# Copyright 2016 OpenMarket Ltd # Copyright 2020-2021 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 datetime import errno import fnmatch import itertools import logging import os import re import shutil import sys import traceback from typing import TYPE_CHECKING, Dict, Generator, Iterable, Optional, Union from urllib import parse as urlparse import attr from twisted.internet.defer import Deferred from twisted.internet.error import DNSLookupError from synapse.api.errors import Codes, SynapseError from synapse.http.client import SimpleHttpClient from synapse.http.server import ( DirectServeJsonResource, respond_with_json, respond_with_json_bytes, ) from synapse.http.servlet import parse_integer, parse_string from synapse.http.site import SynapseRequest from synapse.logging.context import make_deferred_yieldable, run_in_background from synapse.metrics.background_process_metrics import run_as_background_process from synapse.rest.media.v1._base import get_filename_from_headers from synapse.rest.media.v1.media_storage import MediaStorage from synapse.rest.media.v1.oembed import OEmbedProvider from synapse.types import JsonDict from synapse.util import json_encoder from synapse.util.async_helpers import ObservableDeferred from synapse.util.caches.expiringcache import ExpiringCache from synapse.util.stringutils import random_string from ._base import FileInfo if TYPE_CHECKING: from lxml import etree from synapse.rest.media.v1.media_repository import MediaRepository from synapse.server import HomeServer logger = logging.getLogger(__name__) _charset_match = re.compile( br'<\s*meta[^>]*charset\s*=\s*"?([a-z0-9_-]+)"?', flags=re.I ) _xml_encoding_match = re.compile( br'\s*<\s*\?\s*xml[^>]*encoding="([a-z0-9_-]+)"', flags=re.I ) _content_type_match = re.compile(r'.*; *charset="?(.*?)"?(;|$)', flags=re.I) OG_TAG_NAME_MAXLEN = 50 OG_TAG_VALUE_MAXLEN = 1000 ONE_HOUR = 60 * 60 * 1000 ONE_DAY = 24 * ONE_HOUR @attr.s(slots=True, frozen=True, auto_attribs=True) class MediaInfo: """ Information parsed from downloading media being previewed. """ # The Content-Type header of the response. media_type: str # The length (in bytes) of the downloaded media. media_length: int # The media filename, according to the server. This is parsed from the # returned headers, if possible. download_name: Optional[str] # The time of the preview. created_ts_ms: int # Information from the media storage provider about where the file is stored # on disk. filesystem_id: str filename: str # The URI being previewed. uri: str # The HTTP response code. response_code: int # The timestamp (in milliseconds) of when this preview expires. expires: int # The ETag header of the response. etag: Optional[str] class PreviewUrlResource(DirectServeJsonResource): """ Generating URL previews is a complicated task which many potential pitfalls. See docs/development/url_previews.md for discussion of the design and algorithm followed in this module. """ isLeaf = True def __init__( self, hs: "HomeServer", media_repo: "MediaRepository", media_storage: MediaStorage, ): super().__init__() self.auth = hs.get_auth() self.clock = hs.get_clock() self.filepaths = media_repo.filepaths self.max_spider_size = hs.config.max_spider_size self.server_name = hs.hostname self.store = hs.get_datastore() self.client = SimpleHttpClient( hs, treq_args={"browser_like_redirects": True}, ip_whitelist=hs.config.url_preview_ip_range_whitelist, ip_blacklist=hs.config.url_preview_ip_range_blacklist, use_proxy=True, ) self.media_repo = media_repo self.primary_base_path = media_repo.primary_base_path self.media_storage = media_storage self._oembed = OEmbedProvider(hs, self.client) # We run the background jobs if we're the instance specified (or no # instance is specified, where we assume there is only one instance # serving media). instance_running_jobs = hs.config.media.media_instance_running_background_jobs self._worker_run_media_background_jobs = ( instance_running_jobs is None or instance_running_jobs == hs.get_instance_name() ) self.url_preview_url_blacklist = hs.config.url_preview_url_blacklist self.url_preview_accept_language = hs.config.url_preview_accept_language # memory cache mapping urls to an ObservableDeferred returning # JSON-encoded OG metadata self._cache: ExpiringCache[str, ObservableDeferred] = ExpiringCache( cache_name="url_previews", clock=self.clock, # don't spider URLs more often than once an hour expiry_ms=ONE_HOUR, ) if self._worker_run_media_background_jobs: self._cleaner_loop = self.clock.looping_call( self._start_expire_url_cache_data, 10 * 1000 ) async def _async_render_OPTIONS(self, request: SynapseRequest) -> None: request.setHeader(b"Allow", b"OPTIONS, GET") respond_with_json(request, 200, {}, send_cors=True) async def _async_render_GET(self, request: SynapseRequest) -> None: # XXX: if get_user_by_req fails, what should we do in an async render? requester = await self.auth.get_user_by_req(request) url = parse_string(request, "url", required=True) ts = parse_integer(request, "ts") if ts is None: ts = self.clock.time_msec() # XXX: we could move this into _do_preview if we wanted. url_tuple = urlparse.urlsplit(url) for entry in self.url_preview_url_blacklist: match = True for attrib in entry: pattern = entry[attrib] value = getattr(url_tuple, attrib) logger.debug( "Matching attrib '%s' with value '%s' against pattern '%s'", attrib, value, pattern, ) if value is None: match = False continue if pattern.startswith("^"): if not re.match(pattern, getattr(url_tuple, attrib)): match = False continue else: if not fnmatch.fnmatch(getattr(url_tuple, attrib), pattern): match = False continue if match: logger.warning("URL %s blocked by url_blacklist entry %s", url, entry) raise SynapseError( 403, "URL blocked by url pattern blacklist entry", Codes.UNKNOWN ) # the in-memory cache: # * ensures that only one request is active at a time # * takes load off the DB for the thundering herds # * also caches any failures (unlike the DB) so we don't keep # requesting the same endpoint observable = self._cache.get(url) if not observable: download = run_in_background(self._do_preview, url, requester.user, ts) observable = ObservableDeferred(download, consumeErrors=True) self._cache[url] = observable else: logger.info("Returning cached response") og = await make_deferred_yieldable(observable.observe()) respond_with_json_bytes(request, 200, og, send_cors=True) async def _do_preview(self, url: str, user: str, ts: int) -> bytes: """Check the db, and download the URL and build a preview Args: url: The URL to preview. user: The user requesting the preview. ts: The timestamp requested for the preview. Returns: json-encoded og data """ # check the URL cache in the DB (which will also provide us with # historical previews, if we have any) cache_result = await self.store.get_url_cache(url, ts) if ( cache_result and cache_result["expires_ts"] > ts and cache_result["response_code"] / 100 == 2 ): # It may be stored as text in the database, not as bytes (such as # PostgreSQL). If so, encode it back before handing it on. og = cache_result["og"] if isinstance(og, str): og = og.encode("utf8") return og # If this URL can be accessed via oEmbed, use that instead. url_to_download = url oembed_url = self._oembed.get_oembed_url(url) if oembed_url: url_to_download = oembed_url media_info = await self._download_url(url_to_download, user) logger.debug("got media_info of '%s'", media_info) # The number of milliseconds that the response should be considered valid. expiration_ms = media_info.expires if _is_media(media_info.media_type): file_id = media_info.filesystem_id dims = await self.media_repo._generate_thumbnails( None, file_id, file_id, media_info.media_type, url_cache=True ) og = { "og:description": media_info.download_name, "og:image": f"mxc://{self.server_name}/{media_info.filesystem_id}", "og:image:type": media_info.media_type, "matrix:image:size": media_info.media_length, } if dims: og["og:image:width"] = dims["width"] og["og:image:height"] = dims["height"] else: logger.warning("Couldn't get dims for %s" % url) # define our OG response for this media elif _is_html(media_info.media_type): # TODO: somehow stop a big HTML tree from exploding synapse's RAM with open(media_info.filename, "rb") as file: body = file.read() encoding = get_html_media_encoding(body, media_info.media_type) og = decode_and_calc_og(body, media_info.uri, encoding) await self._precache_image_url(user, media_info, og) elif oembed_url and _is_json(media_info.media_type): # Handle an oEmbed response. with open(media_info.filename, "rb") as file: body = file.read() oembed_response = self._oembed.parse_oembed_response(url, body) og = oembed_response.open_graph_result # Use the cache age from the oEmbed result, instead of the HTTP response. if oembed_response.cache_age is not None: expiration_ms = oembed_response.cache_age await self._precache_image_url(user, media_info, og) else: logger.warning("Failed to find any OG data in %s", url) og = {} # filter out any stupidly long values keys_to_remove = [] for k, v in og.items(): # values can be numeric as well as strings, hence the cast to str if len(k) > OG_TAG_NAME_MAXLEN or len(str(v)) > OG_TAG_VALUE_MAXLEN: logger.warning( "Pruning overlong tag %s from OG data", k[:OG_TAG_NAME_MAXLEN] ) keys_to_remove.append(k) for k in keys_to_remove: del og[k] logger.debug("Calculated OG for %s as %s", url, og) jsonog = json_encoder.encode(og) # Cap the amount of time to consider a response valid. expiration_ms = min(expiration_ms, ONE_DAY) # store OG in history-aware DB cache await self.store.store_url_cache( url, media_info.response_code, media_info.etag, media_info.created_ts_ms + expiration_ms, jsonog, media_info.filesystem_id, media_info.created_ts_ms, ) return jsonog.encode("utf8") async def _download_url(self, url: str, user: str) -> MediaInfo: # 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): try: logger.debug("Trying to get preview for url '%s'", url) length, headers, uri, code = await self.client.get_file( url, output_stream=f, max_size=self.max_spider_size, headers={"Accept-Language": self.url_preview_accept_language}, ) except SynapseError: # Pass SynapseErrors through directly, so that the servlet # handler will return a SynapseError to the client instead of # blank data or a 500. raise except DNSLookupError: # DNS lookup returned no results # Note: This will also be the case if one of the resolved IP # addresses is blacklisted raise SynapseError( 502, "DNS resolution failure during URL preview generation", Codes.UNKNOWN, ) except Exception as e: # FIXME: pass through 404s and other error messages nicely logger.warning("Error downloading %s: %r", url, e) raise SynapseError( 500, "Failed to download content: %s" % (traceback.format_exception_only(sys.exc_info()[0], e),), Codes.UNKNOWN, ) await finish() if b"Content-Type" in headers: media_type = headers[b"Content-Type"][0].decode("ascii") else: media_type = "application/octet-stream" download_name = get_filename_from_headers(headers) # FIXME: we should calculate a proper expiration based on the # Cache-Control and Expire headers. But for now, assume 1 hour. expires = ONE_HOUR etag = headers[b"ETag"][0].decode("ascii") if b"ETag" in headers else None try: time_now_ms = self.clock.time_msec() await self.store.store_local_media( media_id=file_id, media_type=media_type, time_now_ms=time_now_ms, upload_name=download_name, media_length=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=media_type, media_length=length, download_name=download_name, created_ts_ms=time_now_ms, filesystem_id=file_id, filename=fname, uri=uri, response_code=code, expires=expires, etag=etag, ) async def _precache_image_url( self, user: str, 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._download_url( _rebase_url(og["og:image"], media_info.uri), user ) 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"] 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.""" # TODO: Delete from backup media store 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 # 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 OSError as e: # If the path doesn't exist, meh if e.errno != errno.ENOENT: logger.warning("Failed to remove media: %r: %s", media_id, e) continue removed_media.append(media_id) try: dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id) for dir in dirs: os.rmdir(dir) except Exception: pass 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 - 2 * ONE_DAY 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 OSError as e: # If the path doesn't exist, meh if e.errno != errno.ENOENT: logger.warning("Failed to remove media: %r: %s", media_id, e) continue try: dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id) for dir in dirs: os.rmdir(dir) except Exception: pass thumbnail_dir = self.filepaths.url_cache_thumbnail_directory(media_id) try: shutil.rmtree(thumbnail_dir) except OSError as e: # If the path doesn't exist, meh if e.errno != errno.ENOENT: logger.warning("Failed to remove media: %r: %s", media_id, e) continue removed_media.append(media_id) try: dirs = self.filepaths.url_cache_thumbnail_dirs_to_delete(media_id) for dir in dirs: os.rmdir(dir) except Exception: pass 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 get_html_media_encoding(body: bytes, content_type: str) -> str: """ Get the encoding of the body based on the (presumably) HTML body or media_type. The precedence used for finding a character encoding is: 1. meta tag with a charset declared. 2. The XML document's character encoding attribute. 3. The Content-Type header. 4. Fallback to UTF-8. Args: body: The HTML document, as bytes. content_type: The Content-Type header. Returns: The character encoding of the body, as a string. """ # Limit searches to the first 1kb, since it ought to be at the top. body_start = body[:1024] # Let's try and figure out if it has an encoding set in a meta tag. match = _charset_match.search(body_start) if match: return match.group(1).decode("ascii") # TODO Support # If we didn't find a match, see if it an XML document with an encoding. match = _xml_encoding_match.match(body_start) if match: return match.group(1).decode("ascii") # If we don't find a match, we'll look at the HTTP Content-Type, and # if that doesn't exist, we'll fall back to UTF-8. content_match = _content_type_match.match(content_type) if content_match: return content_match.group(1) return "utf-8" def decode_and_calc_og( body: bytes, media_uri: str, request_encoding: Optional[str] = None ) -> JsonDict: """ Calculate metadata for an HTML document. This uses lxml to parse the HTML document into the OG response. If errors occur during processing of the document, an empty response is returned. Args: body: The HTML document, as bytes. media_url: The URI used to download the body. request_encoding: The character encoding of the body, as a string. Returns: The OG response as a dictionary. """ # If there's no body, nothing useful is going to be found. if not body: return {} from lxml import etree # Create an HTML parser. If this fails, log and return no metadata. try: parser = etree.HTMLParser(recover=True, encoding=request_encoding) except LookupError: # blindly consider the encoding as utf-8. parser = etree.HTMLParser(recover=True, encoding="utf-8") except Exception as e: logger.warning("Unable to create HTML parser: %s" % (e,)) return {} def _attempt_calc_og(body_attempt: Union[bytes, str]) -> Dict[str, Optional[str]]: # Attempt to parse the body. If this fails, log and return no metadata. tree = etree.fromstring(body_attempt, parser) # The data was successfully parsed, but no tree was found. if tree is None: return {} return _calc_og(tree, media_uri) # Attempt to parse the body. If this fails, log and return no metadata. try: return _attempt_calc_og(body) except UnicodeDecodeError: # blindly try decoding the body as utf-8, which seems to fix # the charset mismatches on https://google.com return _attempt_calc_og(body.decode("utf-8", "ignore")) def _calc_og(tree: "etree.Element", media_uri: str) -> Dict[str, Optional[str]]: """ Calculate metadata for an HTML document. This uses lxml to search the HTML document for Open Graph data. Args: tree: The parsed HTML document. media_url: The URI used to download the body. Returns: The Open Graph response as a dictionary. """ # if we see any image URLs in the OG response, then spider them # (although the client could choose to do this by asking for previews of those # URLs to avoid DoSing the server) # "og:type" : "video", # "og:url" : "https://www.youtube.com/watch?v=LXDBoHyjmtw", # "og:site_name" : "YouTube", # "og:video:type" : "application/x-shockwave-flash", # "og:description" : "Fun stuff happening here", # "og:title" : "RemoteJam - Matrix team hack for Disrupt Europe Hackathon", # "og:image" : "https://i.ytimg.com/vi/LXDBoHyjmtw/maxresdefault.jpg", # "og:video:url" : "http://www.youtube.com/v/LXDBoHyjmtw?version=3&autohide=1", # "og:video:width" : "1280" # "og:video:height" : "720", # "og:video:secure_url": "https://www.youtube.com/v/LXDBoHyjmtw?version=3", og: Dict[str, Optional[str]] = {} for tag in tree.xpath("//*/meta[starts-with(@property, 'og:')]"): if "content" in tag.attrib: # if we've got more than 50 tags, someone is taking the piss if len(og) >= 50: logger.warning("Skipping OG for page with too many 'og:' tags") return {} og[tag.attrib["property"]] = tag.attrib["content"] # TODO: grab article: meta tags too, e.g.: # "article:publisher" : "https://www.facebook.com/thethudonline" /> # "article:author" content="https://www.facebook.com/thethudonline" /> # "article:tag" content="baby" /> # "article:section" content="Breaking News" /> # "article:published_time" content="2016-03-31T19:58:24+00:00" /> # "article:modified_time" content="2016-04-01T18:31:53+00:00" /> if "og:title" not in og: # do some basic spidering of the HTML title = tree.xpath("(//title)[1] | (//h1)[1] | (//h2)[1] | (//h3)[1]") if title and title[0].text is not None: og["og:title"] = title[0].text.strip() else: og["og:title"] = None if "og:image" not in og: # TODO: extract a favicon failing all else meta_image = tree.xpath( "//*/meta[translate(@itemprop, 'IMAGE', 'image')='image']/@content" ) if meta_image: og["og:image"] = _rebase_url(meta_image[0], media_uri) else: # TODO: consider inlined CSS styles as well as width & height attribs images = tree.xpath("//img[@src][number(@width)>10][number(@height)>10]") images = sorted( images, key=lambda i: ( -1 * float(i.attrib["width"]) * float(i.attrib["height"]) ), ) if not images: images = tree.xpath("//img[@src]") if images: og["og:image"] = images[0].attrib["src"] if "og:description" not in og: meta_description = tree.xpath( "//*/meta" "[translate(@name, 'DESCRIPTION', 'description')='description']" "/@content" ) if meta_description: og["og:description"] = meta_description[0] else: og["og:description"] = _calc_description(tree) elif og["og:description"]: # This must be a non-empty string at this point. assert isinstance(og["og:description"], str) og["og:description"] = summarize_paragraphs([og["og:description"]]) # TODO: delete the url downloads to stop diskfilling, # as we only ever cared about its OG return og def _calc_description(tree: "etree.Element") -> Optional[str]: """ Calculate a text description based on an HTML document. Grabs any text nodes which are inside the tag, unless they are within an HTML5 semantic markup tag (
,