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Add a *limit* argument to nameprep to allow ToASCII and ToUnicode to reject extremely large input early. This replaces the check in python#99092, while allowing any number of harmless "characters mapped to nothing" (RFC 3454 §3.1). The default stays unlimited, to not change behaviour for users that call nameprep manually (and don't necessarily follow up with punycode).
Documentation build overview
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sethmlarson
reviewed
Sep 17, 2026
| raise UnicodeEncodeError("idna", label, 0, len(label), "label too long") | ||
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| def ToUnicode(label): | ||
| if len(label) > 1024: |
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This breaks protection for decoding:
Line 263 in 8759666
By the time we reach nameprep we have already gone through punycode.
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Of course I missed something obvious. Thanks; I'll fix tomorrow.
encukou
marked this pull request as draft
September 17, 2026 16:37
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Add a limit argument to nameprep to allow ToASCII and ToUnicode to reject extremely large input early.
This replaces the check in #99092, while allowing any number of harmless "characters mapped to nothing" (RFC 3454 §3.1).
The default stays unlimited, to not change behaviour for users that call nameprep manually (and don't necessarily follow up with punycode).