forked-synapse/synapse/rest/media/v1/preview_url_resource.py
Richard van der Hoff 5570d1c93f
Merge pull request #6334 from matrix-org/rav/url_preview_limit_title_2
Fix exception when OpenGraph tag values are ints
2019-11-05 17:28:11 +00:00

724 lines
27 KiB
Python

# -*- coding: utf-8 -*-
# Copyright 2016 OpenMarket Ltd
#
# 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
import six
from six import string_types
from six.moves import urllib_parse as urlparse
from canonicaljson import json
from twisted.internet import defer
from twisted.internet.error import DNSLookupError
from synapse.api.errors import Codes, SynapseError
from synapse.http.client import SimpleHttpClient
from synapse.http.server import (
DirectServeResource,
respond_with_json,
respond_with_json_bytes,
wrap_json_request_handler,
)
from synapse.http.servlet import parse_integer, parse_string
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.util.async_helpers import ObservableDeferred
from synapse.util.caches.expiringcache import ExpiringCache
from synapse.util.stringutils import random_string
from ._base import FileInfo
logger = logging.getLogger(__name__)
_charset_match = re.compile(br"<\s*meta[^>]*charset\s*=\s*([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
class PreviewUrlResource(DirectServeResource):
isLeaf = True
def __init__(self, hs, media_repo, media_storage):
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,
http_proxy=os.getenv("http_proxy"),
https_proxy=os.getenv("HTTPS_PROXY"),
)
self.media_repo = media_repo
self.primary_base_path = media_repo.primary_base_path
self.media_storage = media_storage
self.url_preview_url_blacklist = hs.config.url_preview_url_blacklist
# memory cache mapping urls to an ObservableDeferred returning
# JSON-encoded OG metadata
self._cache = ExpiringCache(
cache_name="url_previews",
clock=self.clock,
# don't spider URLs more often than once an hour
expiry_ms=60 * 60 * 1000,
)
self._cleaner_loop = self.clock.looping_call(
self._start_expire_url_cache_data, 10 * 1000
)
def render_OPTIONS(self, request):
request.setHeader(b"Allow", b"OPTIONS, GET")
return respond_with_json(request, 200, {}, send_cors=True)
@wrap_json_request_handler
async def _async_render_GET(self, request):
# 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")
if b"ts" in request.args:
ts = parse_integer(request, "ts")
else:
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(defer.maybeDeferred(observable.observe))
respond_with_json_bytes(request, 200, og, send_cors=True)
@defer.inlineCallbacks
def _do_preview(self, url, user, ts):
"""Check the db, and download the URL and build a preview
Args:
url (str):
user (str):
ts (int):
Returns:
Deferred[bytes]: 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 = yield 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, six.text_type):
og = og.encode("utf8")
return og
media_info = yield self._download_url(url, user)
logger.debug("got media_info of '%s'", media_info)
if _is_media(media_info["media_type"]):
file_id = media_info["filesystem_id"]
dims = yield 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": "mxc://%s/%s"
% (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 = None
# Let's try and figure out if it has an encoding set in a meta tag.
# Limit it to the first 1kb, since it ought to be in the meta tags
# at the top.
match = _charset_match.search(body[:1000])
# If we find a match, it should take precedence over the
# Content-Type header, so set it here.
if match:
encoding = 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.
if not encoding:
match = _content_type_match.match(media_info["media_type"])
encoding = match.group(1) if match else "utf-8"
og = decode_and_calc_og(body, media_info["uri"], encoding)
# pre-cache the image for posterity
# 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.
if "og:image" in og and og["og:image"]:
image_info = yield 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 = yield 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"] = "mxc://%s/%s" % (
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"]
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.dumps(og)
# store OG in history-aware DB cache
yield self.store.store_url_cache(
url,
media_info["response_code"],
media_info["etag"],
media_info["expires"] + media_info["created_ts"],
jsonog,
media_info["filesystem_id"],
media_info["created_ts"],
)
return jsonog.encode("utf8")
@defer.inlineCallbacks
def _download_url(self, url, user):
# 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 url '%s'", url)
length, headers, uri, code = yield self.client.get_file(
url, output_stream=f, max_size=self.max_spider_size
)
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,
)
yield finish()
try:
if b"Content-Type" in headers:
media_type = headers[b"Content-Type"][0].decode("ascii")
else:
media_type = "application/octet-stream"
time_now_ms = self.clock.time_msec()
download_name = get_filename_from_headers(headers)
yield self.store.store_local_media(
media_id=file_id,
media_type=media_type,
time_now_ms=self.clock.time_msec(),
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 {
"media_type": media_type,
"media_length": length,
"download_name": download_name,
"created_ts": time_now_ms,
"filesystem_id": file_id,
"filename": fname,
"uri": uri,
"response_code": code,
# FIXME: we should calculate a proper expiration based on the
# Cache-Control and Expire headers. But for now, assume 1 hour.
"expires": 60 * 60 * 1000,
"etag": headers["ETag"][0] if "ETag" in headers else None,
}
def _start_expire_url_cache_data(self):
return run_as_background_process(
"expire_url_cache_data", self._expire_url_cache_data
)
@defer.inlineCallbacks
def _expire_url_cache_data(self):
"""Clean up expired url cache content, media and thumbnails.
"""
# TODO: Delete from backup media store
now = self.clock.time_msec()
logger.info("Running url preview cache expiry")
if not (yield self.store.has_completed_background_updates()):
logger.info("Still running DB updates; skipping expiry")
return
# First we delete expired url cache entries
media_ids = yield 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
yield self.store.delete_url_cache(removed_media)
if removed_media:
logger.info("Deleted %d entries from url cache", len(removed_media))
# 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 * 24 * 60 * 60 * 1000
media_ids = yield 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
yield self.store.delete_url_cache_media(removed_media)
logger.info("Deleted %d media from url cache", len(removed_media))
def decode_and_calc_og(body, media_uri, request_encoding=None):
from lxml import etree
try:
parser = etree.HTMLParser(recover=True, encoding=request_encoding)
tree = etree.fromstring(body, parser)
og = _calc_og(tree, media_uri)
except UnicodeDecodeError:
# blindly try decoding the body as utf-8, which seems to fix
# the charset mismatches on https://google.com
parser = etree.HTMLParser(recover=True, encoding=request_encoding)
tree = etree.fromstring(body.decode("utf-8", "ignore"), parser)
og = _calc_og(tree, media_uri)
return og
def _calc_og(tree, media_uri):
# suck our tree into lxml and define our OG response.
# 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 = {}
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:
# grab any text nodes which are inside the <body/> tag...
# unless they are within an HTML5 semantic markup tag...
# <header/>, <nav/>, <aside/>, <footer/>
# ...or if they are within a <script/> or <style/> tag.
# This is a very very very coarse approximation to a plain text
# render of the page.
# We don't just use XPATH here as that is slow on some machines.
from lxml import etree
TAGS_TO_REMOVE = (
"header",
"nav",
"aside",
"footer",
"script",
"noscript",
"style",
etree.Comment,
)
# Split all the text nodes into paragraphs (by splitting on new
# lines)
text_nodes = (
re.sub(r"\s+", "\n", el).strip()
for el in _iterate_over_text(tree.find("body"), *TAGS_TO_REMOVE)
)
og["og:description"] = summarize_paragraphs(text_nodes)
else:
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 _iterate_over_text(tree, *tags_to_ignore):
"""Iterate over the tree returning text nodes in a depth first fashion,
skipping text nodes inside certain tags.
"""
# This is basically a stack that we extend using itertools.chain.
# This will either consist of an element to iterate over *or* a string
# to be returned.
elements = iter([tree])
while True:
el = next(elements, None)
if el is None:
return
if isinstance(el, string_types):
yield el
elif el.tag not in tags_to_ignore:
# el.text is the text before the first child, so we can immediately
# return it if the text exists.
if el.text:
yield el.text
# We add to the stack all the elements children, interspersed with
# each child's tail text (if it exists). The tail text of a node
# is text that comes *after* the node, so we always include it even
# if we ignore the child node.
elements = itertools.chain(
itertools.chain.from_iterable( # Basically a flatmap
[child, child.tail] if child.tail else [child]
for child in el.iterchildren()
),
elements,
)
def _rebase_url(url, base):
base = list(urlparse.urlparse(base))
url = list(urlparse.urlparse(url))
if not url[0]: # fix up schema
url[0] = base[0] or "http"
if not url[1]: # fix up hostname
url[1] = base[1]
if not url[2].startswith("/"):
url[2] = re.sub(r"/[^/]+$", "/", base[2]) + url[2]
return urlparse.urlunparse(url)
def _is_media(content_type):
if content_type.lower().startswith("image/"):
return True
def _is_html(content_type):
content_type = content_type.lower()
if content_type.startswith("text/html") or content_type.startswith(
"application/xhtml"
):
return True
def summarize_paragraphs(text_nodes, min_size=200, max_size=500):
# Try to get a summary of between 200 and 500 words, respecting
# first paragraph and then word boundaries.
# TODO: Respect sentences?
description = ""
# Keep adding paragraphs until we get to the MIN_SIZE.
for text_node in text_nodes:
if len(description) < min_size:
text_node = re.sub(r"[\t \r\n]+", " ", text_node)
description += text_node + "\n\n"
else:
break
description = description.strip()
description = re.sub(r"[\t ]+", " ", description)
description = re.sub(r"[\t \r\n]*[\r\n]+", "\n\n", description)
# If the concatenation of paragraphs to get above MIN_SIZE
# took us over MAX_SIZE, then we need to truncate mid paragraph
if len(description) > max_size:
new_desc = ""
# This splits the paragraph into words, but keeping the
# (preceeding) whitespace intact so we can easily concat
# words back together.
for match in re.finditer(r"\s*\S+", description):
word = match.group()
# Keep adding words while the total length is less than
# MAX_SIZE.
if len(word) + len(new_desc) < max_size:
new_desc += word
else:
# At this point the next word *will* take us over
# MAX_SIZE, but we also want to ensure that its not
# a huge word. If it is add it anyway and we'll
# truncate later.
if len(new_desc) < min_size:
new_desc += word
break
# Double check that we're not over the limit
if len(new_desc) > max_size:
new_desc = new_desc[:max_size]
# We always add an ellipsis because at the very least
# we chopped mid paragraph.
description = new_desc.strip() + ""
return description if description else None