status-go/vendor/github.com/anacrolix/torrent/bep40.go

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2022-03-10 09:44:48 +00:00
package torrent
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"hash/crc32"
"net"
)
var table = crc32.MakeTable(crc32.Castagnoli)
type peerPriority = uint32
func sameSubnet(ones, bits int, a, b net.IP) bool {
mask := net.CIDRMask(ones, bits)
return a.Mask(mask).Equal(b.Mask(mask))
}
func ipv4Mask(a, b net.IP) net.IPMask {
if !sameSubnet(16, 32, a, b) {
return net.IPv4Mask(0xff, 0xff, 0x55, 0x55)
}
if !sameSubnet(24, 32, a, b) {
return net.IPv4Mask(0xff, 0xff, 0xff, 0x55)
}
return net.IPv4Mask(0xff, 0xff, 0xff, 0xff)
}
func mask(prefix, bytes int) net.IPMask {
ret := make(net.IPMask, bytes)
for i := range ret {
ret[i] = 0x55
}
for i := 0; i < prefix; i++ {
ret[i] = 0xff
}
return ret
}
func ipv6Mask(a, b net.IP) net.IPMask {
for i := 6; i <= 16; i++ {
if !sameSubnet(i*8, 128, a, b) {
return mask(i, 16)
}
}
panic(fmt.Sprintf("%s %s", a, b))
}
func bep40PriorityBytes(a, b IpPort) ([]byte, error) {
if a.IP.Equal(b.IP) {
var ret [4]byte
binary.BigEndian.PutUint16(ret[0:2], a.Port)
binary.BigEndian.PutUint16(ret[2:4], b.Port)
return ret[:], nil
}
if a4, b4 := a.IP.To4(), b.IP.To4(); a4 != nil && b4 != nil {
m := ipv4Mask(a.IP, b.IP)
return append(a4.Mask(m), b4.Mask(m)...), nil
}
if a6, b6 := a.IP.To16(), b.IP.To16(); a6 != nil && b6 != nil {
m := ipv6Mask(a.IP, b.IP)
return append(a6.Mask(m), b6.Mask(m)...), nil
}
return nil, errors.New("incomparable IPs")
}
func bep40Priority(a, b IpPort) (peerPriority, error) {
bs, err := bep40PriorityBytes(a, b)
if err != nil {
return 0, err
}
i := len(bs) / 2
_a, _b := bs[:i], bs[i:]
if bytes.Compare(_a, _b) > 0 {
bs = append(_b, _a...)
}
return crc32.Checksum(bs, table), nil
}
func bep40PriorityIgnoreError(a, b IpPort) peerPriority {
prio, _ := bep40Priority(a, b)
return prio
}