dissertation-2-code/proxy/packet.go

package proxy

import (
	"encoding/binary"
	"time"
)

type Packet interface {
	Marshal() []byte
	Contents() []byte
}

type SimplePacket []byte

// get the raw data of the IP packet
func (p SimplePacket) Marshal() []byte {
	return p
}

func (p SimplePacket) Contents() []byte {
	return p
}

func AppendMac(b []byte, g MacGenerator) []byte {
	footer := make([]byte, 8)
	unixTime := uint64(time.Now().Unix())
	binary.LittleEndian.PutUint64(footer, unixTime)

	b = append(b, footer...)

	mac := g.Generate(b)
	return append(b, mac...)
}

func StripMac(b []byte, v MacVerifier) ([]byte, error) {
	data := b[:len(b)-v.CodeLength()]
	sum := b[len(b)-v.CodeLength():]

	if err := v.Verify(data, sum); err != nil {
		return nil, err
	}

	// TODO: Verify timestamp

	return data[:len(data)-8], nil
}