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1b112840d2
Searches the returned HTML for an oEmbed endpoint using the autodiscovery mechanism (`<link rel=...>`), and will request it to generate the preview.
254 lines
8.9 KiB
Python
254 lines
8.9 KiB
Python
# Copyright 2021 The Matrix.org Foundation C.I.C.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import logging
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import urllib.parse
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from typing import TYPE_CHECKING, List, Optional
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import attr
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from synapse.http.client import SimpleHttpClient
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from synapse.types import JsonDict
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from synapse.util import json_decoder
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if TYPE_CHECKING:
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from lxml import etree
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from synapse.server import HomeServer
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logger = logging.getLogger(__name__)
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@attr.s(slots=True, frozen=True, auto_attribs=True)
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class OEmbedResult:
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# The Open Graph result (converted from the oEmbed result).
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open_graph_result: JsonDict
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# Number of milliseconds to cache the content, according to the oEmbed response.
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#
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# This will be None if no cache-age is provided in the oEmbed response (or
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# if the oEmbed response cannot be turned into an Open Graph response).
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cache_age: Optional[int]
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class OEmbedProvider:
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"""
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A helper for accessing oEmbed content.
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It can be used to check if a URL should be accessed via oEmbed and for
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requesting/parsing oEmbed content.
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"""
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def __init__(self, hs: "HomeServer", client: SimpleHttpClient):
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self._oembed_patterns = {}
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for oembed_endpoint in hs.config.oembed.oembed_patterns:
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api_endpoint = oembed_endpoint.api_endpoint
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# Only JSON is supported at the moment. This could be declared in
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# the formats field. Otherwise, if the endpoint ends in .xml assume
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# it doesn't support JSON.
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if (
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oembed_endpoint.formats is not None
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and "json" not in oembed_endpoint.formats
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) or api_endpoint.endswith(".xml"):
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logger.info(
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"Ignoring oEmbed endpoint due to not supporting JSON: %s",
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api_endpoint,
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)
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continue
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# Iterate through each URL pattern and point it to the endpoint.
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for pattern in oembed_endpoint.url_patterns:
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self._oembed_patterns[pattern] = api_endpoint
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self._client = client
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def get_oembed_url(self, url: str) -> Optional[str]:
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"""
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Check whether the URL should be downloaded as oEmbed content instead.
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Args:
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url: The URL to check.
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Returns:
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A URL to use instead or None if the original URL should be used.
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"""
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for url_pattern, endpoint in self._oembed_patterns.items():
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if url_pattern.fullmatch(url):
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# TODO Specify max height / width.
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# Note that only the JSON format is supported, some endpoints want
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# this in the URL, others want it as an argument.
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endpoint = endpoint.replace("{format}", "json")
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args = {"url": url, "format": "json"}
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query_str = urllib.parse.urlencode(args, True)
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return f"{endpoint}?{query_str}"
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# No match.
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return None
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def autodiscover_from_html(self, tree: "etree.Element") -> Optional[str]:
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"""
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Search an HTML document for oEmbed autodiscovery information.
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Args:
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tree: The parsed HTML body.
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Returns:
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The URL to use for oEmbed information, or None if no URL was found.
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"""
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# Search for link elements with the proper rel and type attributes.
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for tag in tree.xpath(
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"//link[@rel='alternate'][@type='application/json+oembed']"
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):
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if "href" in tag.attrib:
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return tag.attrib["href"]
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# Some providers (e.g. Flickr) use alternative instead of alternate.
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for tag in tree.xpath(
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"//link[@rel='alternative'][@type='application/json+oembed']"
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):
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if "href" in tag.attrib:
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return tag.attrib["href"]
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return None
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def parse_oembed_response(self, url: str, raw_body: bytes) -> OEmbedResult:
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"""
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Parse the oEmbed response into an Open Graph response.
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Args:
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url: The URL which is being previewed (not the one which was
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requested).
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raw_body: The oEmbed response as JSON encoded as bytes.
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Returns:
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json-encoded Open Graph data
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"""
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try:
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# oEmbed responses *must* be UTF-8 according to the spec.
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oembed = json_decoder.decode(raw_body.decode("utf-8"))
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# Ensure there's a version of 1.0.
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oembed_version = oembed["version"]
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if oembed_version != "1.0":
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raise RuntimeError(f"Invalid version: {oembed_version}")
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# Ensure the cache age is None or an int.
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cache_age = oembed.get("cache_age")
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if cache_age:
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cache_age = int(cache_age) * 1000
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# The results.
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open_graph_response = {
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"og:url": url,
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}
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# Use either title or author's name as the title.
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title = oembed.get("title") or oembed.get("author_name")
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if title:
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open_graph_response["og:title"] = title
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# Use the provider name and as the site.
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provider_name = oembed.get("provider_name")
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if provider_name:
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open_graph_response["og:site_name"] = provider_name
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# If a thumbnail exists, use it. Note that dimensions will be calculated later.
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if "thumbnail_url" in oembed:
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open_graph_response["og:image"] = oembed["thumbnail_url"]
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# Process each type separately.
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oembed_type = oembed["type"]
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if oembed_type == "rich":
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calc_description_and_urls(open_graph_response, oembed["html"])
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elif oembed_type == "photo":
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# If this is a photo, use the full image, not the thumbnail.
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open_graph_response["og:image"] = oembed["url"]
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elif oembed_type == "video":
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open_graph_response["og:type"] = "video.other"
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calc_description_and_urls(open_graph_response, oembed["html"])
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open_graph_response["og:video:width"] = oembed["width"]
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open_graph_response["og:video:height"] = oembed["height"]
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elif oembed_type == "link":
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open_graph_response["og:type"] = "website"
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else:
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raise RuntimeError(f"Unknown oEmbed type: {oembed_type}")
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except Exception as e:
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# Trap any exception and let the code follow as usual.
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logger.warning(f"Error parsing oEmbed metadata from {url}: {e:r}")
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open_graph_response = {}
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cache_age = None
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return OEmbedResult(open_graph_response, cache_age)
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def _fetch_urls(tree: "etree.Element", tag_name: str) -> List[str]:
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results = []
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for tag in tree.xpath("//*/" + tag_name):
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if "src" in tag.attrib:
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results.append(tag.attrib["src"])
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return results
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def calc_description_and_urls(open_graph_response: JsonDict, html_body: str) -> None:
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"""
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Calculate description for an HTML document.
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This uses lxml to convert the HTML document into plaintext. If errors
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occur during processing of the document, an empty response is returned.
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Args:
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open_graph_response: The current Open Graph summary. This is updated with additional fields.
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html_body: The HTML document, as bytes.
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Returns:
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The summary
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"""
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# If there's no body, nothing useful is going to be found.
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if not html_body:
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return
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from lxml import etree
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# Create an HTML parser. If this fails, log and return no metadata.
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parser = etree.HTMLParser(recover=True, encoding="utf-8")
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# Attempt to parse the body. If this fails, log and return no metadata.
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tree = etree.fromstring(html_body, parser)
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# The data was successfully parsed, but no tree was found.
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if tree is None:
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return
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# Attempt to find interesting URLs (images, videos, embeds).
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if "og:image" not in open_graph_response:
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image_urls = _fetch_urls(tree, "img")
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if image_urls:
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open_graph_response["og:image"] = image_urls[0]
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video_urls = _fetch_urls(tree, "video") + _fetch_urls(tree, "embed")
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if video_urls:
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open_graph_response["og:video"] = video_urls[0]
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from synapse.rest.media.v1.preview_url_resource import _calc_description
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description = _calc_description(tree)
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if description:
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open_graph_response["og:description"] = description
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