initial WIP of a tentative preview_url endpoint - incomplete, untested, experimental, etc. just putting it here for safekeeping for now

synapse/rest/media/v1/preview_url_resource.py

@@ -0,0 +1,164 @@
+# 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.resource import Resource
+from lxml import html
+from synapse.http.client import SimpleHttpClient
+from synapse.http.server import respond_with_json_bytes
+from simplejson import json
+
+import logging
+logger = logging.getLogger(__name__)
+
+class PreviewUrlResource(Resource):
+    isLeaf = True
+
+    def __init__(self, hs, filepaths):
+        Resource.__init__(self)
+        self.client = SimpleHttpClient(hs)
+        self.filepaths = filepaths
+        self.max_spider_size = hs.config.max_spider_size
+        self.server_name = hs.hostname
+        self.clock = hs.get_clock()
+
+    def render_GET(self, request):
+        self._async_render_GET(request)
+        return NOT_DONE_YET
+
+    @request_handler
+    @defer.inlineCallbacks
+    def _async_render_GET(self, request):
+        url = request.args.get("url")
+        
+        try:
+            # TODO: keep track of whether there's an ongoing request for this preview
+            # and block and return their details if there is one.
+
+            media_info = self._download_url(url)
+        except:
+            os.remove(fname)
+            raise
+
+        if self._is_media(media_type):
+            dims = yield self._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,
+                "og:image:width" : dims.width,
+                "og:image:height" : dims.height,
+            }
+
+            # define our OG response for this media
+        elif self._is_html(media_type):
+            tree = html.parse(media_info.filename)
+
+            # suck it up into lxml and define our OG response.
+            # if we see any 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"        : "article"
+            # "og:url"         : "https://twitter.com/matrixdotorg/status/684074366691356672"
+            # "og:title"       : "Matrix on Twitter"
+            # "og:image"       : "https://pbs.twimg.com/profile_images/500400952029888512/yI0qtFi7_400x400.png"
+            # "og:description" : "“Synapse 0.12 is out! Lots of polishing, performance & bugfixes: /sync API, /r0 prefix, fulltext search, 3PID invites https://t.co/5alhXLLEGP”"
+            # "og:site_name"   : "Twitter"
+
+            og = {}
+            for tag in tree.xpath("//*/meta[starts-with(@property, 'og:')]"):
+                og[tag.attrib['property']] = tag.attrib['content']
+
+            # TODO: store our OG details in a cache (and expire them when stale)
+            # TODO: delete the content to stop diskfilling, as we only ever cared about its OG
+
+        respond_with_json_bytes(request, 200, json.dumps(og), send_cors=True)
+
+    def _download_url(url):
+        requester = yield self.auth.get_user_by_req(request)
+
+        # XXX: horrible duplication with base_resource's _download_remote_file()
+        file_id = random_string(24)
+
+        fname = self.filepaths.local_media_filepath(file_id)
+        self._makedirs(fname)
+
+        try:
+            with open(fname, "wb") as f:
+                length, headers = yield self.client.get_file(
+                    url, output_stream=f, max_size=self.max_spider_size,
+                )
+            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=fname,
+                media_type=media_type,
+                time_now_ms=self.clock.time_msec(),
+                upload_name=download_name,
+                media_length=length,
+                user_id=requester.user,
+            )
+
+        except:
+            os.remove(fname)
+            raise
+
+        return {
+            "media_type": media_type,
+            "media_length": length,
+            "download_name": download_name,
+            "created_ts": time_now_ms,
+            "filesystem_id": file_id,
+            "filename": fname,
+        }
+
+
+    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 == "text/html" or
+           content_type.startswith("application/xhtml"):
+            return True