75 lines
1.7 KiB
Go
75 lines
1.7 KiB
Go
package common
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import (
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"net"
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"sort"
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"strings"
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)
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// GetOutboundIP returns an outbound IP address of this machine.
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// It tries to access the internet and returns the local IP address of the connection.
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// If the machine cannot access the internet, it returns a preferred IP address from network interfaces.
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// It returns nil if no IP address is found.
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func GetOutboundIP() net.IP {
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// See https://stackoverflow.com/a/37382208
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conn, err := net.Dial("udp", "8.8.8.8:80")
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if err == nil {
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defer conn.Close()
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return conn.LocalAddr().(*net.UDPAddr).IP
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}
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// So the machine cannot access the internet. Pick an IP address from network interfaces.
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if ifs, err := net.Interfaces(); err == nil {
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type IP struct {
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net.IP
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net.Interface
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}
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var ips []IP
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for _, i := range ifs {
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if addrs, err := i.Addrs(); err == nil {
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for _, addr := range addrs {
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var ip net.IP
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switch v := addr.(type) {
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case *net.IPNet:
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ip = v.IP
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case *net.IPAddr:
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ip = v.IP
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}
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if ip.IsGlobalUnicast() {
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ips = append(ips, IP{ip, i})
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}
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}
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}
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}
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if len(ips) > 1 {
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sort.Slice(ips, func(i, j int) bool {
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ifi := ips[i].Interface
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ifj := ips[j].Interface
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// ethernet is preferred
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if vi, vj := strings.HasPrefix(ifi.Name, "e"), strings.HasPrefix(ifj.Name, "e"); vi != vj {
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return vi
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}
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ipi := ips[i].IP
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ipj := ips[j].IP
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// IPv4 is preferred
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if vi, vj := ipi.To4() != nil, ipj.To4() != nil; vi != vj {
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return vi
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}
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// en0 is preferred to en1
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if ifi.Name != ifj.Name {
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return ifi.Name < ifj.Name
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}
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// fallback
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return ipi.String() < ipj.String()
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})
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return ips[0].IP
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}
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}
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return nil
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}
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