = None
else:
self._tls_options = tls_client_options_factory.get_options(
self._parsed_uri.host.decode("ascii")
)
self._srv_resolver = srv_resolver
def connect(self, protocol_factory):
logger.info("Connecting to %s:%i", self.host.decode("ascii"), self.port)
return self.ep.connect(protocol_factory)
"""Implements IStreamClientEndpoint interface
"""
return run_in_background(self._do_connect, protocol_factory)
@defer.inlineCallbacks
def _do_connect(self, protocol_factory):
first_exception = None
server_list = yield self._resolve_server()
for server in server_list:
host = server.host
port = server.port
try:
logger.info("Connecting to %s:%i", host.decode("ascii"), port)
endpoint = HostnameEndpoint(self._reactor, host, port)
if self._tls_options:
endpoint = wrapClientTLS(self._tls_options, endpoint)
result = yield make_deferred_yieldable(
endpoint.connect(protocol_factory)
)
return result
except Exception as e:
logger.info(
"Failed to connect to %s:%i: %s", host.decode("ascii"), port, e
)
if not first_exception:
first_exception = e
# We return the first failure because that's probably the most interesting.
if first_exception:
raise first_exception
# This shouldn't happen as we should always have at least one host/port
# to try and if that doesn't work then we'll have an exception.
raise Exception("Failed to resolve server %r" % (self._parsed_uri.netloc,))
@defer.inlineCallbacks
def _resolve_server(self):
"""Resolves the server name to a list of hosts and ports to attempt to
connect to.
Returns:
Deferred[list[Server]]
"""
if self._parsed_uri.scheme != b"matrix":
return [Server(host=self._parsed_uri.host, port=self._parsed_uri.port)]
# Note: We don't do well-known lookup as that needs to have happened
# before now, due to needing to rewrite the Host header of the HTTP
# request.
# We reparse the URI so that defaultPort is -1 rather than 80
parsed_uri = urllib.parse.urlparse(self._parsed_uri.toBytes())
host = parsed_uri.hostname
port = parsed_uri.port
# If there is an explicit port or the host is an IP address we bypass
# SRV lookups and just use the given host/port.
if port or _is_ip_literal(host):
return [Server(host, port or 8448)]
server_list = yield self._srv_resolver.resolve_service(b"_matrix._tcp." + host)
if server_list:
return server_list
# No SRV records, so we fallback to host and 8448
return [Server(host, 8448)]
@attr.s
class _RoutingResult(object):
"""The result returned by `_route_matrix_uri`.
def _is_ip_literal(host):
"""Test if the given host name is either an IPv4 or IPv6 literal.
Contains the parameters needed to direct a federation connection to a particular
server.
Args:
host (bytes)
Where a SRV record points to several servers, this object contains a single server
chosen from the list.
Returns:
bool
"""
host_header = attr.ib()
"""
The value we should assign to the Host header (host:port from the matrix
URI, or .well-known).
host = host.decode("ascii")
:type: bytes
"""
tls_server_name = attr.ib()
"""
The server name we should set in the SNI (typically host, without port, from the
matrix URI or .well-known)
:type: bytes
"""
target_host = attr.ib()
"""
The hostname (or IP literal) we should route the TCP connection to (the target of the
SRV record, or the hostname from the URL/.well-known)
:type: bytes
"""
target_port = attr.ib()
"""
The port we should route the TCP connection to (the target of the SRV record, or
the port from the URL/.well-known, or 8448)
:type: int
"""
try:
IPAddress(host)
return True
except AddrFormatError:
return False

63
synapse/http/federation/srv_resolver.py
View File

@ -32,7 +32,7 @@ logger = logging.getLogger(__name__)
SERVER_CACHE = {}
@attr.s
@attr.s(slots=True, frozen=True)
class Server(object):
"""
Our record of an individual server which can be tried to reach a destination.
@ -53,34 +53,47 @@ class Server(object):
expires = attr.ib(default=0)
def pick_server_from_list(server_list):
"""Randomly choose a server from the server list
Args:
server_list (list[Server]): list of candidate servers
Returns:
Tuple[bytes, int]: (host, port) pair for the chosen server
def _sort_server_list(server_list):
"""Given a list of SRV records sort them into priority order and shuffle
each priority with the given weight.
"""
if not server_list:
raise RuntimeError("pick_server_from_list called with empty list")
priority_map = {}
# TODO: currently we only use the lowest-priority servers. We should maintain a
# cache of servers known to be "down" and filter them out
for server in server_list:
priority_map.setdefault(server.priority, []).append(server)
min_priority = min(s.priority for s in server_list)
eligible_servers = list(s for s in server_list if s.priority == min_priority)
total_weight = sum(s.weight for s in eligible_servers)
target_weight = random.randint(0, total_weight)
results = []
for priority in sorted(priority_map):
servers = priority_map[priority]
for s in eligible_servers:
target_weight -= s.weight
# This algorithms roughly follows the algorithm described in RFC2782,
# changed to remove an off-by-one error.
#
# N.B. Weights can be zero, which means that they should be picked
# rarely.
if target_weight <= 0:
return s.host, s.port
total_weight = sum(s.weight for s in servers)
# this should be impossible.
raise RuntimeError("pick_server_from_list got to end of eligible server list.")
# Total weight can become zero if there are only zero weight servers
# left, which we handle by just shuffling and appending to the results.
while servers and total_weight:
target_weight = random.randint(1, total_weight)
for s in servers:
target_weight -= s.weight
if target_weight <= 0:
break
results.append(s)
servers.remove(s)
total_weight -= s.weight
if servers:
random.shuffle(servers)
results.extend(servers)
return results
class SrvResolver(object):
@ -120,7 +133,7 @@ class SrvResolver(object):
if cache_entry:
if all(s.expires > now for s in cache_entry):
servers = list(cache_entry)
return servers
return _sort_server_list(servers)
try:
answers, _, _ = yield make_deferred_yieldable(
@ -169,4 +182,4 @@ class SrvResolver(object):
)
self._cache[service_name] = list(servers)
return servers
return _sort_server_list(servers)

1
tests/federation/test_federation_server.py
View File

@ -20,7 +20,6 @@ from synapse.federation.federation_server import server_matches_acl_event
from tests import unittest
@unittest.DEBUG
class ServerACLsTestCase(unittest.TestCase):
def test_blacklisted_server(self):
e = _create_acl_event({"allow": ["*"], "deny": ["evil.com"]})

62
tests/http/federation/test_matrix_federation_agent.py
View File

@ -41,9 +41,9 @@ from synapse.http.federation.well_known_resolver import (
from synapse.logging.context import LoggingContext
from synapse.util.caches.ttlcache import TTLCache
from tests import unittest
from tests.http import TestServerTLSConnectionFactory, get_test_ca_cert_file
from tests.server import FakeTransport, ThreadedMemoryReactorClock
from tests.unittest import TestCase
from tests.utils import default_config
logger = logging.getLogger(__name__)
@ -67,7 +67,7 @@ def get_connection_factory():
return test_server_connection_factory
class MatrixFederationAgentTests(TestCase):
class MatrixFederationAgentTests(unittest.TestCase):
def setUp(self):
self.reactor = ThreadedMemoryReactorClock()
@ -1069,8 +1069,64 @@ class MatrixFederationAgentTests(TestCase):
r = self.successResultOf(fetch_d)
self.assertEqual(r.delegated_server, None)
def test_srv_fallbacks(self):
"""Test that other SRV results are tried if the first one fails.
"""
class TestCachePeriodFromHeaders(TestCase):
self.mock_resolver.resolve_service.side_effect = lambda _: [
Server(host=b"target.com", port=8443),
Server(host=b"target.com", port=8444),
]
self.reactor.lookups["target.com"] = "1.2.3.4"
test_d = self._make_get_request(b"matrix://testserv/foo/bar")
# Nothing happened yet
self.assertNoResult(test_d)
self.mock_resolver.resolve_service.assert_called_once_with(
b"_matrix._tcp.testserv"
)
# We should see an attempt to connect to the first server
clients = self.reactor.tcpClients
self.assertEqual(len(clients), 1)
(host, port, client_factory, _timeout, _bindAddress) = clients.pop(0)
self.assertEqual(host, "1.2.3.4")
self.assertEqual(port, 8443)
# Fonx the connection
client_factory.clientConnectionFailed(None, Exception("nope"))
# There's a 300ms delay in HostnameEndpoint
self.reactor.pump((0.4,))
# Hasn't failed yet
self.assertNoResult(test_d)
# We shouldnow see an attempt to connect to the second server
clients = self.reactor.tcpClients
self.assertEqual(len(clients), 1)
(host, port, client_factory, _timeout, _bindAddress) = clients.pop(0)
self.assertEqual(host, "1.2.3.4")
self.assertEqual(port, 8444)
# make a test server, and wire up the client
http_server = self._make_connection(client_factory, expected_sni=b"testserv")
self.assertEqual(len(http_server.requests), 1)
request = http_server.requests[0]
self.assertEqual(request.method, b"GET")
self.assertEqual(request.path, b"/foo/bar")
self.assertEqual(request.requestHeaders.getRawHeaders(b"host"), [b"testserv"])
# finish the request
request.finish()
self.reactor.pump((0.1,))
self.successResultOf(test_d)
class TestCachePeriodFromHeaders(unittest.TestCase):
def test_cache_control(self):
# uppercase
self.assertEqual(

8
tests/http/federation/test_srv_resolver.py
View File

@ -83,8 +83,10 @@ class SrvResolverTestCase(unittest.TestCase):
service_name = b"test_service.example.com"
entry = Mock(spec_set=["expires"])
entry = Mock(spec_set=["expires", "priority", "weight"])
entry.expires = 0
entry.priority = 0
entry.weight = 0
cache = {service_name: [entry]}
resolver = SrvResolver(dns_client=dns_client_mock, cache=cache)
@ -105,8 +107,10 @@ class SrvResolverTestCase(unittest.TestCase):
service_name = b"test_service.example.com"
entry = Mock(spec_set=["expires"])
entry = Mock(spec_set=["expires", "priority", "weight"])
entry.expires = 999999999
entry.priority = 0
entry.weight = 0
cache = {service_name: [entry]}
resolver = SrvResolver(

1
tests/test_visibility.py
View File

@ -74,7 +74,6 @@ class FilterEventsForServerTestCase(tests.unittest.TestCase):
self.assertEqual(events_to_filter[i].event_id, filtered[i].event_id)
self.assertEqual(filtered[i].content["a"], "b")
@tests.unittest.DEBUG
@defer.inlineCallbacks
def test_erased_user(self):
# 4 message events, from erased and unerased users, with a membership