Fix handling of non fully qualified domain names

When PackDomain sees such a name it calls panic.
All panic now use the prefix 'dns:'

dns_test.go

@@ -111,8 +111,24 @@ func TestPack(t *testing.T) {
 			t.Fail()
 		}
 	}
-	ns := NewRR("pool.ntp.org.   390 IN  NS  a.ntpns.org")
-	t.Log("ns", ns.String())
+	x := new(Msg)
+	ns, _ := NewRR("pool.ntp.org.   390 IN  NS  a.ntpns.org")
+	ns.(*RR_NS).Ns = "a.ntpns.org."
+	x.Ns = append(m.Ns, ns)
+	x.Ns = append(m.Ns, ns)
+	x.Ns = append(m.Ns, ns)
+	// This crashes due to the fact the a.ntpns.org isn't a FQDN
+	// How to recover() from a remove panic()?
+	if _, ok := x.Pack(); !ok {
+		t.Log("Packing failed")
+		t.Fail()
+	}
+	x.Answer = make([]RR, 1)
+	x.Answer[0], err = NewRR(rr[0])
+	if _, ok := x.Pack(); !ok {
+		t.Log("Packing failed")
+		t.Fail()
+	}
 }
 
 func TestCompressLenght(t *testing.T) {

msg.go

@@ -205,8 +205,7 @@ func PackDomainName(s string, msg []byte, off int, compression map[string]int, c
 	// Add trailing dot to canonicalize name.
 	lenmsg := len(msg)
 	if n := len(s); n == 0 || s[n-1] != '.' {
-		// Make it fully qualified
-		s += "."
+		panic("dns: name not fully qualified")
 	}
 	// Each dot ends a segment of the name.
 	// We trade each dot byte for a length byte.
@@ -235,13 +234,23 @@ func PackDomainName(s string, msg []byte, off int, compression map[string]int, c
 			if i-begin >= 1<<6 { // top two bits of length must be clear
 				return lenmsg, false
 			}
+			// off can already (we're in a loop) be bigger than len(msg)
+			// this happens when a name isn't fully qualified
+			if off+1 > len(msg)  {
+				return lenmsg, false
+			}
 			msg[off] = byte(i - begin)
 			offset := off
 			off++
+			// TODO(mg): because of the new check above, this can go. But
+			// just leave it as is for the moment.
 			if off > lenmsg {
 				return lenmsg, false
 			}
 			for j := begin; j < i; j++ {
+				if off+1 > len(msg) {
+					return lenmsg, false
+				}
 				msg[off] = bs[j]
 				off++
 				if off > lenmsg {
@@ -1210,7 +1219,7 @@ func (dns *Msg) Pack() (msg []byte, ok bool) {
 	dh.Arcount = uint16(len(extra))
 
 	// TODO(mg): still a little too much, but better than 64K...
-	msg = make([]byte, dns.Len()+1)
+	msg = make([]byte, dns.Len()+10)
 
 	// Pack it in: header and then the pieces.
 	off := 0
@@ -1328,7 +1337,8 @@ func (dns *Msg) String() string {
 
 // Len return the message length when in (un)compressed wire format.
 // If dns.Compress is true compression is taken into account, currently
-// this only counts owner name compression.
+// this only counts owner name compression. There is no check for 
+// nil valued sections (allocated, but contains no RRs).
 func (dns *Msg) Len() int {
 	// Message header is always 12 bytes       
 	l := 12

server.go

@@ -256,7 +256,7 @@ forever:
 		}
 		go d.serve()
 	}
-	panic("not reached")
+	panic("dns: not reached")
 }
 
 // ServeUDP starts a UDP listener for the server.
@@ -290,7 +290,7 @@ func (srv *Server) ServeUDP(l *net.UDPConn) error {
 		}
 		go d.serve()
 	}
-	panic("not reached")
+	panic("dns: not reached")
 }
 
 func newConn(t *net.TCPConn, u *net.UDPConn, a net.Addr, buf []byte, handler Handler, tsig map[string]string) (*conn, error) {

tsig.go

@@ -155,7 +155,7 @@ type timerWireFmt struct {
 // If something goes wrong an error is returned, otherwise it is nil. 
 func TsigGenerate(m *Msg, secret, requestMAC string, timersOnly bool) ([]byte, string, error) {
 	if m.IsTsig() == nil {
-		panic("TSIG not last RR in additional")
+		panic("dns: TSIG not last RR in additional")
 	}
 	// If we barf here, the caller is to blame
 	rawsecret, err := packBase64([]byte(secret))

types.go

@@ -883,7 +883,7 @@ func (rr *RR_NSEC) String() string {
 
 func (rr *RR_NSEC) Len() int {
 	l := len(rr.NextDomain) + 1
-	return rr.Hdr.Len() + l + 32
+	return rr.Hdr.Len() + l + 32 + 1
 	// TODO: +32 is max type bitmap
 }
 
@@ -1420,7 +1420,7 @@ func cmToString(mantissa, exponent uint8) string {
 		}
 		return s
 	}
-	panic("not reached")
+	panic("dns: not reached")
 }
 
 // Map of constructors for each RR wire type.

update.go

@@ -57,7 +57,7 @@ func (u *Msg) NameNotUsed(rr []RR) {
 // "RRset exists (value dependent -- with rdata)" RRs. RFC 2136 section 2.4.2.
 func (u *Msg) RRsetUsedRdata(rr []RR) {
 	if len(u.Question) == 0 {
-		panic("empty question section")
+		panic("dns: empty question section")
 	}
 	u.Answer = make([]RR, len(rr))
 	for i, r := range rr {
@@ -104,7 +104,7 @@ func (u *Msg) RRsetNotUsed(rr []RR) {
 // RRsetAddRdata creates a dynamic update packet that adds an complete RRset, see RFC 2136 section 2.5.1
 func (u *Msg) RRsetAddRdata(rr []RR) {
 	if len(u.Question) == 0 {
-		panic("empty question section")
+		panic("dns: empty question section")
 	}
 	u.Ns = make([]RR, len(rr))
 	for i, r := range rr {

xfr.go

@@ -50,7 +50,7 @@ func (c *Client) XfrReceive(q *Msg, a string) (chan *XfrMsg, error) {
 	default:
 		return nil, ErrXfrType
 	}
-	panic("not reached")
+	panic("dns: not reached")
 }
 
 func (w *reply) axfrReceive(c chan *XfrMsg) {
@@ -84,7 +84,7 @@ func (w *reply) axfrReceive(c chan *XfrMsg) {
 			c <- &XfrMsg{Request: w.req, Reply: in, Rtt: w.rtt, RemoteAddr: w.conn.RemoteAddr(), Error: nil}
 		}
 	}
-	panic("not reached")
+	panic("dns: not reached")
 }
 
 func (w *reply) ixfrReceive(c chan *XfrMsg) {
@@ -132,7 +132,7 @@ func (w *reply) ixfrReceive(c chan *XfrMsg) {
 			c <- &XfrMsg{Request: w.req, Reply: in, Rtt: w.rtt, RemoteAddr: w.conn.RemoteAddr()}
 		}
 	}
-	panic("not reached")
+	panic("dns: not reached")
 }
 
 // XfrSend performs an outgoing Ixfr or Axfr. The function is [AI]xfr agnostic, it is

zgenerate.go

@@ -155,5 +155,5 @@ func modToPrintf(s string) (string, int, string) {
 	default:
 		return "%0" + xs[1] + xs[2], offset, ""
 	}
-	panic("not reached")
+	panic("dns: not reached")
 }