Show HN: Regolith – Regex library that prevents ReDoS CVEs in TypeScript (github.com)

It's very, very weird to speak of TypeScript and JavaScript as two separate languages here.

There is no TypeScript RegExp, there is only the JavaScript RegExp as implemented in various VMs. There is no TypeScript VM, only JavaScript VMs. And there are no TypeScript CVEs unless it's against the TypeScript compiler, language server, etc.

It's great to have a safe options - and it would have been great if the default had been safe.

I think many people are annoyed with ReDos as a bug class. It seems like mostly noise in the CVE trackers, library churn and badge collecting for "researchers". It'd be less of a problem if people stuck to filing CVEs against libraries that might remotely see untrusted input rather than scrambling to collect pointless "scalps" from every tool under the sun that accepts a configuration regex - build tools, very commonly :(

Perhaps you can stop this madness... :)

  > Regolith attempts to be a drop-in replacement for RegExp and requires minimal (to no) changes to be used instead

vs

  > Since Regolith uses Rust bindings to implement the Rust Regex library to achieve linear time worst case, this means that backreferences and look-around aren't available in Regolith either.

Obviously it cannot be a drop-in replacement if the regex dialect differs. That it has a compatible API is not the only relevant factor. I’d recommend removing the top part from the readme.

Another thought: since backreferences and lookaround are the features in JS regexes which _cause_ ReDOS, why not just wrap vanilla JS regex, rejecting patterns including them? Wouldn’t that achieve the same result in a simpler way?

Perhaps regex is just a bad little language for pattern matching.

I have a foggy recollection of compute times exploding for me on a large regex in .Net code and I used a feature I hadn't seen in JavaScript's RegExp that allowed me to mark off sections of already matched parts of the regular expression that prevented it from backtracking.

Perhaps the answer isn't removing features for linear regex, but adding more features to make it more expressive and tunable?

FWIW there's also https://github.com/slevithan/regex "JS regexes future. A template tag for readable, high-performance, native JS regexes with extended syntax, context-aware interpolation, and always-on best practices". From the docs:

Highlights include support for insignificant whitespace and comments, atomic groups and possessive quantifiers (that can help you avoid ReDoS), subroutines and subroutine definition groups (that enable powerful subpattern composition), and context-aware interpolation of regexes, escaped strings, and partial patterns.

I have another nitpick and I hope it's a constructive one.

You provide some performance figures; unfortunately they are caught in an image, no doubt to enable color-coding the results. IMHO that's not ideal, tables should be pure text, even if only for accessibility with screen readers. There are other means to provide guiding highlights, like red and green Unicode code points. GitHub is somewhat unique in its strict policy to remove almost any kind of user-side styling from the READMEs, but providing a "photo snapshot" of parts of the README just to get some colors does not feel like the right solution.

Next thing are the actual figures you provide: those range from 11.822µs (best) to 56.534s (worst). They are displayed as

    11.822µs
    56.534s 

making them look almost like the worst performer took around five times as long as the best performer—until you realize there's a mu in there.

I must say that personally I remove this so-called "human-readable" format almost wherever I can because I find it not human-readable at all. To me a good numerical display should try and keep the decimal points on top of each other, avoid too many non-significant digits, use digit grouping, and, crucially, use a single unit throughout. With those constraints, the two figures become

            11.8µs
    56,534,000.0µs

which incidentally obviates much of the need to color code anything. One could discuss what unit—ns, µs, ms, s—is the most appropriate in the given context but, generally, I feel that big numbers should stand out as having many digits.

Nobody will pick this up because it's much too elaborate and idiosyncratic for this conformist world, but I just love the 'Japanese' way of formatting where you do digit grouping with the SI prefixes, so one hundred and twenty-five meters is 125m, but one thousand one hundred and twenty-five meters doesn't become 1,125m, nor is it 1.125km, but rather 1k125m (preferrably with a thin space as in 1k_125m—imagine a thin non-breakable space there that HN wouldn't let me render).

1G 255M 368k 799B, what's not to like?

Magic-RegExp aims to create a compiled away, type-safe, readable RegEx alternative that makes the process a lot easier. https://blog.logrocket.com/understanding-magic-regexp-regexp...

example from blog:

import { createRegExp, exactly, wordChar, oneOrMore, anyOf, } from "magic-regexp";

const regExp = createRegExp(

  exactly("http")

    .and(exactly("s").optionally())

    .and("://")

    .optionally()

    .and(exactly("www.").optionally())

    .and(oneOrMore(wordChar))

    .and(exactly("."))

    .and(anyOf("com", "org", "io")),

  ["g", "m", "i"]

);

console.log(regExp);

/(https?:\/\/)?(www\.)?\w+\.(com|org|io)/gmi

FWIW JS has a library-layer non-backtracking regex implementation in @bablr/regex. It's still a slightly different dialect of regex than native JS regex which (currently) lacks lookahead and lookbehind support. It's not going to have Rust-y perf, but it shouldn't get ReDoS'd either.