Use http-equiv meta tag charset info when processing HTML documents
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Key: TIKA-332
URL: https://issues.apache.org/jira/browse/TIKA-332
Project: Tika
Issue Type: Improvement
Affects Versions: 0.5
Reporter: Ken Krugler
Priority: Critical
Currently Tika doesn't use the charset info that's optionally present in HTML
documents, via the <meta http-equiv="Content-type" content="text/html;
charset=xxx"> tag.
If the mime-type is detected as being one that's handled by the HtmlParser,
then the first 4-8K of text should be converted from bytes to us-ascii, and
then scanned using a regex something like:
private static final Pattern HTTP_EQUIV_CHARSET_PATTERN =
Pattern.compile("<meta\\s+http-equiv\\s*=\\s*['\"]\\s*Content-Type['\"]\\s+content\\s*=\\s*['\"][^;]+;\\s*charset\\s*=\\s*([^'\"]+)\"");
If a charset is detected, this should take precedence over a charset in the
HTTP response headers, and (obviously) used to convert the bytes to text before
the actual parsing of the document begins.
In a test I did of 100 random HTML pages, roughly 15% contained charset info in
the meta tag that wound up being different from the detected or HTTP response
header charset, so this is a pretty important improvement to make. Without it,
Tika isn't that useful for processing HTML pages.
I believe one of the reasons why ICU4J doesn't do a good job in detecting the
charset for HTML pages is that the first 2K+ of HTML text is often all us-ascii
markup, versus real content. I'll file a separate issue about how to improve
charset detection for HTML pages.
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