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fix: detect HTML charset from <meta> tag to fix garbled output on CJK-locale systems #2104

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fix: detect HTML charset from <meta> tag to fix garbled output on CJK-locale systems #2104

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60 changes: 59 additions & 1 deletion packages/markitdown/src/markitdown/converters/_html_converter.py
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
import io
import re
import warnings
from typing import Any, BinaryIO, Optional
from bs4 import BeautifulSoup
Expand Down Expand Up @@ -39,6 +40,50 @@ def accepts(

return False

def _detect_html_encoding(self, file_stream: BinaryIO) -> Optional[str]:
"""Peek at the HTML content to find charset declaration (<meta charset>).

Follows the HTML5 encoding sniffing algorithm: the <meta charset> tag
(or Content-Type http-equiv) is the authoritative source, taking
precedence over heuristic detection that is unreliable for non-Latin
scripts on some platforms.
"""
cur_pos = file_stream.tell()
try:
# Read first 4 KB — enough to cover <head> and <meta> in any
# reasonable HTML document (HTML5 spec uses 1024 bytes minimum).
raw = file_stream.read(4096)
# Decode as ASCII-superset (Latin-1) so we can scan for meta tags
# without committing to the real encoding yet.
try:
head = raw.decode("ascii")
except UnicodeDecodeError:
head = raw.decode("latin-1")

# Pattern 1: <meta charset="utf-8"> (HTML5)
m = re.search(
r'<meta\b[^>]*\bcharset\s*=\s*["\']?\s*([\w\-\d]+)\s*["\']?',
head,
re.IGNORECASE,
)
if m:
return m.group(1)

# Pattern 2: <meta http-equiv="Content-Type"
# content="text/html; charset=utf-8">
m = re.search(
r'<meta\b[^>]*\bhttp-equiv\s*=\s*["\']?Content-Type["\']?[^>]*\b'
r'content\s*=\s*["\'][^"\']*\bcharset\s*=\s*([\w\-\d]+)',
head,
re.IGNORECASE,
)
if m:
return m.group(1)

return None
finally:
file_stream.seek(cur_pos)

def convert(
self,
file_stream: BinaryIO,
Expand All @@ -49,8 +94,21 @@ def convert(
# strict=True raises RecursionError instead of falling back to plain text.
strict: bool = kwargs.pop("strict", False)

# Determine encoding — prefer the HTML <meta charset> declaration,
# then the stream_info hint, then UTF-8:
# - <meta charset> is the HTML5-authoritative source.
# - stream_info.charset comes from charset_normalizer which can
# mis-detect non-Latin UTF-8 files (e.g. Chinese) on CJK-locale
# Windows systems.
meta_encoding = self._detect_html_encoding(file_stream)
if meta_encoding:
encoding = meta_encoding
elif stream_info.charset is not None:
encoding = stream_info.charset
else:
encoding = "utf-8"

# Parse the stream
encoding = "utf-8" if stream_info.charset is None else stream_info.charset
soup = BeautifulSoup(file_stream, "html.parser", from_encoding=encoding)

# Remove javascript and style blocks
Expand Down