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// Package netutils provides network utility functions.
package netutils
import (
"context"
"crypto/rand"
"encoding/hex"
"fmt"
"io"
"net"
"strings"
"sync"
"github.com/containerd/log"
)
func genMAC(ip net.IP) net.HardwareAddr {
hw := make(net.HardwareAddr, 6)
// The first byte of the MAC address has to comply with these rules:
// 1. Unicast: Set the least-significant bit to 0.
// 2. Address is locally administered: Set the second-least-significant bit (U/L) to 1.
hw[0] = 0x02
// The first 24 bits of the MAC represent the Organizationally Unique Identifier (OUI).
// Since this address is locally administered, we can do whatever we want as long as
// it doesn't conflict with other addresses.
hw[1] = 0x42
// Fill the remaining 4 bytes based on the input
if ip == nil {
rand.Read(hw[2:])
} else {
copy(hw[2:], ip.To4())
}
return hw
}
// GenerateRandomMAC returns a new 6-byte(48-bit) hardware address (MAC)
func GenerateRandomMAC() net.HardwareAddr {
return genMAC(nil)
}
// GenerateMACFromIP returns a locally administered MAC address where the 4 least
// significant bytes are derived from the IPv4 address.
func GenerateMACFromIP(ip net.IP) net.HardwareAddr {
return genMAC(ip)
}
// GenerateRandomName returns a string of the specified length, created by joining the prefix to random hex characters.
// The length must be strictly larger than len(prefix), or an error will be returned.
func GenerateRandomName(prefix string, length int) (string, error) {
if length <= len(prefix) {
return "", fmt.Errorf("invalid length %d for prefix %s", length, prefix)
}
// We add 1 here as integer division will round down, and we want to round up.
b := make([]byte, (length-len(prefix)+1)/2)
if _, err := io.ReadFull(rand.Reader, b); err != nil {
return "", err
}
// By taking a slice here, we ensure that the string is always the correct length.
return (prefix + hex.EncodeToString(b))[:length], nil
}
// ReverseIP accepts a V4 or V6 IP string in the canonical form and returns a reversed IP in
// the dotted decimal form . This is used to setup the IP to service name mapping in the optimal
// way for the DNS PTR queries.
func ReverseIP(IP string) string {
var reverseIP []string
if net.ParseIP(IP).To4() != nil {
reverseIP = strings.Split(IP, ".")
l := len(reverseIP)
for i, j := 0, l-1; i < l/2; i, j = i+1, j-1 {
reverseIP[i], reverseIP[j] = reverseIP[j], reverseIP[i]
}
} else {
reverseIP = strings.Split(IP, ":")
// Reversed IPv6 is represented in dotted decimal instead of the typical
// colon hex notation
for key := range reverseIP {
if len(reverseIP[key]) == 0 { // expand the compressed 0s
reverseIP[key] = strings.Repeat("0000", 8-strings.Count(IP, ":"))
} else if len(reverseIP[key]) < 4 { // 0-padding needed
reverseIP[key] = strings.Repeat("0", 4-len(reverseIP[key])) + reverseIP[key]
}
}
reverseIP = strings.Split(strings.Join(reverseIP, ""), "")
l := len(reverseIP)
for i, j := 0, l-1; i < l/2; i, j = i+1, j-1 {
reverseIP[i], reverseIP[j] = reverseIP[j], reverseIP[i]
}
}
return strings.Join(reverseIP, ".")
}
var (
v6ListenableCached bool
v6ListenableOnce sync.Once
)
// IsV6Listenable returns true when `[::1]:0` is listenable.
// IsV6Listenable returns false mostly when the kernel was booted with `ipv6.disable=1` option.
func IsV6Listenable() bool {
v6ListenableOnce.Do(func() {
ln, err := net.Listen("tcp6", "[::1]:0")
if err != nil {
// When the kernel was booted with `ipv6.disable=1`,
// we get err "listen tcp6 [::1]:0: socket: address family not supported by protocol"
// https://github.com/moby/moby/issues/42288
log.G(context.TODO()).Debugf("v6Listenable=false (%v)", err)
} else {
v6ListenableCached = true
ln.Close()
}
})
return v6ListenableCached
}
// MustParseMAC returns a net.HardwareAddr or panic.
func MustParseMAC(s string) net.HardwareAddr {
mac, err := net.ParseMAC(s)
if err != nil {
panic(err)
}
return mac
}
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