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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 logging
import urllib.parse
from typing import TYPE_CHECKING, Optional
import attr
from synapse.http.client import SimpleHttpClient
from synapse.types import JsonDict
from synapse.util import json_decoder
if TYPE_CHECKING:
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
# Number of seconds 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", client: SimpleHttpClient):
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
self._client = client
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 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"))
# Ensure there's a version of 1.0.
oembed_version = oembed["version"]
if oembed_version != "1.0":
raise RuntimeError(f"Invalid version: {oembed_version}")
# Ensure the cache age is None or an int.
cache_age = oembed.get("cache_age")
if cache_age:
cache_age = int(cache_age)
# The results.
open_graph_response = {"og:title": oembed.get("title")}
# If a thumbnail exists, use it. Note that dimensions will be calculated later.
if "thumbnail_url" in oembed:
open_graph_response["og:image"] = oembed["thumbnail_url"]
# Process each type separately.
oembed_type = oembed["type"]
if oembed_type == "rich":
calc_description_and_urls(open_graph_response, oembed["html"])
elif oembed_type == "photo":
# If this is a photo, use the full image, not the thumbnail.
open_graph_response["og:image"] = oembed["url"]
else:
raise RuntimeError(f"Unknown oEmbed type: {oembed_type}")
except Exception as e:
# Trap any exception and let the code follow as usual.
logger.warning(f"Error parsing oEmbed metadata from {url}: {e:r}")
open_graph_response = {}
cache_age = None
return OEmbedResult(open_graph_response, cache_age)
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.
tree = etree.fromstring(html_body, parser)
# The data was successfully parsed, but no tree was found.
if tree is None:
return
from synapse.rest.media.v1.preview_url_resource import _calc_description
description = _calc_description(tree)
if description:
open_graph_response["og:description"] = description
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