diff --git a/synapse/rest/media/v1/preview_html.py b/synapse/rest/media/v1/preview_html.py
deleted file mode 100644
index 516d0434f0..0000000000
--- a/synapse/rest/media/v1/preview_html.py
+++ /dev/null
@@ -1,501 +0,0 @@
-# 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 codecs
-import logging
-import re
-from typing import (
- TYPE_CHECKING,
- Callable,
- Dict,
- Generator,
- Iterable,
- List,
- Optional,
- Set,
- Union,
-)
-
-if TYPE_CHECKING:
- from lxml import etree
-
-logger = logging.getLogger(__name__)
-
-_charset_match = re.compile(
- rb'<\s*meta[^>]*charset\s*=\s*"?([a-z0-9_-]+)"?', flags=re.I
-)
-_xml_encoding_match = re.compile(
- rb'\s*<\s*\?\s*xml[^>]*encoding="([a-z0-9_-]+)"', flags=re.I
-)
-_content_type_match = re.compile(r'.*; *charset="?(.*?)"?(;|$)', flags=re.I)
-
-# Certain elements aren't meant for display.
-ARIA_ROLES_TO_IGNORE = {"directory", "menu", "menubar", "toolbar"}
-
-
-def _normalise_encoding(encoding: str) -> Optional[str]:
- """Use the Python codec's name as the normalised entry."""
- try:
- return codecs.lookup(encoding).name
- except LookupError:
- return None
-
-
-def _get_html_media_encodings(
- body: bytes, content_type: Optional[str]
-) -> Iterable[str]:
- """
- Get potential encoding of the body based on the (presumably) HTML body or the content-type header.
-
- The precedence used for finding a character encoding is:
-
- 1. <meta> tag with a charset declared.
- 2. The XML document's character encoding attribute.
- 3. The Content-Type header.
- 4. Fallback to utf-8.
- 5. Fallback to windows-1252.
-
- This roughly follows the algorithm used by BeautifulSoup's bs4.dammit.EncodingDetector.
-
- Args:
- body: The HTML document, as bytes.
- content_type: The Content-Type header.
-
- Returns:
- The character encoding of the body, as a string.
- """
- # There's no point in returning an encoding more than once.
- attempted_encodings: Set[str] = set()
-
- # Limit searches to the first 1kb, since it ought to be at the top.
- body_start = body[:1024]
-
- # Check if it has an encoding set in a meta tag.
- match = _charset_match.search(body_start)
- if match:
- encoding = _normalise_encoding(match.group(1).decode("ascii"))
- if encoding:
- attempted_encodings.add(encoding)
- yield encoding
-
- # TODO Support <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
-
- # Check if it has an XML document with an encoding.
- match = _xml_encoding_match.match(body_start)
- if match:
- encoding = _normalise_encoding(match.group(1).decode("ascii"))
- if encoding and encoding not in attempted_encodings:
- attempted_encodings.add(encoding)
- yield encoding
-
- # Check the HTTP Content-Type header for a character set.
- if content_type:
- content_match = _content_type_match.match(content_type)
- if content_match:
- encoding = _normalise_encoding(content_match.group(1))
- if encoding and encoding not in attempted_encodings:
- attempted_encodings.add(encoding)
- yield encoding
-
- # Finally, fallback to UTF-8, then windows-1252.
- for fallback in ("utf-8", "cp1252"):
- if fallback not in attempted_encodings:
- yield fallback
-
-
-def decode_body(
- body: bytes, uri: str, content_type: Optional[str] = None
-) -> Optional["etree.Element"]:
- """
- This uses lxml to parse the HTML document.
-
- Args:
- body: The HTML document, as bytes.
- uri: The URI used to download the body.
- content_type: The Content-Type header.
-
- Returns:
- The parsed HTML body, or None if an error occurred during processed.
- """
- # If there's no body, nothing useful is going to be found.
- if not body:
- return None
-
- # The idea here is that multiple encodings are tried until one works.
- # Unfortunately the result is never used and then LXML will decode the string
- # again with the found encoding.
- for encoding in _get_html_media_encodings(body, content_type):
- try:
- body.decode(encoding)
- except Exception:
- pass
- else:
- break
- else:
- logger.warning("Unable to decode HTML body for %s", uri)
- return None
-
- from lxml import etree
-
- # Create an HTML parser.
- parser = etree.HTMLParser(recover=True, encoding=encoding)
-
- # Attempt to parse the body. Returns None if the body was successfully
- # parsed, but no tree was found.
- return etree.fromstring(body, parser)
-
-
-def _get_meta_tags(
- tree: "etree.Element",
- property: str,
- prefix: str,
- property_mapper: Optional[Callable[[str], Optional[str]]] = None,
-) -> Dict[str, Optional[str]]:
- """
- Search for meta tags prefixed with a particular string.
-
- Args:
- tree: The parsed HTML document.
- property: The name of the property which contains the tag name, e.g.
- "property" for Open Graph.
- prefix: The prefix on the property to search for, e.g. "og" for Open Graph.
- property_mapper: An optional callable to map the property to the Open Graph
- form. Can return None for a key to ignore that key.
-
- Returns:
- A map of tag name to value.
- """
- results: Dict[str, Optional[str]] = {}
- for tag in tree.xpath(
- f"//*/meta[starts-with(@{property}, '{prefix}:')][@content][not(@content='')]"
- ):
- # if we've got more than 50 tags, someone is taking the piss
- if len(results) >= 50:
- logger.warning(
- "Skipping parsing of Open Graph for page with too many '%s:' tags",
- prefix,
- )
- return {}
-
- key = tag.attrib[property]
- if property_mapper:
- key = property_mapper(key)
- # None is a special value used to ignore a value.
- if key is None:
- continue
-
- results[key] = tag.attrib["content"]
-
- return results
-
-
-def _map_twitter_to_open_graph(key: str) -> Optional[str]:
- """
- Map a Twitter card property to the analogous Open Graph property.
-
- Args:
- key: The Twitter card property (starts with "twitter:").
-
- Returns:
- The Open Graph property (starts with "og:") or None to have this property
- be ignored.
- """
- # Twitter card properties with no analogous Open Graph property.
- if key == "twitter:card" or key == "twitter:creator":
- return None
- if key == "twitter:site":
- return "og:site_name"
- # Otherwise, swap twitter to og.
- return "og" + key[7:]
-
-
-def parse_html_to_open_graph(tree: "etree.Element") -> Dict[str, Optional[str]]:
- """
- Parse the HTML document into an Open Graph response.
-
- This uses lxml to search the HTML document for Open Graph data (or
- synthesizes it from the document).
-
- Args:
- tree: The parsed HTML document.
-
- Returns:
- The Open Graph response as a dictionary.
- """
-
- # Search for Open Graph (og:) meta tags, e.g.:
- #
- # "og:type" : "video",
- # "og:url" : "https://www.youtube.com/watch?v=LXDBoHyjmtw",
- # "og:site_name" : "YouTube",
- # "og:video:type" : "application/x-shockwave-flash",
- # "og:description" : "Fun stuff happening here",
- # "og:title" : "RemoteJam - Matrix team hack for Disrupt Europe Hackathon",
- # "og:image" : "https://i.ytimg.com/vi/LXDBoHyjmtw/maxresdefault.jpg",
- # "og:video:url" : "http://www.youtube.com/v/LXDBoHyjmtw?version=3&autohide=1",
- # "og:video:width" : "1280"
- # "og:video:height" : "720",
- # "og:video:secure_url": "https://www.youtube.com/v/LXDBoHyjmtw?version=3",
-
- og = _get_meta_tags(tree, "property", "og")
-
- # TODO: Search for properties specific to the different Open Graph types,
- # such as article: meta tags, e.g.:
- #
- # "article:publisher" : "https://www.facebook.com/thethudonline" />
- # "article:author" content="https://www.facebook.com/thethudonline" />
- # "article:tag" content="baby" />
- # "article:section" content="Breaking News" />
- # "article:published_time" content="2016-03-31T19:58:24+00:00" />
- # "article:modified_time" content="2016-04-01T18:31:53+00:00" />
-
- # Search for Twitter Card (twitter:) meta tags, e.g.:
- #
- # "twitter:site" : "@matrixdotorg"
- # "twitter:creator" : "@matrixdotorg"
- #
- # Twitter cards tags also duplicate Open Graph tags.
- #
- # See https://developer.twitter.com/en/docs/twitter-for-websites/cards/guides/getting-started
- twitter = _get_meta_tags(tree, "name", "twitter", _map_twitter_to_open_graph)
- # Merge the Twitter values with the Open Graph values, but do not overwrite
- # information from Open Graph tags.
- for key, value in twitter.items():
- if key not in og:
- og[key] = value
-
- if "og:title" not in og:
- # Attempt to find a title from the title tag, or the biggest header on the page.
- title = tree.xpath("((//title)[1] | (//h1)[1] | (//h2)[1] | (//h3)[1])/text()")
- if title:
- og["og:title"] = title[0].strip()
- else:
- og["og:title"] = None
-
- if "og:image" not in og:
- meta_image = tree.xpath(
- "//*/meta[translate(@itemprop, 'IMAGE', 'image')='image'][not(@content='')]/@content[1]"
- )
- # If a meta image is found, use it.
- if meta_image:
- og["og:image"] = meta_image[0]
- else:
- # Try to find images which are larger than 10px by 10px.
- #
- # TODO: consider inlined CSS styles as well as width & height attribs
- images = tree.xpath("//img[@src][number(@width)>10][number(@height)>10]")
- images = sorted(
- images,
- key=lambda i: (
- -1 * float(i.attrib["width"]) * float(i.attrib["height"])
- ),
- )
- # If no images were found, try to find *any* images.
- if not images:
- images = tree.xpath("//img[@src][1]")
- if images:
- og["og:image"] = images[0].attrib["src"]
-
- # Finally, fallback to the favicon if nothing else.
- else:
- favicons = tree.xpath("//link[@href][contains(@rel, 'icon')]/@href[1]")
- if favicons:
- og["og:image"] = favicons[0]
-
- if "og:description" not in og:
- # Check the first meta description tag for content.
- meta_description = tree.xpath(
- "//*/meta[translate(@name, 'DESCRIPTION', 'description')='description'][not(@content='')]/@content[1]"
- )
- # If a meta description is found with content, use it.
- if meta_description:
- og["og:description"] = meta_description[0]
- else:
- og["og:description"] = parse_html_description(tree)
- elif og["og:description"]:
- # This must be a non-empty string at this point.
- assert isinstance(og["og:description"], str)
- og["og:description"] = summarize_paragraphs([og["og:description"]])
-
- # TODO: delete the url downloads to stop diskfilling,
- # as we only ever cared about its OG
- return og
-
-
-def parse_html_description(tree: "etree.Element") -> Optional[str]:
- """
- Calculate a text description based on an HTML document.
-
- Grabs any text nodes which are inside the <body/> tag, unless they are within
- an HTML5 semantic markup tag (<header/>, <nav/>, <aside/>, <footer/>), or
- if they are within a <script/>, <svg/> or <style/> tag, or if they are within
- a tag whose content is usually only shown to old browsers
- (<iframe/>, <video/>, <canvas/>, <picture/>).
-
- This is a very very very coarse approximation to a plain text render of the page.
-
- Args:
- tree: The parsed HTML document.
-
- Returns:
- The plain text description, or None if one cannot be generated.
- """
- # We don't just use XPATH here as that is slow on some machines.
-
- from lxml import etree
-
- TAGS_TO_REMOVE = {
- "header",
- "nav",
- "aside",
- "footer",
- "script",
- "noscript",
- "style",
- "svg",
- "iframe",
- "video",
- "canvas",
- "img",
- "picture",
- etree.Comment,
- }
-
- # Split all the text nodes into paragraphs (by splitting on new
- # lines)
- text_nodes = (
- re.sub(r"\s+", "\n", el).strip()
- for el in _iterate_over_text(tree.find("body"), TAGS_TO_REMOVE)
- )
- return summarize_paragraphs(text_nodes)
-
-
-def _iterate_over_text(
- tree: Optional["etree.Element"],
- tags_to_ignore: Set[Union[str, "etree.Comment"]],
- stack_limit: int = 1024,
-) -> Generator[str, None, None]:
- """Iterate over the tree returning text nodes in a depth first fashion,
- skipping text nodes inside certain tags.
-
- Args:
- tree: The parent element to iterate. Can be None if there isn't one.
- tags_to_ignore: Set of tags to ignore
- stack_limit: Maximum stack size limit for depth-first traversal.
- Nodes will be dropped if this limit is hit, which may truncate the
- textual result.
- Intended to limit the maximum working memory when generating a preview.
- """
-
- if tree is None:
- return
-
- # This is a stack whose items are elements to iterate over *or* strings
- # to be returned.
- elements: List[Union[str, "etree.Element"]] = [tree]
- while elements:
- el = elements.pop()
-
- if isinstance(el, str):
- yield el
- elif el.tag not in tags_to_ignore:
- # If the element isn't meant for display, ignore it.
- if el.get("role") in ARIA_ROLES_TO_IGNORE:
- continue
-
- # el.text is the text before the first child, so we can immediately
- # return it if the text exists.
- if el.text:
- yield el.text
-
- # We add to the stack all the element's children, interspersed with
- # each child's tail text (if it exists).
- #
- # We iterate in reverse order so that earlier pieces of text appear
- # closer to the top of the stack.
- for child in el.iterchildren(reversed=True):
- if len(elements) > stack_limit:
- # We've hit our limit for working memory
- break
-
- if child.tail:
- # The tail text of a node is text that comes *after* the node,
- # so we always include it even if we ignore the child node.
- elements.append(child.tail)
-
- elements.append(child)
-
-
-def summarize_paragraphs(
- text_nodes: Iterable[str], min_size: int = 200, max_size: int = 500
-) -> Optional[str]:
- """
- Try to get a summary respecting first paragraph and then word boundaries.
-
- Args:
- text_nodes: The paragraphs to summarize.
- min_size: The minimum number of words to include.
- max_size: The maximum number of words to include.
-
- Returns:
- A summary of the text nodes, or None if that was not possible.
- """
-
- # TODO: Respect sentences?
-
- description = ""
-
- # Keep adding paragraphs until we get to the MIN_SIZE.
- for text_node in text_nodes:
- if len(description) < min_size:
- text_node = re.sub(r"[\t \r\n]+", " ", text_node)
- description += text_node + "\n\n"
- else:
- break
-
- description = description.strip()
- description = re.sub(r"[\t ]+", " ", description)
- description = re.sub(r"[\t \r\n]*[\r\n]+", "\n\n", description)
-
- # If the concatenation of paragraphs to get above MIN_SIZE
- # took us over MAX_SIZE, then we need to truncate mid paragraph
- if len(description) > max_size:
- new_desc = ""
-
- # This splits the paragraph into words, but keeping the
- # (preceding) whitespace intact so we can easily concat
- # words back together.
- for match in re.finditer(r"\s*\S+", description):
- word = match.group()
-
- # Keep adding words while the total length is less than
- # MAX_SIZE.
- if len(word) + len(new_desc) < max_size:
- new_desc += word
- else:
- # At this point the next word *will* take us over
- # MAX_SIZE, but we also want to ensure that its not
- # a huge word. If it is add it anyway and we'll
- # truncate later.
- if len(new_desc) < min_size:
- new_desc += word
- break
-
- # Double check that we're not over the limit
- if len(new_desc) > max_size:
- new_desc = new_desc[:max_size]
-
- # We always add an ellipsis because at the very least
- # we chopped mid paragraph.
- description = new_desc.strip() + "…"
- return description if description else None
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