func decodeSCTPEmptyLayer(data []byte, p gopacket.PacketBuilder) error {
	sc := &SCTPEmptyLayer{
		SCTPChunk: decodeSCTPChunk(data),
	}
	p.AddLayer(sc)
	return p.NextDecoder(gopacket.DecodeFunc(decodeWithSCTPChunkTypePrefix))
}

func decodeSCTPCookieEcho(data []byte, p gopacket.PacketBuilder) error {
	sc := &SCTPCookieEcho{
		SCTPChunk: decodeSCTPChunk(data),
	}
	sc.Cookie = data[4:sc.Length]
	p.AddLayer(sc)
	return p.NextDecoder(gopacket.DecodeFunc(decodeWithSCTPChunkTypePrefix))
}

func decodeSCTPShutdown(data []byte, p gopacket.PacketBuilder) error {
	sc := &SCTPShutdown{
		SCTPChunk:        decodeSCTPChunk(data),
		CumulativeTSNAck: binary.BigEndian.Uint32(data[4:8]),
	}
	p.AddLayer(sc)
	return p.NextDecoder(gopacket.DecodeFunc(decodeWithSCTPChunkTypePrefix))
}

func decodeICMPv4(data []byte, p gopacket.PacketBuilder) error {
	i := &ICMPv4{}
	err := i.DecodeFromBytes(data, p)
	if err != nil {
		return err
	}
	p.AddLayer(i)
	return p.NextDecoder(gopacket.LayerTypePayload)
}

func decodeIPv6HopByHop(data []byte, p gopacket.PacketBuilder) error {
	i := &IPv6HopByHop{}
	err := i.DecodeFromBytes(data, p)
	p.AddLayer(i)
	if err != nil {
		return err
	}
	return p.NextDecoder(i.NextHeader)
}

func decodeDHCPv4(data []byte, p gopacket.PacketBuilder) error {
	dhcp := &DHCPv4{}
	err := dhcp.DecodeFromBytes(data, p)
	if err != nil {
		return err
	}
	p.AddLayer(dhcp)
	return p.NextDecoder(gopacket.LayerTypePayload)
}

func decodeIPSecESP(data []byte, p gopacket.PacketBuilder) error {
	i := &IPSecESP{
		BaseLayer: BaseLayer{data, nil},
		SPI:       binary.BigEndian.Uint32(data[:4]),
		Seq:       binary.BigEndian.Uint32(data[4:8]),
		Encrypted: data[8:],
	}
	p.AddLayer(i)
	return nil
}

// decodeDNS decodes the byte slice into a DNS type. It also
// setups the application Layer in PacketBuilder.
func decodeDNS(data []byte, p gopacket.PacketBuilder) error {
	d := &DNS{}
	err := d.DecodeFromBytes(data, p)
	if err != nil {
		return err
	}
	p.AddLayer(d)
	p.SetApplicationLayer(d)
	return nil
}

func decodeEthernetCTP(data []byte, p gopacket.PacketBuilder) error {
	c := &EthernetCTP{
		SkipCount: binary.LittleEndian.Uint16(data[:2]),
		BaseLayer: BaseLayer{data[:2], data[2:]},
	}
	if c.SkipCount%2 != 0 {
		return fmt.Errorf("EthernetCTP skip count is odd: %d", c.SkipCount)
	}
	p.AddLayer(c)
	return p.NextDecoder(gopacket.DecodeFunc(decodeEthernetCTPFromFunctionType))
}

func decodeSNAP(data []byte, p gopacket.PacketBuilder) error {
	s := &SNAP{
		OrganizationalCode: data[:3],
		Type:               EthernetType(binary.BigEndian.Uint16(data[3:5])),
		BaseLayer:          BaseLayer{data[:5], data[5:]},
	}
	p.AddLayer(s)
	// BUG(gconnell):  When decoding SNAP, we treat the SNAP type as an Ethernet
	// type.  This may not actually be an ethernet type in all cases,
	// depending on the organizational code.  Right now, we don't check.
	return p.NextDecoder(s.Type)
}

func decodingLayerDecoder(d layerDecodingLayer, data []byte, p gopacket.PacketBuilder) error {
	err := d.DecodeFromBytes(data, p)
	if err != nil {
		return err
	}
	p.AddLayer(d)
	next := d.NextLayerType()
	if next == gopacket.LayerTypeZero {
		return nil
	}
	return p.NextDecoder(next)
}

// decodePPPoE decodes the PPPoE header (see http://tools.ietf.org/html/rfc2516).
func decodePPPoE(data []byte, p gopacket.PacketBuilder) error {
	pppoe := &PPPoE{
		Version:   data[0] >> 4,
		Type:      data[0] & 0x0F,
		Code:      PPPoECode(data[1]),
		SessionId: binary.BigEndian.Uint16(data[2:4]),
		Length:    binary.BigEndian.Uint16(data[4:6]),
	}
	pppoe.BaseLayer = BaseLayer{data[:6], data[6 : 6+pppoe.Length]}
	p.AddLayer(pppoe)
	return p.NextDecoder(pppoe.Code)
}

func decodeIPv6Fragment(data []byte, p gopacket.PacketBuilder) error {
	i := &IPv6Fragment{
		BaseLayer:      BaseLayer{data[:8], data[8:]},
		NextHeader:     IPProtocol(data[0]),
		Reserved1:      data[1],
		FragmentOffset: binary.BigEndian.Uint16(data[2:4]) >> 3,
		Reserved2:      data[3] & 0x6 >> 1,
		MoreFragments:  data[3]&0x1 != 0,
		Identification: binary.BigEndian.Uint32(data[4:8]),
	}
	p.AddLayer(i)
	return p.NextDecoder(gopacket.DecodeFragment)
}

func decodeSCTPHeartbeat(data []byte, p gopacket.PacketBuilder) error {
	sc := &SCTPHeartbeat{
		SCTPChunk: decodeSCTPChunk(data),
	}
	paramData := data[4:sc.Length]
	for len(paramData) > 0 {
		p := SCTPHeartbeatParameter(decodeSCTPParameter(paramData))
		paramData = paramData[p.ActualLength:]
		sc.Parameters = append(sc.Parameters, p)
	}
	p.AddLayer(sc)
	return p.NextDecoder(gopacket.DecodeFunc(decodeWithSCTPChunkTypePrefix))
}

func decodeNortelDiscovery(data []byte, p gopacket.PacketBuilder) error {
	c := &NortelDiscovery{}
	if len(data) < 11 {
		return fmt.Errorf("Invalid NortelDiscovery packet length %d", len(data))
	}
	c.IPAddress = data[0:4]
	c.SegmentID = data[4:7]
	c.Chassis = NDPChassisType(data[7])
	c.Backplane = NDPBackplaneType(data[8])
	c.State = NDPState(data[9])
	c.NumLinks = uint8(data[10])
	p.AddLayer(c)
	return nil
}

func decodeIPv6Destination(data []byte, p gopacket.PacketBuilder) error {
	i := &IPv6Destination{
		ipv6ExtensionBase: decodeIPv6ExtensionBase(data),
		// We guess we'll 1-2 options, one regular option at least, then maybe one
		// padding option.
		Options: make([]IPv6DestinationOption, 0, 2),
	}
	var opt *IPv6DestinationOption
	for d := i.Contents[2:]; len(d) > 0; d = d[opt.ActualLength:] {
		i.Options = append(i.Options, IPv6DestinationOption(decodeIPv6HeaderTLVOption(d)))
		opt = &i.Options[len(i.Options)-1]
	}
	p.AddLayer(i)
	return p.NextDecoder(i.NextHeader)
}

func decodeIPSecAH(data []byte, p gopacket.PacketBuilder) error {
	i := &IPSecAH{
		ipv6ExtensionBase: ipv6ExtensionBase{
			NextHeader:   IPProtocol(data[0]),
			HeaderLength: data[1],
		},
		Reserved: binary.BigEndian.Uint16(data[2:4]),
		SPI:      binary.BigEndian.Uint32(data[4:8]),
		Seq:      binary.BigEndian.Uint32(data[8:12]),
	}
	i.ActualLength = (int(i.HeaderLength) + 2) * 4
	i.AuthenticationData = data[12:i.ActualLength]
	i.Contents = data[:i.ActualLength]
	i.Payload = data[i.ActualLength:]
	p.AddLayer(i)
	return p.NextDecoder(i.NextHeader)
}

func decodeSCTPInit(data []byte, p gopacket.PacketBuilder) error {
	sc := &SCTPInit{
		SCTPChunk:                      decodeSCTPChunk(data),
		InitiateTag:                    binary.BigEndian.Uint32(data[4:8]),
		AdvertisedReceiverWindowCredit: binary.BigEndian.Uint32(data[8:12]),
		OutboundStreams:                binary.BigEndian.Uint16(data[12:14]),
		InboundStreams:                 binary.BigEndian.Uint16(data[14:16]),
		InitialTSN:                     binary.BigEndian.Uint32(data[16:20]),
	}
	paramData := data[20:sc.ActualLength]
	for len(paramData) > 0 {
		p := SCTPInitParameter(decodeSCTPParameter(paramData))
		paramData = paramData[p.ActualLength:]
		sc.Parameters = append(sc.Parameters, p)
	}
	p.AddLayer(sc)
	return p.NextDecoder(gopacket.DecodeFunc(decodeWithSCTPChunkTypePrefix))
}

func decodeIPv6(data []byte, p gopacket.PacketBuilder) error {
	ip6 := &IPv6{}
	err := ip6.DecodeFromBytes(data, p)
	p.AddLayer(ip6)
	p.SetNetworkLayer(ip6)
	if ip6.HopByHop != nil {
		// TODO(gconnell):  Since HopByHop is now an integral part of the IPv6
		// layer, should it actually be added as its own layer?  I'm leaning towards
		// no.
		p.AddLayer(ip6.HopByHop)
	}
	if err != nil {
		return err
	}
	if ip6.HopByHop != nil {
		return p.NextDecoder(ip6.HopByHop.NextHeader)
	}
	return p.NextDecoder(ip6.NextHeader)
}

func decodeCiscoDiscovery(data []byte, p gopacket.PacketBuilder) error {
	c := &CiscoDiscovery{
		Version:  data[0],
		TTL:      data[1],
		Checksum: binary.BigEndian.Uint16(data[2:4]),
	}
	if c.Version != 1 && c.Version != 2 {
		return fmt.Errorf("Invalid CiscoDiscovery version number %d", c.Version)
	}
	var err error
	c.Values, err = decodeCiscoDiscoveryTLVs(data[4:])
	if err != nil {
		return err
	}
	c.Contents = data[0:4]
	c.Payload = data[4:]
	p.AddLayer(c)
	return p.NextDecoder(gopacket.DecodeFunc(decodeCiscoDiscoveryInfo))
}