vendor/src/github.com/coreos/go-systemd/examples/activation/listen.go

// Activation example used by the activation unit tests.
package main

import (
	"fmt"
	"os"

	"github.com/coreos/go-systemd/activation"
)

func fixListenPid() {
	if os.Getenv("FIX_LISTEN_PID") != "" {
		// HACK: real systemd would set LISTEN_PID before exec'ing but
		// this is too difficult in golang for the purpose of a test.
		// Do not do this in real code.
		os.Setenv("LISTEN_PID", fmt.Sprintf("%d", os.Getpid()))
	}
}

func main() {
	fixListenPid()

	listeners, _ := activation.Listeners(false)

	if len(listeners) == 0 {
		panic("No listeners")
	}

	if os.Getenv("LISTEN_PID") == "" || os.Getenv("LISTEN_FDS") == "" {
		panic("Should not unset envs")
	}

	listeners, err := activation.Listeners(true)
	if err != nil {
		panic(err)
	}

	if os.Getenv("LISTEN_PID") != "" || os.Getenv("LISTEN_FDS") != "" {
		panic("Can not unset envs")
	}

	c0, _ := listeners[0].Accept()
	c1, _ := listeners[1].Accept()

	// Write out the expected strings to the two pipes
	c0.Write([]byte("Hello world"))
	c1.Write([]byte("Goodbye world"))

	return
}