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refactor(compiler): improve regular expression for stripping comments (#43456)

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Previously, the regular expression used by the compiler's ShadowDOM CSS
shim to strip comments from CSS text was susceptible to [catastrophic
backtracking][1], which could lead to exponential (O(2^n)) increase in
complexity/execution time. More specifically, this would be triggered if
the processed text contained an unterminated comment with lots of
leading whitespace (i.e. `/*`, followed by lots of whitespace characters
and no closing `*/`).

Although such input is unlikely in real-world scenarios, this commit
improves the regular expression to not be susceptible to this issue.

[1]: https://www.regular-expressions.info/catastrophic.html

PR Close #43456
This commit is contained in:
George Kalpakas
2021-09-15 11:39:33 +03:00
committed by Jessica Janiuk
parent 7efa47075c
commit 2292a9cbd9
1 changed files with 1 additions and 1 deletions
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packages/compiler/src/shadow_css.ts
+1 -1
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@@ -629,7 +629,7 @@ const _polyfillHostRe = /-shadowcsshost/gim;
const _colonHostRe = /:host/gim;
const _colonHostContextRe = /:host-context/gim;
const _commentRe = /\/\*\s*[\s\S]*?\*\//g;
const _commentRe = /\/\*[\s\S]*?\*\//g;
function stripComments(input: string): string {
return input.replace(_commentRe, '');