# # This file is licensed under the Affero General Public License (AGPL) version 3. # # Copyright (C) 2023 New Vector, Ltd # # This program is free software: you can redistribute it and/or modify # it under the terms of the GNU Affero General Public License as # published by the Free Software Foundation, either version 3 of the # License, or (at your option) any later version. # # See the GNU Affero General Public License for more details: # . # # Originally licensed under the Apache License, Version 2.0: # . # # [This file includes modifications made by New Vector Limited] # # import logging import random import time from io import BytesIO from typing import Callable, Dict, Optional, Tuple import attr from twisted.internet import defer from twisted.internet.interfaces import IReactorTime from twisted.web.client import RedirectAgent from twisted.web.http import stringToDatetime from twisted.web.http_headers import Headers from twisted.web.iweb import IAgent, IResponse from synapse.http.client import BodyExceededMaxSize, read_body_with_max_size 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 # The maximum size (in bytes) to allow a well-known file to be. WELL_KNOWN_MAX_SIZE = 50 * 1024 # 50 KiB # 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[bytes, Optional[bytes]] = TTLCache("well-known") _had_valid_well_known_cache: TTLCache[bytes, bool] = TTLCache("had-valid-well-known") @attr.s(slots=True, frozen=True, auto_attribs=True) class WellKnownLookupResult: delegated_server: Optional[bytes] class WellKnownResolver: """Handles well-known lookups for matrix servers.""" def __init__( self, reactor: IReactorTime, agent: IAgent, user_agent: bytes, well_known_cache: Optional[TTLCache[bytes, Optional[bytes]]] = None, had_well_known_cache: Optional[TTLCache[bytes, bool]] = 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: Optional[bytes] cache_period: float result, cache_period = await self._fetch_well_known(server_name) 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 permanent # 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. Raises: _FetchWellKnownFailure if we fail to lookup a result 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_stream = BytesIO() await make_deferred_yieldable( read_body_with_max_size(response, body_stream, WELL_KNOWN_MAX_SIZE) ) body = body_stream.getvalue() 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 BodyExceededMaxSize: # If the well-known file was too large, do not keep attempting # to download it, but consider it a temporary error. logger.warning( "Requested .well-known file for %s is too large > %r bytes", server_name.decode("ascii"), WELL_KNOWN_MAX_SIZE, ) raise _FetchWellKnownFailure(temporary=True) 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 = {} cache_control_headers = headers.getRawHeaders(b"cache-control") or [] for hdr in cache_control_headers: 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(slots=True) 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: bool = attr.ib()