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![Patrick Cloke](/assets/img/avatar_default.png)
slots use less memory (and attribute access is faster) while slightly limiting the flexibility of the class attributes. This focuses on objects which are instantiated "often" and for short periods of time.
319 lines
11 KiB
Python
319 lines
11 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2019 The Matrix.org Foundation C.I.C.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import logging
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import random
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import time
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from typing import Callable, Dict, Optional, Tuple
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import attr
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from twisted.internet import defer
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from twisted.web.client import RedirectAgent, readBody
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from twisted.web.http import stringToDatetime
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from twisted.web.http_headers import Headers
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from twisted.web.iweb import IResponse
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from synapse.logging.context import make_deferred_yieldable
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from synapse.util import Clock, json_decoder
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from synapse.util.caches.ttlcache import TTLCache
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from synapse.util.metrics import Measure
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# period to cache .well-known results for by default
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WELL_KNOWN_DEFAULT_CACHE_PERIOD = 24 * 3600
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# jitter factor to add to the .well-known default cache ttls
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WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER = 0.1
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# period to cache failure to fetch .well-known for
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WELL_KNOWN_INVALID_CACHE_PERIOD = 1 * 3600
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# period to cache failure to fetch .well-known if there has recently been a
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# valid well-known for that domain.
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WELL_KNOWN_DOWN_CACHE_PERIOD = 2 * 60
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# period to remember there was a valid well-known after valid record expires
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WELL_KNOWN_REMEMBER_DOMAIN_HAD_VALID = 2 * 3600
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# cap for .well-known cache period
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WELL_KNOWN_MAX_CACHE_PERIOD = 48 * 3600
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# lower bound for .well-known cache period
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WELL_KNOWN_MIN_CACHE_PERIOD = 5 * 60
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# Attempt to refetch a cached well-known N% of the TTL before it expires.
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# e.g. if set to 0.2 and we have a cached entry with a TTL of 5mins, then
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# we'll start trying to refetch 1 minute before it expires.
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WELL_KNOWN_GRACE_PERIOD_FACTOR = 0.2
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# Number of times we retry fetching a well-known for a domain we know recently
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# had a valid entry.
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WELL_KNOWN_RETRY_ATTEMPTS = 3
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logger = logging.getLogger(__name__)
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_well_known_cache = TTLCache("well-known")
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_had_valid_well_known_cache = TTLCache("had-valid-well-known")
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@attr.s(slots=True, frozen=True)
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class WellKnownLookupResult:
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delegated_server = attr.ib()
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class WellKnownResolver:
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"""Handles well-known lookups for matrix servers.
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"""
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def __init__(
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self,
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reactor,
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agent,
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user_agent,
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well_known_cache=None,
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had_well_known_cache=None,
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):
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self._reactor = reactor
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self._clock = Clock(reactor)
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if well_known_cache is None:
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well_known_cache = _well_known_cache
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if had_well_known_cache is None:
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had_well_known_cache = _had_valid_well_known_cache
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self._well_known_cache = well_known_cache
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self._had_valid_well_known_cache = had_well_known_cache
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self._well_known_agent = RedirectAgent(agent)
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self.user_agent = user_agent
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async def get_well_known(self, server_name: bytes) -> WellKnownLookupResult:
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"""Attempt to fetch and parse a .well-known file for the given server
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Args:
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server_name: name of the server, from the requested url
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Returns:
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The result of the lookup
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"""
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try:
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prev_result, expiry, ttl = self._well_known_cache.get_with_expiry(
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server_name
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)
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now = self._clock.time()
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if now < expiry - WELL_KNOWN_GRACE_PERIOD_FACTOR * ttl:
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return WellKnownLookupResult(delegated_server=prev_result)
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except KeyError:
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prev_result = None
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# TODO: should we linearise so that we don't end up doing two .well-known
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# requests for the same server in parallel?
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try:
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with Measure(self._clock, "get_well_known"):
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result, cache_period = await self._fetch_well_known(
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server_name
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) # type: Tuple[Optional[bytes], float]
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except _FetchWellKnownFailure as e:
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if prev_result and e.temporary:
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# This is a temporary failure and we have a still valid cached
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# result, so lets return that. Hopefully the next time we ask
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# the remote will be back up again.
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return WellKnownLookupResult(delegated_server=prev_result)
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result = None
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if self._had_valid_well_known_cache.get(server_name, False):
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# We have recently seen a valid well-known record for this
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# server, so we cache the lack of well-known for a shorter time.
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cache_period = WELL_KNOWN_DOWN_CACHE_PERIOD
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else:
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cache_period = WELL_KNOWN_INVALID_CACHE_PERIOD
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# add some randomness to the TTL to avoid a stampeding herd
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cache_period *= random.uniform(
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1 - WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER,
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1 + WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER,
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)
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if cache_period > 0:
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self._well_known_cache.set(server_name, result, cache_period)
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return WellKnownLookupResult(delegated_server=result)
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async def _fetch_well_known(self, server_name: bytes) -> Tuple[bytes, float]:
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"""Actually fetch and parse a .well-known, without checking the cache
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Args:
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server_name: name of the server, from the requested url
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Raises:
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_FetchWellKnownFailure if we fail to lookup a result
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Returns:
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The lookup result and cache period.
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"""
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had_valid_well_known = self._had_valid_well_known_cache.get(server_name, False)
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# We do this in two steps to differentiate between possibly transient
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# errors (e.g. can't connect to host, 503 response) and more permenant
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# errors (such as getting a 404 response).
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response, body = await self._make_well_known_request(
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server_name, retry=had_valid_well_known
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)
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try:
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if response.code != 200:
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raise Exception("Non-200 response %s" % (response.code,))
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parsed_body = json_decoder.decode(body.decode("utf-8"))
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logger.info("Response from .well-known: %s", parsed_body)
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result = parsed_body["m.server"].encode("ascii")
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except defer.CancelledError:
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# Bail if we've been cancelled
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raise
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except Exception as e:
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logger.info("Error parsing well-known for %s: %s", server_name, e)
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raise _FetchWellKnownFailure(temporary=False)
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cache_period = _cache_period_from_headers(
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response.headers, time_now=self._reactor.seconds
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)
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if cache_period is None:
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cache_period = WELL_KNOWN_DEFAULT_CACHE_PERIOD
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# add some randomness to the TTL to avoid a stampeding herd every 24 hours
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# after startup
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cache_period *= random.uniform(
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1 - WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER,
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1 + WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER,
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)
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else:
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cache_period = min(cache_period, WELL_KNOWN_MAX_CACHE_PERIOD)
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cache_period = max(cache_period, WELL_KNOWN_MIN_CACHE_PERIOD)
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# We got a success, mark as such in the cache
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self._had_valid_well_known_cache.set(
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server_name,
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bool(result),
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cache_period + WELL_KNOWN_REMEMBER_DOMAIN_HAD_VALID,
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)
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return result, cache_period
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async def _make_well_known_request(
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self, server_name: bytes, retry: bool
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) -> Tuple[IResponse, bytes]:
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"""Make the well known request.
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This will retry the request if requested and it fails (with unable
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to connect or receives a 5xx error).
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Args:
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server_name: name of the server, from the requested url
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retry: Whether to retry the request if it fails.
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Returns:
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Returns the response object and body. Response may be a non-200 response.
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"""
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uri = b"https://%s/.well-known/matrix/server" % (server_name,)
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uri_str = uri.decode("ascii")
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headers = {
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b"User-Agent": [self.user_agent],
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}
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i = 0
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while True:
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i += 1
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logger.info("Fetching %s", uri_str)
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try:
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response = await make_deferred_yieldable(
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self._well_known_agent.request(
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b"GET", uri, headers=Headers(headers)
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)
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)
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body = await make_deferred_yieldable(readBody(response))
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if 500 <= response.code < 600:
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raise Exception("Non-200 response %s" % (response.code,))
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return response, body
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except defer.CancelledError:
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# Bail if we've been cancelled
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raise
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except Exception as e:
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if not retry or i >= WELL_KNOWN_RETRY_ATTEMPTS:
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logger.info("Error fetching %s: %s", uri_str, e)
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raise _FetchWellKnownFailure(temporary=True)
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logger.info("Error fetching %s: %s. Retrying", uri_str, e)
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# Sleep briefly in the hopes that they come back up
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await self._clock.sleep(0.5)
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def _cache_period_from_headers(
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headers: Headers, time_now: Callable[[], float] = time.time
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) -> Optional[float]:
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cache_controls = _parse_cache_control(headers)
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if b"no-store" in cache_controls:
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return 0
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if b"max-age" in cache_controls:
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max_age = cache_controls[b"max-age"]
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if max_age:
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try:
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return int(max_age)
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except ValueError:
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pass
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expires = headers.getRawHeaders(b"expires")
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if expires is not None:
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try:
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expires_date = stringToDatetime(expires[-1])
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return expires_date - time_now()
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except ValueError:
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# RFC7234 says 'A cache recipient MUST interpret invalid date formats,
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# especially the value "0", as representing a time in the past (i.e.,
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# "already expired").
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return 0
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return None
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def _parse_cache_control(headers: Headers) -> Dict[bytes, Optional[bytes]]:
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cache_controls = {}
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for hdr in headers.getRawHeaders(b"cache-control", []):
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for directive in hdr.split(b","):
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splits = [x.strip() for x in directive.split(b"=", 1)]
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k = splits[0].lower()
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v = splits[1] if len(splits) > 1 else None
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cache_controls[k] = v
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return cache_controls
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@attr.s(slots=True)
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class _FetchWellKnownFailure(Exception):
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# True if we didn't get a non-5xx HTTP response, i.e. this may or may not be
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# a temporary failure.
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temporary = attr.ib()
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