badge.go

package badge

import (
	"bytes"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
)

func New(username []byte, id uint32, key []byte) []byte {
	if username == nil || len(username) > 255 || len(username) == 0 {
		return nil
	}

	badge := make([]byte, (len(username))+54)
	hex.Encode(badge[:2], []byte{byte(uint8(len(username)))})

	for i := 2; i <= len(username)+1; i++ {
		badge[i] = username[i-2]
	}

	idb := make([]byte, 4)

	idb[3] = byte((id & 0xff000000) >> 24)
	idb[2] = byte((id & 0x00ff0000) >> 16)
	idb[1] = byte((id & 0x0000ff00) >> 8)
	idb[0] = byte((id & 0x000000ff))

	hex.Encode(badge[2+(len(username)):], idb)

	h := hmac.New(sha256.New, key)
	h.Write(badge[:10+len(username)])

	base64.URLEncoding.Encode(badge[10+len(username):], h.Sum(nil))

	return badge
}

func Get(badge []byte, key []byte) ([]byte, uint32, bool) {
	if len(badge) < 46 {
		return nil, 0, false
	}

	lb := make([]byte, 1)
	hex.Decode(lb, badge[:2])

	l := uint8(lb[0])
	if l > 255 || len(badge) != (int(l)+54) {
		return nil, 0, false
	}

	username := make([]byte, l)
	for a := 0; a < int(l); a++ {
		username[a] = badge[a+2]
	}

	idb := make([]byte, 4)
	hex.Decode(idb, badge[2+l:l+10])

	var i uint32

	i |= uint32(idb[3]) << 24
	i |= uint32(idb[2]) << 16
	i |= uint32(idb[1]) << 8
	i |= uint32(idb[0])

	h := hmac.New(sha256.New, key)
	h.Write(badge[:10+l])

	t := make([]byte, 44)

	base64.URLEncoding.Encode(t, h.Sum(nil))

	if !bytes.Equal(t, badge[10+l:]) {
		return nil, 0, false
	}

	return username, i, true
}