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package dns
// Holds a bunch of helper functions for dealing with labels.
// SplitDomainName splits a name string into it's labels.
// www.miek.nl. returns []string{"www", "miek", "nl"}
// .www.miek.nl. returns []string{"", "www", "miek", "nl"},
// The root label (.) returns nil. Note that using
// strings.Split(s) will work in most cases, but does not handle
// escaped dots (\.) for instance.
// s must be a syntactically valid domain name, see IsDomainName.
func SplitDomainName(s string) (labels []string) {
if len(s) == 0 {
return nil
}
fqdnEnd := 0 // offset of the final '.' or the length of the name
idx := Split(s)
begin := 0
if IsFqdn(s) {
fqdnEnd = len(s) - 1
} else {
fqdnEnd = len(s)
}
switch len(idx) {
case 0:
return nil
case 1:
// no-op
default:
for _, end := range idx[1:] {
labels = append(labels, s[begin:end-1])
begin = end
}
}
return append(labels, s[begin:fqdnEnd])
}
// CompareDomainName compares the names s1 and s2 and
// returns how many labels they have in common starting from the *right*.
// The comparison stops at the first inequality. The names are downcased
// before the comparison.
//
// www.miek.nl. and miek.nl. have two labels in common: miek and nl
// www.miek.nl. and www.bla.nl. have one label in common: nl
//
// s1 and s2 must be syntactically valid domain names.
func CompareDomainName(s1, s2 string) (n int) {
// the first check: root label
if s1 == "." || s2 == "." {
return 0
}
l1 := Split(s1)
l2 := Split(s2)
j1 := len(l1) - 1 // end
i1 := len(l1) - 2 // start
j2 := len(l2) - 1
i2 := len(l2) - 2
// the second check can be done here: last/only label
// before we fall through into the for-loop below
if equal(s1[l1[j1]:], s2[l2[j2]:]) {
n++
} else {
return
}
for {
if i1 < 0 || i2 < 0 {
break
}
if equal(s1[l1[i1]:l1[j1]], s2[l2[i2]:l2[j2]]) {
n++
} else {
break
}
j1--
i1--
j2--
i2--
}
return
}
// CountLabel counts the the number of labels in the string s.
// s must be a syntactically valid domain name.
func CountLabel(s string) (labels int) {
if s == "." {
return
}
off := 0
end := false
for {
off, end = NextLabel(s, off)
labels++
if end {
return
}
}
}
// Split splits a name s into its label indexes.
// www.miek.nl. returns []int{0, 4, 9}, www.miek.nl also returns []int{0, 4, 9}.
// The root name (.) returns nil. Also see SplitDomainName.
// s must be a syntactically valid domain name.
func Split(s string) []int {
if s == "." {
return nil
}
idx := make([]int, 1, 3)
off := 0
end := false
for {
off, end = NextLabel(s, off)
if end {
return idx
}
idx = append(idx, off)
}
}
// NextLabel returns the index of the start of the next label in the
// string s starting at offset.
// The bool end is true when the end of the string has been reached.
// Also see PrevLabel.
func NextLabel(s string, offset int) (i int, end bool) {
quote := false
for i = offset; i < len(s)-1; i++ {
switch s[i] {
case '\\':
quote = !quote
default:
quote = false
case '.':
if quote {
quote = !quote
continue
}
return i + 1, false
}
}
return i + 1, true
}
// PrevLabel returns the index of the label when starting from the right and
// jumping n labels to the left.
// The bool start is true when the start of the string has been overshot.
// Also see NextLabel.
func PrevLabel(s string, n int) (i int, start bool) {
if n == 0 {
return len(s), false
}
lab := Split(s)
if lab == nil {
return 0, true
}
if n > len(lab) {
return 0, true
}
return lab[len(lab)-n], false
}
// equal compares a and b while ignoring case. It returns true when equal otherwise false.
func equal(a, b string) bool {
// might be lifted into API function.
la := len(a)
lb := len(b)
if la != lb {
return false
}
for i := la - 1; i >= 0; i-- {
ai := a[i]
bi := b[i]
if ai >= 'A' && ai <= 'Z' {
ai |= 'a' - 'A'
}
if bi >= 'A' && bi <= 'Z' {
bi |= 'a' - 'A'
}
if ai != bi {
return false
}
}
return true
}
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