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package linux
import (
"fmt"
"net"
"os"
"strconv"
"golang.org/x/sys/unix"
)
// GetSystemdListeners returns the socket-activated network listeners, if any.
//
// The 'start' parameter must be SystemdListenFDsStart, except in unit tests,
// see the docstring of SystemdListenFDsStart below.
func GetSystemdListeners(start int) []net.Listener {
defer func() {
_ = os.Unsetenv("LISTEN_PID")
_ = os.Unsetenv("LISTEN_FDS")
}()
pid, err := strconv.Atoi(os.Getenv("LISTEN_PID"))
if err != nil {
return nil
}
if pid != os.Getpid() {
return nil
}
fds, err := strconv.Atoi(os.Getenv("LISTEN_FDS"))
if err != nil {
return nil
}
listeners := []net.Listener{}
for i := start; i < start+fds; i++ {
unix.CloseOnExec(i)
file := os.NewFile(uintptr(i), fmt.Sprintf("inherited-fd%d", i))
listener, err := net.FileListener(file)
if err != nil {
continue
}
listeners = append(listeners, listener)
}
return listeners
}
// SystemdListenFDsStart is the number of the first file descriptor that might
// have been opened by systemd when socket activation is enabled. It's always 3
// in real-world usage (i.e. the first file descriptor opened after stdin,
// stdout and stderr), so this constant should always be the value passed to
// GetListeners, except for unit tests.
const SystemdListenFDsStart = 3
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