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Diffstat (limited to 'synapse/rest/media/v1/preview_html.py')
| -rw-r--r-- | synapse/rest/media/v1/preview_html.py | 501 |
1 files changed, 0 insertions, 501 deletions
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 |