dissertation-2-code/proxy/packet.go

package proxy

import (
	"encoding/binary"
	"time"
)

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

type SimplePacket struct {
	Data      []byte
	timestamp time.Time
}

// create a packet from the raw data of an IP packet
func NewSimplePacket(data []byte) Packet {
	return SimplePacket{
		Data:      data,
		timestamp: time.Now(),
	}
}

// rebuild a packet from the wrapped format
func UnmarshalSimplePacket(data []byte) (SimplePacket, error) {
	p := SimplePacket{
		Data: data[:len(data)-8],
	}

	unixTime := int64(binary.LittleEndian.Uint64(data[len(data)-8:]))
	p.timestamp = time.Unix(unixTime, 0)

	return p, nil
}

// get the raw data of the IP packet
func (p SimplePacket) Marshal() []byte {
	footer := make([]byte, 8)

	unixTime := uint64(p.timestamp.Unix())
	binary.LittleEndian.PutUint64(footer, unixTime)

	return append(p.Data, footer...)
}

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

func AppendMac(b []byte, g MacGenerator) []byte {
	mac := g.Generate(b)
	b = append(b, mac...)
	return b
}

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
	}

	return data, nil
}