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package failover
import (
"fmt"
"net"
"os"
"time"
"golang.org/x/net/icmp"
"golang.org/x/net/ipv4"
"github.com/go-errors/errors"
)
// mtuOverhead defines the total MTU overhead for an ICMP ECHO message: 20 bytes IP header + 8 bytes ICMP header
var mtuOverhead = 28
type Pinger struct {
listener net.PacketConn
buffer []byte
}
func NewPinger(size int) (*Pinger, error) {
l, err := icmp.ListenPacket("udp4", "0.0.0.0")
if err != nil {
return nil, errors.WrapPrefix(err, "failed creating ping", 0)
}
return &Pinger{listener: l, buffer: make([]byte, size-mtuOverhead)}, nil
}
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
}
got, err := icmp.ParseMessage(ipv4.ICMPTypeEchoReply.Protocol(), r[:n])
if err != nil {
return err
}
switch got.Type {
case ipv4.ICMPTypeEchoReply:
return nil
default:
return errors.Errorf("Not a ping echo reply, got %+v", got)
}
}
func (p Pinger) Send(gateway string, seq int) error {
errorMessage := fmt.Sprintf("failed sending ping, seq %d", seq)
// Make a new ICMP message
m := icmp.Message{
Type: ipv4.ICMPTypeEcho, 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 errors.WrapPrefix(err, errorMessage, 0)
}
// And send it to the gateway IP!
_, err = p.listener.WriteTo(b, &net.UDPAddr{IP: net.ParseIP(gateway)})
if err != nil {
return errors.WrapPrefix(err, errorMessage, 0)
}
return nil
}
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