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