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Ensure each charset is attempted only once during media preview. (#11089)

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There's no point in trying more than once since it is guaranteed to
continually fail.
This commit is contained in:
Patrick Cloke 2021-10-14 14:51:44 -04:00 committed by GitHub
parent e2f0b49b3f
commit efd0074ab7
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3 changed files with 64 additions and 14 deletions
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1
changelog.d/11089.bugfix Normal file
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@ -0,0 +1 @@
Fix a long-standing bug when attempting to preview URLs which are in the `windows-1252` character encoding.

34
synapse/rest/media/v1/preview_url_resource.py
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@ -12,6 +12,7 @@
# 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 datetime
import errno
import fnmatch
@ -22,7 +23,7 @@ import re
import shutil
import sys
import traceback
from typing import TYPE_CHECKING, Dict, Generator, Iterable, Optional, Tuple, Union
from typing import TYPE_CHECKING, Dict, Generator, Iterable, Optional, Set, Tuple, Union
from urllib import parse as urlparse
import attr
@ -631,6 +632,14 @@ class PreviewUrlResource(DirectServeJsonResource):
logger.debug("No media removed from url cache")
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.
@ -652,30 +661,43 @@ def get_html_media_encodings(body: bytes, content_type: Optional[str]) -> Iterab
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:
yield match.group(1).decode("ascii")
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:
yield match.group(1).decode("ascii")
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:
yield content_match.group(1)
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.
yield "utf-8"
yield "windows-1252"
for fallback in ("utf-8", "cp1252"):
if fallback not in attempted_encodings:
yield fallback
def decode_body(

43
tests/test_preview.py
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@ -307,7 +307,7 @@ class CalcOgTestCase(unittest.TestCase):
self.assertEqual(og, {"og:title": "ÿÿ Foo", "og:description": "Some text."})
def test_windows_1252(self):
"""A body which uses windows-1252, but doesn't declare that."""
"""A body which uses cp1252, but doesn't declare that."""
html = b"""
<html>
<head><title>\xf3</title></head>
@ -333,7 +333,7 @@ class MediaEncodingTestCase(unittest.TestCase):
""",
"text/html",
)
self.assertEqual(list(encodings), ["ascii", "utf-8", "windows-1252"])
self.assertEqual(list(encodings), ["ascii", "utf-8", "cp1252"])
# A less well-formed version.
encodings = get_html_media_encodings(
@ -345,7 +345,7 @@ class MediaEncodingTestCase(unittest.TestCase):
""",
"text/html",
)
self.assertEqual(list(encodings), ["ascii", "utf-8", "windows-1252"])
self.assertEqual(list(encodings), ["ascii", "utf-8", "cp1252"])
def test_meta_charset_underscores(self):
"""A character encoding contains underscore."""
@ -358,7 +358,7 @@ class MediaEncodingTestCase(unittest.TestCase):
""",
"text/html",
)
self.assertEqual(list(encodings), ["Shift_JIS", "utf-8", "windows-1252"])
self.assertEqual(list(encodings), ["shift_jis", "utf-8", "cp1252"])
def test_xml_encoding(self):
"""A character encoding is found via the meta tag."""
@ -370,7 +370,7 @@ class MediaEncodingTestCase(unittest.TestCase):
""",
"text/html",
)
self.assertEqual(list(encodings), ["ascii", "utf-8", "windows-1252"])
self.assertEqual(list(encodings), ["ascii", "utf-8", "cp1252"])
def test_meta_xml_encoding(self):
"""Meta tags take precedence over XML encoding."""
@ -384,7 +384,7 @@ class MediaEncodingTestCase(unittest.TestCase):
""",
"text/html",
)
self.assertEqual(list(encodings), ["UTF-16", "ascii", "utf-8", "windows-1252"])
self.assertEqual(list(encodings), ["utf-16", "ascii", "utf-8", "cp1252"])
def test_content_type(self):
"""A character encoding is found via the Content-Type header."""
@ -399,9 +399,36 @@ class MediaEncodingTestCase(unittest.TestCase):
)
for header in headers:
encodings = get_html_media_encodings(b"", header)
self.assertEqual(list(encodings), ["ascii", "utf-8", "windows-1252"])
self.assertEqual(list(encodings), ["ascii", "utf-8", "cp1252"])
def test_fallback(self):
"""A character encoding cannot be found in the body or header."""
encodings = get_html_media_encodings(b"", "text/html")
self.assertEqual(list(encodings), ["utf-8", "windows-1252"])
self.assertEqual(list(encodings), ["utf-8", "cp1252"])
def test_duplicates(self):
"""Ensure each encoding is only attempted once."""
encodings = get_html_media_encodings(
b"""
<?xml version="1.0" encoding="utf8"?>
<html>
<head><meta charset="UTF-8">
</head>
</html>
""",
'text/html; charset="UTF_8"',
)
self.assertEqual(list(encodings), ["utf-8", "cp1252"])
def test_unknown_invalid(self):
"""A character encoding should be ignored if it is unknown or invalid."""
encodings = get_html_media_encodings(
b"""
<html>
<head><meta charset="invalid">
</head>
</html>
""",
'text/html; charset="invalid"',
)
self.assertEqual(list(encodings), ["utf-8", "cp1252"])