Handle additional errors when previewing URLs. (#9333)

* Handle the case of lxml not finding a document tree.
* Parse the document encoding from the XML tag.
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Patrick Cloke 2021-02-08 12:33:30 -05:00 committed by GitHub
parent b0b2cac057
commit 0963d39ea6
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3 changed files with 145 additions and 30 deletions

1
changelog.d/9333.bugfix Normal file
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@ -0,0 +1 @@
Fix additional errors when previewing URLs: "AttributeError 'NoneType' object has no attribute 'xpath'" and "ValueError: Unicode strings with encoding declaration are not supported. Please use bytes input or XML fragments without declaration.".

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@ -58,7 +58,10 @@ if TYPE_CHECKING:
logger = logging.getLogger(__name__)
_charset_match = re.compile(br"<\s*meta[^>]*charset\s*=\s*([a-z0-9-]+)", flags=re.I)
_charset_match = re.compile(br'<\s*meta[^>]*charset\s*=\s*"?([a-z0-9-]+)"?', flags=re.I)
_xml_encoding_match = re.compile(
br'\s*<\s*\?\s*xml[^>]*encoding="([a-z0-9-]+)"', flags=re.I
)
_content_type_match = re.compile(r'.*; *charset="?(.*?)"?(;|$)', flags=re.I)
OG_TAG_NAME_MAXLEN = 50
@ -300,24 +303,7 @@ class PreviewUrlResource(DirectServeJsonResource):
with open(media_info["filename"], "rb") as file:
body = file.read()
encoding = None
# Let's try and figure out if it has an encoding set in a meta tag.
# Limit it to the first 1kb, since it ought to be in the meta tags
# at the top.
match = _charset_match.search(body[:1000])
# If we find a match, it should take precedence over the
# Content-Type header, so set it here.
if match:
encoding = match.group(1).decode("ascii")
# If we don't find a match, we'll look at the HTTP Content-Type, and
# if that doesn't exist, we'll fall back to UTF-8.
if not encoding:
content_match = _content_type_match.match(media_info["media_type"])
encoding = content_match.group(1) if content_match else "utf-8"
encoding = get_html_media_encoding(body, media_info["media_type"])
og = decode_and_calc_og(body, media_info["uri"], encoding)
# pre-cache the image for posterity
@ -689,6 +675,48 @@ class PreviewUrlResource(DirectServeJsonResource):
logger.debug("No media removed from url cache")
def get_html_media_encoding(body: bytes, content_type: str) -> str:
"""
Get the encoding of the body based on the (presumably) HTML body or media_type.
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.
Args:
body: The HTML document, as bytes.
content_type: The Content-Type header.
Returns:
The character encoding of the body, as a string.
"""
# Limit searches to the first 1kb, since it ought to be at the top.
body_start = body[:1024]
# Let's try and figure out if it has an encoding set in a meta tag.
match = _charset_match.search(body_start)
if match:
return match.group(1).decode("ascii")
# TODO Support <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
# If we didn't find a match, see if it an XML document with an encoding.
match = _xml_encoding_match.match(body_start)
if match:
return match.group(1).decode("ascii")
# If we don't find a match, we'll look at the HTTP Content-Type, and
# if that doesn't exist, we'll fall back to UTF-8.
content_match = _content_type_match.match(content_type)
if content_match:
return content_match.group(1)
return "utf-8"
def decode_and_calc_og(
body: bytes, media_uri: str, request_encoding: Optional[str] = None
) -> Dict[str, Optional[str]]:
@ -725,6 +753,11 @@ def decode_and_calc_og(
def _attempt_calc_og(body_attempt: Union[bytes, str]) -> Dict[str, Optional[str]]:
# Attempt to parse the body. If this fails, log and return no metadata.
tree = etree.fromstring(body_attempt, parser)
# The data was successfully parsed, but no tree was found.
if tree is None:
return {}
return _calc_og(tree, media_uri)
# Attempt to parse the body. If this fails, log and return no metadata.

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@ -15,6 +15,7 @@
from synapse.rest.media.v1.preview_url_resource import (
decode_and_calc_og,
get_html_media_encoding,
summarize_paragraphs,
)
@ -26,7 +27,7 @@ except ImportError:
lxml = None
class PreviewTestCase(unittest.TestCase):
class SummarizeTestCase(unittest.TestCase):
if not lxml:
skip = "url preview feature requires lxml"
@ -144,12 +145,12 @@ class PreviewTestCase(unittest.TestCase):
)
class PreviewUrlTestCase(unittest.TestCase):
class CalcOgTestCase(unittest.TestCase):
if not lxml:
skip = "url preview feature requires lxml"
def test_simple(self):
html = """
html = b"""
<html>
<head><title>Foo</title></head>
<body>
@ -163,7 +164,7 @@ class PreviewUrlTestCase(unittest.TestCase):
self.assertEqual(og, {"og:title": "Foo", "og:description": "Some text."})
def test_comment(self):
html = """
html = b"""
<html>
<head><title>Foo</title></head>
<body>
@ -178,7 +179,7 @@ class PreviewUrlTestCase(unittest.TestCase):
self.assertEqual(og, {"og:title": "Foo", "og:description": "Some text."})
def test_comment2(self):
html = """
html = b"""
<html>
<head><title>Foo</title></head>
<body>
@ -202,7 +203,7 @@ class PreviewUrlTestCase(unittest.TestCase):
)
def test_script(self):
html = """
html = b"""
<html>
<head><title>Foo</title></head>
<body>
@ -217,7 +218,7 @@ class PreviewUrlTestCase(unittest.TestCase):
self.assertEqual(og, {"og:title": "Foo", "og:description": "Some text."})
def test_missing_title(self):
html = """
html = b"""
<html>
<body>
Some text.
@ -230,7 +231,7 @@ class PreviewUrlTestCase(unittest.TestCase):
self.assertEqual(og, {"og:title": None, "og:description": "Some text."})
def test_h1_as_title(self):
html = """
html = b"""
<html>
<meta property="og:description" content="Some text."/>
<body>
@ -244,7 +245,7 @@ class PreviewUrlTestCase(unittest.TestCase):
self.assertEqual(og, {"og:title": "Title", "og:description": "Some text."})
def test_missing_title_and_broken_h1(self):
html = """
html = b"""
<html>
<body>
<h1><a href="foo"/></h1>
@ -258,13 +259,20 @@ class PreviewUrlTestCase(unittest.TestCase):
self.assertEqual(og, {"og:title": None, "og:description": "Some text."})
def test_empty(self):
html = ""
"""Test a body with no data in it."""
html = b""
og = decode_and_calc_og(html, "http://example.com/test.html")
self.assertEqual(og, {})
def test_no_tree(self):
"""A valid body with no tree in it."""
html = b"\x00"
og = decode_and_calc_og(html, "http://example.com/test.html")
self.assertEqual(og, {})
def test_invalid_encoding(self):
"""An invalid character encoding should be ignored and treated as UTF-8, if possible."""
html = """
html = b"""
<html>
<head><title>Foo</title></head>
<body>
@ -290,3 +298,76 @@ class PreviewUrlTestCase(unittest.TestCase):
"""
og = decode_and_calc_og(html, "http://example.com/test.html")
self.assertEqual(og, {"og:title": "ÿÿ Foo", "og:description": "Some text."})
class MediaEncodingTestCase(unittest.TestCase):
def test_meta_charset(self):
"""A character encoding is found via the meta tag."""
encoding = get_html_media_encoding(
b"""
<html>
<head><meta charset="ascii">
</head>
</html>
""",
"text/html",
)
self.assertEqual(encoding, "ascii")
# A less well-formed version.
encoding = get_html_media_encoding(
b"""
<html>
<head>< meta charset = ascii>
</head>
</html>
""",
"text/html",
)
self.assertEqual(encoding, "ascii")
def test_xml_encoding(self):
"""A character encoding is found via the meta tag."""
encoding = get_html_media_encoding(
b"""
<?xml version="1.0" encoding="ascii"?>
<html>
</html>
""",
"text/html",
)
self.assertEqual(encoding, "ascii")
def test_meta_xml_encoding(self):
"""Meta tags take precedence over XML encoding."""
encoding = get_html_media_encoding(
b"""
<?xml version="1.0" encoding="ascii"?>
<html>
<head><meta charset="UTF-16">
</head>
</html>
""",
"text/html",
)
self.assertEqual(encoding, "UTF-16")
def test_content_type(self):
"""A character encoding is found via the Content-Type header."""
# Test a few variations of the header.
headers = (
'text/html; charset="ascii";',
"text/html;charset=ascii;",
'text/html; charset="ascii"',
"text/html; charset=ascii",
'text/html; charset="ascii;',
'text/html; charset=ascii";',
)
for header in headers:
encoding = get_html_media_encoding(b"", header)
self.assertEqual(encoding, "ascii")
def test_fallback(self):
"""A character encoding cannot be found in the body or header."""
encoding = get_html_media_encoding(b"", "text/html")
self.assertEqual(encoding, "utf-8")