Efficient Matching with Memoization for Regexes with Look-around and Atomic Grouping (Extended Version)

Hiroya Fujinami; Ichiro Hasuo

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arXiv · 2401.12639

Efficient Matching with Memoization for Regexes with Look-around and Atomic Grouping (Extended Version)

Hiroya Fujinami·Ichiro Hasuo

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Abstract

Regular expression (regex) matching is fundamental in many applications, especially in web services. However, matching by backtracking -- preferred by most real-world implementations for its practical performance and backward compatibility -- can suffer from so-called catastrophic backtracking, which makes the number of backtracking super-linear and leads to the well-known ReDoS vulnerability. Inspired by a recent algorithm by Davis et al. that runs in linear time for (non-extended) regexes, we study efficient backtracking matching for regexes with two common extensions, namely look-around and atomic grouping. We present linear-time backtracking matching algorithms for these extended regexes. Their efficiency relies on memoization, much like the one by Davis et al.; we also strive for smaller memoization tables by carefully trimming their range. Our experiments -- we used some real-world regexes with the aforementioned extensions -- confirm the performance advantage of our algorithms.

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Hiroya Fujinami, Ichiro Hasuo. 2024-01-23. Efficient Matching with Memoization for Regexes with Look-around and Atomic Grouping (Extended Version). https://arxiv.org/abs/2401.12639

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