Refactor media modules. (#15146)

* Removes the `v1` directory from `test.rest.media.v1`.
* Moves the non-REST code from `synapse.rest.media.v1` to `synapse.media`.
* Flatten the `v1` directory from `synapse.rest.media`,  but leave compatiblity
  with 3rd party media repositories and spam checkers.

1 files changed, 265 insertions, 0 deletions

diff --git a/synapse/media/oembed.py b/synapse/media/oembed.py
new file mode 100644
index 0000000000..c0eaf04be5
--- /dev/null
+++ b/synapse/media/oembed.py
@@ -0,0 +1,265 @@
+#  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
+
+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.
+        for tag in tree.xpath(
+            "//link[@rel='alternate'][@type='application/json+oembed']"
+        ):
+            if "href" in tag.attrib:
+                return tag.attrib["href"]
+
+        # Some providers (e.g. Flickr) use alternative instead of alternate.
+        for tag in tree.xpath(
+            "//link[@rel='alternative'][@type='application/json+oembed']"
+        ):
+            if "href" in tag.attrib:
+                return 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 = []
+    for tag in tree.xpath("//*/" + tag_name):
+        if "src" in tag.attrib:
+            results.append(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.
+    tree = etree.fromstring(html_body, parser)
+
+    # The data was successfully parsed, but no tree was found.
+    if tree is None:
+        return
+
+    # 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