forked-synapse/synapse/rest/media/v1/preview_url_resource.py

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# -*- 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
from typing import Dict, Optional
import six
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from six import string_types
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from six.moves import urllib_parse as urlparse
from canonicaljson import json
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from twisted.internet import defer
from twisted.internet.error import DNSLookupError
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from synapse.api.errors import Codes, SynapseError
from synapse.http.client import SimpleHttpClient
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from synapse.http.server import (
DirectServeResource,
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respond_with_json,
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respond_with_json_bytes,
wrap_json_request_handler,
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)
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
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from synapse.util.caches.expiringcache import ExpiringCache
from synapse.util.stringutils import random_string
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from ._base import FileInfo
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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
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class PreviewUrlResource(DirectServeResource):
isLeaf = True
def __init__(self, hs, media_repo, media_storage):
super().__init__()
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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
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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.getenvb(b"http_proxy"),
https_proxy=os.getenvb(b"HTTPS_PROXY"),
)
self.media_repo = media_repo
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self.primary_base_path = media_repo.primary_base_path
self.media_storage = media_storage
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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(
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cache_name="url_previews",
clock=self.clock,
# don't spider URLs more often than once an hour
expiry_ms=60 * 60 * 1000,
)
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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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def render_OPTIONS(self, request):
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request.setHeader(b"Allow", b"OPTIONS, GET")
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return respond_with_json(request, 200, {}, send_cors=True)
@wrap_json_request_handler
async def _async_render_GET(self, request):
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# 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)
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logger.debug(
"Matching attrib '%s' with value '%s' against pattern '%s'",
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attrib,
value,
pattern,
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)
if value is None:
match = False
continue
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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(
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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:
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download = run_in_background(self._do_preview, url, requester.user, ts)
observable = ObservableDeferred(download, consumeErrors=True)
self._cache[url] = observable
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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)
async 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 = await self.store.get_url_cache(url, ts)
if (
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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):
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og = og.encode("utf8")
return og
media_info = await self._download_url(url, user)
logger.debug("got media_info of '%s'", media_info)
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if _is_media(media_info["media_type"]):
file_id = media_info["filesystem_id"]
dims = await self.media_repo._generate_thumbnails(
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None, file_id, file_id, media_info["media_type"], url_cache=True
)
og = {
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"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:
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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
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elif _is_html(media_info["media_type"]):
# TODO: somehow stop a big HTML tree from exploding synapse's RAM
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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:
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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:
content_match = _content_type_match.match(media_info["media_type"])
encoding = content_match.group(1) if content_match else "utf-8"
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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.
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if "og:image" in og and og["og:image"]:
image_info = await self._download_url(
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_rebase_url(og["og:image"], media_info["uri"]), user
)
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if _is_media(image_info["media_type"]):
# TODO: make sure we don't choke on white-on-transparent images
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file_id = image_info["filesystem_id"]
dims = await self.media_repo._generate_thumbnails(
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None, file_id, file_id, image_info["media_type"], url_cache=True
)
if dims:
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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" % (
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self.server_name,
image_info["filesystem_id"],
)
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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)
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jsonog = json.dumps(og)
# store OG in history-aware DB cache
await self.store.store_url_cache(
url,
media_info["response_code"],
media_info["etag"],
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media_info["expires"] + media_info["created_ts"],
jsonog,
media_info["filesystem_id"],
media_info["created_ts"],
)
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return jsonog.encode("utf8")
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async 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?
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file_id = datetime.date.today().isoformat() + "_" + random_string(16)
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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 = await self.client.get_file(
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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(
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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(
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500,
"Failed to download content: %s"
% (traceback.format_exception_only(sys.exc_info()[0], e),),
Codes.UNKNOWN,
)
await finish()
try:
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if b"Content-Type" in headers:
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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)
await 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,
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user_id=user,
url_cache=url,
)
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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(
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"expire_url_cache_data", self._expire_url_cache_data
)
async def _expire_url_cache_data(self):
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"""Clean up expired url cache content, media and thumbnails.
"""
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# TODO: Delete from backup media store
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now = self.clock.time_msec()
logger.info("Running url preview cache expiry")
if not (await self.store.db.updates.has_completed_background_updates()):
logger.info("Still running DB updates; skipping expiry")
return
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# First we delete expired url cache entries
media_ids = await self.store.get_expired_url_cache(now)
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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)
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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:
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pass
await self.store.delete_url_cache(removed_media)
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if removed_media:
logger.info("Deleted %d entries from url cache", len(removed_media))
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# 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 = await self.store.get_url_cache_media_before(expire_before)
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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)
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continue
try:
dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id)
for dir in dirs:
os.rmdir(dir)
except Exception:
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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)
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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:
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pass
await self.store.delete_url_cache_media(removed_media)
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logger.info("Deleted %d media from url cache", len(removed_media))
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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)
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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 = {} # type: Dict[str, Optional[str]]
for tag in tree.xpath("//*/meta[starts-with(@property, 'og:')]"):
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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 {}
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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" />
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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:
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og["og:title"] = title[0].text.strip()
else:
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og["og:title"] = None
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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:
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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]")
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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:
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og["og:image"] = images[0].attrib["src"]
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if "og:description" not in og:
meta_description = tree.xpath(
"//*/meta"
"[translate(@name, 'DESCRIPTION', 'description')='description']"
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"/@content"
)
if meta_description:
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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",
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etree.Comment,
)
# Split all the text nodes into paragraphs (by splitting on new
# lines)
text_nodes = (
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re.sub(r"\s+", "\n", el).strip()
for el in _iterate_over_text(tree.find("body"), *TAGS_TO_REMOVE)
)
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og["og:description"] = summarize_paragraphs(text_nodes)
else:
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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
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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()
),
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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]
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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()
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if content_type.startswith("text/html") or content_type.startswith(
"application/xhtml"
):
return True
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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?
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description = ""
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# Keep adding paragraphs until we get to the MIN_SIZE.
for text_node in text_nodes:
if len(description) < min_size:
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text_node = re.sub(r"[\t \r\n]+", " ", text_node)
description += text_node + "\n\n"
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else:
break
description = description.strip()
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description = re.sub(r"[\t ]+", " ", description)
description = re.sub(r"[\t \r\n]*[\r\n]+", "\n\n", description)
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# 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):
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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.
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description = new_desc.strip() + ""
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return description if description else None