Improve time complexity of tokenization regex used in diffSentences #580
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ExplodingCabbage
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fix-bad-time-complexity-of-diffSentences-regex
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The performance bug here was essentially the same as what I describe at https://markamery.com/blog/quadratic-time-regexes/; essentially, doing a regex search using a regex that starts with a pattern repeated with
+or*is by default a quadratic time operation, unless you put a lookbehind before it, which we weren't doing.While adding tests to check I wasn't breaking anything with this fix, I realised some existing behaviour was perverse, so settled on a fix that changed some of the perverse behaviour while also fixing the "ReDOS" issue (Snyk reported it via email as such).
(As with many "ReDOS" "vulns", I have conflicting & complicated thoughts on whether it's reasonable to consider this a security vulnerability in the first place, as Snyk do. That question of labeling doesn't change that it's bad and should be fixed, though.)