Use proper error in packing and unpacking

All the relevant functions now return an error instead of
a simple boolean. This greatly approves the feedback to coders.

Spotted some fishy error handling along the way and fix that too.

client.go

@@ -101,9 +101,9 @@ func (c *Client) Exchange(m *Msg, a string) (r *Msg, err error) {
 func (c *Client) ExchangeRtt(m *Msg, a string) (r *Msg, rtt time.Duration, err error) {
 	var n int
 	var w *reply
-	out, ok := m.Pack()
-	if !ok {
-		return nil, 0, ErrPack
+	out, err := m.Pack()
+	if err != nil {
+		return nil, 0, err
 	}
 	var in []byte
 	switch c.Net {
@@ -123,8 +123,8 @@ func (c *Client) ExchangeRtt(m *Msg, a string) (r *Msg, rtt time.Duration, err e
 	}
 	r = new(Msg)
 	r.Size = n
-	if ok := r.Unpack(in[:n]); !ok {
-		return nil, w.rtt, ErrUnpack
+	if err := r.Unpack(in[:n]); err != nil {
+		return nil, w.rtt, err
 	}
 	return r, w.rtt, nil
 }
@@ -158,8 +158,8 @@ func (w *reply) receive() (*Msg, error) {
 		return nil, err
 	}
 	p = p[:n]
-	if ok := m.Unpack(p); !ok {
-		return nil, ErrUnpack
+	if err := m.Unpack(p); err != nil {
+		return nil, err
 	}
 	w.rtt = time.Since(w.t)
 	m.Size = n
@@ -260,10 +260,9 @@ func (w *reply) send(m *Msg) (err error) {
 		}
 		w.tsigRequestMAC = mac
 	} else {
-		ok := false
-		out, ok = m.Pack()
-		if !ok {
-			return ErrPack
+		out, err = m.Pack()
+		if err != nil {
+			return err
 		}
 	}
 	w.t = time.Now()

dnssec.go

@@ -119,8 +119,8 @@ func (k *RR_DNSKEY) KeyTag() uint16 {
 		keywire.Algorithm = k.Algorithm
 		keywire.PublicKey = k.PublicKey
 		wire := make([]byte, DefaultMsgSize)
-		n, ok := PackStruct(keywire, wire, 0)
-		if !ok {
+		n, err := PackStruct(keywire, wire, 0)
+		if err != nil {
 			return 0
 		}
 		wire = wire[:n]
@@ -157,15 +157,15 @@ func (k *RR_DNSKEY) ToDS(h int) *RR_DS {
 	keywire.Algorithm = k.Algorithm
 	keywire.PublicKey = k.PublicKey
 	wire := make([]byte, DefaultMsgSize)
-	n, ok := PackStruct(keywire, wire, 0)
-	if !ok {
+	n, err := PackStruct(keywire, wire, 0)
+	if err != nil {
 		return nil
 	}
 	wire = wire[:n]
 
 	owner := make([]byte, 255)
-	off, ok1 := PackDomainName(k.Hdr.Name, owner, 0, nil, false)
-	if !ok1 {
+	off, err1 := PackDomainName(k.Hdr.Name, owner, 0, nil, false)
+	if err1 != nil  {
 		return nil
 	}
 	owner = owner[:off]
@@ -237,9 +237,9 @@ func (rr *RR_RRSIG) Sign(k PrivateKey, rrset []RR) error {
 
 	// Create the desired binary blob
 	signdata := make([]byte, DefaultMsgSize)
-	n, ok := PackStruct(sigwire, signdata, 0)
-	if !ok {
-		return ErrPack
+	n, err := PackStruct(sigwire, signdata, 0)
+	if err != nil {
+		return err
 	}
 	signdata = signdata[:n]
 	wire := rawSignatureData(rrset, rr)
@@ -349,9 +349,9 @@ func (rr *RR_RRSIG) Verify(k *RR_DNSKEY, rrset []RR) error {
 	sigwire.SignerName = strings.ToLower(rr.SignerName)
 	// Create the desired binary blob
 	signeddata := make([]byte, DefaultMsgSize)
-	n, ok := PackStruct(sigwire, signeddata, 0)
-	if !ok {
-		return ErrPack
+	n, err := PackStruct(sigwire, signeddata, 0)
+	if err != nil {
+		return err
 	}
 	signeddata = signeddata[:n]
 	wire := rawSignatureData(rrset, rr)
@@ -684,8 +684,8 @@ func rawSignatureData(rrset []RR, s *RR_RRSIG) (buf []byte) {
 		}
 		// 6.2. Canonical RR Form. (5) - origTTL
 		wire := make([]byte, r.Len()*2)
-		off, ok1 := PackRR(r1, wire, 0, nil, false)
-		if !ok1 {
+		off, err1 := PackRR(r1, wire, 0, nil, false)
+		if err1 != nil {
 			return nil
 		}
 		wire = wire[:off]