Method DecodeFromBytes

layers/bfd.go:329–397

DecodeFromBytes analyses a byte slice and attempts to decode it as a BFD control packet. Upon succeeds, it loads the BFD object with information about the packet and returns nil. Upon failure, it returns an error (non nil).

(data []byte, df gopacket.DecodeFeedback)

// and returns nil.
// Upon failure, it returns an error (non nil).
func (d *BFD) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {

	// If the data block is too short to be a BFD record, then return an error.
	if len(data) < bfdMinimumRecordSizeInBytes {
		df.SetTruncated()
		return errors.New("BFD packet too short")
	}

	pLen := uint8(data[3])
	if len(data) != int(pLen) {
		return errors.New("BFD packet length does not match")
	}

	// BFD type embeds type BaseLayer which contains two fields:
	//    Contents is supposed to contain the bytes of the data at this level.
	//    Payload is supposed to contain the payload of this level.
	// Here we set the baselayer to be the bytes of the BFD record.
	d.BaseLayer = BaseLayer{Contents: data[:len(data)]}

	// Extract the fields from the block of bytes.
	// To make sense of this, refer to the packet diagram
	// above and the section on endian conventions.

	// The first few fields are all packed into the first 32 bits. Unpack them.
	d.Version = BFDVersion(((data[0] & 0xE0) >> 5))
	d.Diagnostic = BFDDiagnostic(data[0] & 0x1F)
	data = data[1:]

	d.State = BFDState((data[0] & 0xC0) >> 6)
	d.Poll = data[0]&0x20 != 0
	d.Final = data[0]&0x10 != 0
	d.ControlPlaneIndependent = data[0]&0x08 != 0
	d.AuthPresent = data[0]&0x04 != 0
	d.Demand = data[0]&0x02 != 0
	d.Multipoint = data[0]&0x01 != 0
	data = data[1:]

	data, d.DetectMultiplier = data[1:], BFDDetectMultiplier(data[0])
	data, _ = data[1:], uint8(data[0]) // Consume length

	// The remaining fields can just be copied in big endian order.
	data, d.MyDiscriminator = data[4:], BFDDiscriminator(binary.BigEndian.Uint32(data[:4]))
	data, d.YourDiscriminator = data[4:], BFDDiscriminator(binary.BigEndian.Uint32(data[:4]))
	data, d.DesiredMinTxInterval = data[4:], BFDTimeInterval(binary.BigEndian.Uint32(data[:4]))
	data, d.RequiredMinRxInterval = data[4:], BFDTimeInterval(binary.BigEndian.Uint32(data[:4]))
	data, d.RequiredMinEchoRxInterval = data[4:], BFDTimeInterval(binary.BigEndian.Uint32(data[:4]))

	if d.AuthPresent && (len(data) > 2) {
		d.AuthHeader = &BFDAuthHeader{}
		data, d.AuthHeader.AuthType = data[1:], BFDAuthType(data[0])
		data, _ = data[1:], uint8(data[0]) // Consume length
		data, d.AuthHeader.KeyID = data[1:], BFDAuthKeyID(data[0])

		switch d.AuthHeader.AuthType {
		case BFDAuthTypePassword:
			d.AuthHeader.Data = BFDAuthData(data)
		case BFDAuthTypeKeyedMD5, BFDAuthTypeMeticulousKeyedMD5:
			// Skipped reserved byte