text: # -*- 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.
  
  from twisted.web.server import NOT_DONE_YET
  from twisted.internet import defer
  from twisted.web.resource import Resource
  
  from synapse.api.errors import (
      SynapseError, Codes,
  )
  from synapse.util.stringutils import random_string
  from synapse.util.caches.expiringcache import ExpiringCache
  from synapse.http.client import SpiderHttpClient
  from synapse.http.server import (
      request_handler, respond_with_json_bytes
  )
  from synapse.util.async import ObservableDeferred
  from synapse.util.stringutils import is_ascii
  
  import os
  import re
  import fnmatch
  import cgi
  import ujson as json
  import urlparse
  import itertools
  
  import logging
  logger = logging.getLogger(__name__)
  
  
  class PreviewUrlResource(Resource):
      isLeaf = True
  
      def __init__(self, hs, media_repo):
          Resource.__init__(self)
  
          self.auth = hs.get_auth()
          self.clock = hs.get_clock()
          self.version_string = hs.version_string
          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 = SpiderHttpClient(hs)
          self.media_repo = media_repo
  
          self.url_preview_url_blacklist = hs.config.url_preview_url_blacklist
  
          # simple memory cache mapping urls to 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.cache.start()
  
          self.downloads = {}
  
      def render_GET(self, request):
          self._async_render_GET(request)
          return NOT_DONE_YET
  
      @request_handler()
      @defer.inlineCallbacks
      def _async_render_GET(self, request):
  
          # XXX: if get_user_by_req fails, what should we do in an async render?
          requester = yield self.auth.get_user_by_req(request)
          url = request.args.get("url")[0]
          if "ts" in request.args:
              ts = int(request.args.get("ts")[0])
          else:
              ts = self.clock.time_msec()
  
          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.warn(
                      "URL %s blocked by url_blacklist entry %s", url, entry
                  )
                  raise SynapseError(
                      403, "URL blocked by url pattern blacklist entry",
                      Codes.UNKNOWN
                  )
  
          # first check the memory cache - good to handle all the clients on this
          # HS thundering away to preview the same URL at the same time.
          og = self.cache.get(url)
          if og:
              respond_with_json_bytes(request, 200, json.dumps(og), send_cors=True)
              return
  
          # then 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["download_ts"] + cache_result["expires"] > ts and
              cache_result["response_code"] / 100 == 2
          ):
              respond_with_json_bytes(
                  request, 200, cache_result["og"].encode('utf-8'),
                  send_cors=True
              )
              return
  
          # Ensure only one download for a given URL is active at a time
          download = self.downloads.get(url)
          if download is None:
              download = self._download_url(url, requester.user)
              download = ObservableDeferred(
                  download,
                  consumeErrors=True
              )
              self.downloads[url] = download
  
              @download.addBoth
              def callback(media_info):
                  del self.downloads[url]
                  return media_info
          media_info = yield download.observe()
  
          # FIXME: we should probably update our cache now anyway, so that
          # even if the OG calculation raises, we don't keep hammering on the
          # remote server.  For now, leave it uncached to aid debugging OG
          # calculation problems
  
          logger.debug("got media_info of '%s'" % media_info)
  
          if _is_media(media_info['media_type']):
              dims = yield self.media_repo._generate_local_thumbnails(
                  media_info['filesystem_id'], media_info
              )
  
              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.warn("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
  
              file = open(media_info['filename'])
              body = file.read()
              file.close()
  
              # clobber the encoding from the content-type, or default to utf-8
              # XXX: this overrides any <meta/> or XML charset headers in the body
              # which may pose problems, but so far seems to work okay.
              match = re.match(r'.*; *charset=(.*?)(;|$)', media_info['media_type'], re.I)
              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']), requester.user
                  )
  
                  if _is_media(image_info['media_type']):
                      # TODO: make sure we don't choke on white-on-transparent images
                      dims = yield self.media_repo._generate_local_thumbnails(
                          image_info['filesystem_id'], image_info
                      )
                      if dims:
                          og["og:image:width"] = dims['width']
                          og["og:image:height"] = dims['height']
                      else:
                          logger.warn("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.warn("Failed to find any OG data in %s", url)
              og = {}
  
          logger.debug("Calculated OG for %s as %s" % (url, og))
  
          # store OG in ephemeral in-memory cache
          self.cache[url] = 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"],
              json.dumps(og),
              media_info["filesystem_id"],
              media_info["created_ts"],
          )
  
          respond_with_json_bytes(request, 200, json.dumps(og), send_cors=True)
  
      @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?
  
          # XXX: horrible duplication with base_resource's _download_remote_file()
          file_id = random_string(24)
  
          fname = self.filepaths.local_media_filepath(file_id)
          self.media_repo._makedirs(fname)
  
          try:
              with open(fname, "wb") as f:
                  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,
                  )
                  # FIXME: pass through 404s and other error messages nicely
  
              media_type = headers["Content-Type"][0]
              time_now_ms = self.clock.time_msec()
  
              content_disposition = headers.get("Content-Disposition", None)
              if content_disposition:
                  _, params = cgi.parse_header(content_disposition[0],)
                  download_name = None
  
                  # First check if there is a valid UTF-8 filename
                  download_name_utf8 = params.get("filename*", None)
                  if download_name_utf8:
                      if download_name_utf8.lower().startswith("utf-8''"):
                          download_name = download_name_utf8[7:]
  
                  # If there isn't check for an ascii name.
                  if not download_name:
                      download_name_ascii = params.get("filename", None)
                      if download_name_ascii and is_ascii(download_name_ascii):
                          download_name = download_name_ascii
  
                  if download_name:
                      download_name = urlparse.unquote(download_name)
                      try:
                          download_name = download_name.decode("utf-8")
                      except UnicodeDecodeError:
                          download_name = None
              else:
                  download_name = None
  
              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,
              )
  
          except Exception as e:
              os.remove(fname)
              raise SynapseError(
                  500, ("Failed to download content: %s" % e),
                  Codes.UNKNOWN
              )
  
          defer.returnValue({
              "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 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:
              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", "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)
  
      # 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 = elements.next()
          if isinstance(el, basestring):
              yield el
          elif el is not None and 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("\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() + u"…"
      return description if description else None
  