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