fix: reject hostnames with trailing hyphen in RFC 952 validator - #1569
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zemzale merged 1 commit intoApr 29, 2026
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The previous RFC 952 hostname regex allowed labels ending with a hyphen (e.g. "foo-.example.com"), which violates RFC 952. Replace it with a per-label pattern matching the RFC 1123 structure but requiring a leading letter, so each label must start and end with an alphanumeric character. Signed-off-by: Ahmed Kamal <[email protected]>
nodivbyzero
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fqdnRegexStringRFC1123 matched each label with
[a-zA-Z0-9]{1}[a-zA-Z0-9-]{0,62}, which allows a label to end in a
hyphen (e.g. "foo-.example.com" or "example.com-"). The hostname
validators were fixed for the same issue in go-playground#1565 (RFC 1123) and go-playground#1569
(RFC 952), but the fqdn pattern, whose comment says it should match
hostnameRegexStringRFC1123, was left behind.
Use the same label shape [a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])? so
a label must start and end with an alphanumeric. The non-numeric TLD,
the optional trailing dot, and hyphens inside the last label (go-playground#1548) are
preserved.
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Fixes Or Enhances
Similar to the recent fix #1565 6bcb7bc RFC 952 is now fixed to reject hostname labels with trailing hyphen
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