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package failover
import (
"fmt"
"net"
"os"
"time"
"golang.org/x/net/icmp"
"golang.org/x/net/ipv4"
"golang.org/x/net/ipv6"
)
var (
// mtuV4Overhead defines the total MTU overhead for an ICMP ECHO message: 20 bytes IP header + 8 bytes ICMP header
mtuV4Overhead = 28
// mtuV6Overhead defines the total MTU v6 overhead for an ICMP ECHO message: 40 bytes IP header + 8 bytes ICMP header
mtuV6Overhead = 48
)
// Pinger sends pings
type Pinger struct {
listener net.PacketConn
buffer []byte
gateway net.Addr
v4 bool
}
// Read reads from the ping listener with deadline `deadline`
func (p Pinger) Read(deadline time.Time) error {
// First set the deadline to read
err := p.listener.SetReadDeadline(deadline)
if err != nil {
return err
}
r := make([]byte, 1500)
n, _, err := p.listener.ReadFrom(r)
if err != nil {
return err
}
var t icmp.Type
if p.v4 {
t = ipv4.ICMPTypeEchoReply
} else {
t = ipv6.ICMPTypeEchoReply
}
got, err := icmp.ParseMessage(t.Protocol(), r[:n])
if err != nil {
return err
}
switch got.Type {
case t:
return nil
default:
return fmt.Errorf("not a ping echo reply, got: %+v", got)
}
}
// Send sends a single ping
func (p Pinger) Send(seq int) error {
errorMessage := fmt.Sprintf("failed sending ping, seq %d", seq)
// Make a new ICMP message
var t icmp.Type
if p.v4 {
t = ipv4.ICMPTypeEcho
} else {
t = ipv6.ICMPTypeEchoRequest
}
m := icmp.Message{
Type: t,
Code: 0,
Body: &icmp.Echo{
ID: os.Getpid() & 0xffff,
Seq: seq,
Data: p.buffer,
},
}
// Marshal the message to bytes
b, err := m.Marshal(nil)
if err != nil {
return fmt.Errorf("%s with error: %w", errorMessage, err)
}
// And send it to the gateway IP!
_, err = p.listener.WriteTo(b, p.gateway)
if err != nil {
return fmt.Errorf("%s with error: %w", errorMessage, err)
}
return nil
}
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