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package models
import (
"crypto/sha1"
"encoding/hex"
"fmt"
"io"
"math/rand"
"time"
)
const InfohashLength = 20
// Infohash is a 160 bit (20 byte) value
type Infohash []byte
// InfohashFromString converts a 40 digit hexadecimal string to an Infohash
func InfohashFromString(s string) (*Infohash, error) {
switch len(s) {
case 20:
// Binary string
ih := Infohash([]byte(s))
return &ih, nil
case 40:
// Hex string
b, err := hex.DecodeString(s)
if err != nil {
return nil, err
}
ih := Infohash(b)
return &ih, nil
default:
return nil, fmt.Errorf("invalid length %d", len(s))
}
}
func (ih Infohash) String() string {
return hex.EncodeToString(ih)
}
func (ih Infohash) Bytes() []byte {
return []byte(ih)
}
func (ih Infohash) Valid() bool {
// TODO
return len(ih) == 20
}
func (ih Infohash) Equal(other Infohash) bool {
if len(ih) != len(other) {
return false
}
for i := 0; i < len(ih); i++ {
if ih[i] != other[i] {
return false
}
}
return true
}
// Distance determines the distance to another infohash as an integer
func (ih Infohash) Distance(other Infohash) int {
i := 0
for ; i < 20; i++ {
if ih[i] != other[i] {
break
}
}
if i == 20 {
return 160
}
xor := ih[i] ^ other[i]
j := 0
for (xor & 0x80) == 0 {
xor <<= 1
j++
}
return 8*i + j
}
func GenerateNeighbour(first, second Infohash) Infohash {
s := append(second[:10], first[10:]...)
return Infohash(s)
}
func GenInfohash() (ih Infohash) {
random := rand.New(rand.NewSource(time.Now().UnixNano()))
hash := sha1.New()
io.WriteString(hash, time.Now().String())
io.WriteString(hash, string(random.Int()))
return Infohash(hash.Sum(nil))
}
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