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fix(fqdn): reject domain labels with a trailing hyphen #1592

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fix(fqdn): reject domain labels with a trailing hyphen #1592

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b9dd58f
fix(fqdn): reject domain labels with a trailing hyphen
mahirhir Jun 28, 2026
47c584f
test(fqdn): cover the 63-character max label length
mahirhir Jul 11, 2026
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12 changes: 6 additions & 6 deletions regexes.go
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Original file line number Diff line number Diff line change
Expand Up @@ -56,12 +56,12 @@ const (
latitudeRegexString = "^[-+]?([1-8]?\\d(\\.\\d+)?|90(\\.0+)?)$"
longitudeRegexString = "^[-+]?(180(\\.0+)?|((1[0-7]\\d)|([1-9]?\\d))(\\.\\d+)?)$"
sSNRegexString = `^[0-9]{3}[ -]?(0[1-9]|[1-9][0-9])[ -]?([1-9][0-9]{3}|[0-9][1-9][0-9]{2}|[0-9]{2}[1-9][0-9]|[0-9]{3}[1-9])$`
hostnameRegexStringRFC952 = `^[a-zA-Z]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(\.[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$` // https://tools.ietf.org/html/rfc952
hostnameRegexStringRFC1123 = `^[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(\.[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$` // accepts hostname starting with a digit https://tools.ietf.org/html/rfc1123
fqdnRegexStringRFC1123 = `^([a-zA-Z0-9]{1}[a-zA-Z0-9-]{0,62})(\.[a-zA-Z0-9]{1}[a-zA-Z0-9-]{0,62})*?(\.[a-zA-Z]{1}[a-zA-Z0-9-]{0,62})\.?$` // same as hostnameRegexStringRFC1123 but must contain a non numerical TLD (possibly ending with '.')
btcAddressRegexString = `^[13][a-km-zA-HJ-NP-Z1-9]{25,34}$` // bitcoin address
btcAddressUpperRegexStringBech32 = `^BC1[02-9AC-HJ-NP-Z]{7,76}$` // bitcoin bech32 address https://en.bitcoin.it/wiki/Bech32
btcAddressLowerRegexStringBech32 = `^bc1[02-9ac-hj-np-z]{7,76}$` // bitcoin bech32 address https://en.bitcoin.it/wiki/Bech32
hostnameRegexStringRFC952 = `^[a-zA-Z]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(\.[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$` // https://tools.ietf.org/html/rfc952
hostnameRegexStringRFC1123 = `^[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(\.[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$` // accepts hostname starting with a digit https://tools.ietf.org/html/rfc1123
fqdnRegexStringRFC1123 = `^([a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)(\.[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*?(\.[a-zA-Z]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)\.?$` // same as hostnameRegexStringRFC1123 but must contain a non numerical TLD (possibly ending with '.')
btcAddressRegexString = `^[13][a-km-zA-HJ-NP-Z1-9]{25,34}$` // bitcoin address
btcAddressUpperRegexStringBech32 = `^BC1[02-9AC-HJ-NP-Z]{7,76}$` // bitcoin bech32 address https://en.bitcoin.it/wiki/Bech32
btcAddressLowerRegexStringBech32 = `^bc1[02-9ac-hj-np-z]{7,76}$` // bitcoin bech32 address https://en.bitcoin.it/wiki/Bech32
ethAddressRegexString = `^0x[0-9a-fA-F]{40}$`
ethAddressUpperRegexString = `^0x[0-9A-F]{40}$`
ethAddressLowerRegexString = `^0x[0-9a-f]{40}$`
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6 changes: 6 additions & 0 deletions validator_test.go
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Expand Up @@ -11108,6 +11108,12 @@ func TestFQDNValidation(t *testing.T) {
{"24.example24.com", true},
{"test.24.example.com", true},
{"test-site-http.test-site", true},
{"foo-.example.com", false},

@georgepsarakis georgepsarakis Jul 5, 2026

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Perhaps some test cases confirming label length (63 characters) would be helpful as an addition to the test suite? I believe the regex seems correct, but it may be beneficial for future contributors, what do you think?

{"foo.bar-.com", false},
{"example.com-", false},
{strings.Repeat("a", 63) + ".com", true},
{strings.Repeat("a", 64) + ".com", false},
{"-foo.example.com", false},
{"test24.example24.com..", false},
{"example", false},
{"192.168.0.1", false},
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