Allow configuration of the oEmbed URLs. (#10714)

This adds configuration options (under an `oembed` section) to
configure which URLs are matched to use oEmbed for URL
previews.

changelog.d/10714.feature

@@ -0,0 +1 @@
+Allow configuration of the oEmbed URLs used for URL previews.

docs/sample_config.yaml

@@ -1075,6 +1075,27 @@ url_preview_accept_language:
 #   - en
 
 
+# oEmbed allows for easier embedding content from a website. It can be
+# used for generating URLs previews of services which support it.
+#
+oembed:
+  # A default list of oEmbed providers is included with Synapse.
+  #
+  # Uncomment the following to disable using these default oEmbed URLs.
+  # Defaults to 'false'.
+  #
+  #disable_default_providers: true
+
+  # Additional files with oEmbed configuration (each should be in the
+  # form of providers.json).
+  #
+  # By default, this list is empty (so only the default providers.json
+  # is used).
+  #
+  #additional_providers:
+  #  - oembed/my_providers.json
+
+
 ## Captcha ##
 # See docs/CAPTCHA_SETUP.md for full details of configuring this.
 

synapse/config/homeserver.py

@@ -30,6 +30,7 @@
 from .logger import LoggingConfig
 from .metrics import MetricsConfig
 from .modules import ModulesConfig
+from .oembed import OembedConfig
 from .oidc import OIDCConfig
 from .password_auth_providers import PasswordAuthProviderConfig
 from .push import PushConfig
@@ -65,6 +66,7 @@ class HomeServerConfig(RootConfig):
         LoggingConfig,
         RatelimitConfig,
         ContentRepositoryConfig,
+        OembedConfig,
         CaptchaConfig,
         VoipConfig,
         RegistrationConfig,

synapse/config/oembed.py

@@ -0,0 +1,180 @@
+# 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 json
+import re
+from typing import Any, Dict, Iterable, List, Pattern
+from urllib import parse as urlparse
+
+import attr
+import pkg_resources
+
+from synapse.types import JsonDict
+
+from ._base import Config, ConfigError
+from ._util import validate_config
+
+
+@attr.s(slots=True, frozen=True, auto_attribs=True)
+class OEmbedEndpointConfig:
+    # The API endpoint to fetch.
+    api_endpoint: str
+    # The patterns to match.
+    url_patterns: List[Pattern]
+
+
+class OembedConfig(Config):
+    """oEmbed Configuration"""
+
+    section = "oembed"
+
+    def read_config(self, config, **kwargs):
+        oembed_config: Dict[str, Any] = config.get("oembed") or {}
+
+        # A list of patterns which will be used.
+        self.oembed_patterns: List[OEmbedEndpointConfig] = list(
+            self._parse_and_validate_providers(oembed_config)
+        )
+
+    def _parse_and_validate_providers(
+        self, oembed_config: dict
+    ) -> Iterable[OEmbedEndpointConfig]:
+        """Extract and parse the oEmbed providers from the given JSON file.
+
+        Returns a generator which yields the OidcProviderConfig objects
+        """
+        # Whether to use the packaged providers.json file.
+        if not oembed_config.get("disable_default_providers") or False:
+            providers = json.load(
+                pkg_resources.resource_stream("synapse", "res/providers.json")
+            )
+            yield from self._parse_and_validate_provider(
+                providers, config_path=("oembed",)
+            )
+
+        # The JSON files which includes additional provider information.
+        for i, file in enumerate(oembed_config.get("additional_providers") or []):
+            # TODO Error checking.
+            with open(file) as f:
+                providers = json.load(f)
+
+            yield from self._parse_and_validate_provider(
+                providers,
+                config_path=(
+                    "oembed",
+                    "additional_providers",
+                    f"<item {i}>",
+                ),
+            )
+
+    def _parse_and_validate_provider(
+        self, providers: List[JsonDict], config_path: Iterable[str]
+    ) -> Iterable[OEmbedEndpointConfig]:
+        # Ensure it is the proper form.
+        validate_config(
+            _OEMBED_PROVIDER_SCHEMA,
+            providers,
+            config_path=config_path,
+        )
+
+        # Parse it and yield each result.
+        for provider in providers:
+            # Each provider might have multiple API endpoints, each which
+            # might have multiple patterns to match.
+            for endpoint in provider["endpoints"]:
+                api_endpoint = endpoint["url"]
+                patterns = [
+                    self._glob_to_pattern(glob, config_path)
+                    for glob in endpoint["schemes"]
+                ]
+                yield OEmbedEndpointConfig(api_endpoint, patterns)
+
+    def _glob_to_pattern(self, glob: str, config_path: Iterable[str]) -> Pattern:
+        """
+        Convert the glob into a sane regular expression to match against. The
+        rules followed will be slightly different for the domain portion vs.
+        the rest.
+
+        1. The scheme must be one of HTTP / HTTPS (and have no globs).
+        2. The domain can have globs, but we limit it to characters that can
+           reasonably be a domain part.
+           TODO: This does not attempt to handle Unicode domain names.
+           TODO: The domain should not allow wildcard TLDs.
+        3. Other parts allow a glob to be any one, or more, characters.
+        """
+        results = urlparse.urlparse(glob)
+
+        # Ensure the scheme does not have wildcards (and is a sane scheme).
+        if results.scheme not in {"http", "https"}:
+            raise ConfigError(f"Insecure oEmbed scheme: {results.scheme}", config_path)
+
+        pattern = urlparse.urlunparse(
+            [
+                results.scheme,
+                re.escape(results.netloc).replace("\\*", "[a-zA-Z0-9_-]+"),
+            ]
+            + [re.escape(part).replace("\\*", ".+") for part in results[2:]]
+        )
+        return re.compile(pattern)
+
+    def generate_config_section(self, **kwargs):
+        return """\
+        # oEmbed allows for easier embedding content from a website. It can be
+        # used for generating URLs previews of services which support it.
+        #
+        oembed:
+          # A default list of oEmbed providers is included with Synapse.
+          #
+          # Uncomment the following to disable using these default oEmbed URLs.
+          # Defaults to 'false'.
+          #
+          #disable_default_providers: true
+
+          # Additional files with oEmbed configuration (each should be in the
+          # form of providers.json).
+          #
+          # By default, this list is empty (so only the default providers.json
+          # is used).
+          #
+          #additional_providers:
+          #  - oembed/my_providers.json
+        """
+
+
+_OEMBED_PROVIDER_SCHEMA = {
+    "type": "array",
+    "items": {
+        "type": "object",
+        "properties": {
+            "provider_name": {"type": "string"},
+            "provider_url": {"type": "string"},
+            "endpoints": {
+                "type": "array",
+                "items": {
+                    "type": "object",
+                    "properties": {
+                        "schemes": {
+                            "type": "array",
+                            "items": {"type": "string"},
+                        },
+                        "url": {"type": "string"},
+                        "formats": {"type": "array", "items": {"type": "string"}},
+                        "discovery": {"type": "boolean"},
+                    },
+                    "required": ["schemes", "url"],
+                },
+            },
+        },
+        "required": ["provider_name", "provider_url", "endpoints"],
+    },
+}

synapse/res/providers.json

@@ -0,0 +1,17 @@
+[
+    {
+        "provider_name": "Twitter",
+        "provider_url": "http://www.twitter.com/",
+        "endpoints": [
+            {
+                "schemes": [
+                    "https://twitter.com/*/status/*",
+                    "https://*.twitter.com/*/status/*",
+                    "https://twitter.com/*/moments/*",
+                    "https://*.twitter.com/*/moments/*"
+                ],
+                "url": "https://publish.twitter.com/oembed"
+            }
+        ]
+    }
+]

synapse/rest/media/v1/oembed.py

@@ -0,0 +1,135 @@
+#  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
+from typing import TYPE_CHECKING, Optional
+
+import attr
+
+from synapse.http.client import SimpleHttpClient
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+logger = logging.getLogger(__name__)
+
+
+@attr.s(slots=True, auto_attribs=True)
+class OEmbedResult:
+    # Either HTML content or URL must be provided.
+    html: Optional[str]
+    url: Optional[str]
+    title: Optional[str]
+    # Number of seconds to cache the content.
+    cache_age: int
+
+
+class OEmbedError(Exception):
+    """An error occurred processing the oEmbed object."""
+
+
+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:
+            for pattern in oembed_endpoint.url_patterns:
+                self._oembed_patterns[pattern] = oembed_endpoint.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):
+                return endpoint
+
+        # No match.
+        return None
+
+    async def get_oembed_content(self, endpoint: str, url: str) -> OEmbedResult:
+        """
+        Request content from an oEmbed endpoint.
+
+        Args:
+            endpoint: The oEmbed API endpoint.
+            url: The URL to pass to the API.
+
+        Returns:
+            An object representing the metadata returned.
+
+        Raises:
+            OEmbedError if fetching or parsing of the oEmbed information fails.
+        """
+        try:
+            logger.debug("Trying to get oEmbed content for url '%s'", url)
+            result = await self._client.get_json(
+                endpoint,
+                # TODO Specify max height / width.
+                # Note that only the JSON format is supported.
+                args={"url": url},
+            )
+
+            # Ensure there's a version of 1.0.
+            if result.get("version") != "1.0":
+                raise OEmbedError("Invalid version: %s" % (result.get("version"),))
+
+            oembed_type = result.get("type")
+
+            # Ensure the cache age is None or an int.
+            cache_age = result.get("cache_age")
+            if cache_age:
+                cache_age = int(cache_age)
+
+            oembed_result = OEmbedResult(None, None, result.get("title"), cache_age)
+
+            # HTML content.
+            if oembed_type == "rich":
+                oembed_result.html = result.get("html")
+                return oembed_result
+
+            if oembed_type == "photo":
+                oembed_result.url = result.get("url")
+                return oembed_result
+
+            # TODO Handle link and video types.
+
+            if "thumbnail_url" in result:
+                oembed_result.url = result.get("thumbnail_url")
+                return oembed_result
+
+            raise OEmbedError("Incompatible oEmbed information.")
+
+        except OEmbedError as e:
+            # Trap OEmbedErrors first so we can directly re-raise them.
+            logger.warning("Error parsing oEmbed metadata from %s: %r", url, e)
+            raise
+
+        except Exception as e:
+            # Trap any exception and let the code follow as usual.
+            # FIXME: pass through 404s and other error messages nicely
+            logger.warning("Error downloading oEmbed metadata from %s: %r", url, e)
+            raise OEmbedError() from e