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gh-98433: Fix quadratic time idna decoding. #99092
gh-98433: Fix quadratic time idna decoding. #99092
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I'm okay with leaving this length limit out either entirely - or just out of the backports if release managers are uncomfortable with this in a bugfix.
I view it as protection from other as yet unknown future idna or punycode decoder logic bugs to avoid wasting cpu time. The only reference numbers related to my arbitrary input length limit choice are: A DNS hostname is 255 bytes at most. A label within a DNS name is 63 bytes at most.
The "Nothing" characters in question that are removed in
nameprep()
in https://github.com/python/cpython/blob/main/Lib/encodings/idna.py#L18 are non-ascii unicode oddities.Other IDNA decoding libraries in the wild like the well known ICU library do not limit the length at this level of API, instead leaving that to higher levels in the application: