Add it

msg.go

@@ -171,9 +171,9 @@ var Rcode_str = map[int]string{
 // use it. Thus, if in the future we need to define new message
 // structs, no new pack/unpack/printing code needs to be written.
 
-// Pack a domain name s into msg[off:].
+// PackDomainName packs a domain name s into msg[off:].
 // Domain names are a sequence of counted strings
-// split at the dots.  They end with a zero-length string.
+// split at the dots. They end with a zero-length string.
 func PackDomainName(s string, msg []byte, off int) (off1 int, ok bool) {
 	// Add trailing dot to canonicalize name.
 	lenmsg := len(msg)

rr.go

@@ -0,0 +1,89 @@
+package dns
+
+import (
+	"strings"
+)
+
+// Helper functions
+
+// Only return those RR with the type t
+func SieveRR(rr []RR, t uint16) (l []RR) {
+	for _, r := range rr {
+		if r.Header().Rrtype == t {
+			l = append(l, r)
+		}
+	}
+	return
+}
+
+// DnameLength returns the length of a packed dname.
+func DomainNameLength(s string) int { // TODO better name
+	// Special case for '.'
+	if s == "." {
+		return 1
+	}
+
+	// Add trailing dot to canonicalize name.
+	if n := len(s); n == 0 || s[n-1] != '.' {
+		return n + 1
+	} else {
+		return n + 1
+	}
+	panic("not reached")
+	return 0
+}
+
+// Return a slice with the full name, one label shorter,
+// shorter, until we, hit the root
+// Each name is fully qualified.
+// The root labels is added as last
+func LabelSlice(s string) []string {
+	if s[len(s)-1] != '.' {
+		s += "."
+	}
+	ss := strings.Split(s, ".")
+	labels := make([]string, 0)
+	for i := 0; i < len(ss)-1; i++ {
+		labels = append(labels, strings.Join(ss[i:], "."))
+	}
+	labels = append(labels, ".")
+	return labels
+}
+
+// LabelSliceReverse reverse a label slice
+func LabelSliceReverse(l []string) []string {
+	for i, j := 0, len(l)-1; i < j; i, j = i+1, j-1 {
+		l[i], l[j] = l[j], l[i]
+	}
+	return l
+}
+
+// Labels returns i labels from the left side of the name. 
+// The counting start with 0. The returned names are fully
+// qualified.
+// So for "a.miek.nl." it returns [ a.miek.nl. miek.nl. nl. . ]
+func Labels(s string, i int) string {
+	ss := strings.Split(s, ".")
+	return strings.Join(ss[:i+1], ".")
+	// TODO fully qualified
+}
+
+// Labels returns the number of labels in a domain name.
+func LabelCount(a string) (c uint8) {
+	// walk the string and count the dots
+	// except when it is escaped
+	esc := false
+	for _, v := range a {
+		switch v {
+		case '.':
+			if esc {
+				esc = !esc
+				continue
+			}
+			c++
+		case '\\':
+			esc = true
+		}
+	}
+	return
+}