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// Copyright 2019 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package iptables
import (
"fmt"
"net"
"os/exec"
"time"
)
const iptablesBinary = "iptables"
// filterTable calls `iptables -t filter` with the given args.
func filterTable(args ...string) error {
args = append([]string{"-t", "filter"}, args...)
cmd := exec.Command(iptablesBinary, args...)
if out, err := cmd.CombinedOutput(); err != nil {
return fmt.Errorf("error running iptables with args %v\nerror: %v\noutput: %s", args, err, string(out))
}
return nil
}
// listenUDP listens on a UDP port and returns the value of net.Conn.Read() for
// the first read on that port.
func listenUDP(port int, timeout time.Duration) error {
localAddr := net.UDPAddr{
Port: port,
}
conn, err := net.ListenUDP(network, &localAddr)
if err != nil {
return err
}
defer conn.Close()
conn.SetDeadline(time.Now().Add(timeout))
_, err = conn.Read([]byte{0})
return err
}
// sendUDPLoop sends 1 byte UDP packets repeatedly to the IP and port specified
// over a duration.
func sendUDPLoop(ip net.IP, port int, duration time.Duration) error {
// Send packets for a few seconds.
remote := net.UDPAddr{
IP: ip,
Port: port,
}
conn, err := net.DialUDP(network, nil, &remote)
if err != nil {
return err
}
defer conn.Close()
to := time.After(duration)
for timedOut := false; !timedOut; {
// This may return an error (connection refused) if the remote
// hasn't started listening yet or they're dropping our
// packets. So we ignore Write errors and depend on the remote
// to report a failure if it doesn't get a packet it needs.
conn.Write([]byte{0})
select {
case <-to:
timedOut = true
default:
time.Sleep(200 * time.Millisecond)
}
}
return nil
}
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