forked-synapse/synapse/media/oembed.py

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# Copyright 2021 The Matrix.org Foundation C.I.C.
#
# 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 html
import logging
import urllib.parse
from typing import TYPE_CHECKING, List, Optional, cast
import attr
from synapse.media.preview_html import parse_html_description
from synapse.types import JsonDict
from synapse.util import json_decoder
if TYPE_CHECKING:
from lxml import etree
from synapse.server import HomeServer
logger = logging.getLogger(__name__)
@attr.s(slots=True, frozen=True, auto_attribs=True)
class OEmbedResult:
# The Open Graph result (converted from the oEmbed result).
open_graph_result: JsonDict
# The author_name of the oEmbed result
author_name: Optional[str]
# Number of milliseconds to cache the content, according to the oEmbed response.
#
# This will be None if no cache-age is provided in the oEmbed response (or
# if the oEmbed response cannot be turned into an Open Graph response).
cache_age: Optional[int]
class OEmbedProvider:
"""
A helper for accessing oEmbed content.
It can be used to check if a URL should be accessed via oEmbed and for
requesting/parsing oEmbed content.
"""
def __init__(self, hs: "HomeServer"):
self._oembed_patterns = {}
for oembed_endpoint in hs.config.oembed.oembed_patterns:
api_endpoint = oembed_endpoint.api_endpoint
# Only JSON is supported at the moment. This could be declared in
# the formats field. Otherwise, if the endpoint ends in .xml assume
# it doesn't support JSON.
if (
oembed_endpoint.formats is not None
and "json" not in oembed_endpoint.formats
) or api_endpoint.endswith(".xml"):
logger.info(
"Ignoring oEmbed endpoint due to not supporting JSON: %s",
api_endpoint,
)
continue
# Iterate through each URL pattern and point it to the endpoint.
for pattern in oembed_endpoint.url_patterns:
self._oembed_patterns[pattern] = api_endpoint
def get_oembed_url(self, url: str) -> Optional[str]:
"""
Check whether the URL should be downloaded as oEmbed content instead.
Args:
url: The URL to check.
Returns:
A URL to use instead or None if the original URL should be used.
"""
for url_pattern, endpoint in self._oembed_patterns.items():
if url_pattern.fullmatch(url):
# TODO Specify max height / width.
# Note that only the JSON format is supported, some endpoints want
# this in the URL, others want it as an argument.
endpoint = endpoint.replace("{format}", "json")
args = {"url": url, "format": "json"}
query_str = urllib.parse.urlencode(args, True)
return f"{endpoint}?{query_str}"
# No match.
return None
def autodiscover_from_html(self, tree: "etree._Element") -> Optional[str]:
"""
Search an HTML document for oEmbed autodiscovery information.
Args:
tree: The parsed HTML body.
Returns:
The URL to use for oEmbed information, or None if no URL was found.
"""
# Search for link elements with the proper rel and type attributes.
# Cast: the type returned by xpath depends on the xpath expression: mypy can't deduce this.
for tag in cast(
List["etree._Element"],
tree.xpath("//link[@rel='alternate'][@type='application/json+oembed']"),
):
if "href" in tag.attrib:
return cast(str, tag.attrib["href"])
# Some providers (e.g. Flickr) use alternative instead of alternate.
# Cast: the type returned by xpath depends on the xpath expression: mypy can't deduce this.
for tag in cast(
List["etree._Element"],
tree.xpath("//link[@rel='alternative'][@type='application/json+oembed']"),
):
if "href" in tag.attrib:
return cast(str, tag.attrib["href"])
return None
def parse_oembed_response(self, url: str, raw_body: bytes) -> OEmbedResult:
"""
Parse the oEmbed response into an Open Graph response.
Args:
url: The URL which is being previewed (not the one which was
requested).
raw_body: The oEmbed response as JSON encoded as bytes.
Returns:
json-encoded Open Graph data
"""
try:
# oEmbed responses *must* be UTF-8 according to the spec.
oembed = json_decoder.decode(raw_body.decode("utf-8"))
except ValueError:
return OEmbedResult({}, None, None)
# The version is a required string field, but not always provided,
# or sometimes provided as a float. Be lenient.
oembed_version = oembed.get("version", "1.0")
if oembed_version != "1.0" and oembed_version != 1:
return OEmbedResult({}, None, None)
# Attempt to parse the cache age, if possible.
try:
cache_age = int(oembed.get("cache_age")) * 1000
except (TypeError, ValueError):
# If the cache age cannot be parsed (e.g. wrong type or invalid
# string), ignore it.
cache_age = None
# The oEmbed response converted to Open Graph.
open_graph_response: JsonDict = {"og:url": url}
title = oembed.get("title")
if title and isinstance(title, str):
# A common WordPress plug-in seems to incorrectly escape entities
# in the oEmbed response.
open_graph_response["og:title"] = html.unescape(title)
author_name = oembed.get("author_name")
if not isinstance(author_name, str):
author_name = None
# Use the provider name and as the site.
provider_name = oembed.get("provider_name")
if provider_name and isinstance(provider_name, str):
open_graph_response["og:site_name"] = provider_name
# If a thumbnail exists, use it. Note that dimensions will be calculated later.
thumbnail_url = oembed.get("thumbnail_url")
if thumbnail_url and isinstance(thumbnail_url, str):
open_graph_response["og:image"] = thumbnail_url
# Process each type separately.
oembed_type = oembed.get("type")
if oembed_type == "rich":
html_str = oembed.get("html")
if isinstance(html_str, str):
calc_description_and_urls(open_graph_response, html_str)
elif oembed_type == "photo":
# If this is a photo, use the full image, not the thumbnail.
url = oembed.get("url")
if url and isinstance(url, str):
open_graph_response["og:image"] = url
elif oembed_type == "video":
open_graph_response["og:type"] = "video.other"
html_str = oembed.get("html")
if html_str and isinstance(html_str, str):
calc_description_and_urls(open_graph_response, oembed["html"])
for size in ("width", "height"):
val = oembed.get(size)
if type(val) is int:
open_graph_response[f"og:video:{size}"] = val
elif oembed_type == "link":
open_graph_response["og:type"] = "website"
else:
logger.warning("Unknown oEmbed type: %s", oembed_type)
return OEmbedResult(open_graph_response, author_name, cache_age)
def _fetch_urls(tree: "etree._Element", tag_name: str) -> List[str]:
results = []
# Cast: the type returned by xpath depends on the xpath expression: mypy can't deduce this.
for tag in cast(List["etree._Element"], tree.xpath("//*/" + tag_name)):
if "src" in tag.attrib:
results.append(cast(str, tag.attrib["src"]))
return results
def calc_description_and_urls(open_graph_response: JsonDict, html_body: str) -> None:
"""
Calculate description for an HTML document.
This uses lxml to convert the HTML document into plaintext. If errors
occur during processing of the document, an empty response is returned.
Args:
open_graph_response: The current Open Graph summary. This is updated with additional fields.
html_body: The HTML document, as bytes.
Returns:
The summary
"""
# If there's no body, nothing useful is going to be found.
if not html_body:
return
from lxml import etree
# Create an HTML parser. If this fails, log and return no metadata.
parser = etree.HTMLParser(recover=True, encoding="utf-8")
# Attempt to parse the body. If this fails, log and return no metadata.
# TODO Develop of lxml-stubs has this correct.
tree = etree.fromstring(html_body, parser) # type: ignore[arg-type]
# The data was successfully parsed, but no tree was found.
if tree is None:
return # type: ignore[unreachable]
# Attempt to find interesting URLs (images, videos, embeds).
if "og:image" not in open_graph_response:
image_urls = _fetch_urls(tree, "img")
if image_urls:
open_graph_response["og:image"] = image_urls[0]
video_urls = _fetch_urls(tree, "video") + _fetch_urls(tree, "embed")
if video_urls:
open_graph_response["og:video"] = video_urls[0]
description = parse_html_description(tree)
if description:
open_graph_response["og:description"] = description