func (ip6 *IPv6) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
	ip6.Version = uint8(data[0]) >> 4
	ip6.TrafficClass = uint8((binary.BigEndian.Uint16(data[0:2]) >> 4) & 0x00FF)
	ip6.FlowLabel = binary.BigEndian.Uint32(data[0:4]) & 0x000FFFFF
	ip6.Length = binary.BigEndian.Uint16(data[4:6])
	ip6.NextHeader = IPProtocol(data[6])
	ip6.HopLimit = data[7]
	ip6.SrcIP = data[8:24]
	ip6.DstIP = data[24:40]
	ip6.HopByHop = nil
	// We initially set the payload to all bytes after 40.  ip6.Length or the
	// HopByHop jumbogram option can both change this eventually, though.
	ip6.BaseLayer = BaseLayer{data[:40], data[40:]}

	// We treat a HopByHop IPv6 option as part of the IPv6 packet, since its
	// options are crucial for understanding what's actually happening per packet.
	if ip6.NextHeader == IPProtocolIPv6HopByHop {
		ip6.hbh.DecodeFromBytes(ip6.Payload, df)
		hbhLen := len(ip6.hbh.Contents)
		// Reset IPv6 contents to include the HopByHop header.
		ip6.BaseLayer = BaseLayer{data[:40+hbhLen], data[40+hbhLen:]}
		ip6.HopByHop = &ip6.hbh
		if ip6.Length == 0 {
			for _, o := range ip6.hbh.Options {
				if o.OptionType == IPv6HopByHopOptionJumbogram {
					if len(o.OptionData) != 4 {
						return fmt.Errorf("Invalid jumbo packet option length")
					}
					payloadLength := binary.BigEndian.Uint32(o.OptionData)
					pEnd := int(payloadLength)
					if pEnd > len(ip6.Payload) {
						df.SetTruncated()
					} else {
						ip6.Payload = ip6.Payload[:pEnd]
						ip6.hbh.Payload = ip6.Payload
					}
					return nil
				}
			}
			return fmt.Errorf("IPv6 length 0, but HopByHop header does not have jumbogram option")
		}
	}
	if ip6.Length == 0 {
		return fmt.Errorf("IPv6 length 0, but next header is %v, not HopByHop", ip6.NextHeader)
	} else {
		pEnd := int(ip6.Length)
		if pEnd > len(ip6.Payload) {
			df.SetTruncated()
			pEnd = len(ip6.Payload)
		}
		ip6.Payload = ip6.Payload[:pEnd]
	}
	return nil
}

func (i *ICMPv4) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
	if len(data) < 8 {
		df.SetTruncated()
		return tooShort
	}
	i.TypeCode = ICMPv4TypeCode(binary.BigEndian.Uint16(data[:2]))
	i.Checksum = binary.BigEndian.Uint16(data[2:4])
	i.Id = binary.BigEndian.Uint16(data[4:6])
	i.Seq = binary.BigEndian.Uint16(data[6:8])
	i.BaseLayer = BaseLayer{data[:8], data[8:]}
	return nil
}

func (eth *Ethernet) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
	if len(data) < 14 {
		return errors.New("Ethernet packet too small")
	}
	eth.DstMAC = net.HardwareAddr(data[0:6])
	eth.SrcMAC = net.HardwareAddr(data[6:12])
	eth.EthernetType = EthernetType(binary.BigEndian.Uint16(data[12:14]))
	eth.BaseLayer = BaseLayer{data[:14], data[14:]}
	if eth.EthernetType < 0x0600 {
		eth.Length = uint16(eth.EthernetType)
		eth.EthernetType = EthernetTypeLLC
		if cmp := len(eth.Payload) - int(eth.Length); cmp < 0 {
			df.SetTruncated()
		} else if cmp > 0 {
			// Strip off bytes at the end, since we have too many bytes
			eth.Payload = eth.Payload[:len(eth.Payload)-cmp]
		}
		//	fmt.Println(eth)
	}
	return nil
}

func (udp *UDP) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
	udp.SrcPort = UDPPort(binary.BigEndian.Uint16(data[0:2]))
	udp.sPort = data[0:2]
	udp.DstPort = UDPPort(binary.BigEndian.Uint16(data[2:4]))
	udp.dPort = data[2:4]
	udp.Length = binary.BigEndian.Uint16(data[4:6])
	udp.Checksum = binary.BigEndian.Uint16(data[6:8])
	udp.BaseLayer = BaseLayer{Contents: data[:8]}
	switch {
	case udp.Length >= 8:
		hlen := int(udp.Length)
		if hlen > len(data) {
			df.SetTruncated()
			hlen = len(data)
		}
		udp.Payload = data[8:hlen]
	case udp.Length == 0: // Jumbogram, use entire rest of data
		udp.Payload = data[8:]
	default:
		return fmt.Errorf("UDP packet too small: %d bytes", udp.Length)
	}
	return nil
}

func (tcp *TCP) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
	tcp.SrcPort = TCPPort(binary.BigEndian.Uint16(data[0:2]))
	tcp.sPort = data[0:2]
	tcp.DstPort = TCPPort(binary.BigEndian.Uint16(data[2:4]))
	tcp.dPort = data[2:4]
	tcp.Seq = binary.BigEndian.Uint32(data[4:8])
	tcp.Ack = binary.BigEndian.Uint32(data[8:12])
	tcp.DataOffset = data[12] >> 4
	tcp.FIN = data[13]&0x01 != 0
	tcp.SYN = data[13]&0x02 != 0
	tcp.RST = data[13]&0x04 != 0
	tcp.PSH = data[13]&0x08 != 0
	tcp.ACK = data[13]&0x10 != 0
	tcp.URG = data[13]&0x20 != 0
	tcp.ECE = data[13]&0x40 != 0
	tcp.CWR = data[13]&0x80 != 0
	tcp.NS = data[12]&0x01 != 0
	tcp.Window = binary.BigEndian.Uint16(data[14:16])
	tcp.Checksum = binary.BigEndian.Uint16(data[16:18])
	tcp.Urgent = binary.BigEndian.Uint16(data[18:20])
	tcp.Options = tcp.opts[:0]
	if tcp.DataOffset < 5 {
		return fmt.Errorf("Invalid TCP data offset %d < 5", tcp.DataOffset)
	}
	dataStart := int(tcp.DataOffset) * 4
	if dataStart > len(data) {
		df.SetTruncated()
		tcp.Payload = nil
		tcp.Contents = data
		return errors.New("TCP data offset greater than packet length")
	}
	tcp.Contents = data[:dataStart]
	tcp.Payload = data[dataStart:]
	// From here on, data points just to the header options.
	data = data[20:dataStart]
	for len(data) > 0 {
		if tcp.Options == nil {
			// Pre-allocate to avoid allocating a slice.
			tcp.Options = tcp.opts[:0]
		}
		tcp.Options = append(tcp.Options, TCPOption{OptionType: data[0]})
		opt := &tcp.Options[len(tcp.Options)-1]
		switch opt.OptionType {
		case 0: // End of options
			opt.OptionLength = 1
			tcp.Padding = data[1:]
			break
		case 1: // 1 byte padding
			opt.OptionLength = 1
		default:
			opt.OptionLength = data[1]
			if opt.OptionLength < 2 {
				return fmt.Errorf("Invalid TCP option length %d < 2", opt.OptionLength)
			} else if int(opt.OptionLength) > len(data) {
				return fmt.Errorf("Invalid TCP option length %d exceeds remaining %d bytes", opt.OptionLength, len(data))
			}
			opt.OptionData = data[2:opt.OptionLength]
		}
		data = data[opt.OptionLength:]
	}
	return nil
}

// DecodeFromBytes decodes the given bytes into this layer.
func (ip *IPv4) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
	flagsfrags := binary.BigEndian.Uint16(data[6:8])

	ip.Version = uint8(data[0]) >> 4
	ip.IHL = uint8(data[0]) & 0x0F
	ip.TOS = data[1]
	ip.Length = binary.BigEndian.Uint16(data[2:4])
	ip.Id = binary.BigEndian.Uint16(data[4:6])
	ip.Flags = IPv4Flag(flagsfrags >> 13)
	ip.FragOffset = flagsfrags & 0x1FFF
	ip.TTL = data[8]
	ip.Protocol = IPProtocol(data[9])
	ip.Checksum = binary.BigEndian.Uint16(data[10:12])
	ip.SrcIP = data[12:16]
	ip.DstIP = data[16:20]
	// Set up an initial guess for contents/payload... we'll reset these soon.
	ip.BaseLayer = BaseLayer{Contents: data}

	if ip.Length < 20 {
		return fmt.Errorf("Invalid (too small) IP length (%d < 20)", ip.Length)
	} else if ip.IHL < 5 {
		return fmt.Errorf("Invalid (too small) IP header length (%d < 5)", ip.IHL)
	} else if int(ip.IHL*4) > int(ip.Length) {
		return fmt.Errorf("Invalid IP header length > IP length (%d > %d)", ip.IHL, ip.Length)
	}
	if cmp := len(data) - int(ip.Length); cmp > 0 {
		data = data[:ip.Length]
	} else if cmp < 0 {
		df.SetTruncated()
		if int(ip.IHL)*4 > len(data) {
			return fmt.Errorf("Not all IP header bytes available")
		}
	}
	ip.Contents = data[:ip.IHL*4]
	ip.Payload = data[ip.IHL*4:]
	// From here on, data contains the header options.
	data = data[20 : ip.IHL*4]
	// Pull out IP options
	for len(data) > 0 {
		if ip.Options == nil {
			// Pre-allocate to avoid growing the slice too much.
			ip.Options = make([]IPv4Option, 0, 4)
		}
		opt := IPv4Option{OptionType: data[0]}
		switch opt.OptionType {
		case 0: // End of options
			opt.OptionLength = 1
			ip.Options = append(ip.Options, opt)
			ip.Padding = data[1:]
			break
		case 1: // 1 byte padding
			opt.OptionLength = 1
		default:
			opt.OptionLength = data[1]
			opt.OptionData = data[2:opt.OptionLength]
		}
		if len(data) >= int(opt.OptionLength) {
			data = data[opt.OptionLength:]
		} else {
			return fmt.Errorf("IP option length exceeds remaining IP header size, option type %v length %v", opt.OptionType, opt.OptionLength)
		}
		ip.Options = append(ip.Options, opt)
	}
	return nil
}

// DecodeFromBytes decodes the slice into the DNS struct.
func (d *DNS) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
	d.buffer = d.buffer[:0]

	if len(data) < 12 {
		df.SetTruncated()
		return fmt.Errorf("DNS packet too short")
	}
	d.ID = binary.BigEndian.Uint16(data[:2])
	d.QR = data[2]&0x80 != 0
	d.OpCode = DNSOpCode(data[2]>>3) & 0x0F
	d.AA = data[2]&0x04 != 0
	d.TC = data[2]&0x02 != 0
	d.RD = data[2]&0x01 != 0
	d.RA = data[3]&0x80 != 0
	d.Z = uint8(data[3]>>4) & 0x7
	d.ResponseCode = DNSResponseCode(data[3] & 0xF)
	d.QDCount = binary.BigEndian.Uint16(data[4:6])
	d.ANCount = binary.BigEndian.Uint16(data[6:8])
	d.NSCount = binary.BigEndian.Uint16(data[8:10])
	d.ARCount = binary.BigEndian.Uint16(data[10:12])

	d.Questions = d.Questions[:0]
	d.Answers = d.Answers[:0]
	d.Authorities = d.Authorities[:0]
	d.Additionals = d.Additionals[:0]

	offset := 12
	var err error
	for i := 0; i < int(d.QDCount); i++ {
		var q DNSQuestion
		if offset, err = q.decode(data, offset, df, &d.buffer); err != nil {
			return err
		}
		d.Questions = append(d.Questions, q)
	}

	// For some horrible reason, if we do the obvious thing in this loop:
	//   var r DNSResourceRecord
	//   if blah := r.decode(blah); err != nil {
	//     return err
	//   }
	//   d.Foo = append(d.Foo, r)
	// the Go compiler thinks that 'r' escapes to the heap, causing a malloc for
	// every Answer, Authority, and Additional.  To get around this, we do
	// something really silly:  we append an empty resource record to our slice,
	// then use the last value in the slice to call decode.  Since the value is
	// already in the slice, there's no WAY it can escape... on the other hand our
	// code is MUCH uglier :(
	for i := 0; i < int(d.ANCount); i++ {
		d.Answers = append(d.Answers, DNSResourceRecord{})
		if offset, err = d.Answers[i].decode(data, offset, df, &d.buffer); err != nil {
			d.Answers = d.Answers[:i] // strip off erroneous value
			return err
		}
	}
	for i := 0; i < int(d.NSCount); i++ {
		d.Authorities = append(d.Authorities, DNSResourceRecord{})
		if offset, err = d.Authorities[i].decode(data, offset, df, &d.buffer); err != nil {
			d.Authorities = d.Authorities[:i] // strip off erroneous value
			return err
		}
	}
	for i := 0; i < int(d.ARCount); i++ {
		d.Additionals = append(d.Additionals, DNSResourceRecord{})
		if offset, err = d.Additionals[i].decode(data, offset, df, &d.buffer); err != nil {
			d.Additionals = d.Additionals[:i] // strip off erroneous value
			return err
		}
	}

	if uint16(len(d.Questions)) != d.QDCount {
		return errors.New("Invalid query decoding, not the right number of questions")
	} else if uint16(len(d.Answers)) != d.ANCount {
		return errors.New("Invalid query decoding, not the right number of answers")
	} else if uint16(len(d.Authorities)) != d.NSCount {
		return errors.New("Invalid query decoding, not the right number of authorities")
	} else if uint16(len(d.Additionals)) != d.ARCount {
		return errors.New("Invalid query decoding, not the right number of additionals info")
	}
	return nil
}