diff --git a/edns.go b/edns.go
index d244f7c6..75a07ea3 100644
--- a/edns.go
+++ b/edns.go
@@ -47,7 +47,8 @@ func (rr *OPT) String() string {
 		switch o.(type) {
 		case *EDNS0_NSID:
 			s += "\n; NSID: " + o.String()
-			h, e := o.pack()
+			h := make([]byte, o.Len())
+			_, e := o.Pack(h)
 			var r string
 			if e == nil {
 				for _, c := range h {
@@ -82,8 +83,7 @@ func (rr *OPT) len(off int, compression map[string]struct{}) int {
 	l := rr.Hdr.len(off, compression)
 	for _, o := range rr.Option {
 		l += 4 // Account for 2-byte option code and 2-byte option length.
-		lo, _ := o.pack()
-		l += len(lo)
+		l += o.Len()
 	}
 	return l
 }
@@ -152,15 +152,19 @@ func (rr *OPT) SetDo(do ...bool) {
 type EDNS0 interface {
 	// Option returns the option code for the option.
 	Option() uint16
-	// pack returns the bytes of the option data.
-	pack() ([]byte, error)
-	// unpack sets the data as found in the buffer. Is also sets
+	// Len returns the length (number of bytes) of the option data when
+	// packed
+	Len() int
+	// Pack writes the option data into the buffer. The buffer should be at
+	// least Len() bytes long. Returns the number of bytes written.
+	Pack(b []byte) (int, error)
+	// Unpack sets the data as found in the buffer. Is also sets
 	// the length of the slice as the length of the option data.
-	unpack([]byte) error
+	Unpack([]byte) (int, error)
 	// String returns the string representation of the option.
 	String() string
 	// copy returns a deep-copy of the option.
-	copy() EDNS0
+	Copy() EDNS0
 }
 
 // EDNS0_NSID option is used to retrieve a nameserver
@@ -180,19 +184,20 @@ type EDNS0_NSID struct {
 	Nsid string // This string needs to be hex encoded
 }
 
-func (e *EDNS0_NSID) pack() ([]byte, error) {
-	h, err := hex.DecodeString(e.Nsid)
-	if err != nil {
-		return nil, err
-	}
-	return h, nil
+func (e *EDNS0_NSID) Len() int {
+	return hex.DecodedLen(len(e.Nsid))
+}
+
+func (e *EDNS0_NSID) Pack(b []byte) (int, error) {
+	nsid := []byte(e.Nsid)
+	return hex.Decode(nsid, b)
 }
 
 // Option implements the EDNS0 interface.
-func (e *EDNS0_NSID) Option() uint16        { return EDNS0NSID } // Option returns the option code.
-func (e *EDNS0_NSID) unpack(b []byte) error { e.Nsid = hex.EncodeToString(b); return nil }
-func (e *EDNS0_NSID) String() string        { return e.Nsid }
-func (e *EDNS0_NSID) copy() EDNS0           { return &EDNS0_NSID{e.Code, e.Nsid} }
+func (e *EDNS0_NSID) Option() uint16               { return EDNS0NSID } // Option returns the option code.
+func (e *EDNS0_NSID) Unpack(b []byte) (int, error) { e.Nsid = hex.EncodeToString(b); return len(b), nil }
+func (e *EDNS0_NSID) String() string               { return e.Nsid }
+func (e *EDNS0_NSID) Copy() EDNS0                  { return &EDNS0_NSID{e.Code, e.Nsid} }
 
 // EDNS0_SUBNET is the subnet option that is used to give the remote nameserver
 // an idea of where the client lives. See RFC 7871. It can then give back a different
@@ -225,77 +230,82 @@ type EDNS0_SUBNET struct {
 // Option implements the EDNS0 interface.
 func (e *EDNS0_SUBNET) Option() uint16 { return EDNS0SUBNET }
 
-func (e *EDNS0_SUBNET) pack() ([]byte, error) {
-	b := make([]byte, 4)
+func (e *EDNS0_SUBNET) Len() int {
+	return 4 + int((e.SourceNetmask + 8 - 1) / 8) // division rounding up
+}
+
+func (e *EDNS0_SUBNET) Pack(b []byte) (int, error) {
 	binary.BigEndian.PutUint16(b[0:], e.Family)
 	b[2] = e.SourceNetmask
 	b[3] = e.SourceScope
+	var copied int = 0
 	switch e.Family {
 	case 0:
 		// "dig" sets AddressFamily to 0 if SourceNetmask is also 0
 		// We might don't need to complain either
 		if e.SourceNetmask != 0 {
-			return nil, errors.New("dns: bad address family")
+			return 0, errors.New("dns: bad address family")
 		}
 	case 1:
 		if e.SourceNetmask > net.IPv4len*8 {
-			return nil, errors.New("dns: bad netmask")
+			return 0, errors.New("dns: bad netmask")
 		}
 		if len(e.Address.To4()) != net.IPv4len {
-			return nil, errors.New("dns: bad address")
+			return 0, errors.New("dns: bad address")
 		}
 		ip := e.Address.To4().Mask(net.CIDRMask(int(e.SourceNetmask), net.IPv4len*8))
-		needLength := (e.SourceNetmask + 8 - 1) / 8 // division rounding up
-		b = append(b, ip[:needLength]...)
+		needLength := int((e.SourceNetmask + 8 - 1) / 8) // division rounding up
+		copied = copy(b[4:], ip[:needLength])
 	case 2:
 		if e.SourceNetmask > net.IPv6len*8 {
-			return nil, errors.New("dns: bad netmask")
+			return 0, errors.New("dns: bad netmask")
 		}
 		if len(e.Address) != net.IPv6len {
-			return nil, errors.New("dns: bad address")
+			return 0, errors.New("dns: bad address")
 		}
 		ip := e.Address.Mask(net.CIDRMask(int(e.SourceNetmask), net.IPv6len*8))
-		needLength := (e.SourceNetmask + 8 - 1) / 8 // division rounding up
-		b = append(b, ip[:needLength]...)
+		needLength := int((e.SourceNetmask + 8 - 1) / 8) // division rounding up
+		copied = copy(b[4:], ip[:needLength])
 	default:
-		return nil, errors.New("dns: bad address family")
+		return 0, errors.New("dns: bad address family")
 	}
-	return b, nil
+	return 4 + copied, nil
 }
 
-func (e *EDNS0_SUBNET) unpack(b []byte) error {
+func (e *EDNS0_SUBNET) Unpack(b []byte) (int, error) {
 	if len(b) < 4 {
-		return ErrBuf
+		return 0, ErrBuf
 	}
 	e.Family = binary.BigEndian.Uint16(b)
 	e.SourceNetmask = b[2]
 	e.SourceScope = b[3]
+	var l int = 0
 	switch e.Family {
 	case 0:
 		// "dig" sets AddressFamily to 0 if SourceNetmask is also 0
 		// It's okay to accept such a packet
 		if e.SourceNetmask != 0 {
-			return errors.New("dns: bad address family")
+			return 0, errors.New("dns: bad address family")
 		}
 		e.Address = net.IPv4(0, 0, 0, 0)
 	case 1:
 		if e.SourceNetmask > net.IPv4len*8 || e.SourceScope > net.IPv4len*8 {
-			return errors.New("dns: bad netmask")
+			return 0, errors.New("dns: bad netmask")
 		}
 		addr := make(net.IP, net.IPv4len)
-		copy(addr, b[4:])
+		l = copy(addr, b[4:])
 		e.Address = addr.To16()
 	case 2:
 		if e.SourceNetmask > net.IPv6len*8 || e.SourceScope > net.IPv6len*8 {
-			return errors.New("dns: bad netmask")
+			return 0, errors.New("dns: bad netmask")
 		}
 		addr := make(net.IP, net.IPv6len)
-		copy(addr, b[4:])
+		l = copy(addr, b[4:])
 		e.Address = addr
 	default:
-		return errors.New("dns: bad address family")
+		return 0, errors.New("dns: bad address family")
 	}
-	return nil
+	return 4 + l, nil
 }
 
 func (e *EDNS0_SUBNET) String() (s string) {
@@ -310,7 +320,7 @@ func (e *EDNS0_SUBNET) String() (s string) {
 	return
 }
 
-func (e *EDNS0_SUBNET) copy() EDNS0 {
+func (e *EDNS0_SUBNET) Copy() EDNS0 {
 	return &EDNS0_SUBNET{
 		e.Code,
 		e.Family,
@@ -343,19 +353,23 @@ type EDNS0_COOKIE struct {
 	Cookie string // Hex-encoded cookie data
 }
 
-func (e *EDNS0_COOKIE) pack() ([]byte, error) {
-	h, err := hex.DecodeString(e.Cookie)
-	if err != nil {
-		return nil, err
-	}
-	return h, nil
+func (e *EDNS0_COOKIE) Len() int {
+	return hex.DecodedLen(len(e.Cookie))
+}
+
+func (e *EDNS0_COOKIE) Pack(b []byte) (int, error) {
+	cookie := []byte(e.Cookie)
+	return hex.Decode(cookie, b)
 }
 
 // Option implements the EDNS0 interface.
-func (e *EDNS0_COOKIE) Option() uint16        { return EDNS0COOKIE }
-func (e *EDNS0_COOKIE) unpack(b []byte) error { e.Cookie = hex.EncodeToString(b); return nil }
-func (e *EDNS0_COOKIE) String() string        { return e.Cookie }
-func (e *EDNS0_COOKIE) copy() EDNS0           { return &EDNS0_COOKIE{e.Code, e.Cookie} }
+func (e *EDNS0_COOKIE) Option() uint16 { return EDNS0COOKIE }
+func (e *EDNS0_COOKIE) Unpack(b []byte) (int, error) {
+	e.Cookie = hex.EncodeToString(b)
+	return len(b), nil
+}
+func (e *EDNS0_COOKIE) String() string { return e.Cookie }
+func (e *EDNS0_COOKIE) Copy() EDNS0    { return &EDNS0_COOKIE{e.Code, e.Cookie} }
 
 // The EDNS0_UL (Update Lease) (draft RFC) option is used to tell the server to set
 // an expiration on an update RR. This is helpful for clients that cannot clean
@@ -378,32 +392,39 @@ type EDNS0_UL struct {
 // Option implements the EDNS0 interface.
 func (e *EDNS0_UL) Option() uint16 { return EDNS0UL }
 func (e *EDNS0_UL) String() string { return fmt.Sprintf("%d %d", e.Lease, e.KeyLease) }
-func (e *EDNS0_UL) copy() EDNS0    { return &EDNS0_UL{e.Code, e.Lease, e.KeyLease} }
+func (e *EDNS0_UL) Copy() EDNS0    { return &EDNS0_UL{e.Code, e.Lease, e.KeyLease} }
 
-// Copied: http://golang.org/src/pkg/net/dnsmsg.go
-func (e *EDNS0_UL) pack() ([]byte, error) {
-	var b []byte
+func (e *EDNS0_UL) Len() int {
 	if e.KeyLease == 0 {
-		b = make([]byte, 4)
-	} else {
-		b = make([]byte, 8)
-		binary.BigEndian.PutUint32(b[4:], e.KeyLease)
+		return 4
 	}
-	binary.BigEndian.PutUint32(b, e.Lease)
-	return b, nil
+	return 8
+
 }
 
-func (e *EDNS0_UL) unpack(b []byte) error {
-	switch len(b) {
+// Copied: http://golang.org/src/pkg/net/dnsmsg.go
+func (e *EDNS0_UL) Pack(b []byte) (int, error) {
+	l := 4
+	if e.KeyLease != 0 {
+		binary.BigEndian.PutUint32(b[4:], e.KeyLease)
+		l += 4
+	}
+	binary.BigEndian.PutUint32(b, e.Lease)
+	return l, nil
+}
+
+func (e *EDNS0_UL) Unpack(b []byte) (int, error) {
+	l := len(b)
+	switch l {
 	case 4:
 		e.KeyLease = 0
 	case 8:
 		e.KeyLease = binary.BigEndian.Uint32(b[4:])
 	default:
-		return ErrBuf
+		return 0, ErrBuf
 	}
 	e.Lease = binary.BigEndian.Uint32(b)
-	return nil
+	return l, nil
 }
 
 // EDNS0_LLQ stands for Long Lived Queries: http://tools.ietf.org/html/draft-sekar-dns-llq-01
@@ -420,26 +441,29 @@ type EDNS0_LLQ struct {
 // Option implements the EDNS0 interface.
 func (e *EDNS0_LLQ) Option() uint16 { return EDNS0LLQ }
 
-func (e *EDNS0_LLQ) pack() ([]byte, error) {
-	b := make([]byte, 18)
+func (e *EDNS0_LLQ) Len() int {
+	return 18
+}
+
+func (e *EDNS0_LLQ) Pack(b []byte) (int, error) {
 	binary.BigEndian.PutUint16(b[0:], e.Version)
 	binary.BigEndian.PutUint16(b[2:], e.Opcode)
 	binary.BigEndian.PutUint16(b[4:], e.Error)
 	binary.BigEndian.PutUint64(b[6:], e.Id)
 	binary.BigEndian.PutUint32(b[14:], e.LeaseLife)
-	return b, nil
+	return 18, nil
 }
 
-func (e *EDNS0_LLQ) unpack(b []byte) error {
+func (e *EDNS0_LLQ) Unpack(b []byte) (int, error) {
 	if len(b) < 18 {
-		return ErrBuf
+		return 0, ErrBuf
 	}
 	e.Version = binary.BigEndian.Uint16(b[0:])
 	e.Opcode = binary.BigEndian.Uint16(b[2:])
 	e.Error = binary.BigEndian.Uint16(b[4:])
 	e.Id = binary.BigEndian.Uint64(b[6:])
 	e.LeaseLife = binary.BigEndian.Uint32(b[14:])
-	return nil
+	return 18, nil
 }
 
 func (e *EDNS0_LLQ) String() string {
@@ -448,7 +472,7 @@ func (e *EDNS0_LLQ) String() string {
 		" " + strconv.FormatUint(uint64(e.LeaseLife), 10)
 	return s
 }
-func (e *EDNS0_LLQ) copy() EDNS0 {
+func (e *EDNS0_LLQ) Copy() EDNS0 {
 	return &EDNS0_LLQ{e.Code, e.Version, e.Opcode, e.Error, e.Id, e.LeaseLife}
 }
 
@@ -459,9 +483,13 @@ type EDNS0_DAU struct {
 }
 
 // Option implements the EDNS0 interface.
-func (e *EDNS0_DAU) Option() uint16        { return EDNS0DAU }
-func (e *EDNS0_DAU) pack() ([]byte, error) { return e.AlgCode, nil }
-func (e *EDNS0_DAU) unpack(b []byte) error { e.AlgCode = b; return nil }
+func (e *EDNS0_DAU) Option() uint16             { return EDNS0DAU }
+func (e *EDNS0_DAU) Len() int                   { return len(e.AlgCode) }
+func (e *EDNS0_DAU) Pack(b []byte) (int, error) { return copy(b, e.AlgCode), nil }
+func (e *EDNS0_DAU) Unpack(b []byte) (int, error) {
+	e.AlgCode = make([]byte, len(b))
+	return copy(e.AlgCode, b), nil
+}
 
 func (e *EDNS0_DAU) String() string {
 	s := ""
@@ -474,7 +502,7 @@ func (e *EDNS0_DAU) String() string {
 	}
 	return s
 }
-func (e *EDNS0_DAU) copy() EDNS0 { return &EDNS0_DAU{e.Code, e.AlgCode} }
+func (e *EDNS0_DAU) Copy() EDNS0 { return &EDNS0_DAU{e.Code, e.AlgCode} }
 
 // EDNS0_DHU implements the EDNS0 "DS Hash Understood" option. See RFC 6975.
 type EDNS0_DHU struct {
@@ -483,9 +511,13 @@ type EDNS0_DHU struct {
 }
 
 // Option implements the EDNS0 interface.
-func (e *EDNS0_DHU) Option() uint16        { return EDNS0DHU }
-func (e *EDNS0_DHU) pack() ([]byte, error) { return e.AlgCode, nil }
-func (e *EDNS0_DHU) unpack(b []byte) error { e.AlgCode = b; return nil }
+func (e *EDNS0_DHU) Option() uint16             { return EDNS0DHU }
+func (e *EDNS0_DHU) Len() int                   { return len(e.AlgCode) }
+func (e *EDNS0_DHU) Pack(b []byte) (int, error) { return copy(b, e.AlgCode), nil }
+func (e *EDNS0_DHU) Unpack(b []byte) (int, error) {
+	e.AlgCode = make([]byte, len(b))
+	return copy(e.AlgCode, b), nil
+}
 
 func (e *EDNS0_DHU) String() string {
 	s := ""
@@ -498,7 +530,7 @@ func (e *EDNS0_DHU) String() string {
 	}
 	return s
 }
-func (e *EDNS0_DHU) copy() EDNS0 { return &EDNS0_DHU{e.Code, e.AlgCode} }
+func (e *EDNS0_DHU) Copy() EDNS0 { return &EDNS0_DHU{e.Code, e.AlgCode} }
 
 // EDNS0_N3U implements the EDNS0 "NSEC3 Hash Understood" option. See RFC 6975.
 type EDNS0_N3U struct {
@@ -507,9 +539,13 @@ type EDNS0_N3U struct {
 }
 
 // Option implements the EDNS0 interface.
-func (e *EDNS0_N3U) Option() uint16        { return EDNS0N3U }
-func (e *EDNS0_N3U) pack() ([]byte, error) { return e.AlgCode, nil }
-func (e *EDNS0_N3U) unpack(b []byte) error { e.AlgCode = b; return nil }
+func (e *EDNS0_N3U) Option() uint16             { return EDNS0N3U }
+func (e *EDNS0_N3U) Len() int                   { return len(e.AlgCode) }
+func (e *EDNS0_N3U) Pack(b []byte) (int, error) { return copy(b, e.AlgCode), nil }
+func (e *EDNS0_N3U) Unpack(b []byte) (int, error) {
+	e.AlgCode = make([]byte, len(b))
+	return copy(e.AlgCode, b), nil
+}
 
 func (e *EDNS0_N3U) String() string {
 	// Re-use the hash map
@@ -523,7 +559,7 @@ func (e *EDNS0_N3U) String() string {
 	}
 	return s
 }
-func (e *EDNS0_N3U) copy() EDNS0 { return &EDNS0_N3U{e.Code, e.AlgCode} }
+func (e *EDNS0_N3U) Copy() EDNS0 { return &EDNS0_N3U{e.Code, e.AlgCode} }
 
 // EDNS0_EXPIRE implementes the EDNS0 option as described in RFC 7314.
 type EDNS0_EXPIRE struct {
@@ -534,20 +570,26 @@ type EDNS0_EXPIRE struct {
 // Option implements the EDNS0 interface.
 func (e *EDNS0_EXPIRE) Option() uint16 { return EDNS0EXPIRE }
 func (e *EDNS0_EXPIRE) String() string { return strconv.FormatUint(uint64(e.Expire), 10) }
-func (e *EDNS0_EXPIRE) copy() EDNS0    { return &EDNS0_EXPIRE{e.Code, e.Expire} }
+func (e *EDNS0_EXPIRE) Copy() EDNS0    { return &EDNS0_EXPIRE{e.Code, e.Expire} }
 
-func (e *EDNS0_EXPIRE) pack() ([]byte, error) {
-	b := make([]byte, 4)
-	binary.BigEndian.PutUint32(b, e.Expire)
-	return b, nil
+func (e *EDNS0_EXPIRE) Len() int {
+	return 4
 }
 
-func (e *EDNS0_EXPIRE) unpack(b []byte) error {
+func (e *EDNS0_EXPIRE) Pack(b []byte) (int, error) {
 	if len(b) < 4 {
-		return ErrBuf
+		return 0, ErrBuf
+	}
+	binary.BigEndian.PutUint32(b, e.Expire)
+	return 4, nil
+}
+
+func (e *EDNS0_EXPIRE) Unpack(b []byte) (int, error) {
+	if len(b) < 4 {
+		return 0, ErrBuf
 	}
 	e.Expire = binary.BigEndian.Uint32(b)
-	return nil
+	return 4, nil
 }
 
 // The EDNS0_LOCAL option is used for local/experimental purposes. The option
@@ -573,28 +615,31 @@ func (e *EDNS0_LOCAL) Option() uint16 { return e.Code }
 func (e *EDNS0_LOCAL) String() string {
 	return strconv.FormatInt(int64(e.Code), 10) + ":0x" + hex.EncodeToString(e.Data)
 }
-func (e *EDNS0_LOCAL) copy() EDNS0 {
+func (e *EDNS0_LOCAL) Copy() EDNS0 {
 	b := make([]byte, len(e.Data))
 	copy(b, e.Data)
 	return &EDNS0_LOCAL{e.Code, b}
 }
 
-func (e *EDNS0_LOCAL) pack() ([]byte, error) {
-	b := make([]byte, len(e.Data))
-	copied := copy(b, e.Data)
-	if copied != len(e.Data) {
-		return nil, ErrBuf
-	}
-	return b, nil
+func (e *EDNS0_LOCAL) Len() int {
+	return len(e.Data)
 }
 
-func (e *EDNS0_LOCAL) unpack(b []byte) error {
+func (e *EDNS0_LOCAL) Pack(b []byte) (int, error) {
+	copied := copy(b, e.Data)
+	if copied != len(e.Data) {
+		return 0, ErrBuf
+	}
+	return copied, nil
+}
+
+func (e *EDNS0_LOCAL) Unpack(b []byte) (int, error) {
 	e.Data = make([]byte, len(b))
 	copied := copy(e.Data, b)
 	if copied != len(b) {
-		return ErrBuf
+		return 0, ErrBuf
 	}
-	return nil
+	return copied, nil
 }
 
 // EDNS0_TCP_KEEPALIVE is an EDNS0 option that instructs the server to keep
@@ -608,37 +653,40 @@ type EDNS0_TCP_KEEPALIVE struct {
 // Option implements the EDNS0 interface.
 func (e *EDNS0_TCP_KEEPALIVE) Option() uint16 { return EDNS0TCPKEEPALIVE }
 
-func (e *EDNS0_TCP_KEEPALIVE) pack() ([]byte, error) {
+func (e *EDNS0_TCP_KEEPALIVE) Len() int {
+	return int(4 + e.Length)
+}
+
+func (e *EDNS0_TCP_KEEPALIVE) Pack(b []byte) (int, error) {
 	if e.Timeout != 0 && e.Length != 2 {
-		return nil, errors.New("dns: timeout specified but length is not 2")
+		return 0, errors.New("dns: timeout specified but length is not 2")
 	}
 	if e.Timeout == 0 && e.Length != 0 {
-		return nil, errors.New("dns: timeout not specified but length is not 0")
+		return 0, errors.New("dns: timeout not specified but length is not 0")
 	}
-	b := make([]byte, 4+e.Length)
 	binary.BigEndian.PutUint16(b[0:], e.Code)
 	binary.BigEndian.PutUint16(b[2:], e.Length)
 	if e.Length == 2 {
 		binary.BigEndian.PutUint16(b[4:], e.Timeout)
 	}
-	return b, nil
+	return e.Len(), nil
 }
 
-func (e *EDNS0_TCP_KEEPALIVE) unpack(b []byte) error {
+func (e *EDNS0_TCP_KEEPALIVE) Unpack(b []byte) (int, error) {
 	if len(b) < 4 {
-		return ErrBuf
+		return 0, ErrBuf
 	}
 	e.Length = binary.BigEndian.Uint16(b[2:4])
 	if e.Length != 0 && e.Length != 2 {
-		return errors.New("dns: length mismatch, want 0/2 but got " + strconv.FormatUint(uint64(e.Length), 10))
+		return 0, errors.New("dns: length mismatch, want 0/2 but got " + strconv.FormatUint(uint64(e.Length), 10))
 	}
 	if e.Length == 2 {
 		if len(b) < 6 {
-			return ErrBuf
+			return 0, ErrBuf
 		}
 		e.Timeout = binary.BigEndian.Uint16(b[4:6])
 	}
-	return nil
+	return e.Len(), nil
 }
 
 func (e *EDNS0_TCP_KEEPALIVE) String() (s string) {
@@ -650,7 +698,7 @@ func (e *EDNS0_TCP_KEEPALIVE) String() (s string) {
 	}
 	return
 }
-func (e *EDNS0_TCP_KEEPALIVE) copy() EDNS0 { return &EDNS0_TCP_KEEPALIVE{e.Code, e.Length, e.Timeout} }
+func (e *EDNS0_TCP_KEEPALIVE) Copy() EDNS0 { return &EDNS0_TCP_KEEPALIVE{e.Code, e.Length, e.Timeout} }
 
 // EDNS0_PADDING option is used to add padding to a request/response. The default
 // value of padding SHOULD be 0x0 but other values MAY be used, for instance if
@@ -660,11 +708,15 @@ type EDNS0_PADDING struct {
 }
 
 // Option implements the EDNS0 interface.
-func (e *EDNS0_PADDING) Option() uint16        { return EDNS0PADDING }
-func (e *EDNS0_PADDING) pack() ([]byte, error) { return e.Padding, nil }
-func (e *EDNS0_PADDING) unpack(b []byte) error { e.Padding = b; return nil }
-func (e *EDNS0_PADDING) String() string        { return fmt.Sprintf("%0X", e.Padding) }
-func (e *EDNS0_PADDING) copy() EDNS0 {
+func (e *EDNS0_PADDING) Option() uint16             { return EDNS0PADDING }
+func (e *EDNS0_PADDING) Len() int                   { return len(e.Padding) }
+func (e *EDNS0_PADDING) Pack(b []byte) (int, error) { return copy(b, e.Padding), nil }
+func (e *EDNS0_PADDING) Unpack(b []byte) (int, error) {
+	e.Padding = make([]byte, len(b))
+	return copy(e.Padding, b), nil
+}
+func (e *EDNS0_PADDING) String() string { return fmt.Sprintf("%0X", e.Padding) }
+func (e *EDNS0_PADDING) Copy() EDNS0 {
 	b := make([]byte, len(e.Padding))
 	copy(b, e.Padding)
 	return &EDNS0_PADDING{b}
diff --git a/edns_test.go b/edns_test.go
index d18961ed..e8bfc8c9 100644
--- a/edns_test.go
+++ b/edns_test.go
@@ -94,13 +94,14 @@ func TestEDNS0_SUBNETUnpack(t *testing.T) {
 			s1.SourceNetmask = net.IPv4len * 8
 		}
 
-		b, err := s1.pack()
+		b := make([]byte, s1.Len())
+		_, err := s1.Pack(b)
 		if err != nil {
 			t.Fatalf("failed to pack: %v", err)
 		}
 
 		var s2 EDNS0_SUBNET
-		if err := s2.unpack(b); err != nil {
+		if _, err := s2.Unpack(b); err != nil {
 			t.Fatalf("failed to unpack: %v", err)
 		}
 
@@ -120,12 +121,13 @@ func TestEDNS0_UL(t *testing.T) {
 	}
 	for _, c := range cases {
 		expect := EDNS0_UL{EDNS0UL, c.l, c.kl}
-		b, err := expect.pack()
+		b := make([]byte, expect.Len())
+		_, err := expect.Pack(b)
 		if err != nil {
 			t.Fatalf("failed to pack: %v", err)
 		}
 		actual := EDNS0_UL{EDNS0UL, ^uint32(0), ^uint32(0)}
-		if err := actual.unpack(b); err != nil {
+		if _, err := actual.Unpack(b); err != nil {
 			t.Fatalf("failed to unpack: %v", err)
 		}
 		if expect != actual {
diff --git a/msg_helpers.go b/msg_helpers.go
index 0e96f0f3..19746ecc 100644
--- a/msg_helpers.go
+++ b/msg_helpers.go
@@ -426,63 +426,63 @@ Option:
 	switch code {
 	case EDNS0NSID:
 		e := new(EDNS0_NSID)
-		if err := e.unpack(msg[off : off+int(optlen)]); err != nil {
+		if _, err := e.Unpack(msg[off : off+int(optlen)]); err != nil {
 			return nil, len(msg), err
 		}
 		edns = append(edns, e)
 		off += int(optlen)
 	case EDNS0SUBNET:
 		e := new(EDNS0_SUBNET)
-		if err := e.unpack(msg[off : off+int(optlen)]); err != nil {
+		if _, err := e.Unpack(msg[off : off+int(optlen)]); err != nil {
 			return nil, len(msg), err
 		}
 		edns = append(edns, e)
 		off += int(optlen)
 	case EDNS0COOKIE:
 		e := new(EDNS0_COOKIE)
-		if err := e.unpack(msg[off : off+int(optlen)]); err != nil {
+		if _, err := e.Unpack(msg[off : off+int(optlen)]); err != nil {
 			return nil, len(msg), err
 		}
 		edns = append(edns, e)
 		off += int(optlen)
 	case EDNS0UL:
 		e := new(EDNS0_UL)
-		if err := e.unpack(msg[off : off+int(optlen)]); err != nil {
+		if _, err := e.Unpack(msg[off : off+int(optlen)]); err != nil {
 			return nil, len(msg), err
 		}
 		edns = append(edns, e)
 		off += int(optlen)
 	case EDNS0LLQ:
 		e := new(EDNS0_LLQ)
-		if err := e.unpack(msg[off : off+int(optlen)]); err != nil {
+		if _, err := e.Unpack(msg[off : off+int(optlen)]); err != nil {
 			return nil, len(msg), err
 		}
 		edns = append(edns, e)
 		off += int(optlen)
 	case EDNS0DAU:
 		e := new(EDNS0_DAU)
-		if err := e.unpack(msg[off : off+int(optlen)]); err != nil {
+		if _, err := e.Unpack(msg[off : off+int(optlen)]); err != nil {
 			return nil, len(msg), err
 		}
 		edns = append(edns, e)
 		off += int(optlen)
 	case EDNS0DHU:
 		e := new(EDNS0_DHU)
-		if err := e.unpack(msg[off : off+int(optlen)]); err != nil {
+		if _, err := e.Unpack(msg[off : off+int(optlen)]); err != nil {
 			return nil, len(msg), err
 		}
 		edns = append(edns, e)
 		off += int(optlen)
 	case EDNS0N3U:
 		e := new(EDNS0_N3U)
-		if err := e.unpack(msg[off : off+int(optlen)]); err != nil {
+		if _, err := e.Unpack(msg[off : off+int(optlen)]); err != nil {
 			return nil, len(msg), err
 		}
 		edns = append(edns, e)
 		off += int(optlen)
 	case EDNS0PADDING:
 		e := new(EDNS0_PADDING)
-		if err := e.unpack(msg[off : off+int(optlen)]); err != nil {
+		if _, err := e.Unpack(msg[off : off+int(optlen)]); err != nil {
 			return nil, len(msg), err
 		}
 		edns = append(edns, e)
@@ -490,7 +490,7 @@ Option:
 	default:
 		e := new(EDNS0_LOCAL)
 		e.Code = code
-		if err := e.unpack(msg[off : off+int(optlen)]); err != nil {
+		if _, err := e.Unpack(msg[off : off+int(optlen)]); err != nil {
 			return nil, len(msg), err
 		}
 		edns = append(edns, e)
@@ -506,7 +506,8 @@ Option:
 
 func packDataOpt(options []EDNS0, msg []byte, off int) (int, error) {
 	for _, el := range options {
-		b, err := el.pack()
+		b := make([]byte, el.Len())
+		_, err := el.Pack(b)
 		if err != nil || off+4 > len(msg) {
 			return len(msg), &Error{err: "overflow packing opt"}
 		}
diff --git a/ztypes.go b/ztypes.go
index f7ec8352..4060788b 100644
--- a/ztypes.go
+++ b/ztypes.go
@@ -805,7 +805,7 @@ func (rr *OPENPGPKEY) copy() RR {
 func (rr *OPT) copy() RR {
 	Option := make([]EDNS0, len(rr.Option))
 	for i, e := range rr.Option {
-		Option[i] = e.copy()
+		Option[i] = e.Copy()
 	}
 	return &OPT{rr.Hdr, Option}
 }