msg.Service: add HostType() method (#627)

This method parses the Host field in the service. It returns 1 or 3
things 1) it is a host 2) an IPv4 address or an 3) IPv6 address.
This simplifies some code a bit and allows for 1 way of parsing the Host
field.

This *only* parse the Host field, Mail and/or Text values should be
checked separately.

We reuse the dns.TypeXXX values for this as to not invent anything new.

middleware/etcd/msg/type.go

@@ -0,0 +1,33 @@
+package msg
+
+import (
+	"net"
+
+	"github.com/miekg/dns"
+)
+
+// HostType returns the DNS type of what is encoded in the Service Host field. We're reusing
+// dns.TypeXXX to not reinvent a new set of identifiers.
+//
+// dns.TypeA: the service's Host field contains an A record.
+// dns.TypeAAAA: the service's Host field contains an AAAA record.
+// dns.TypeANY: the service's Host field contains a name.
+//
+// Note that a service can double/triple as a TXT record or MX record.
+func (s *Service) HostType() (what uint16, normalized net.IP) {
+
+	ip := net.ParseIP(s.Host)
+
+	switch {
+	case ip == nil:
+		return dns.TypeANY, nil
+
+	case ip.To4() != nil:
+		return dns.TypeA, ip.To4()
+
+	case ip.To4() == nil:
+		return dns.TypeAAAA, ip.To16()
+	}
+	// This should never be reached.
+	return dns.TypeNone, nil
+}

middleware/etcd/msg/type_test.go

@@ -0,0 +1,31 @@
+package msg
+
+import (
+	"testing"
+
+	"github.com/miekg/dns"
+)
+
+func TestType(t *testing.T) {
+	tests := []struct {
+		serv         Service
+		expectedType uint16
+	}{
+		{Service{Host: "example.org"}, dns.TypeANY},
+		{Service{Host: "127.0.0.1"}, dns.TypeA},
+		{Service{Host: "2000::3"}, dns.TypeAAAA},
+		{Service{Host: "2000..3"}, dns.TypeANY},
+		{Service{Host: "127.0.0.257"}, dns.TypeANY},
+		{Service{Host: "127.0.0.252", Mail: true}, dns.TypeA},
+		{Service{Host: "127.0.0.252", Mail: true, Text: "a"}, dns.TypeA},
+		{Service{Host: "127.0.0.254", Mail: false, Text: "a"}, dns.TypeA},
+	}
+
+	for i, tc := range tests {
+		what, _ := tc.serv.HostType()
+		if what != tc.expectedType {
+			t.Errorf("Test %d: Expected what %v, but got %v", i, tc.expectedType, what)
+		}
+	}
+
+}