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15ffc4143c
By scraping Open Graph information from the HTML even when an autodiscovery endpoint is found. The results are then combined to capture as much information as possible from the page.
256 lines
9.0 KiB
Python
256 lines
9.0 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.rest.media.v1.preview_html import parse_html_description
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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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# The author_name of the oEmbed result
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author_name: Optional[str]
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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"):
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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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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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# The version is a required string field, but not always provided,
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# or sometimes provided as a float. Be lenient.
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oembed_version = oembed.get("version", "1.0")
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if oembed_version != "1.0" and oembed_version != 1:
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raise RuntimeError(f"Invalid oEmbed 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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title = oembed.get("title")
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if title:
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open_graph_response["og:title"] = title
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author_name = oembed.get("author_name")
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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("Error parsing oEmbed metadata from %s: %r", url, e)
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open_graph_response = {}
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author_name = None
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cache_age = None
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return OEmbedResult(open_graph_response, author_name, 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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description = parse_html_description(tree)
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if description:
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open_graph_response["og:description"] = description
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