path_attributes.go

package packet

import (
	"bytes"
	"fmt"

	"github.com/taktv6/tflow2/convert"
)

func decodePathAttrs(buf *bytes.Buffer, tpal uint16, opt *Options) (*PathAttribute, error) {
	var ret *PathAttribute
	var eol *PathAttribute
	var pa *PathAttribute
	var err error
	var consumed uint16

	p := uint16(0)
	for p < tpal {
		pa, consumed, err = decodePathAttr(buf, opt)
		if err != nil {
			return nil, fmt.Errorf("Unable to decode path attr: %v", err)
		}
		p += consumed

		if ret == nil {
			ret = pa
			eol = pa
		} else {
			eol.Next = pa
			eol = pa
		}
	}

	return ret, nil
}

func decodePathAttr(buf *bytes.Buffer, opt *Options) (pa *PathAttribute, consumed uint16, err error) {
	pa = &PathAttribute{}

	err = decodePathAttrFlags(buf, pa)
	if err != nil {
		return nil, consumed, fmt.Errorf("Unable to get path attribute flags: %v", err)
	}
	consumed++

	err = decode(buf, []interface{}{&pa.TypeCode})
	if err != nil {
		return nil, consumed, err
	}
	consumed++

	n, err := pa.setLength(buf)
	if err != nil {
		return nil, consumed, err
	}
	consumed += uint16(n)

	switch pa.TypeCode {
	case OriginAttr:
		if err := pa.decodeOrigin(buf); err != nil {
			return nil, consumed, fmt.Errorf("Failed to decode Origin: %v", err)
		}
	case ASPathAttr:
		asnLength := uint8(2)
		if opt.Supports4OctetASN {
			asnLength = 4
		}

		if err := pa.decodeASPath(buf, asnLength); err != nil {
			return nil, consumed, fmt.Errorf("Failed to decode AS Path: %v", err)
		}
	case AS4PathAttr:
		if err := pa.decodeASPath(buf, 4); err != nil {
			return nil, consumed, fmt.Errorf("Failed to decode AS4 Path: %v", err)
		}
	case NextHopAttr:
		if err := pa.decodeNextHop(buf); err != nil {
			return nil, consumed, fmt.Errorf("Failed to decode Next-Hop: %v", err)
		}
	case MEDAttr:
		if err := pa.decodeMED(buf); err != nil {
			return nil, consumed, fmt.Errorf("Failed to decode MED: %v", err)
		}
	case LocalPrefAttr:
		if err := pa.decodeLocalPref(buf); err != nil {
			return nil, consumed, fmt.Errorf("Failed to decode local pref: %v", err)
		}
	case AggregatorAttr:
		if err := pa.decodeAggregator(buf); err != nil {
			return nil, consumed, fmt.Errorf("Failed to decode Aggregator: %v", err)
		}
	case AtomicAggrAttr:
		// Nothing to do for 0 octet long attribute
	case CommunitiesAttr:
		if err := pa.decodeCommunities(buf); err != nil {
			return nil, consumed, fmt.Errorf("Failed to decode Community: %v", err)
		}
	case AS4AggregatorAttr:
		if err := pa.decodeAS4Aggregator(buf); err != nil {
			return nil, consumed, fmt.Errorf("Failed to skip not supported AS4Aggregator: %v", err)
		}
	case LargeCommunitiesAttr:
		if err := pa.decodeLargeCommunities(buf); err != nil {
			return nil, consumed, fmt.Errorf("Failed to decode large communities: %v", err)
		}
	default:
		if err := pa.decodeUnknown(buf); err != nil {
			return nil, consumed, fmt.Errorf("Failed to decode unknown attribute: %v", err)
		}
	}

	return pa, consumed + pa.Length, nil
}

func (pa *PathAttribute) decodeUnknown(buf *bytes.Buffer) error {
	u := make([]byte, pa.Length)

	p := uint16(0)
	err := decode(buf, []interface{}{&u})
	if err != nil {
		return fmt.Errorf("Unable to decode: %v", err)
	}

	pa.Value = u
	p += pa.Length

	return nil
}

func (pa *PathAttribute) decodeOrigin(buf *bytes.Buffer) error {
	origin := uint8(0)

	p := uint16(0)
	err := decode(buf, []interface{}{&origin})
	if err != nil {
		return fmt.Errorf("Unable to decode: %v", err)
	}

	pa.Value = origin
	p++

	return dumpNBytes(buf, pa.Length-p)
}

func (pa *PathAttribute) decodeASPath(buf *bytes.Buffer, asnLength uint8) error {
	pa.Value = make(ASPath, 0)
	p := uint16(0)
	for p < pa.Length {
		segment := ASPathSegment{}

		err := decode(buf, []interface{}{&segment.Type, &segment.Count})
		if err != nil {
			return err
		}
		p += 2

		if segment.Type != ASSet && segment.Type != ASSequence {
			return fmt.Errorf("Invalid AS Path segment type: %d", segment.Type)
		}

		if segment.Count == 0 {
			return fmt.Errorf("Invalid AS Path segment length: %d", segment.Count)
		}

		segment.ASNs = make([]uint32, segment.Count)
		for i := uint8(0); i < segment.Count; i++ {
			asn, err := pa.decodeASN(buf, asnLength)
			if err != nil {
				return err
			}
			p += uint16(asnLength)

			segment.ASNs[i] = asn
		}

		pa.Value = append(pa.Value.(ASPath), segment)
	}

	return nil
}

func (pa *PathAttribute) decodeASN(buf *bytes.Buffer, asnSize uint8) (asn uint32, err error) {
	if asnSize == 4 {
		return pa.decode4ByteASN(buf)
	}

	return pa.decode2ByteASN(buf)
}

func (pa *PathAttribute) decode4ByteASN(buf *bytes.Buffer) (asn uint32, err error) {
	asn4 := uint32(0)
	err = decode(buf, []interface{}{&asn4})
	if err != nil {
		return 0, err
	}

	return uint32(asn4), nil
}

func (pa *PathAttribute) decode2ByteASN(buf *bytes.Buffer) (asn uint32, err error) {
	asn4 := uint16(0)
	err = decode(buf, []interface{}{&asn4})
	if err != nil {
		return 0, err
	}

	return uint32(asn4), nil
}

func (pa *PathAttribute) decodeNextHop(buf *bytes.Buffer) error {
	return pa.decodeUint32(buf, "next hop")
}

func (pa *PathAttribute) decodeMED(buf *bytes.Buffer) error {
	return pa.decodeUint32(buf, "MED")
}

func (pa *PathAttribute) decodeLocalPref(buf *bytes.Buffer) error {
	return pa.decodeUint32(buf, "local pref")
}

func (pa *PathAttribute) decodeAggregator(buf *bytes.Buffer) error {
	aggr := Aggretator{}
	p := uint16(0)

	err := decode(buf, []interface{}{&aggr.ASN})
	if err != nil {
		return err
	}
	p += 2

	addr := [4]byte{}
	n, err := buf.Read(addr[:])
	if err != nil {
		return err
	}
	if n != 4 {
		return fmt.Errorf("Unable to read next hop: buf.Read read %d bytes", n)
	}
	aggr.Addr = fourBytesToUint32(addr)

	pa.Value = aggr
	p += 4

	return dumpNBytes(buf, pa.Length-p)
}

func (pa *PathAttribute) decodeCommunities(buf *bytes.Buffer) error {
	if pa.Length%CommunityLen != 0 {
		return fmt.Errorf("Unable to read community path attribute. Length %d is not divisible by 4", pa.Length)
	}

	count := pa.Length / CommunityLen
	coms := make([]uint32, count)

	for i := uint16(0); i < count; i++ {
		v, err := read4BytesAsUint32(buf)
		if err != nil {
			return err
		}
		coms[i] = v
	}

	pa.Value = coms
	return nil
}

func (pa *PathAttribute) decodeLargeCommunities(buf *bytes.Buffer) error {
	if pa.Length%LargeCommunityLen != 0 {
		return fmt.Errorf("Unable to read large community path attribute. Length %d is not divisible by 12", pa.Length)
	}

	count := pa.Length / LargeCommunityLen
	coms := make([]LargeCommunity, count)

	for i := uint16(0); i < count; i++ {
		com := LargeCommunity{}

		v, err := read4BytesAsUint32(buf)
		if err != nil {
			return err
		}
		com.GlobalAdministrator = v

		v, err = read4BytesAsUint32(buf)
		if err != nil {
			return err
		}
		com.DataPart1 = v

		v, err = read4BytesAsUint32(buf)
		if err != nil {
			return err
		}
		com.DataPart2 = v

		coms[i] = com
	}

	pa.Value = coms
	return nil
}

func (pa *PathAttribute) decodeAS4Aggregator(buf *bytes.Buffer) error {
	return pa.decodeUint32(buf, "AS4Aggregator")
}

func (pa *PathAttribute) decodeUint32(buf *bytes.Buffer, attrName string) error {
	v, err := read4BytesAsUint32(buf)
	if err != nil {
		return fmt.Errorf("Unable to decode %s: %v", attrName, err)
	}

	pa.Value = v

	p := uint16(4)
	err = dumpNBytes(buf, pa.Length-p)
	if err != nil {
		return fmt.Errorf("dumpNBytes failed: %v", err)
	}

	return nil
}

func (pa *PathAttribute) setLength(buf *bytes.Buffer) (int, error) {
	bytesRead := 0
	if pa.ExtendedLength {
		err := decode(buf, []interface{}{&pa.Length})
		if err != nil {
			return 0, err
		}
		bytesRead = 2
	} else {
		x := uint8(0)
		err := decode(buf, []interface{}{&x})
		if err != nil {
			return 0, err
		}
		pa.Length = uint16(x)
		bytesRead = 1
	}
	return bytesRead, nil
}

// dumpNBytes is used to dump n bytes of buf. This is useful in case an path attributes
// length doesn't match a fixed length's attributes length (e.g. ORIGIN is always an octet)
func dumpNBytes(buf *bytes.Buffer, n uint16) error {
	if n <= 0 {
		return nil
	}
	dump := make([]byte, n)
	err := decode(buf, []interface{}{&dump})
	if err != nil {
		return err
	}
	return nil
}

func (pa *PathAttribute) serialize(buf *bytes.Buffer, opt *Options) uint8 {
	pathAttrLen := uint8(0)

	switch pa.TypeCode {
	case OriginAttr:
		pathAttrLen = pa.serializeOrigin(buf)
	case ASPathAttr:
		pathAttrLen = pa.serializeASPath(buf, opt)
	case NextHopAttr:
		pathAttrLen = pa.serializeNextHop(buf)
	case MEDAttr:
		pathAttrLen = pa.serializeMED(buf)
	case LocalPrefAttr:
		pathAttrLen = pa.serializeLocalpref(buf)
	case AtomicAggrAttr:
		pathAttrLen = pa.serializeAtomicAggregate(buf)
	case AggregatorAttr:
		pathAttrLen = pa.serializeAggregator(buf)
	case CommunitiesAttr:
		pathAttrLen = pa.serializeCommunities(buf)
	case LargeCommunitiesAttr:
		pathAttrLen = pa.serializeLargeCommunities(buf)
	}

	return pathAttrLen
}

func (pa *PathAttribute) serializeOrigin(buf *bytes.Buffer) uint8 {
	attrFlags := uint8(0)
	attrFlags = setTransitive(attrFlags)
	buf.WriteByte(attrFlags)
	buf.WriteByte(OriginAttr)
	length := uint8(1)
	buf.WriteByte(length)
	buf.WriteByte(pa.Value.(uint8))
	return 4
}

func (pa *PathAttribute) serializeASPath(buf *bytes.Buffer, opt *Options) uint8 {
	attrFlags := uint8(0)
	attrFlags = setTransitive(attrFlags)
	buf.WriteByte(attrFlags)
	buf.WriteByte(ASPathAttr)

	asnLength := uint8(2)
	if opt.Supports4OctetASN {
		asnLength = 4
	}

	length := uint8(0)
	segmentsBuf := bytes.NewBuffer(nil)
	for _, segment := range pa.Value.(ASPath) {
		segmentsBuf.WriteByte(segment.Type)
		segmentsBuf.WriteByte(uint8(len(segment.ASNs)))

		for _, asn := range segment.ASNs {
			if asnLength == 2 {
				segmentsBuf.Write(convert.Uint16Byte(uint16(asn)))
			} else {
				segmentsBuf.Write(convert.Uint32Byte(asn))
			}
		}
		fmt.Println(segment.ASNs)
		length += 2 + uint8(len(segment.ASNs))*asnLength
	}

	buf.WriteByte(length)
	buf.Write(segmentsBuf.Bytes())

	return length + 2
}

func (pa *PathAttribute) serializeNextHop(buf *bytes.Buffer) uint8 {
	attrFlags := uint8(0)
	attrFlags = setTransitive(attrFlags)
	buf.WriteByte(attrFlags)
	buf.WriteByte(NextHopAttr)
	length := uint8(4)
	buf.WriteByte(length)
	addr := pa.Value.(uint32)
	buf.Write(convert.Uint32Byte(addr))
	return 7
}

func (pa *PathAttribute) serializeMED(buf *bytes.Buffer) uint8 {
	attrFlags := uint8(0)
	attrFlags = setOptional(attrFlags)
	buf.WriteByte(attrFlags)
	buf.WriteByte(MEDAttr)
	length := uint8(4)
	buf.WriteByte(length)
	buf.Write(convert.Uint32Byte(pa.Value.(uint32)))
	return 7
}

func (pa *PathAttribute) serializeLocalpref(buf *bytes.Buffer) uint8 {
	attrFlags := uint8(0)
	attrFlags = setTransitive(attrFlags)
	buf.WriteByte(attrFlags)
	buf.WriteByte(LocalPrefAttr)
	length := uint8(4)
	buf.WriteByte(length)
	buf.Write(convert.Uint32Byte(pa.Value.(uint32)))
	return 7
}

func (pa *PathAttribute) serializeAtomicAggregate(buf *bytes.Buffer) uint8 {
	attrFlags := uint8(0)
	attrFlags = setTransitive(attrFlags)
	buf.WriteByte(attrFlags)
	buf.WriteByte(AtomicAggrAttr)
	length := uint8(0)
	buf.WriteByte(length)
	return 3
}

func (pa *PathAttribute) serializeAggregator(buf *bytes.Buffer) uint8 {
	attrFlags := uint8(0)
	attrFlags = setOptional(attrFlags)
	attrFlags = setTransitive(attrFlags)
	buf.WriteByte(attrFlags)
	buf.WriteByte(AggregatorAttr)
	length := uint8(2)
	buf.WriteByte(length)
	buf.Write(convert.Uint16Byte(pa.Value.(uint16)))
	return 5
}

func (pa *PathAttribute) serializeCommunities(buf *bytes.Buffer) uint8 {
	coms := pa.Value.([]uint32)
	if len(coms) == 0 {
		return 0
	}

	attrFlags := uint8(0)
	attrFlags = setOptional(attrFlags)
	attrFlags = setTransitive(attrFlags)
	attrFlags = setPartial(attrFlags)
	buf.WriteByte(attrFlags)
	buf.WriteByte(CommunitiesAttr)

	length := uint8(CommunityLen * len(coms))

	buf.WriteByte(length)

	for _, com := range coms {
		buf.Write(convert.Uint32Byte(com))
	}

	return length
}

func (pa *PathAttribute) serializeLargeCommunities(buf *bytes.Buffer) uint8 {
	coms := pa.Value.([]LargeCommunity)
	if len(coms) == 0 {
		return 0
	}

	attrFlags := uint8(0)
	attrFlags = setOptional(attrFlags)
	attrFlags = setTransitive(attrFlags)
	attrFlags = setPartial(attrFlags)
	buf.WriteByte(attrFlags)
	buf.WriteByte(LargeCommunitiesAttr)

	length := uint8(LargeCommunityLen * len(coms))

	buf.WriteByte(length)

	for _, com := range coms {
		buf.Write(convert.Uint32Byte(com.GlobalAdministrator))
		buf.Write(convert.Uint32Byte(com.DataPart1))
		buf.Write(convert.Uint32Byte(com.DataPart2))
	}

	return length
}

func fourBytesToUint32(address [4]byte) uint32 {
	return uint32(address[0])<<24 + uint32(address[1])<<16 + uint32(address[2])<<8 + uint32(address[3])
}

func read4BytesAsUint32(buf *bytes.Buffer) (uint32, error) {
	b := [4]byte{}
	n, err := buf.Read(b[:])
	if err != nil {
		return 0, err
	}
	if n != 4 {
		return 0, fmt.Errorf("Unable to read as uint32. Expected 4 bytes but got only %d", n)
	}

	return fourBytesToUint32(b), nil
}