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"} // The root label (.) returns nil. Note that using // strings.Split(s) will work in most cases, but does not handle // escaped dots (\.) for instance. 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 s[len(s)-1] == '.' { fqdnEnd = len(s) - 1 } else { fqdnEnd = len(s) } switch len(idx) { case 0: return nil case 1: // no-op default: end := 0 for i := 1; i < len(idx); i++ { end = idx[i] labels = append(labels, s[begin:end-1]) begin = end } } labels = append(labels, s[begin:fqdnEnd]) return labels } // 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 not 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 func CompareDomainName(s1, s2 string) (n int) { s1 = Fqdn(s1) s2 = Fqdn(s2) l1 := Split(s1) l2 := Split(s2) // the first check: root label if l1 == nil || l2 == nil { return } 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 s1[l1[j1]:] == s2[l2[j2]:] { n++ } else { return } for { if i1 < 0 || i2 < 0 { break } if 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. func CountLabel(s string) (labels int) { if s == "." { return } off := 0 end := false for { off, end = NextLabel(s, off) labels++ if end { return } } panic("dns: not reached") } // 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 dns.SplitDomainName. 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) } panic("dns: not reached") } // 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. 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. 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 }