Adrien Grand created LUCENE-8779:
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Summary: MinHashFilter generates invalid terms
Key: LUCENE-8779
URL: https://issues.apache.org/jira/browse/LUCENE-8779
Project: Lucene - Core
Issue Type: Improvement
Reporter: Adrien Grand
This problem was reported at
https://github.com/elastic/elasticsearch/issues/41556: MinHashFilter computes a
hash and then folds its bits into the chars of the term. However this might
generate invalid terms that eg. end with a character that is a high surrogate.
This doesn't trigger exceptions at index time because we are lenient with
unmatched surrogates when converting to a binary term.
{code}
} else {
// surrogate pair
// confirm valid high surrogate
if (code < 0xDC00 && (i < end-1)) {
int utf32 = (int) s.charAt(i+1);
// confirm valid low surrogate and write pair
if (utf32 >= 0xDC00 && utf32 <= 0xDFFF) {
utf32 = (code << 10) + utf32 + SURROGATE_OFFSET;
i++;
out[upto++] = (byte)(0xF0 | (utf32 >> 18));
out[upto++] = (byte)(0x80 | ((utf32 >> 12) & 0x3F));
out[upto++] = (byte)(0x80 | ((utf32 >> 6) & 0x3F));
out[upto++] = (byte)(0x80 | (utf32 & 0x3F));
continue;
}
}
// replace unpaired surrogate or out-of-order low surrogate
// with substitution character
out[upto++] = (byte) 0xEF;
out[upto++] = (byte) 0xBF;
out[upto++] = (byte) 0xBD;
}
{code}
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