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- # -*- coding: utf-8 -*-
- # Copyright 2019 The Matrix.org Foundation C.I.C.
- #
- # Licensed under the Apache License, Version 2.0 (the "License");
- # you may not use this file except in compliance with the License.
- # You may obtain a copy of the License at
- #
- # http://www.apache.org/licenses/LICENSE-2.0
- #
- # Unless required by applicable law or agreed to in writing, software
- # distributed under the License is distributed on an "AS IS" BASIS,
- # 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 logging
- import random
- import time
- from typing import Callable, Dict, Optional, Tuple
- import attr
- from twisted.internet import defer
- from twisted.web.client import RedirectAgent, readBody
- from twisted.web.http import stringToDatetime
- from twisted.web.http_headers import Headers
- from twisted.web.iweb import IResponse
- from synapse.logging.context import make_deferred_yieldable
- from synapse.util import Clock, json_decoder
- from synapse.util.caches.ttlcache import TTLCache
- from synapse.util.metrics import Measure
- # period to cache .well-known results for by default
- WELL_KNOWN_DEFAULT_CACHE_PERIOD = 24 * 3600
- # jitter factor to add to the .well-known default cache ttls
- WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER = 0.1
- # period to cache failure to fetch .well-known for
- WELL_KNOWN_INVALID_CACHE_PERIOD = 1 * 3600
- # period to cache failure to fetch .well-known if there has recently been a
- # valid well-known for that domain.
- WELL_KNOWN_DOWN_CACHE_PERIOD = 2 * 60
- # period to remember there was a valid well-known after valid record expires
- WELL_KNOWN_REMEMBER_DOMAIN_HAD_VALID = 2 * 3600
- # cap for .well-known cache period
- 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
- # Number of times we retry fetching a well-known for a domain we know recently
- # had a valid entry.
- WELL_KNOWN_RETRY_ATTEMPTS = 3
- logger = logging.getLogger(__name__)
- _well_known_cache = TTLCache("well-known")
- _had_valid_well_known_cache = TTLCache("had-valid-well-known")
- @attr.s(slots=True, frozen=True)
- class WellKnownLookupResult:
- delegated_server = attr.ib()
- class WellKnownResolver:
- """Handles well-known lookups for matrix servers.
- """
- def __init__(
- self,
- reactor,
- agent,
- user_agent,
- well_known_cache=None,
- had_well_known_cache=None,
- ):
- self._reactor = reactor
- self._clock = Clock(reactor)
- if well_known_cache is None:
- well_known_cache = _well_known_cache
- if had_well_known_cache is None:
- had_well_known_cache = _had_valid_well_known_cache
- self._well_known_cache = well_known_cache
- self._had_valid_well_known_cache = had_well_known_cache
- self._well_known_agent = RedirectAgent(agent)
- self.user_agent = user_agent
- async def get_well_known(self, server_name: bytes) -> WellKnownLookupResult:
- """Attempt to fetch and parse a .well-known file for the given server
- Args:
- server_name: name of the server, from the requested url
- Returns:
- The result of the lookup
- """
- try:
- 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:
- 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 = await self._fetch_well_known(
- server_name
- ) # type: Tuple[Optional[bytes], float]
- 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
- if self._had_valid_well_known_cache.get(server_name, False):
- # We have recently seen a valid well-known record for this
- # server, so we cache the lack of well-known for a shorter time.
- cache_period = WELL_KNOWN_DOWN_CACHE_PERIOD
- else:
- cache_period = WELL_KNOWN_INVALID_CACHE_PERIOD
- # add some randomness to the TTL to avoid a stampeding herd
- cache_period *= random.uniform(
- 1 - WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER,
- 1 + 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)
- async def _fetch_well_known(self, server_name: bytes) -> Tuple[bytes, float]:
- """Actually fetch and parse a .well-known, without checking the cache
- Args:
- server_name: name of the server, from the requested url
- Raises:
- _FetchWellKnownFailure if we fail to lookup a result
- Returns:
- The lookup result and cache period.
- """
- had_valid_well_known = self._had_valid_well_known_cache.get(server_name, False)
- # 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).
- response, body = await self._make_well_known_request(
- server_name, retry=had_valid_well_known
- )
- try:
- if response.code != 200:
- raise Exception("Non-200 response %s" % (response.code,))
- parsed_body = json_decoder.decode(body.decode("utf-8"))
- logger.info("Response from .well-known: %s", parsed_body)
- result = parsed_body["m.server"].encode("ascii")
- except defer.CancelledError:
- # Bail if we've been cancelled
- raise
- except Exception as e:
- logger.info("Error parsing well-known for %s: %s", server_name, e)
- raise _FetchWellKnownFailure(temporary=False)
- cache_period = _cache_period_from_headers(
- response.headers, time_now=self._reactor.seconds
- )
- if cache_period is None:
- cache_period = WELL_KNOWN_DEFAULT_CACHE_PERIOD
- # add some randomness to the TTL to avoid a stampeding herd every 24 hours
- # after startup
- cache_period *= random.uniform(
- 1 - WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER,
- 1 + WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER,
- )
- else:
- cache_period = min(cache_period, WELL_KNOWN_MAX_CACHE_PERIOD)
- cache_period = max(cache_period, WELL_KNOWN_MIN_CACHE_PERIOD)
- # We got a success, mark as such in the cache
- self._had_valid_well_known_cache.set(
- server_name,
- bool(result),
- cache_period + WELL_KNOWN_REMEMBER_DOMAIN_HAD_VALID,
- )
- return result, cache_period
- async def _make_well_known_request(
- self, server_name: bytes, retry: bool
- ) -> Tuple[IResponse, bytes]:
- """Make the well known request.
- This will retry the request if requested and it fails (with unable
- to connect or receives a 5xx error).
- Args:
- server_name: name of the server, from the requested url
- retry: Whether to retry the request if it fails.
- Returns:
- Returns the response object and body. Response may be a non-200 response.
- """
- uri = b"https://%s/.well-known/matrix/server" % (server_name,)
- uri_str = uri.decode("ascii")
- headers = {
- b"User-Agent": [self.user_agent],
- }
- i = 0
- while True:
- i += 1
- logger.info("Fetching %s", uri_str)
- try:
- response = await make_deferred_yieldable(
- self._well_known_agent.request(
- b"GET", uri, headers=Headers(headers)
- )
- )
- body = await make_deferred_yieldable(readBody(response))
- if 500 <= response.code < 600:
- raise Exception("Non-200 response %s" % (response.code,))
- return response, body
- except defer.CancelledError:
- # Bail if we've been cancelled
- raise
- except Exception as e:
- if not retry or i >= WELL_KNOWN_RETRY_ATTEMPTS:
- logger.info("Error fetching %s: %s", uri_str, e)
- raise _FetchWellKnownFailure(temporary=True)
- logger.info("Error fetching %s: %s. Retrying", uri_str, e)
- # Sleep briefly in the hopes that they come back up
- await self._clock.sleep(0.5)
- def _cache_period_from_headers(
- headers: Headers, time_now: Callable[[], float] = time.time
- ) -> Optional[float]:
- cache_controls = _parse_cache_control(headers)
- if b"no-store" in cache_controls:
- return 0
- if b"max-age" in cache_controls:
- max_age = cache_controls[b"max-age"]
- if max_age:
- try:
- return int(max_age)
- except ValueError:
- pass
- expires = headers.getRawHeaders(b"expires")
- if expires is not None:
- try:
- expires_date = stringToDatetime(expires[-1])
- return expires_date - time_now()
- except ValueError:
- # RFC7234 says 'A cache recipient MUST interpret invalid date formats,
- # especially the value "0", as representing a time in the past (i.e.,
- # "already expired").
- return 0
- return None
- def _parse_cache_control(headers: Headers) -> Dict[bytes, Optional[bytes]]:
- cache_controls = {}
- for hdr in headers.getRawHeaders(b"cache-control", []):
- for directive in hdr.split(b","):
- splits = [x.strip() for x in directive.split(b"=", 1)]
- k = splits[0].lower()
- 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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