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https://mau.dev/maunium/synapse.git
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e24ff8ebe3
The presence of this method was confusing, and mostly present for backwards compatibility. Let's get rid of it. Part of #11733
780 lines
28 KiB
Python
780 lines
28 KiB
Python
# Copyright 2016 OpenMarket Ltd
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# Copyright 2020-2021 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 datetime
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import errno
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import fnmatch
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import logging
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import os
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import re
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import shutil
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import sys
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import traceback
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from typing import TYPE_CHECKING, BinaryIO, Iterable, Optional, Tuple
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from urllib import parse as urlparse
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from urllib.request import urlopen
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import attr
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from twisted.internet.defer import Deferred
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from twisted.internet.error import DNSLookupError
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from synapse.api.errors import Codes, SynapseError
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from synapse.http.client import SimpleHttpClient
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from synapse.http.server import (
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DirectServeJsonResource,
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respond_with_json,
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respond_with_json_bytes,
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)
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from synapse.http.servlet import parse_integer, parse_string
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from synapse.http.site import SynapseRequest
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from synapse.logging.context import make_deferred_yieldable, run_in_background
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from synapse.metrics.background_process_metrics import run_as_background_process
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from synapse.rest.media.v1._base import get_filename_from_headers
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from synapse.rest.media.v1.media_storage import MediaStorage
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from synapse.rest.media.v1.oembed import OEmbedProvider
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from synapse.rest.media.v1.preview_html import (
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decode_body,
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parse_html_to_open_graph,
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rebase_url,
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)
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from synapse.types import JsonDict, UserID
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from synapse.util import json_encoder
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from synapse.util.async_helpers import ObservableDeferred
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from synapse.util.caches.expiringcache import ExpiringCache
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from synapse.util.stringutils import random_string
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from ._base import FileInfo
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if TYPE_CHECKING:
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from synapse.rest.media.v1.media_repository import MediaRepository
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from synapse.server import HomeServer
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logger = logging.getLogger(__name__)
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OG_TAG_NAME_MAXLEN = 50
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OG_TAG_VALUE_MAXLEN = 1000
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ONE_HOUR = 60 * 60 * 1000
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ONE_DAY = 24 * ONE_HOUR
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IMAGE_CACHE_EXPIRY_MS = 2 * ONE_DAY
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@attr.s(slots=True, frozen=True, auto_attribs=True)
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class DownloadResult:
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length: int
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uri: str
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response_code: int
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media_type: str
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download_name: Optional[str]
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expires: int
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etag: Optional[str]
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@attr.s(slots=True, frozen=True, auto_attribs=True)
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class MediaInfo:
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"""
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Information parsed from downloading media being previewed.
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"""
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# The Content-Type header of the response.
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media_type: str
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# The length (in bytes) of the downloaded media.
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media_length: int
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# The media filename, according to the server. This is parsed from the
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# returned headers, if possible.
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download_name: Optional[str]
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# The time of the preview.
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created_ts_ms: int
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# Information from the media storage provider about where the file is stored
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# on disk.
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filesystem_id: str
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filename: str
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# The URI being previewed.
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uri: str
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# The HTTP response code.
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response_code: int
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# The timestamp (in milliseconds) of when this preview expires.
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expires: int
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# The ETag header of the response.
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etag: Optional[str]
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class PreviewUrlResource(DirectServeJsonResource):
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"""
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Generating URL previews is a complicated task which many potential pitfalls.
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See docs/development/url_previews.md for discussion of the design and
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algorithm followed in this module.
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"""
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isLeaf = True
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def __init__(
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self,
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hs: "HomeServer",
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media_repo: "MediaRepository",
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media_storage: MediaStorage,
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):
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super().__init__()
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self.auth = hs.get_auth()
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self.clock = hs.get_clock()
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self.filepaths = media_repo.filepaths
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self.max_spider_size = hs.config.media.max_spider_size
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self.server_name = hs.hostname
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self.store = hs.get_datastores().main
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self.client = SimpleHttpClient(
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hs,
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treq_args={"browser_like_redirects": True},
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ip_whitelist=hs.config.media.url_preview_ip_range_whitelist,
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ip_blacklist=hs.config.media.url_preview_ip_range_blacklist,
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use_proxy=True,
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)
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self.media_repo = media_repo
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self.primary_base_path = media_repo.primary_base_path
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self.media_storage = media_storage
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self._oembed = OEmbedProvider(hs)
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# We run the background jobs if we're the instance specified (or no
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# instance is specified, where we assume there is only one instance
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# serving media).
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instance_running_jobs = hs.config.media.media_instance_running_background_jobs
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self._worker_run_media_background_jobs = (
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instance_running_jobs is None
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or instance_running_jobs == hs.get_instance_name()
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)
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self.url_preview_url_blacklist = hs.config.media.url_preview_url_blacklist
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self.url_preview_accept_language = hs.config.media.url_preview_accept_language
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# memory cache mapping urls to an ObservableDeferred returning
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# JSON-encoded OG metadata
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self._cache: ExpiringCache[str, ObservableDeferred] = ExpiringCache(
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cache_name="url_previews",
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clock=self.clock,
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# don't spider URLs more often than once an hour
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expiry_ms=ONE_HOUR,
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)
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if self._worker_run_media_background_jobs:
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self._cleaner_loop = self.clock.looping_call(
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self._start_expire_url_cache_data, 10 * 1000
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)
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async def _async_render_OPTIONS(self, request: SynapseRequest) -> None:
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request.setHeader(b"Allow", b"OPTIONS, GET")
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respond_with_json(request, 200, {}, send_cors=True)
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async def _async_render_GET(self, request: SynapseRequest) -> None:
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# XXX: if get_user_by_req fails, what should we do in an async render?
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requester = await self.auth.get_user_by_req(request)
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url = parse_string(request, "url", required=True)
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ts = parse_integer(request, "ts")
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if ts is None:
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ts = self.clock.time_msec()
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# XXX: we could move this into _do_preview if we wanted.
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url_tuple = urlparse.urlsplit(url)
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for entry in self.url_preview_url_blacklist:
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match = True
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for attrib in entry:
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pattern = entry[attrib]
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value = getattr(url_tuple, attrib)
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logger.debug(
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"Matching attrib '%s' with value '%s' against pattern '%s'",
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attrib,
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value,
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pattern,
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)
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if value is None:
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match = False
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continue
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if pattern.startswith("^"):
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if not re.match(pattern, getattr(url_tuple, attrib)):
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match = False
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continue
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else:
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if not fnmatch.fnmatch(getattr(url_tuple, attrib), pattern):
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match = False
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continue
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if match:
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logger.warning("URL %s blocked by url_blacklist entry %s", url, entry)
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raise SynapseError(
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403, "URL blocked by url pattern blacklist entry", Codes.UNKNOWN
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)
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# the in-memory cache:
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# * ensures that only one request is active at a time
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# * takes load off the DB for the thundering herds
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# * also caches any failures (unlike the DB) so we don't keep
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# requesting the same endpoint
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observable = self._cache.get(url)
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if not observable:
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download = run_in_background(self._do_preview, url, requester.user, ts)
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observable = ObservableDeferred(download, consumeErrors=True)
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self._cache[url] = observable
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else:
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logger.info("Returning cached response")
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og = await make_deferred_yieldable(observable.observe())
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respond_with_json_bytes(request, 200, og, send_cors=True)
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async def _do_preview(self, url: str, user: UserID, ts: int) -> bytes:
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"""Check the db, and download the URL and build a preview
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Args:
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url: The URL to preview.
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user: The user requesting the preview.
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ts: The timestamp requested for the preview.
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Returns:
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json-encoded og data
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"""
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# check the URL cache in the DB (which will also provide us with
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# historical previews, if we have any)
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cache_result = await self.store.get_url_cache(url, ts)
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if (
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cache_result
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and cache_result["expires_ts"] > ts
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and cache_result["response_code"] / 100 == 2
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):
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# It may be stored as text in the database, not as bytes (such as
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# PostgreSQL). If so, encode it back before handing it on.
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og = cache_result["og"]
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if isinstance(og, str):
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og = og.encode("utf8")
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return og
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# If this URL can be accessed via oEmbed, use that instead.
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url_to_download = url
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oembed_url = self._oembed.get_oembed_url(url)
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if oembed_url:
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url_to_download = oembed_url
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media_info = await self._handle_url(url_to_download, user)
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logger.debug("got media_info of '%s'", media_info)
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# The number of milliseconds that the response should be considered valid.
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expiration_ms = media_info.expires
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author_name: Optional[str] = None
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if _is_media(media_info.media_type):
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file_id = media_info.filesystem_id
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dims = await self.media_repo._generate_thumbnails(
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None, file_id, file_id, media_info.media_type, url_cache=True
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)
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og = {
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"og:description": media_info.download_name,
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"og:image": f"mxc://{self.server_name}/{media_info.filesystem_id}",
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"og:image:type": media_info.media_type,
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"matrix:image:size": media_info.media_length,
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}
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if dims:
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og["og:image:width"] = dims["width"]
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og["og:image:height"] = dims["height"]
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else:
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logger.warning("Couldn't get dims for %s" % url)
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# define our OG response for this media
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elif _is_html(media_info.media_type):
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# TODO: somehow stop a big HTML tree from exploding synapse's RAM
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with open(media_info.filename, "rb") as file:
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body = file.read()
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tree = decode_body(body, media_info.uri, media_info.media_type)
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if tree is not None:
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# Check if this HTML document points to oEmbed information and
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# defer to that.
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oembed_url = self._oembed.autodiscover_from_html(tree)
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og_from_oembed: JsonDict = {}
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if oembed_url:
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oembed_info = await self._handle_url(
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oembed_url, user, allow_data_urls=True
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)
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(
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og_from_oembed,
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author_name,
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expiration_ms,
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) = await self._handle_oembed_response(
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url, oembed_info, expiration_ms
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)
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# Parse Open Graph information from the HTML in case the oEmbed
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# response failed or is incomplete.
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og_from_html = parse_html_to_open_graph(tree, media_info.uri)
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# Compile the Open Graph response by using the scraped
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# information from the HTML and overlaying any information
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# from the oEmbed response.
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og = {**og_from_html, **og_from_oembed}
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await self._precache_image_url(user, media_info, og)
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else:
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og = {}
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elif oembed_url:
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# Handle the oEmbed information.
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og, author_name, expiration_ms = await self._handle_oembed_response(
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url, media_info, expiration_ms
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)
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await self._precache_image_url(user, media_info, og)
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else:
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logger.warning("Failed to find any OG data in %s", url)
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og = {}
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# If we don't have a title but we have author_name, copy it as
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# title
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if not og.get("og:title") and author_name:
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og["og:title"] = author_name
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# filter out any stupidly long values
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keys_to_remove = []
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for k, v in og.items():
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# values can be numeric as well as strings, hence the cast to str
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if len(k) > OG_TAG_NAME_MAXLEN or len(str(v)) > OG_TAG_VALUE_MAXLEN:
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logger.warning(
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"Pruning overlong tag %s from OG data", k[:OG_TAG_NAME_MAXLEN]
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)
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keys_to_remove.append(k)
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for k in keys_to_remove:
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del og[k]
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logger.debug("Calculated OG for %s as %s", url, og)
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jsonog = json_encoder.encode(og)
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# Cap the amount of time to consider a response valid.
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expiration_ms = min(expiration_ms, ONE_DAY)
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# store OG in history-aware DB cache
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await self.store.store_url_cache(
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url,
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media_info.response_code,
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media_info.etag,
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media_info.created_ts_ms + expiration_ms,
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jsonog,
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media_info.filesystem_id,
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media_info.created_ts_ms,
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)
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return jsonog.encode("utf8")
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async def _download_url(self, url: str, output_stream: BinaryIO) -> DownloadResult:
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"""
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Fetches a remote URL and parses the headers.
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Args:
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url: The URL to fetch.
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output_stream: The stream to write the content to.
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Returns:
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A tuple of:
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Media length, URL downloaded, the HTTP response code,
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the media type, the downloaded file name, the number of
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milliseconds the result is valid for, the etag header.
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"""
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try:
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logger.debug("Trying to get preview for url '%s'", url)
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length, headers, uri, code = await self.client.get_file(
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url,
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output_stream=output_stream,
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max_size=self.max_spider_size,
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headers={
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b"Accept-Language": self.url_preview_accept_language,
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# Use a custom user agent for the preview because some sites will only return
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# Open Graph metadata to crawler user agents. Omit the Synapse version
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# string to avoid leaking information.
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b"User-Agent": [
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"Synapse (bot; +https://github.com/matrix-org/synapse)"
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],
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},
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is_allowed_content_type=_is_previewable,
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)
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except SynapseError:
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# Pass SynapseErrors through directly, so that the servlet
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# handler will return a SynapseError to the client instead of
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# blank data or a 500.
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raise
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except DNSLookupError:
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# DNS lookup returned no results
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# Note: This will also be the case if one of the resolved IP
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# addresses is blacklisted
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raise SynapseError(
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502,
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"DNS resolution failure during URL preview generation",
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Codes.UNKNOWN,
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)
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except Exception as e:
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# FIXME: pass through 404s and other error messages nicely
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logger.warning("Error downloading %s: %r", url, e)
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raise SynapseError(
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500,
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"Failed to download content: %s"
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% (traceback.format_exception_only(sys.exc_info()[0], e),),
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Codes.UNKNOWN,
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)
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if b"Content-Type" in headers:
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media_type = headers[b"Content-Type"][0].decode("ascii")
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else:
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media_type = "application/octet-stream"
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download_name = get_filename_from_headers(headers)
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# FIXME: we should calculate a proper expiration based on the
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# Cache-Control and Expire headers. But for now, assume 1 hour.
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expires = ONE_HOUR
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etag = headers[b"ETag"][0].decode("ascii") if b"ETag" in headers else None
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return DownloadResult(
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length, uri, code, media_type, download_name, expires, etag
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)
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async def _parse_data_url(
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self, url: str, output_stream: BinaryIO
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) -> DownloadResult:
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"""
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Parses a data: URL.
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Args:
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url: The URL to parse.
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output_stream: The stream to write the content to.
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Returns:
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A tuple of:
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Media length, URL downloaded, the HTTP response code,
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the media type, the downloaded file name, the number of
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milliseconds the result is valid for, the etag header.
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"""
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try:
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logger.debug("Trying to parse data url '%s'", url)
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with urlopen(url) as url_info:
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# TODO Can this be more efficient.
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output_stream.write(url_info.read())
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except Exception as e:
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logger.warning("Error parsing data: URL %s: %r", url, e)
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raise SynapseError(
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500,
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"Failed to parse data URL: %s"
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% (traceback.format_exception_only(sys.exc_info()[0], e),),
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Codes.UNKNOWN,
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)
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return DownloadResult(
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# Read back the length that has been written.
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length=output_stream.tell(),
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uri=url,
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# If it was parsed, consider this a 200 OK.
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response_code=200,
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# urlopen shoves the media-type from the data URL into the content type
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# header object.
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media_type=url_info.headers.get_content_type(),
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# Some features are not supported by data: URLs.
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download_name=None,
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expires=ONE_HOUR,
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etag=None,
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)
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async def _handle_url(
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self, url: str, user: UserID, allow_data_urls: bool = False
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) -> MediaInfo:
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"""
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Fetches content from a URL and parses the result to generate a MediaInfo.
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It uses the media storage provider to persist the fetched content and
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|
stores the mapping into the database.
|
|
|
|
Args:
|
|
url: The URL to fetch.
|
|
user: The user who ahs requested this URL.
|
|
allow_data_urls: True if data URLs should be allowed.
|
|
|
|
Returns:
|
|
A MediaInfo object describing the fetched content.
|
|
"""
|
|
|
|
# TODO: we should probably honour robots.txt... except in practice
|
|
# we're most likely being explicitly triggered by a human rather than a
|
|
# bot, so are we really a robot?
|
|
|
|
file_id = datetime.date.today().isoformat() + "_" + random_string(16)
|
|
|
|
file_info = FileInfo(server_name=None, file_id=file_id, url_cache=True)
|
|
|
|
with self.media_storage.store_into_file(file_info) as (f, fname, finish):
|
|
if url.startswith("data:"):
|
|
if not allow_data_urls:
|
|
raise SynapseError(
|
|
500, "Previewing of data: URLs is forbidden", Codes.UNKNOWN
|
|
)
|
|
|
|
download_result = await self._parse_data_url(url, f)
|
|
else:
|
|
download_result = await self._download_url(url, f)
|
|
|
|
await finish()
|
|
|
|
try:
|
|
time_now_ms = self.clock.time_msec()
|
|
|
|
await self.store.store_local_media(
|
|
media_id=file_id,
|
|
media_type=download_result.media_type,
|
|
time_now_ms=time_now_ms,
|
|
upload_name=download_result.download_name,
|
|
media_length=download_result.length,
|
|
user_id=user,
|
|
url_cache=url,
|
|
)
|
|
|
|
except Exception as e:
|
|
logger.error("Error handling downloaded %s: %r", url, e)
|
|
# TODO: we really ought to delete the downloaded file in this
|
|
# case, since we won't have recorded it in the db, and will
|
|
# therefore not expire it.
|
|
raise
|
|
|
|
return MediaInfo(
|
|
media_type=download_result.media_type,
|
|
media_length=download_result.length,
|
|
download_name=download_result.download_name,
|
|
created_ts_ms=time_now_ms,
|
|
filesystem_id=file_id,
|
|
filename=fname,
|
|
uri=download_result.uri,
|
|
response_code=download_result.response_code,
|
|
expires=download_result.expires,
|
|
etag=download_result.etag,
|
|
)
|
|
|
|
async def _precache_image_url(
|
|
self, user: UserID, media_info: MediaInfo, og: JsonDict
|
|
) -> None:
|
|
"""
|
|
Pre-cache the image (if one exists) for posterity
|
|
|
|
Args:
|
|
user: The user requesting the preview.
|
|
media_info: The media being previewed.
|
|
og: The Open Graph dictionary. This is modified with image information.
|
|
"""
|
|
# If there's no image or it is blank, there's nothing to do.
|
|
if "og:image" not in og or not og["og:image"]:
|
|
return
|
|
|
|
# FIXME: it might be cleaner to use the same flow as the main /preview_url
|
|
# request itself and benefit from the same caching etc. But for now we
|
|
# just rely on the caching on the master request to speed things up.
|
|
image_info = await self._handle_url(
|
|
rebase_url(og["og:image"], media_info.uri), user, allow_data_urls=True
|
|
)
|
|
|
|
if _is_media(image_info.media_type):
|
|
# TODO: make sure we don't choke on white-on-transparent images
|
|
file_id = image_info.filesystem_id
|
|
dims = await self.media_repo._generate_thumbnails(
|
|
None, file_id, file_id, image_info.media_type, url_cache=True
|
|
)
|
|
if dims:
|
|
og["og:image:width"] = dims["width"]
|
|
og["og:image:height"] = dims["height"]
|
|
else:
|
|
logger.warning("Couldn't get dims for %s", og["og:image"])
|
|
|
|
og["og:image"] = f"mxc://{self.server_name}/{image_info.filesystem_id}"
|
|
og["og:image:type"] = image_info.media_type
|
|
og["matrix:image:size"] = image_info.media_length
|
|
else:
|
|
del og["og:image"]
|
|
|
|
async def _handle_oembed_response(
|
|
self, url: str, media_info: MediaInfo, expiration_ms: int
|
|
) -> Tuple[JsonDict, Optional[str], int]:
|
|
"""
|
|
Parse the downloaded oEmbed info.
|
|
|
|
Args:
|
|
url: The URL which is being previewed (not the one which was
|
|
requested).
|
|
media_info: The media being previewed.
|
|
expiration_ms: The length of time, in milliseconds, the media is valid for.
|
|
|
|
Returns:
|
|
A tuple of:
|
|
The Open Graph dictionary, if the oEmbed info can be parsed.
|
|
The author name if it could be retrieved from oEmbed.
|
|
The (possibly updated) length of time, in milliseconds, the media is valid for.
|
|
"""
|
|
# If JSON was not returned, there's nothing to do.
|
|
if not _is_json(media_info.media_type):
|
|
return {}, None, expiration_ms
|
|
|
|
with open(media_info.filename, "rb") as file:
|
|
body = file.read()
|
|
|
|
oembed_response = self._oembed.parse_oembed_response(url, body)
|
|
open_graph_result = oembed_response.open_graph_result
|
|
|
|
# Use the cache age from the oEmbed result, if one was given.
|
|
if open_graph_result and oembed_response.cache_age is not None:
|
|
expiration_ms = oembed_response.cache_age
|
|
|
|
return open_graph_result, oembed_response.author_name, expiration_ms
|
|
|
|
def _start_expire_url_cache_data(self) -> Deferred:
|
|
return run_as_background_process(
|
|
"expire_url_cache_data", self._expire_url_cache_data
|
|
)
|
|
|
|
async def _expire_url_cache_data(self) -> None:
|
|
"""Clean up expired url cache content, media and thumbnails."""
|
|
|
|
assert self._worker_run_media_background_jobs
|
|
|
|
now = self.clock.time_msec()
|
|
|
|
logger.debug("Running url preview cache expiry")
|
|
|
|
if not (await self.store.db_pool.updates.has_completed_background_updates()):
|
|
logger.info("Still running DB updates; skipping expiry")
|
|
return
|
|
|
|
def try_remove_parent_dirs(dirs: Iterable[str]) -> None:
|
|
"""Attempt to remove the given chain of parent directories
|
|
|
|
Args:
|
|
dirs: The list of directory paths to delete, with children appearing
|
|
before their parents.
|
|
"""
|
|
for dir in dirs:
|
|
try:
|
|
os.rmdir(dir)
|
|
except FileNotFoundError:
|
|
# Already deleted, continue with deleting the rest
|
|
pass
|
|
except OSError as e:
|
|
# Failed, skip deleting the rest of the parent dirs
|
|
if e.errno != errno.ENOTEMPTY:
|
|
logger.warning(
|
|
"Failed to remove media directory: %r: %s", dir, e
|
|
)
|
|
break
|
|
|
|
# First we delete expired url cache entries
|
|
media_ids = await self.store.get_expired_url_cache(now)
|
|
|
|
removed_media = []
|
|
for media_id in media_ids:
|
|
fname = self.filepaths.url_cache_filepath(media_id)
|
|
try:
|
|
os.remove(fname)
|
|
except FileNotFoundError:
|
|
pass # If the path doesn't exist, meh
|
|
except OSError as e:
|
|
logger.warning("Failed to remove media: %r: %s", media_id, e)
|
|
continue
|
|
|
|
removed_media.append(media_id)
|
|
|
|
dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id)
|
|
try_remove_parent_dirs(dirs)
|
|
|
|
await self.store.delete_url_cache(removed_media)
|
|
|
|
if removed_media:
|
|
logger.info("Deleted %d entries from url cache", len(removed_media))
|
|
else:
|
|
logger.debug("No entries removed from url cache")
|
|
|
|
# Now we delete old images associated with the url cache.
|
|
# These may be cached for a bit on the client (i.e., they
|
|
# may have a room open with a preview url thing open).
|
|
# So we wait a couple of days before deleting, just in case.
|
|
expire_before = now - IMAGE_CACHE_EXPIRY_MS
|
|
media_ids = await self.store.get_url_cache_media_before(expire_before)
|
|
|
|
removed_media = []
|
|
for media_id in media_ids:
|
|
fname = self.filepaths.url_cache_filepath(media_id)
|
|
try:
|
|
os.remove(fname)
|
|
except FileNotFoundError:
|
|
pass # If the path doesn't exist, meh
|
|
except OSError as e:
|
|
logger.warning("Failed to remove media: %r: %s", media_id, e)
|
|
continue
|
|
|
|
dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id)
|
|
try_remove_parent_dirs(dirs)
|
|
|
|
thumbnail_dir = self.filepaths.url_cache_thumbnail_directory(media_id)
|
|
try:
|
|
shutil.rmtree(thumbnail_dir)
|
|
except FileNotFoundError:
|
|
pass # If the path doesn't exist, meh
|
|
except OSError as e:
|
|
logger.warning("Failed to remove media: %r: %s", media_id, e)
|
|
continue
|
|
|
|
removed_media.append(media_id)
|
|
|
|
dirs = self.filepaths.url_cache_thumbnail_dirs_to_delete(media_id)
|
|
# Note that one of the directories to be deleted has already been
|
|
# removed by the `rmtree` above.
|
|
try_remove_parent_dirs(dirs)
|
|
|
|
await self.store.delete_url_cache_media(removed_media)
|
|
|
|
if removed_media:
|
|
logger.info("Deleted %d media from url cache", len(removed_media))
|
|
else:
|
|
logger.debug("No media removed from url cache")
|
|
|
|
|
|
def _is_media(content_type: str) -> bool:
|
|
return content_type.lower().startswith("image/")
|
|
|
|
|
|
def _is_html(content_type: str) -> bool:
|
|
content_type = content_type.lower()
|
|
return content_type.startswith("text/html") or content_type.startswith(
|
|
"application/xhtml"
|
|
)
|
|
|
|
|
|
def _is_json(content_type: str) -> bool:
|
|
return content_type.lower().startswith("application/json")
|
|
|
|
|
|
def _is_previewable(content_type: str) -> bool:
|
|
"""Returns True for content types for which we will perform URL preview and False
|
|
otherwise."""
|
|
|
|
return _is_html(content_type) or _is_media(content_type) or _is_json(content_type)
|