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Support rendering previews with data: URLs in them (#11767)

Browse source 
Images which are data URLs will no longer break URL
previews and will properly be "downloaded" and
thumbnailed.
This commit is contained in:
Patrick Cloke 2022-01-24 08:58:18 -05:00 committed by GitHub
parent c3040dd5cc
commit 807efd26ae
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6 changed files with 299 additions and 74 deletions
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1
changelog.d/11767.bugfix Normal file
View file

@ -0,0 +1 @@
Fix a long-standing bug when previewing Reddit URLs which do not contain an image.

31
synapse/rest/media/v1/preview_html.py
View file

@ -321,14 +321,33 @@ def _iterate_over_text(
def rebase_url(url: str, base: str) -> str:
base_parts = list(urlparse.urlparse(base))
"""
Resolves a potentially relative `url` against an absolute `base` URL.
For example:
>>> rebase_url("subpage", "https://example.com/foo/")
'https://example.com/foo/subpage'
>>> rebase_url("sibling", "https://example.com/foo")
'https://example.com/sibling'
>>> rebase_url("/bar", "https://example.com/foo/")
'https://example.com/bar'
>>> rebase_url("https://alice.com/a/", "https://example.com/foo/")
'https://alice.com/a'
"""
base_parts = urlparse.urlparse(base)
# Convert the parsed URL to a list for (potential) modification.
url_parts = list(urlparse.urlparse(url))
if not url_parts[0]: # fix up schema
url_parts[0] = base_parts[0] or "http"
if not url_parts[1]: # fix up hostname
url_parts[1] = base_parts[1]
# Add a scheme, if one does not exist.
if not url_parts[0]:
url_parts[0] = base_parts.scheme or "http"
# Fix up the hostname, if this is not a data URL.
if url_parts[0] != "data" and not url_parts[1]:
url_parts[1] = base_parts.netloc
# If the path does not start with a /, nest it under the base path's last
# directory.
if not url_parts[2].startswith("/"):
url_parts[2] = re.sub(r"/[^/]+$", "/", base_parts[2]) + url_parts[2]
url_parts[2] = re.sub(r"/[^/]+$", "/", base_parts.path) + url_parts[2]
return urlparse.urlunparse(url_parts)

224
synapse/rest/media/v1/preview_url_resource.py
View file

@ -21,8 +21,9 @@ import re
import shutil
import sys
import traceback
from typing import TYPE_CHECKING, Iterable, Optional, Tuple
from typing import TYPE_CHECKING, BinaryIO, Iterable, Optional, Tuple
from urllib import parse as urlparse
from urllib.request import urlopen
import attr
@ -70,6 +71,17 @@ ONE_DAY = 24 * ONE_HOUR
IMAGE_CACHE_EXPIRY_MS = 2 * ONE_DAY
@attr.s(slots=True, frozen=True, auto_attribs=True)
class DownloadResult:
length: int
uri: str
response_code: int
media_type: str
download_name: Optional[str]
expires: int
etag: Optional[str]
@attr.s(slots=True, frozen=True, auto_attribs=True)
class MediaInfo:
"""
@ -256,7 +268,7 @@ class PreviewUrlResource(DirectServeJsonResource):
if oembed_url:
url_to_download = oembed_url
media_info = await self._download_url(url_to_download, user)
media_info = await self._handle_url(url_to_download, user)
logger.debug("got media_info of '%s'", media_info)
@ -297,7 +309,9 @@ class PreviewUrlResource(DirectServeJsonResource):
oembed_url = self._oembed.autodiscover_from_html(tree)
og_from_oembed: JsonDict = {}
if oembed_url:
oembed_info = await self._download_url(oembed_url, user)
oembed_info = await self._handle_url(
oembed_url, user, allow_data_urls=True
)
(
og_from_oembed,
author_name,
@ -367,7 +381,135 @@ class PreviewUrlResource(DirectServeJsonResource):
return jsonog.encode("utf8")
async def _download_url(self, url: str, user: UserID) -> MediaInfo:
async def _download_url(self, url: str, output_stream: BinaryIO) -> DownloadResult:
"""
Fetches a remote URL and parses the headers.
Args:
url: The URL to fetch.
output_stream: The stream to write the content to.
Returns:
A tuple of:
Media length, URL downloaded, the HTTP response code,
the media type, the downloaded file name, the number of
milliseconds the result is valid for, the etag header.
"""
try:
logger.debug("Trying to get preview for url '%s'", url)
length, headers, uri, code = await self.client.get_file(
url,
output_stream=output_stream,
max_size=self.max_spider_size,
headers={"Accept-Language": self.url_preview_accept_language},
)
except SynapseError:
# Pass SynapseErrors through directly, so that the servlet
# handler will return a SynapseError to the client instead of
# blank data or a 500.
raise
except DNSLookupError:
# DNS lookup returned no results
# Note: This will also be the case if one of the resolved IP
# addresses is blacklisted
raise SynapseError(
502,
"DNS resolution failure during URL preview generation",
Codes.UNKNOWN,
)
except Exception as e:
# FIXME: pass through 404s and other error messages nicely
logger.warning("Error downloading %s: %r", url, e)
raise SynapseError(
500,
"Failed to download content: %s"
% (traceback.format_exception_only(sys.exc_info()[0], e),),
Codes.UNKNOWN,
)
if b"Content-Type" in headers:
media_type = headers[b"Content-Type"][0].decode("ascii")
else:
media_type = "application/octet-stream"
download_name = get_filename_from_headers(headers)
# FIXME: we should calculate a proper expiration based on the
# Cache-Control and Expire headers. But for now, assume 1 hour.
expires = ONE_HOUR
etag = headers[b"ETag"][0].decode("ascii") if b"ETag" in headers else None
return DownloadResult(
length, uri, code, media_type, download_name, expires, etag
)
async def _parse_data_url(
self, url: str, output_stream: BinaryIO
) -> DownloadResult:
"""
Parses a data: URL.
Args:
url: The URL to parse.
output_stream: The stream to write the content to.
Returns:
A tuple of:
Media length, URL downloaded, the HTTP response code,
the media type, the downloaded file name, the number of
milliseconds the result is valid for, the etag header.
"""
try:
logger.debug("Trying to parse data url '%s'", url)
with urlopen(url) as url_info:
# TODO Can this be more efficient.
output_stream.write(url_info.read())
except Exception as e:
logger.warning("Error parsing data: URL %s: %r", url, e)
raise SynapseError(
500,
"Failed to parse data URL: %s"
% (traceback.format_exception_only(sys.exc_info()[0], e),),
Codes.UNKNOWN,
)
return DownloadResult(
# Read back the length that has been written.
length=output_stream.tell(),
uri=url,
# If it was parsed, consider this a 200 OK.
response_code=200,
# urlopen shoves the media-type from the data URL into the content type
# header object.
media_type=url_info.headers.get_content_type(),
# Some features are not supported by data: URLs.
download_name=None,
expires=ONE_HOUR,
etag=None,
)
async def _handle_url(
self, url: str, user: UserID, allow_data_urls: bool = False
) -> MediaInfo:
"""
Fetches content from a URL and parses the result to generate a MediaInfo.
It uses the media storage provider to persist the fetched content and
stores the mapping into the database.
Args:
url: The URL to fetch.
user: The user who ahs requested this URL.
allow_data_urls: True if data URLs should be allowed.
Returns:
A MediaInfo object describing the fetched content.
"""
# TODO: we should probably honour robots.txt... except in practice
# we're most likely being explicitly triggered by a human rather than a
# bot, so are we really a robot?
@ -377,61 +519,27 @@ class PreviewUrlResource(DirectServeJsonResource):
file_info = FileInfo(server_name=None, file_id=file_id, url_cache=True)
with self.media_storage.store_into_file(file_info) as (f, fname, finish):
try:
logger.debug("Trying to get preview for url '%s'", url)
length, headers, uri, code = await self.client.get_file(
url,
output_stream=f,
max_size=self.max_spider_size,
headers={"Accept-Language": self.url_preview_accept_language},
)
except SynapseError:
# Pass SynapseErrors through directly, so that the servlet
# handler will return a SynapseError to the client instead of
# blank data or a 500.
raise
except DNSLookupError:
# DNS lookup returned no results
# Note: This will also be the case if one of the resolved IP
# addresses is blacklisted
raise SynapseError(
502,
"DNS resolution failure during URL preview generation",
Codes.UNKNOWN,
)
except Exception as e:
# FIXME: pass through 404s and other error messages nicely
logger.warning("Error downloading %s: %r", url, e)
if url.startswith("data:"):
if not allow_data_urls:
raise SynapseError(
500, "Previewing of data: URLs is forbidden", Codes.UNKNOWN
)
raise SynapseError(
500,
"Failed to download content: %s"
% (traceback.format_exception_only(sys.exc_info()[0], e),),
Codes.UNKNOWN,
)
await finish()
if b"Content-Type" in headers:
media_type = headers[b"Content-Type"][0].decode("ascii")
download_result = await self._parse_data_url(url, f)
else:
media_type = "application/octet-stream"
download_result = await self._download_url(url, f)
download_name = get_filename_from_headers(headers)
# FIXME: we should calculate a proper expiration based on the
# Cache-Control and Expire headers. But for now, assume 1 hour.
expires = ONE_HOUR
etag = headers[b"ETag"][0].decode("ascii") if b"ETag" in headers else None
await finish()
try:
time_now_ms = self.clock.time_msec()
await self.store.store_local_media(
media_id=file_id,
media_type=media_type,
media_type=download_result.media_type,
time_now_ms=time_now_ms,
upload_name=download_name,
media_length=length,
upload_name=download_result.download_name,
media_length=download_result.length,
user_id=user,
url_cache=url,
)
@ -444,16 +552,16 @@ class PreviewUrlResource(DirectServeJsonResource):
raise
return MediaInfo(
media_type=media_type,
media_length=length,
download_name=download_name,
media_type=download_result.media_type,
media_length=download_result.length,
download_name=download_result.download_name,
created_ts_ms=time_now_ms,
filesystem_id=file_id,
filename=fname,
uri=uri,
response_code=code,
expires=expires,
etag=etag,
uri=download_result.uri,
response_code=download_result.response_code,
expires=download_result.expires,
etag=download_result.etag,
)
async def _precache_image_url(
@ -474,8 +582,8 @@ class PreviewUrlResource(DirectServeJsonResource):
# FIXME: it might be cleaner to use the same flow as the main /preview_url
# request itself and benefit from the same caching etc. But for now we
# just rely on the caching on the master request to speed things up.
image_info = await self._download_url(
rebase_url(og["og:image"], media_info.uri), user
image_info = await self._handle_url(
rebase_url(og["og:image"], media_info.uri), user, allow_data_urls=True
)
if _is_media(image_info.media_type):

34
tests/test_preview.py → tests/rest/media/v1/test_html_preview.py
View file

@ -16,10 +16,11 @@ from synapse.rest.media.v1.preview_html import (
_get_html_media_encodings,
decode_body,
parse_html_to_open_graph,
rebase_url,
summarize_paragraphs,
)
from . import unittest
from tests import unittest
try:
import lxml
@ -447,3 +448,34 @@ class MediaEncodingTestCase(unittest.TestCase):
'text/html; charset="invalid"',
)
self.assertEqual(list(encodings), ["utf-8", "cp1252"])
class RebaseUrlTestCase(unittest.TestCase):
def test_relative(self):
"""Relative URLs should be resolved based on the context of the base URL."""
self.assertEqual(
rebase_url("subpage", "https://example.com/foo/"),
"https://example.com/foo/subpage",
)
self.assertEqual(
rebase_url("sibling", "https://example.com/foo"),
"https://example.com/sibling",
)
self.assertEqual(
rebase_url("/bar", "https://example.com/foo/"),
"https://example.com/bar",
)
def test_absolute(self):
"""Absolute URLs should not be modified."""
self.assertEqual(
rebase_url("https://alice.com/a/", "https://example.com/foo/"),
"https://alice.com/a/",
)
def test_data(self):
"""Data URLs should not be modified."""
self.assertEqual(
rebase_url("data:,Hello%2C%20World%21", "https://example.com/foo/"),
"data:,Hello%2C%20World%21",
)

81
tests/rest/media/v1/test_url_preview.py
View file

@ -12,9 +12,11 @@
# 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 base64
import json
import os
import re
from urllib.parse import urlencode
from twisted.internet._resolver import HostResolution
from twisted.internet.address import IPv4Address, IPv6Address
@ -23,6 +25,7 @@ from twisted.test.proto_helpers import AccumulatingProtocol
from synapse.config.oembed import OEmbedEndpointConfig
from synapse.rest.media.v1.preview_url_resource import IMAGE_CACHE_EXPIRY_MS
from synapse.types import JsonDict
from synapse.util.stringutils import parse_and_validate_mxc_uri
from tests import unittest
@ -142,6 +145,14 @@ class URLPreviewTests(unittest.HomeserverTestCase):
def create_test_resource(self):
return self.hs.get_media_repository_resource()
def _assert_small_png(self, json_body: JsonDict) -> None:
"""Assert properties from the SMALL_PNG test image."""
self.assertTrue(json_body["og:image"].startswith("mxc://"))
self.assertEqual(json_body["og:image:height"], 1)
self.assertEqual(json_body["og:image:width"], 1)
self.assertEqual(json_body["og:image:type"], "image/png")
self.assertEqual(json_body["matrix:image:size"], 67)
def test_cache_returns_correct_type(self):
self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
@ -569,6 +580,66 @@ class URLPreviewTests(unittest.HomeserverTestCase):
server.data,
)
def test_data_url(self):
"""
Requesting to preview a data URL is not supported.
"""
self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
data = base64.b64encode(SMALL_PNG).decode()
query_params = urlencode(
{
"url": f'<html><head><img src="data:image/png;base64,{data}" /></head></html>'
}
)
channel = self.make_request(
"GET",
f"preview_url?{query_params}",
shorthand=False,
)
self.pump()
self.assertEqual(channel.code, 500)
def test_inline_data_url(self):
"""
An inline image (as a data URL) should be parsed properly.
"""
self.lookups["matrix.org"] = [(IPv4Address, "10.1.2.3")]
data = base64.b64encode(SMALL_PNG)
end_content = (
b"<html><head>" b'<img src="data:image/png;base64,%s" />' b"</head></html>"
) % (data,)
channel = self.make_request(
"GET",
"preview_url?url=http://matrix.org",
shorthand=False,
await_result=False,
)
self.pump()
client = self.reactor.tcpClients[0][2].buildProtocol(None)
server = AccumulatingProtocol()
server.makeConnection(FakeTransport(client, self.reactor))
client.makeConnection(FakeTransport(server, self.reactor))
client.dataReceived(
(
b"HTTP/1.0 200 OK\r\nContent-Length: %d\r\n"
b'Content-Type: text/html; charset="utf8"\r\n\r\n'
)
% (len(end_content),)
+ end_content
)
self.pump()
self.assertEqual(channel.code, 200)
self._assert_small_png(channel.json_body)
def test_oembed_photo(self):
"""Test an oEmbed endpoint which returns a 'photo' type which redirects the preview to a new URL."""
self.lookups["publish.twitter.com"] = [(IPv4Address, "10.1.2.3")]
@ -626,10 +697,7 @@ class URLPreviewTests(unittest.HomeserverTestCase):
self.assertEqual(channel.code, 200)
body = channel.json_body
self.assertEqual(body["og:url"], "http://twitter.com/matrixdotorg/status/12345")
self.assertTrue(body["og:image"].startswith("mxc://"))
self.assertEqual(body["og:image:height"], 1)
self.assertEqual(body["og:image:width"], 1)
self.assertEqual(body["og:image:type"], "image/png")
self._assert_small_png(body)
def test_oembed_rich(self):
"""Test an oEmbed endpoint which returns HTML content via the 'rich' type."""
@ -820,10 +888,7 @@ class URLPreviewTests(unittest.HomeserverTestCase):
self.assertEqual(
body["og:url"], "http://www.twitter.com/matrixdotorg/status/12345"
)
self.assertTrue(body["og:image"].startswith("mxc://"))
self.assertEqual(body["og:image:height"], 1)
self.assertEqual(body["og:image:width"], 1)
self.assertEqual(body["og:image:type"], "image/png")
self._assert_small_png(body)
def _download_image(self):
"""Downloads an image into the URL cache.

2
tests/server.py
View file

@ -313,7 +313,7 @@ def make_request(
req = request(channel, site)
req.content = BytesIO(content)
# Twisted expects to be at the end of the content when parsing the request.
req.content.seek(SEEK_END)
req.content.seek(0, SEEK_END)
if access_token:
req.requestHeaders.addRawHeader(