CVE-2021-3803: fix(parse): Replace regex with hand-rolled parser (#9) · fb55/nth-check@9894c1d

@@ -1,7 +1,9 @@

// Following http://www.w3.org/TR/css3-selectors/#nth-child-pseudo

// [ ['-‘|’+’]? INTEGER? {N} [ S* ['-‘|’+’] S* INTEGER ]?

const RE_NTH_ELEMENT = /^([±]?\d*n)?\s*(?:([±]?)\s*(\d+))?$/;

// Whitespace as per https://www.w3.org/TR/selectors-3/#lex is " \t\r\n\f"

const whitespace = new Set([9, 10, 12, 13, 32]);

const ZERO = "0".charCodeAt(0);

const NINE = "9".charCodeAt(0);

/**

* Parses an expression.

@@ -19,24 +21,72 @@ export function parse(formula: string): [a: number, b: number] {

return [2, 1];

}

const parsed = formula.match(RE_NTH_ELEMENT);

// Parse [ ['-‘|’+’]? INTEGER? {N} [ S* ['-‘|’+’] S* INTEGER ]?

if (!parsed) {

let idx = 0;

let a = 0;

let sign = readSign();

let number = readNumber();

if (idx < formula.length && formula.charAt(idx) === “n”) {

idx++;

a = sign * (number ?? 1);

skipWhitespace();

if (idx < formula.length) {

sign = readSign();

skipWhitespace();

number = readNumber();

} else {

sign = number = 0;

}

}

// Throw if there is anything else

if (number === null || idx < formula.length) {

throw new Error(`n-th rule couldn’t be parsed (‘${formula}’)`);

}

let a;

return [a, sign * number];

if (parsed[1]) {

a = parseInt(parsed[1], 10);

if (isNaN(a)) {

a = parsed[1].startsWith("-") ? -1 : 1;

function readSign() {

if (formula.charAt(idx) === "-") {

idx++;

return -1;

}

} else a = 0;

const b =

(parsed[2] === "-" ? -1 : 1) *

(parsed[3] ? parseInt(parsed[3], 10) : 0);

if (formula.charAt(idx) === “+”) {

idx++;

}

return [a, b];

return 1;

}

function readNumber() {

const start = idx;

let value = 0;

while (

idx < formula.length &&

formula.charCodeAt(idx) >= ZERO &&

formula.charCodeAt(idx) <= NINE

) {

value = value * 10 + (formula.charCodeAt(idx) - ZERO);

idx++;

}

// Return `null` if we didn’t read anything.

return idx === start ? null : value;

}

function skipWhitespace() {

while (

idx < formula.length &&

whitespace.has(formula.charCodeAt(idx))

) {

idx++;

}

}

}